Category Archives: Quantum Physics

From the earliest batteries through vacuum tubes, solid state, and integrated circuits, electronics has staved off stagnation. Engineers and scientists have remade it repeatedly, vaulting it over one hurdle after another to keep alive a record of innovation unmatched in industrial history.

It is a spectacular and diverse account through which runs a common theme. When a galvanic pile twitches a frog's leg, when a triode amplifies a signal, or when a microprocessor stores a bit in a random access memory, the same agent is at work: the movement of electric charge. Engineers are far from exhausting the possibilities of this magnificent mechanism. But even if a dead end is not yet visible, the foreseeable hurdles are high enough to set some searching for the physics that will carry electronics on to its next stage. In so doing, it could help up the ante in the semiconductor stakes, ushering in such marvels as nonvolatile memories with enormous capacity, ultrafast logic devices that can change function on the fly, and maybe even processors powerful enough to begin to rival biological brains.v A growing band of experimenters think they have seen the future of electronics, and it is spin. This fundamental yet elusive property of electrons and other subatomic particles underlies permanent magnetism, and is often regarded as a strange form of nano-world angular momentum.

Microelectronics researchers have been investigating spin for at least 20 years. Indeed, their discoveries revolutionized hard-disk drives, which since 1998 have used a spin-based phenomenon to cram more bits than ever on to their disks. Within three years, Motorola Inc. and IBM Corp. are expected to take the next step, introducing the first commercial semiconductor chips to exploit spin--a new form of random access memory called M (for magnetic) RAM. Fast, rugged, and nonvolatile, MRAMs are expected to carve out a niche from the US $10.6-billion-a-year flash memory market. If engineers can bring the costs down enough, MRAMs may eventually start digging into the $35 billion RAM market as well.

The sultans of spin say memory will be just the beginning. They have set their sights on logic, emboldened by experimental results over the past two or three years that have shown the budding technologies of spin to be surprisingly compatible with the materials and methods of plain old charge-based semiconductor electronics. In February 2000, the Defense Advance Research Projects Agency announced a $15-million-a-year, five-year program to focus on new kinds of semiconductor materials and devices that exploit spin. It was the same Arlington, Va., agency's largesse of $60 million or so over the past five years that helped move MRAMs from the blackboard to the verge of commercial production.

Subatomic spookiness

Now proponents envision an entirely new form of electronics, called spintronics. It would be based on devices that used the spin of electrons to control the movement of charge. Farther down the road (maybe a lot farther), researchers might even succeed in making devices that used spin itself to store and process data, without any need to move charge at all. Spintronics would use much less power than conventional electronics, because the energy needed to change a spin is a minute fraction of what is needed to push charge around.

Other advantages of spintronics include nonvolatility: spins don't change when the power is turned off. And the peculiar nature of spin--and the quantum theory that describes it--points to other weird, wonderful possibilities, such as: logic gates whose function--AND, OR, NOR, and so on--could be changed a billion times a second; electronic devices that would work directly with beams of polarized light as well as voltages; and memory elements that could be in two different states at the same time. "It offers completely different types of functionality" from today's electronics, said David D. Awschalom, who leads the Center for Spintronics and Quantum Computation at the University of California at Santa Barbara. "The most exciting possibilities are the ones we're not thinking about."

Much of the research is still preliminary, Awschalom cautions. A lot of experiments are still performed at cryogenic temperatures. And no one has even managed to demonstrate a useful semiconductor transistor or transistor-like device based on spin, let alone a complex logic circuit. Nevertheless, researchers at dozens of organizations are racing to make spin-based transistors and logic, and encouraging results from groups led by Awschalom and others have given ground for a sense that major breakthroughs are imminent.

"A year and a half ago, when I was giving a talk [and] said something about magnetic logic, before I went on with the rest of my talk I'd preface my statement with, '...and now, let's return to the planet Earth,'" said Samuel D. Bader, a group leader in the materials science division at Argonne National Laboratory, in Illinois. "I can drop that line now," he added.

Quantum mechanical mystery

Spin remains an unplumbed mystery. "It has a reputation of not being really fathomable," said Jeff M. Byers, a leading spin theorist at the Naval Research Laboratory (NRL), in Washington, D.C. "And it's somewhat deserved."

Physicists know that spin is the root cause of magnetism, and that, like charge or mass, it is an intrinsic property of the two great classes of subatomic particles: fermions, such as electrons, protons, and neutrons; and bosons, including photons, pions, and more. What distinguishes them, by the way, is that a boson's spin is measurable as an integer number (0, 1, 2...) of units, whereas fermions have a spin of 1/2, 3/2, 5/2.... units.

Much of spin's elusiveness stems from the fact that it goes right to the heart of quantum theory, the foundation of modern physics. Devised in the early decades of the 20th century, quantum theory is an elaborate conceptual framework, based on the notion that the exchange of energy at the subatomic level is constrained to certain levels, or quantities--in a word, quantized.

Paul Dirac, an electrical engineering graduate of Bristol University, in England, turned Cambridge mathematician, postulated the existence of spin in the late 1920s. In work that won him a Nobel prize, he reconciled equations for energy and momentum from quantum theory with those of Einstein's special theory of relativity.

Spin is hard to grasp because it lacks an exact analog in the macroscopic world we inhabit. It is named after its closest real-world counterpart: the angular momentum of a spinning body. But whereas the ordinary angular momentum of a whirling planet, say, or curve ball vanishes the moment the object stops spinning and hence is extrinsic, spin is a kind of intrinsic angular momentum that a particle cannot gain or lose.

"Imagine an electronics technology founded on such a bizarre property of the universe," said Byers.

Of course, the analogy between angular momentum and spin only goes so far. Particle spin does not arise out of rotation as we know it, nor does the electron have physical dimensions, such as a radius. So the idea of the electron having angular momentum in the classical meaning of the term doesn't make sense. Confused? "Welcome to the club," Byers said, with a laugh.

The smallest magnets

Fortunately, a deep grasp of spin is not necessary to understand the promise of the recent advances. The usual imperfect analogies that somehow manage to render the quantum world meaningful for mortal minds turn out to be rather useful--as is spin's role in magnetism, a macroscopic manifestation of spin.

Start with the fact that spin is the characteristic that makes the electron a tiny magnet, complete with north and south poles. The orientation of the tiny magnet's north-south axis depends on the particle's axis of spin. In the atoms of an ordinary material, some of these spin axes point "up" (with respect to, say, an ambient magnetic field) and an equal number point "down." The particle's spin is associated with a magnetic moment, which may be thought of as the handle that lets a magnetic field torque the electron's axis of spin. Thus in an ordinary material, the up moments cancel the down ones, so no surplus moment piles up that could hold a picture to a refrigerator.

For that, you need a ferromagnetic material, such as iron, nickel, or cobalt. These have tiny regions called domains in which an excess of electrons have spins with axes pointing either up or down--at least, until heat destroys their magnetism, above the metal's Curie temperature. The many domains are ordinarily randomly scattered and evenly divided between majority-up and majority-down. But an externally applied magnetic field will move the walls between the domains and line up all the domains in the direction of the field, so that they point in the same direction. The result is a permanent magnet.

Ferromagnetic materials are central to many spintronics devices. Use a voltage to push a current of electrons through a ferromagnetic material, and it acts like a spin polarizer, aligning the spin axes of the transiting electrons so that they are up or down. One of the most basic and important spintronic devices, the magnetic tunnel junction, is just two layers of ferromagnetic material separated by an extremely thin, nonconductive barrier [see figure, "How a Magnetic Tunnel Junction Works" ]. The device was first demonstrated by the French physicist M. Jullire in the mid-1970s.

ILLUSTRATIONS: STEVE STANKIEWICZ

How a Magnetic Tunnel Junction Works: One of the most fundamental spintronic devices, the magnetic tunnel junction, is just two layers of ferromagnetic material [light blue] separated by a nonmagnetic barrier [darker blue]. In the top illustration, when the spin orientation [white arrows] of the electrons in the two ferromagnetic layers are the same, a voltage is quite likely to pressure the electrons to tunnel through the barrier, resulting in high current flow. But flipping the spins in one of the two layers [yellow arrows, bottom illustration], so that the two layers have oppositely aligned spins, restricts the flow of current.

It works like this: suppose the spins of the electrons in the ferromagnetic layers on either side of the barrier are oriented in the same direction. Then applying a voltage across the three-layer device is quite likely to cause electrons to tunnel through the thin barrier, resulting in high current flow. But flipping the spins in one of the two ferromagnetic layers, so that the two layers have opposite alignment, restricts the flow of current through the barrier [bottom]. Tunnel junctions are the basis of the MRAMs developed by IBM and Motorola, one per memory cell.

Any memory device can also be used to build logic circuits, in theory at least, and spin devices such as tunnel junctions are no exception. The idea has been explored by Mark Johnson, a leading spin researcher at the Naval Research Laboratory, and others. Lately, work in this area has shifted to a newly formed program at Honeywell Inc., Minneapolis, Minn. The challenges to the devices' use for programmable logic are formidable. To quote William Black, principal engineer at the Rocket Chips subsidiary of Xilinx, a leading maker of programmable logic in San Jose, Calif., "The basic device doesn't have gain and the switching threshold typically is not very well controlled." To call that "the biggest technical impediment," as he does, sounds like an understatement.

Relativistic transistors

Already on the drawing board are spin-based devices that would act something like conventional transistors--and that might even produce gain. There are several competing ideas. The most enduring one is known as the spin field-effect transistor (FET). A more recent proposal puts a new spin, so to speak, on an almost mythical device physicists have pursued for decades: the resonant tunneling transistor.

In an ordinary FET, a metal gate controls the flow of current from a source to a drain through the underlying semiconductor. A voltage applied to the gate sets up an electric field, and that field in turn varies the amount of current that can flow between source and drain. More voltage produces more current.

In 1990 Supriyo Datta and Biswajit A. Das, then both at Purdue University, in West Lafayette, Ind., proposed a spin FET in a seminal article published in the journal Applied Physics Letters. The two theorized about an FET in which the source and drain were both ferromagnetic metals, with the same alignment of electron spins. Electrons would be injected into the source, which would align the spins so that their axes were oriented the same way as those in the source and drain. These spin-polarized electrons would shoot through the source and travel at 1 percent or so of the speed of light toward the drain.

This speed is important, because electrons moving at so-called relativistic speeds are subject to certain significant effects. One is that an applied electric field acts as though it were a magnetic field. So a voltage applied to the gate would torque the spin-polarized electrons racing from source to drain and flip their direction of spin. Thus electron spins would become polarized in the opposite direction to the drain, and could not enter it so easily. The current going from the source to the drain would plummet.

Note that the application of the voltage would cut off current, rather than turn it on, as in a conventional FET. Otherwise, the basic operation would be rather similar--but with a couple of advantages. To turn the current on or off would require only the flipping of spins, which takes very little energy. Also, the polarization of the source and drain could be flipped independently, offering intriguing possibilities unlike anything that can be done with a conventional FET. For example, Johnson patented the idea of using an external circuit to flip the polarization of the drain, turning the single-transistor device into a nonvolatile memory cell.

A recent German breakthrough will "revolutionize" a majorspintronics subfield, one expert declared

Alas, 11 years after the paper by Datta and Das, no one has managed to make a working spin FET. Major efforts have been led by top researchers, such as Johnson at the NRL, Michael Flatt at the University of Iowa, Michael L. Roukes at the California Institute of Technology, Hideo Ohno of Tohoku University in Japan, Laurens W. Molenkamp, then at the University of Aachen in Germany, and Anthony Bland at the University of Cambridge in England. The main problem has been maintaining the polarization of the spins: the ferromagnetic source does in fact align the spins of electrons injected into it, but the polarization does not survive as the electrons shoot out of the source and into the semiconductor between the source and drain.

Recent work in Berlin, Germany, may change all that. In a result published last July in Physical Review Letters, Klaus H. Ploog and his colleagues at the Paul Drude Institute disclosed that they had used a film of iron, grown on gallium arsenide, to polarize spins of electrons injected into the GaAs. Not only was the experiment carried out at room temperature, but the efficiency of the injection, at 2 percent, was high in comparison with similar experiments. The work was "extremely important," said the Naval Research Laboratory's Johnson. "It will revolutionize this subfield. A year from now many spin-FET researchers will be working with iron."

The other kind of proposed spin transistor would exploit a quantum phenomenon called resonant tunneling. The device would be an extension of the resonant tunneling diode. At the heart of this device is an infinitesimal region, known as a quantum well, in which electrons can be confined. However, at a specific, resonant voltage that corresponds to the quantum energy of the well, the electrons tend to slip--the technical term is "tunnel"--freely through the barriers enclosing the well.

Generally, the spin state of the electron is irrelevant to the tunneling, because the up and down electrons have the same amount of energy. But by various means, researchers can design a device in which the spin-up and spin-down energy levels are different, so that there are two different tunneling pathways. The two tunnels would be accessed with different voltages; each voltage would correspond to one or the other of the two spin states. At one voltage, a certain level of spin-down current would flow. At some other voltage, a different level of spin-up current would go through the quantum well's barriers.

One way of splitting the energy levels is to make the two barriers of different materials, so that the potential energy that confines the electrons within the quantum well is different on either side of the well. That difference in the confining potentials translates, for a moving electron, into two regions within the quantum well, which have magnetic fields that are different from each other. Those asymmetric fields in turn give rise to the different resonant energy levels for the up and down spin states. A device based on these principles is the goal of a team led by Thomas McGill at the California Institute of Technology, with members at HRL Laboratories LLC, Jet Propulsion Laboratory, Los Alamos National Laboratory, and the University of Iowa.

Another method of splitting the energy levels is to simply put them in a magnetic field. This approach is being taken by a collaborative effort of nine institutions, led by Bruce D. McCombe at the University at Buffalo, New York.

Neither team has managed to build a working device, but the promise of such a device has kept interest high. A specific voltage would produce a certain current of, say, spin-up electrons. Using a tiny current to flip the spins would enable a larger current of spin-down electrons to flow at the same voltage. Thus a small current could, in theory anyway, be amplified.

Ray of hope

As these researchers refine the resonant and ballistic devices, they are looking over their shoulders at colleagues who are forging a whole new class of experimental device. This surging competition is based on devices that create or detect spin-polarized electrons in semiconductors, rather than in ferromagnetic metals. In these experiments, researchers use lasers to get around the difficulties of injecting polarized spin into semiconductors. By shining beams of polarized laser light onto ordinary semiconductors, such as gallium arsenide and zinc selenide, they create pools of SPIN-POLARIZED ELECTRONS.

Some observers lament the dependence on laser beams. They find it hard to imagine how the devices could ever be miniaturized to the extent necessary to compete with conventional electronics, let alone work smoothly with them on the same integrated circuit. Also, in some semiconductors, such as GaAs, the spin polarization persists only at cryogenic temperatures.

In an early experiment, Michael Oestreich, then at Philips University in Marburg, Germany, showed that electric fields could push pools of spin-polarized electrons through nonmagnetic semiconductors such as GaAs. The experiment was reported in the September 1998 Applied Physics Letters.

Then over the past three years, a breathtaking series of findings has turned the field into a thriving subdiscipline. Several key results were achieved in Awschalom's laboratory at Santa Barbara. He and his co-workers demonstrated that pools of spin-coherent electrons could retain their polarization for an unexpectedly long time--hundreds of nanoseconds. Working separately, Awschalom, Oestreich, and others also created pools of spin-polarized electrons and moved them across semiconductor boundaries without the electrons' losing their polarization.

If not for these capabilities, spin would have no future in electronics. Recall that a practical device will be operated by altering its orientation of spin. That means that the spin coherence has to last, at a minimum, longer than it takes to alter the orientation of that spin polarization. Also, spintronic devices, like conventional ones, will be built with multiple layers of semiconductors, so moving spin-polarized pools across junctions between layers without losing the coherence will be essential.

Awschalom and his co-workers used a pulsed, polarized laser to establish pools of spin-coherent electrons. The underlying physics revolves around the so-called selection rules. These are quantum-theoretical laws describing whether or not an electron can change energy levels by absorbing or emitting a photon of light. According to those selection rules, light that is circularly polarized will excite only electrons of one spin orientation or the other. Conversely, when spin-coherent electrons combine with holes, the result is photons of circularly polarized light.

Puzzling precession

In his most recent work, Awschalom and his graduate student, Irina Malajovich, collaborated with Nitin Samarth of Pennsylvania State University in University Park and his graduate student, Joseph Berry. As he has in the past, Awschalom performed the experiment on pools of electrons that were not only spin polarized but were also precessing. Precession occurs when a pool of spin-polarized electrons is put in a magnetic field: the field causes their spin axes to rotate in a wobbly way around that field. The frequency and direction of rotation depend on the strength of the magnetic field and on characteristics of the material in which the precession is taking place.

The Santa BarbaraPenn State team used circularly polarized light pulses to create a pool of spin-coherent electrons in GaAs. They applied a magnetic field to make the electrons precess, and then used a voltage to drag the precessing electrons across a junction into another semiconductor, ZnSe. The researchers found that if they used a low voltage to drag the electrons into the ZnSe, the electrons took on the precession characteristics of the ZnSe as soon as they got past the junction. However, if they used a higher voltage, the electrons kept on precessing, as though they were still in the GaAs [see illustration, "Precessional Mystery" ].

ILLUSTRATIONS: STEVE STANKIEWICZ

Precessional Mystery: Given the right circumstances, electrons will synchronously "precess," or whirl about an axis that is itself moving. The angle and rate of this wobbly spin depend in part on the material in which it occurs. Thus, if a voltage pushes an electron out of gallium arsenide [light blue] into zinc selenide [yellow], the electron's precession characteristics change [top]. However, if a higher voltage pushes the electron sharply enough into the ZnSe, the precession characteristics do not change but remain those of GaAs for a while [bottom]. Some researchers believe they will be able to exploit this variability in future devices.

"You can tune the whole behavior of the current, depending on the electric field," Awschalom said in an interview. "That's what was so surprising to us." The group reported its results in the 14 June issue of Nature, prompting theorists around the world to wear out their pencils trying to explain the findings.

Other results from the collaboration were even more intriguing. The Santa Barbara and Penn State researchers performed a similar experiment, except with p-type GaAs and n-type ZnSe. N-type materials rely on electrons to carry current; p-type, on holes. Because the materials were of two different charge-carrier types, an electric field formed around their junction. That field, the experimenters found, was strong enough to pull a pool of spin-coherent electrons from the GaAs immediately into the ZnSe, where the coherence persisted for hundreds of nanoseconds.

The result was encouraging for two reasons. As Awschalom put it, "It showed that you can build n-type and p-type materials and spin can get through the interfaces between them just fine." Equally important, it demonstrated that the spin can be moved from one kind of semiconductor into another without the need for external electric fields, which wouldn't be practical in a commercial device.

"The next big opportunity is to make a spin transistor," Awschalom added. "These results show, in principle, that there is no obvious reason why it won't work well."

Such a device is at least several years away. But even if researchers were on the verge of getting a spin transistor to work in the laboratory, more breakthroughs would be necessary before the device could be practical. For example, the fact that the device would need pulses of circularly polarized laser light would seem an inconvenience, although Awschalom sees a bright side. The gist is that the photons would be used for communications among chips, the magnetic elements for memory, and the spin-based devices for fast, low-power logic.

It's far-fetched now--but no more so than the idea of 1GB DRAMs would have seemed in the days when triodes ruled.

Hot off the presses is Semiconductor Spintronics and Quantum Computation, edited by David D. Awschalom, Nitin Samarth, and Daniel Loss. The 250-page book was released last October by Springer Verlag, Berlin/Heidelberg; ISBN: 3540421769.

The November/December issue of American Scientist, published by the scientific research society Sigma Xi, included an eight-page overview titled "Spintronics" by Sankar Das Sarma. See Vol. 89, pp. 516523.

Honeywell Inc.'s Romney R. Katti and Theodore Zhu described the company's magnetic RAM technology in "Attractive Magnetic Memories," IEEE Circuits & Devices, Vol. 17, March 2001, pp. 2634.

Continue reading here:

The Quest for the Spin Transistor - IEEE Spectrum

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Everything we know about soil science might be wrong - The Counter

Photo: Intel Corp.

I have in my notebooks from [1956] a complete description of the tunnel diode, the speaker told the audience at a symposium on innovation at the MIT Club of New York, in New York City, in December 1976. It was quite a revelation, because the speaker wasnt Leo Esaki, who had won the 1973 Nobel Prize in physics for inventing the tunnel diode in the late 1950s. It was Robert N. Noyce, cofounder of Intel Corp., Santa Clara, Calif.; inventor of the first practical integrated circuit; and a man who, as far as anyone knew before that speech, had no connection to the most storied electronic device never to be manufactured in large numbers.

Engineers coveted the tunnel diode for its extremely fast switching timestens of picosecondsat a time when transistors loped along at milliseconds. But it never found commercial success, though it was occasionally used as a very fast switch. As a two-terminal device, the diode could not readily be designed for amplification, unlike a three-terminal transistor, whose circuit applications were then growing astronomically. Nevertheless, the tunnel diode was a seminal invention. It provided the first physical evidence that the phenomenon of tunneling, a key postulate of quantum mechanics, was more than an intriguing theory.

Quantum mechanics, the foundation of modern physics, is an elaborate conceptual framework that predicts the behavior of matter and radiation at the atomic level. One of its most fundamental notions is that the exchange of energy at the subatomic level is constrained to certain levels, or quantitiesin a word, quantized.

Many of the core concepts and phenomena of quantum mechanics are almost completely counterintuitive. For example, consider a piece of semiconductor joined to an insulator. From the point of view of classical physics theory, the electrons in the semiconductor are like rubber balls, and the insulator is like a low garden wall. An electron would have no chance of getting over the barrier unless its energy were higher than the barriers. But according to quantum mechanics, the phenomenon of tunneling ensures that for certain conditions an electron with less energy than the barriers will not bounce off the wall but will instead tunnel right through it.

Ever since the late 1920s, physicists had debated about whether tunneling really occurred in solids. The tunnel diode offered the first compelling experimental evidence that it did.

When Esaki, then a 49-year-old semiconductor research scientist at IBM Corp., won his Nobel Prize in 1973, neither he nor the Nobel committee had any idea about Noyces work. Esaki had made a tunnel diode and measured its current versus voltage behavior 16 years earlier, when he was working at the company now called Sony Corp. in his native Japan. The Nobel committee, in fact, dated Esakis discovery from 1957, roughly contemporaneous with Noyces recollected work in the same field. Stig Lundqvist of the Swedish Royal Academy of Sciences used the electrons as balls against the wall analogy in his speech presenting the 1973 Nobel Prize in physics to Esaki; Ivar Giaever and Brian David Josephson shared the award for discovering different aspects of the tunneling phenomenon in solids.

In Good Company: The eight engineers and scientists, including Robert N. Noyce (right) and Gordon E. Moore (standing second from left), who cofounded Fairchild Semiconductor in 1957, are pictured here on the firms production floor in its earlyyears.Photo: Intel Corp.

Almost every important discovery since the start of the industrial age has a contested history. Heinrich Gobel, from a town near Hanover in Germany, filed suit in 1893 claiming that he, not Thomas Edison, had invented the light bulb years earlier in New York City. Something similar has occurred for the airplane, telephone, rotor encryption machine, television, integrated circuit, and microprocessor, to name but a few. Such counterclaims often have meritinvention and research are often group activities, and discoveries regularly appear in different places at almost precisely the same time. And sometimes such claims come from experimenting hacks eager for a measure of recognition for themselves.

Noyce was no hack, obviouslyhis integrated circuit nestles at the heart of essentially every piece of modern electronics. In fact, the invention of the IC was recognized as a Nobel-level achievement in 2000, when the prize for physics was awarded to Jack S. Kilby, credited by U.S. courts as the coinventor of the IC. Unfortunately for Noyce, he missed his chance to join the pantheon of laureates when he died in 1990; the prizes are not awarded posthumously.

Nor was Noyce pursuing glory when he mentioned his work in his talk at that symposium in 1976. In fact, immediately after claiming to have the invention in his notebooks, Noyce said, The work had been done elsewhere [by Leo Esaki] and was published shortly thereafter. He had mentioned it in the first place only because he thought the way his boss had handled Noyces tunnel diode efforts in 1956 may be instructive in how not to motivate people.

Noyces boss at that time was William B. Shockley, the brilliant, mercurial, ambitious, autocratic, and eccentric physicist. He was the sort of man who thought nothing of publicly subjecting his employees to lie-detector tests. As the young Noyce had his insight about the tunnel diode, Shockley himself was only weeks away from his own Nobel Prize in physics, awarded for his 1947 invention, along with two colleagues, John Bardeen and Walter Brattain, of the transistor.

Shockley had started Shockley Semiconductor Laboratory in 1955 with the self-proclaimed goal of making a million dollars and seeing his name in The Wall Street Journal. Noyce headed the transistor group at Shockley Lab. With a Ph.D. in physical electronics and two years in a transistor research lab at Philco Corp., he was the most experienced semiconductor researcher among Shockleys several dozen employees.

On 14 August 1956, Noyce noted an idea for a negative resistance diode in his lab notebook. With most diodes, current increases with increased voltagethe more voltage applied to the device, the more current passes through it.

In a diode, the current under a forward voltage, or bias, is relatively large, while little current results when the bias is reversed. For a semiconductor diode, such behavior is obtained by adding impurity atoms. Esakis semiconductor was germanium. He used two types of impurities. So-called donor atoms have more electrons in their outer orbits than do the outer orbits of germanium atoms. The excess electrons become free electrons, available for conduction. A semiconductor with an excess of electrons is called n-type.

Similarly, if the germanium is doped with impurity atoms that hold fewer electrons in their outer orbits than germanium, the impurity atoms will take away, or accept, electrons from the semiconductor atoms, leaving behind deficiencies of electrons, known as holes. A semiconductor with an excess of holes, each one considered to have a positive charge, is called a p-type semiconductor.

Germanium can be doped to create p- and n-type sections that butt against each other and form what is called a p-n junction. In a p-n junction, a potential difference normally builds up across a narrow region near where the p-type and n-type semiconductors come into contact. This built-in potential sets up a barrier against the passage of holes into the n-type material and the passage of electrons into the p-type. Applying an external bias across the diode changes the barriers height. A forward biasobtained by connecting a batterys positive terminal to the p side and its negative terminal to the n sidelowers the barrier, allowing electrons to flow easily from the n side to the p side. Reverse the polarity, and the height of the barrier rises, prohibiting the flow of electrons.

Noyce, however, made a startling prediction. First he proposed the existence of a semiconductor whose regions of opposite polarity were each doped with roughly a thousand times more impurities than was usual at the time. When a forward bias increasing from zero was applied to such a heavily doped diode (which Noyce called degenerate), he predicted that current would initially increase at a greater rate than for a normal diode. This phenomenon would occur because the high impurity density would, in effect, make it possible for the balls (electrons) to tunnel through the wall (the junctions potential barrier). At some point, increasing the voltage further would decrease the tunneling current, but at still higher voltages, the current would increase because of the nontunneling diode current.

Noyce discussed his ideas with his friend Gordon E. Moore, a chemist who had joined Shockley Lab a day before Noyce. He then brought his notebook to Shockley, fully expecting him to be impressed. Instead, the boss showed no interest in the idea, Noyce said. The lab was not equipped to do anything profitable with Noyces thoughts, and besides, Shockley was a fiercely competitive man who resented his employees pursuing ideas that he had not personally placed on their research agendas. Disappointed, Noyce closed his lab book and went on to other projects more in line with Shockleys wishes.

Until now, no one other than Moore and Shockley had seen Robert Noyces 1956 description of a tunnel diode. But Noyce copied his work and saved it. How he managed to copy these pages is unclearphotocopy technology was in its infancy in the late 1950s, and Noyce never made note of going back to his Shockley notebooks later in lifebut that the pages are legitimate is indisputable. Leslie Berlin, one of this articles authors, found them in January 2001 tucked in one of Noyces Fairchild notebooks stored in Santa Clara, Calif., at a company that prefers not to be identified.

Berlin compared these copied pages to the only surviving notebook from Shockley Lab: the book belonging to William Shockley housed in the Special Collections of Stanford University, in California. The pages on which Noyces ideas are written are clearly from the same type of lab book that Shockley issued to his staff, and the handwriting is undoubtedly Noyces. This, along with the date of Noyces work (which correlates with his 1976 comments about it), and Moores recollections of the event, further validate their authenticity.

A quick comparison of Noyces notebook pages with Esakis seminal paper, New Phenomenon in Narrow Germanium p-n Junctions, published in Physical Review in January 1958 (and received by that journal in October 1957), shows striking parallels. Both men used an energy-band diagram that represents the electron and hole energies on the y (vertical) axis versus their position in the p-n junction on the x (horizontal) axis [see sidebar, The Noyce Diode,two pages from Noyces notebook].

Noyces energy-level diagram, which is now called an energy-band diagram [on the left-hand page], shows where the electrons and holes are located. It also illustrates the conditions necessary for tunneling current. The upper solid line in the diagram represents the bottom of the semiconductors conduction band; in this band electrons can move freely as a result of the donor atoms. The lower solid line represents the top of the valence band, where acceptor impurities allow holes to move freely. The separation between the conduction and valence bands is the energy gap, or Eg , and is the range in energy where no electrons or holes are permitted. For this reason, Eg is sometimes called the forbidden gap.

In Noyces diagram, the Fermi energy, or Ef , represents the energy boundary for most of the holes in the p-type semiconductor and most of the free electrons in the n-type. For a highly doped, or degenerate, semiconductor, Ef falls below the edge of the valence band and rises above the edge of the conduction band. Electrons sink so they fill the lowest energy levels in the conduction band, while holes float and fill the highest levels of the valence band. Therefore, it is the holes between the top of the valence band and Ef and the free electrons between Ef and the bottom of the conduction band that are significant for tunneling.

The region between the p and the n sides where the valence and conduction band edges bend is called the depletion region; this is where the potential barrier exists. This region narrows for large donor and acceptor concentrations and would be less than 10 nanometers for a tunnel diode.

Note that without an applied bias, the holes on the p side are at a higher energy than the electrons on the n side. For tunneling to occur, there must be holes at the same energy as the free electrons. But a forward bias (a positive voltage connected to the p side), raises Ef and the conduction-band electrons on the n side with respect to Ef on the p side by the amount of the bias voltage. Now there are free electrons at the same energy as the holes, and the electrons can tunnel through the potential barrier to holes on the p side, resulting in a current. As the forward bias is increased, more free electrons and holes are at the same energy and the tunneling current increases.

Both Noyce and Esaki recognized that as the bias increased further, Ef on the n side would be raised further with respect to Ef on the p side and the concentration of free electrons at the same energy as holes would diminish and result in a reduced tunneling current, as shown in Noyces current (I) vs. voltage (V) plot. At a larger bias, the normal diode current would flow at the voltage Eg in Noyces plot.

This plot [on the right-hand page] is very similar to the measured I-V plot that Esaki shows. This phenomenon of decreasing current with increasing voltage is negative resistance, a characteristic that has been exploited to build oscillators.

But there was one important difference between Noyces and Esakis work. Noyce only predicted the drop in current (the evidence of tunneling) would occur. Esaki, who actually built a device to demonstrate his ideas, showed that it would. This difference is crucialmany good ideas die en route from the mind to the lab bench.

Noyces failure to implement his brilliant idea was almost certainly a direct result of Shockleys discouraging comments to him in 1956. Noyce was an experimentalist at heart. (He admired people who did things, his friend Maurice Newstein explained to one of the authors in 2003.) Noyce would later prove a bit of an iconoclast as well, joining a covert effort to build silicon transistors at Shockley whenever the boss, who had decided the lab should focus its attention on an obscure device he had invented called a four-layer diode, was away. But in August 1956, Noyce was 29 years old and not yet six months into his job at Shockley Lab. If his boss told him to drop an idea, at that point he would have done it.

Noyce no longer worked for Shockley when he read Leo Esakis Physical Review article in 1958. In September 1957, he, Moore, and six other Shockley employeesmore than half the senior technical staffhad left their temperamental boss to start their own transistor company, Fairchild Semiconductor. Shockleys business venture, meanwhile, withered (he joined the Stanford faculty in 1963), and he suffered the additional indignity of watching his proteges new company achieve phenomenal success. In less than a decade, Fairchildunder Noyces leadershipgrew to employ 11 000 people and generate more than US $12 million in profits.

The publication of Esakis article caused quite a sensation in the electronics community. At an international physics conference in 1958, the audience for Esakis presentation was overflowing. Interestingly, Esaki credits William Shockley, who explicitly mentioned Esakis work in his keynote address earlier to the conference, with the large attendance at his presentation.

We can never know why Shockley changed his mind about the importance of the diode, but there are several possible explanations. Shockley was infamous for his swings of opinionone person who worked for him said he was regularly jerking the company back and forth. Similar remarks from other colleagues indicate that Shockley may have changed his mind in this case. Moreover, the grudge he bore against the eight Fairchild founders was still fresh in 1958.

After reading Esakis article, Noyce brought his copy of Physical Review to Moore and laid it on his desk. Noyce could not mask the irritation he felt with William Shockley and, even more, with himself for not pursuing his ideas after Shockley dismissed them. If I had gone one step further, he told Moore, who would go on to found Intel with him in 1968, I would have doneit.

Leslie Berlin is a visiting scholar in the Program in the History and Philosophy of Science and Technology at Stanford University, in California. Her biography of Robert Noyce, The Man Behind the Microchip: Robert Noyce and the Invention of Silicon Valley, will be published by Oxford University Press on 1 June.

H. Craig Casey Jr. is Professor Emeritus at Duke University, in Durham, N.C. He is a life fellow of the IEEE and a past president of the Electron Devices Society.

Leo Esakis lecture Long Journey Into Tunneling, which he gave when awarded the Nobel Prize in physics in 1973, is available at http://nobelprize.org/physics/laureates/1973/esaki-lecture.html.

An interactive Web site that graphically illustrates the current mechanisms in a tunnel diode is at http://www.shef.ac.uk/eee/teach/resources/diode/tunnel.html.

For more on William Shockley, see Crystal Fire: The Birth of the Information Age, by Michael Riordan and Lillian Hoddeson (W.W. Norton, 1997).

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Robert Noyce and the Tunnel Diode - IEEE Spectrum

The following is an adapted excerpt from the book The Extended Mind. It is reprinted with permission of the author.

If you'd like to make smarter choices and sounder decisions and who doesn't? you might want to take advantage of a resource you already have close at hand: your interoception. Interoception is, simply stated, an awareness of the inner state of the body. Just as we have sensors that take in information from the outside world (retinas, cochleas, taste buds, olfactory bulbs), we have sensors inside our bodies that send our brains a constant flow of data from within. These sensations are generated in places all over the body in our internal organs, in our muscles, even in our bones and then travel via multiple pathways to a structure in the brain called the insula. Such internal reports are merged with several other streams of information our active thoughts and memories, sensory inputs gathered from the external world and integrated into a single snapshot of our present condition, a sense of "how I feel" in the moment, as well as a sense of the actions we must take to maintain a state of internal balance.

To understand the role interoception can play in smart decision-making, it's important to know that the world is full of far more information than our conscious minds can process. However, we are also able to collect and store the volumes of information we encounter on a non-conscious basis. As we proceed through each day, we are continuously apprehending and storing regularities in our experience, tagging them for future reference. Through this information-gathering and pattern-identifying process, we come to know things but we're typically not able to articulate the content of such knowledge or to ascertain just how we came to know it. This trove of data remains mostly under the surface of consciousness, and that's usually a good thing. Its submerged status preserves our limited stores of attention and working memory for other uses.

A study led by cognitive scientist Pawel Lewicki demonstrates this process in microcosm. Participants in Lewicki's experiment were directed to watch a computer screen on which a cross-shaped target would appear, then disappear, then reappear in a new location; periodically they were asked to predict where the target would show up next. Over the course of several hours of exposure to the target's movements, the participants' predictions grew more and more accurate. They had figured out the pattern behind the target's peregrinations. But they could not put this knowledge into words, even when the experimenters offered them money to do so. The subjects were not able to describe "anything even close to the real nature" of the pattern, Lewicki observes. The movements of the target operated according to a pattern too complex for the conscious mind to accommodate but the capacious realm that lies below consciousness was more than roomy enough to contain it.

"Nonconscious information acquisition," as Lewicki calls it, along with the ensuing application of such information, is happening in our lives all the time. As we navigate a new situation, we're scrolling through our mental archive of stored patterns from the past, checking for ones that apply to our current circumstances. We're not aware that these searches are under way; as Lewicki observes, "The human cognitive system is not equipped to handle such tasks on the consciously controlled level." He adds, "Our conscious thinking needs to rely on notes and flowcharts and lists of 'if-then' statements or on computers to do the same job which our non-consciously operating processing algorithms can do without external help, and instantly."

But if our knowledge of these patterns is not conscious, how then can we make use of it? The answer is that, when a potentially relevant pattern is detected, it's our interoceptive faculty that tips us off: with a shiver or a sigh, a quickening of the breath or a tensing of the muscles. The body is rung like a bell to alert us to this useful and otherwise inaccessible information. Though we typically think of the brain as telling the body what to do, just as much does the body guide the brain with an array of subtle nudges and prods. (One psychologist has called this guide our "somatic rudder.") Researchers have even captured the body in mid-nudge, as it alerts its inhabitant to the appearance of a pattern that she may not have known she was looking for.

Such interoceptive prodding was visible during a gambling game that formed the basis of an experiment led by neuroscientist Antonio Damasio, a professor at the University of Southern California. In the game, presented on a computer screen, players were given a starting purse of two thousand "dollars" and were shown four decks of digital cards. Their task, they were told, was to turn the cards in the decks face-up, choosing which decks to draw from such that they would lose the least amount of money and win the most. As they started clicking to turn over cards, players began encountering rewards bonuses of $50 here, $100 there and also penalties, in which small or large amounts of money were taken away. What the experimenters had arranged, but the players were not told, was that decks A and B were "bad" they held lots of large penalties in store and decks C and D were "good," bestowing more rewards than penalties over time.

How Our Brains Feel Emotion | Antonio Damasio | Big Think http://www.youtube.com

As they played the game, the participants' state of physiological arousal was monitored via electrodes attached to their fingers; these electrodes kept track of their level of "skin conductance." When our nervous systems are stimulated by an awareness of potential threat, we start to perspire in a barely perceptible way. This slight sheen of sweat momentarily turns our skin into a better conductor of electricity. Researchers can thus use skin conductance as a measure of nervous system arousal. Looking over the data collected by the skin sensors, Damasio and his colleagues noticed something interesting: after the participants had been playing for a short while, their skin conductance began to spike when they contemplated clicking on the bad decks of cards. Even more striking, the players started avoiding the bad decks, gravitating increasingly to the good decks. As in the Lewicki study, subjects got better at the task over time, losing less and winning more.

Yet interviews with the participants showed that they had no awareness of why they had begun choosing some decks over others until late in the game, long after their skin conductance had started flaring. By card 10 (about forty-five seconds into the game), measures of skin conductance showed that their bodies were wise to the way the game was rigged. But even ten turns later on card 20 "all indicated that they did not have a clue about what was going on," the researchers noted. It took until card 50 was turned, and several minutes had elapsed, for all the participants to express a conscious hunch that decks A and B were riskier. Their bodies figured it out long before their brains did. Subsequent studies supplied an additional, and crucial, finding: players who were more interoceptively aware were more apt to make smart choices within the game. For them, the body's wise counsel came through loud and clear.

Damasio's fast-paced game shows us something important. The body not only grants us access to information that is more complex than what our conscious minds can accommodate. It also marshals this information at a pace that is far quicker than our conscious minds can handle. The benefits of the body's intervention extend well beyond winning a card game; the real world, after all, is full of dynamic and uncertain situations, in which there is no time to ponder all the pros and cons. When we rely on the conscious mind alone, we lose but when we listen to the body, we gain a winning edge.

Annie Murphy Paul is a science writer who covers research on learning and cognition. She is the author of The Extended Mind: The Power of Thinking Outside the Brain, from which this article is adapted.

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Why information is central to physics and the universe itself - Big Think

The year is 1641. We open in France, where confusingly, everyone is speaking English. A Scottish man has been caught selling weapons to enemies of Louis XIII, and as punishment is forced to wear a red-hot iron mask forever. Cut to the not too distant future, where the mans descendant, Christopher Eccleston, is presenting a lecture about newly weaponised flying metal bugs to some Nato employees. Originally developed to isolate and kill cancer cells, at MARS industries we discovered how to program nanomites to do almost anything. For example eat metal. It turns out nanomites can also be injected into rocket warheads, and thus the back story and premise of GI Joe: The Rise of Cobra is explained in less than a minute.

The opening sets the tone for the film that follows speedy, irony-free B-movie action nonsense, delivered to you with the efficiency of a Big Mac on a Friday night And if it requires Christopher Eccleston to do a PowerPoint presentation so we can get on with watching helicopters blow up in slow motion, then dammit Christopher Eccleston will do a PowerPoint. On top of which, this particular Big Mac is filled with Channing Tatum.

Despite his previous acting highlights including the Step Up dance movies and grinding topless in the background of the video for Ricky Martins She Bangs, when asked about GI Joe in an interview in 2012, Channing Tatum said, I fucking hate that movie. Luckily for us, in 2009 Channing Tatum did a three-movie deal with Paramount and was forced to accept the GI Joe role to avoid being sued.

Despite his dislike of the film, Channing Tatum is still Channing Tatum and both he and his massive arms give it their all and he has gone to the Michael Bay School of Turning Around in Slow Motion While Holding a Machine Gun. After turning around slowly, he and his partner Marlon Wayans load some nanomite warheads into a jeep, refer to a group of muscular male soldiers as ladies and tell them to mount up. Strap in, everyone.

What follows is a plot of such madness and a cast of characters so enormous (IMDb lists 144 in total) its understandable that it required a PowerPoint to set it up. The truck is ambushed by Channing Tatums ex-girlfriend, Sienna Miller, and after a lengthy fight in which several members of elite army unit GI Joe parachute in to save the day, Tatum and Wayans are transported to an underground base in the Egyptian desert to participate in a training montage soundtracked by the UK band Bus Stops dance rap cover of T-Rexs Get It On. (Fun fact: Bus Stop were fronted by rapper and professional football manager Darren Daz Sampson, who went on to represent Britain in 2006s Eurovision Song Contest.) Channing Tatum wins a gladiatorial pugil stick fight with GI Joes resident masked ninja, Snake Eyes, and to celebrate the boys all take their tops off.

A semi-naked Marlon Wayans attempts to charm one of the Joes (they are collectively referred to as Joes) confusingly named Scarlett OHara, as she jogs on a treadmill while reading a book about quantum physics. (It is not clear why she needs to read a book about quantum physics when her job is beating people up dont worry about it.) Tatum puts on something called a Delta 6 accelerator suit and travels to Paris to stop Sienna Miller blowing up the Eiffel Tower, before charging around the Champs-lyses running after tanks, jumping through bus windows and flipping over Renault Mganes. Joseph Gordon Levitt appears to explain cobras to everyone using a CGI snake in a glass box (They are vicious). Chaos reigns.

Writer/director Stephen Sommers was also in charge of both The Mummy and the 90s B-movie classic Deep Rising, and although in comparison GI Joe contains a more noughties post-Transformers fixation on guns and machinery than those two films, there is a similar air of fun, unapologetic action campness throughout. If youre happy to suspend your disbelief to its very limits and relax into 1 hour and 58 minutes of revolving door cast, plot delivered via flashbacks and laughably hammy dialogue, plus Channing Tatum blowing things up in slow motion this is the film for you. And give me that kind of Big Mac silliness over po-faced serious blockbuster action, any day of the week.

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Hear me out: why GI Joe: The Rise of Cobra isnt a bad movie - The Guardian

July 26, 2021• Physics 14, 105

Nanophotonic devices based on tin-vacancy qubits in diamond show promise as building blocks of quantum repeaters, an important step toward the realization of long-range quantum networks.

Building long-range quantum networks is one of the most important and ambitious goals of quantum science and engineering. To connect these networks into a quantum internet will require intermediate stations where quantum informationcarried by photonscan be manipulated and refreshed. These stations, known as quantum repeaters, contain long-lived qubits with an optical interface that allows the photons to be entangled with the spins encoding these qubits. Color centers in solids are prime candidates for quantum repeaters, as they can have long coherence times, spin-selective optical transitions, and compatibility with photonic devices, such as cavities, that facilitate photon emission and routing. The tin-vacancy (SnV) center in diamond, a relatively new and promising color center [1], features several of these key elements. Until recently, however, these SnV centers had not been integrated into cavities in which their emission would be enhanced. Now, a team led by Jelena Vukovi at Stanford University has succeeded in integrating an SnV center into a nanophotonic device and has achieved 90% photon emission into the desired cavity mode [2]. This work is an important step toward the realization of long-range quantum networks.

A color center forms in a crystalline solid when one or more lattice atoms are missing or substituted by another species. Such complexes can absorb and emit light and, if they have a ground state with nonzero spin, can be used as a qubit. Intense research is dedicated to exploring color centers in diamond as building blocks of quantum networks [3]. The most studied diamond color center for quantum technology applications is the nitrogen vacancy (NV). With its remarkably long coherence time and spin-selective transition, the NV center has played a central role in the development of quantum networks, including the recent seminal demonstration of a three-node network with entanglement swapping capabilities [4]. Despite its successes, though, the NV suffers from a few shortcomings that limit its suitability for quantum networks. One issue is vibrational noise, which causes the majority of photons to be emitted incoherently, thereby reducing the success probability of spin-photon entanglement schemes. The other issue is the permanent electric dipole of this color center, leading to sensitivity to nearby charges. Such charge noise, which can destroy information stored in a qubit, is exacerbated when the NV is near surfaces, as in nanophotonic devices.

These limitations have led researchers to consider alternative qubits. A prominent family of diamond color centers currently under intense investigation consists of complexes made up of two carbon vacancies between which is a group-IV atom, an atom with four valence electrons. The inversion symmetry of these systems leads to a vanishing permanent electric dipole moment, making them suitable for integration in nanophotonic structures. Moreover, most of the emitted photons have frequencies in the desirable zero-phonon line, where there is no vibrational noise. One of the most studied group-IV centers in diamond is the silicon-vacancy (SiV) center, which has been integrated into nanophotonic devices and used in the first demonstration of memory-enhanced quantum communication [5]. However, the operation of an SiV center requires complex and expensive cryogenic technology based on dilution refrigeration to reach temperatures at which the coherence times are sufficiently long for applications [6].

The SnV center [7] has emerged as a potential solution. It has a number of desirable attributes: It obeys inversion symmetry, making it insensitive to charge noise; it emits photons primarily through the zero-phonon line; it exhibits longer coherence times than SiV; and it can be operated at a few kelvin, a temperature that can be reached with simpler technology than dilution refrigerators. These features make SnV particularly promising for use as a quantum network node. While optical initialization of SnV spins has been demonstrated [7], this color center had notuntil nowbeen integrated into nanophotonic structures, as required for applications.

For their demonstration, the Stanford team fabricated high-quality nanophotonic cavities from a diamond plate [2]. They first implanted tin atoms within the diamond. Typically, this integration of heavy impurity atoms into nanophotonic devices comes at the price of damaging the diamond surface and degrading the emitter quality. The authors overcame this problem using their novel color-center generation method that ensures precise placement of Sn impurity atoms below a high-quality diamond substrate [8]. The team then constructed photonic crystal cavities into the diamond plate. Each long, thin cavity had an array of holes etched along it. The cavities were also partly suspended in the air to make the light confinement stronger.

The researchers succeeded in efficiently coupling light in and out of the cavities via inverse-designed couplers that they developed in earlier work [9]. They could tune the cavity wavelength by depositing condensed argon on the device. When the wavelength of the cavity matched that of the optical transition of the color centers, the team observed a 40-fold enhancement of emission intensity compared with the off-resonant case. Furthermore, while the photons retained their sharp linewidths, the spontaneous emission rate was considerably enhanced. This narrow emission meant that photons have nearly 100% probability of being emitted into a single cavity mode. These elements are necessary for establishing high enough entanglement rates in quantum repeaters.

These new results, together with the recent demonstration of coherent optical control of the SnV spin state [10], are key steps toward the creation of SnV-based networks. The remaining critical step toward this goal is the creation of a high-fidelity quantum memory register composed of carbon-13 atomsthe only isotope of carbon with nonzero spinin the diamond lattice that can store quantum information transferred to and from the SnV center. Upon such a demonstration, the SnV center would be in a position to outshine its diamond-based predecessors.

Evangelia Takou is a Ph.D. candidate in the Department of Physics at Virginia Tech. Prior to joining Virginia Tech, she obtained a masters degree in condensed-matter physics and atomic physics in 2019 and an undergraduate degree in physics in 2018 at the University of Crete in Greece. In the second year of her Ph.D. studies, she was awarded the Ray F. Tipsword graduate scholarship. She was also selected to receive a competitive graduate school doctoral assistantship from the College of Science at Virginia Tech. Currently, she is working on theoretical protocols for the control of qubits based on color centers.

Sophia Economou is a professor of physics at Virginia Tech. She obtained her Ph.D. in 2006 from the University of California, San Diego, where she worked on theoretical aspects of optically controlled spin qubits. After that, she spent several years at the Naval Research Laboratory in Washington, D.C., first as an NRC postdoc and later as a staff researcher. Her current research interests include quantum computing with various types of qubits, including spin-based, superconducting, and photons. She is also interested in photonic entanglement in quantum networks as well as quantum simulation algorithms for solving many-body problems on quantum devices.

Alison E. Rugar, Shahriar Aghaeimeibodi, Daniel Riedel, Constantin Dory, Haiyu Lu, Patrick J. McQuade, Zhi-Xun Shen, Nicholas A. Melosh, and Jelena Vukovi

Phys. Rev. X 11, 031021 (2021)

Published July 26, 2021

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Tin Qubits Give Diamond a New Shine - Physics

- Organized by IIIT Hyderabad, Quantum Ecosystems Technology Council of India, IEEE Quantum Initiative, in association with PSA, Govt of India - Launchpad for Quantum Ecosystems and Technology Council of India ( QETCI) HYDERABAD, India, July 26, 2021 /PRNewswire/ -- The National Quantum Science and Technology Symposium (NQSTS), organized by IIIT Hyderabad, Quantum Ecosystems Technology Council of India, IEEE Quantum Initiative, in association with PSA, Govt of India is being held online from 26 July - 3 August 2021.

Through talks delivered by some of India's best quantum experts from government, academia and industry, the symposium will cover diverse aspects of the field and provide an overview of the scope and impact of quantum computing in India.

NQSTS launched the Quantum Ecosystems and Technology Council of India (QETCI), headed by Reena Dayal,which will work closely with various members of quantum ecosystems across government, academia, industry, startups and investors to accelerate the quantum ecosystem in India.

The symposium features several eminent keynote speakers - Prof Vijay Raghavan, PSA to Govt of India; Prof K Sivan, Chairman ISRO; Ajay Prakash Sawhney, Secretary MEITY; Dr KR MuraliMohan, Mission Director NM-ICPS, DST; Jayesh Ranjan, Principal Secretary, IC&T Govt of Telangana and Prof P J Narayanan, Director IIIT Hyderabad. It also includes several keynote speakers from Microsoft, Amazon, IBM, QNU Labs, TCS and IQM.

Speaking at the inauguration, Prof. P J Narayanan, Director, IIITH, said, 'Quantum computing is a truly futuristic area with huge potential that we must invest in today to reap benefits in the near future. IIIT Hyderabad had recognized the importance of this area and started research in related areas about 10 years. Our group today has 6 faculty members with mix of expertise in Physics, Mathematics, Computer Science, etc. We have a productive group consisting of Masters, PhD, as well as B.Tech students conducting research on different aspects of quantum computing, producing papers in journals and conferences, etc. To give greater push to this area, we have formed a Centre for Quantum Science & Technology (CQST) and hope to develop it into a major national and international player in the area of Quantum Information Sciences, from creating quantum computers to developing quantum computing models to quantum algorithms and their applications to various areas like Healthcare, Sciences, Machine Learning, etc. It is only natural that IIIT Hyderabad stay ahead in these areas for years to come, just as we have done in other areas of computing and communications.' Prof K Sivan, Chairman ISRO, said, 'India will be quantum-enabled in this decade. We will infuse the encryption of the satellite data with the power of quantum mechanics.' Commending the symposium, Ajay Prakash Sawhney, Secretary MEITY, said, 'Congratulations to the Quantum Ecosystems and Technology Council of India and IIIT Hyderabad for working towards bringing together the quantum ecosystem through this symposium. This is the right time for international corporates to establish their quantum presence in India, and for Indian companies to have dedicated teams on quantum technologies to take up the challenges that abound in this field.' The symposium organising committee was led by Prof Indranil Chakravarty. More details on the symposium at https://nqsts.com About IIIT-Hyderabad The International Institute of Information Technology, Hyderabad (IIITH) is an autonomous research university founded in 1998 that focuses on the core areas of Information Technology, such as Computer Science, Electronics and Communications, and their applications in other domains through inter-disciplinary research that has a greater social impact. Some of its research domains include Visual Information Technologies, Human Language Technologies, Data Engineering, VLSI and Embedded Systems, Computer Architecture, Wireless Communications, Algorithms and Information Security, Robotics, Building Science, Cognitive Science, Earthquake Engineering, Computational Natural Sciences and Bioinformatics, Education Technologies, Power Systems, IT in Agriculture and e-Governance.

Website: https://www.iiit.ac.in/ Logo: https://mma.prnewswire.com/media/600789/IIIT_Hyderabad_Logo.jpg PWR PWR

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First-of-Its-Kind National Quantum Science And Technology Symposium - Yahoo India News

Can you guess the size of the thinnest magnet? It is just one atom thick.

Scientists from the University of California Berkeley have created the first 2D magnet, just an atom thick. This ultra-thin magnet is also chemically stable and retains magnetism at room temperatures. The research is published inNature Communications.

The new magnet can revolutionize the research of ferromagnetism and the development of new types of memory devices. It could be a game-changer for the field of quantum physics.

Previous ultra-thin 2D magnets had to be kept at ultracold conditions to retain the chemical properties and magnetism, making it impossible to use them in practical application.

According to material scientist Jie Yao from the University of California, State-of-the-art 2D magnets need very low temperatures to function. But for practical reasons, a data center needs to run at room temperature. Our 2D magnet is not only the first that operates at room temperature or higher, but it is also the first magnet to reach the true 2D limit: Its as thin as a single atom!

Scientists made this state-of-the-art magnet using cobalt-doped van der Waals zinc oxide. A carefully measured ratio of Graphene oxide is mixed in acetate dihydrates of zinc and cobalt. When this mixture is baked in a vacuum, the mixture cools into a single layer of zinc oxide interspersed with cobalt atoms sandwiched between layers of graphene. The graphene layer is burned off by burning in the air, leaving a single layer of cobalt-doped zinc oxide.

The amount of cobalt scattered among the zinc oxide determines the strength of magnetism. A sweet spot of 12 percentage of cobalt makes the layer strongly magnetic. The material also was found to be stable even at temperatures around 212 degrees Fahrenheit.

Electrons are small magnets with North and South poles. They have their own tiny magnetic field, and their magnetic orientations cancel each other out in most materials. However, in ferromagnetic materials, electrons with the same magnetic orientation group themselves in domains. All the domains are oriented in the same direction in a magnetic material.

According to the researchers, the free electrons in the zinc oxide could be acting as intermediaries to keep the film magnetic even at high temperatures.

This material opens up new possibilities in various technological fields include memory devices and quantum computing. Further analysis is required to understand the limitations of this material.

Source: ScienceAlert

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Physicists have created the Worlds thinnest magnet Just one atom thick - News Landed

"I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem."

The American physicist Richard Feynman said this about the notorious puzzles and paradoxes of quantum mechanics, the theory physicists use to describe the tiniest objects in the Universe. But he might as well have been talking about the equally knotty problem of consciousness.

Some scientists think we already understand what consciousness is, or that it is a mere illusion. But many others feel we have not grasped where consciousness comes from at all.

The perennial puzzle of consciousness has even led some researchers to invoke quantum physics to explain it. That notion has always been met with skepticism, which is not surprising: it does not sound wise to explain one mystery with another. But such ideas are not obviously absurd, and neither are they arbitrary.

For one thing, the mind seemed, to the great discomfort of physicists, to force its way into early quantum theory. What's more, quantum computers are predicted to be capable of accomplishing things ordinary computers cannot, which reminds us of how our brains can achieve things that are still beyond artificial intelligence. "Quantum consciousness" is widely derided as mystical woo, but it just will not go away.

Quantum mechanics is the best theory we have for describing the world at the nuts-and-bolts level of atoms and subatomic particles. Perhaps the most renowned of its mysteries is the fact that the outcome of a quantum experiment can change depending on whether or not we choose to measure some property of the particles involved.

When this "observer effect" was first noticed by the early pioneers of quantum theory, they were deeply troubled. It seemed to undermine the basic assumption behind all science: that there is an objective world out there, irrespective of us. If the way the world behaves depends on how or if we look at it, what can "reality" really mean?

The most famous intrusion of the mind into quantum mechanics comes in the "double-slit experiment"

Some of those researchers felt forced to conclude that objectivity was an illusion, and that consciousness has to be allowed an active role in quantum theory. To others, that did not make sense. Surely, Albert Einstein once complained, the Moon does not exist only when we look at it!

Today some physicists suspect that, whether or not consciousness influences quantum mechanics, it might in fact arise because of it. They think that quantum theory might be needed to fully understand how the brain works.

Might it be that, just as quantum objects can apparently be in two places at once, so a quantum brain can hold onto two mutually-exclusive ideas at the same time?

These ideas are speculative, and it may turn out that quantum physics has no fundamental role either for or in the workings of the mind. But if nothing else, these possibilities show just how strangely quantum theory forces us to think.

The most famous intrusion of the mind into quantum mechanics comes in the "double-slit experiment". Imagine shining a beam of light at a screen that contains two closely-spaced parallel slits. Some of the light passes through the slits, whereupon it strikes another screen.

Light can be thought of as a kind of wave, and when waves emerge from two slits like this they can interfere with each other. If their peaks coincide, they reinforce each other, whereas if a peak and a trough coincide, they cancel out. This wave interference is called diffraction, and it produces a series of alternating bright and dark stripes on the back screen, where the light waves are either reinforced or cancelled out.

The implication seems to be that each particle passes simultaneously through both slits

This experiment was understood to be a characteristic of wave behaviour over 200 years ago, well before quantum theory existed.

The double slit experiment can also be performed with quantum particles like electrons; tiny charged particles that are components of atoms. In a counter-intuitive twist, these particles can behave like waves. That means they can undergo diffraction when a stream of them passes through the two slits, producing an interference pattern.

Now suppose that the quantum particles are sent through the slits one by one, and their arrival at the screen is likewise seen one by one. Now there is apparently nothing for each particle to interfere with along its route yet nevertheless the pattern of particle impacts that builds up over time reveals interference bands.

The implication seems to be that each particle passes simultaneously through both slits and interferes with itself. This combination of "both paths at once" is known as a superposition state.

But here is the really odd thing.

If we place a detector inside or just behind one slit, we can find out whether any given particle goes through it or not. In that case, however, the interference vanishes. Simply by observing a particle's path even if that observation should not disturb the particle's motion we change the outcome.

The physicist Pascual Jordan, who worked with quantum guru Niels Bohr in Copenhagen in the 1920s, put it like this: "observations not only disturb what has to be measured, they produce it We compel [a quantum particle] to assume a definite position." In other words, Jordan said, "we ourselves produce the results of measurements."

If that is so, objective reality seems to go out of the window.

And it gets even stranger.

If nature seems to be changing its behaviour depending on whether we "look" or not, we could try to trick it into showing its hand. To do so, we could measure which path a particle took through the double slits, but only after it has passed through them. By then, it ought to have "decided" whether to take one path or both.

The sheer act of noticing, rather than any physical disturbance caused by measuring, can cause the collapse

An experiment for doing this was proposed in the 1970s by the American physicist John Wheeler, and this "delayed choice" experiment was performed in the following decade. It uses clever techniques to make measurements on the paths of quantum particles (generally, particles of light, called photons) after they should have chosen whether to take one path or a superposition of two.

It turns out that, just as Bohr confidently predicted, it makes no difference whether we delay the measurement or not. As long as we measure the photon's path before its arrival at a detector is finally registered, we lose all interference.

It is as if nature "knows" not just if we are looking, but if we are planning to look.

Whenever, in these experiments, we discover the path of a quantum particle, its cloud of possible routes "collapses" into a single well-defined state. What's more, the delayed-choice experiment implies that the sheer act of noticing, rather than any physical disturbance caused by measuring, can cause the collapse. But does this mean that true collapse has only happened when the result of a measurement impinges on our consciousness?

It is hard to avoid the implication that consciousness and quantum mechanics are somehow linked

That possibility was admitted in the 1930s by the Hungarian physicist Eugene Wigner. "It follows that the quantum description of objects is influenced by impressions entering my consciousness," he wrote. "Solipsism may be logically consistent with present quantum mechanics."

Wheeler even entertained the thought that the presence of living beings, which are capable of "noticing", has transformed what was previously a multitude of possible quantum pasts into one concrete history. In this sense, Wheeler said, we become participants in the evolution of the Universe since its very beginning. In his words, we live in a "participatory universe."

To this day, physicists do not agree on the best way to interpret these quantum experiments, and to some extent what you make of them is (at the moment) up to you. But one way or another, it is hard to avoid the implication that consciousness and quantum mechanics are somehow linked.

Beginning in the 1980s, the British physicist Roger Penrose suggested that the link might work in the other direction. Whether or not consciousness can affect quantum mechanics, he said, perhaps quantum mechanics is involved in consciousness.

What if, Penrose asked, there are molecular structures in our brains that are able to alter their state in response to a single quantum event. Could not these structures then adopt a superposition state, just like the particles in the double slit experiment? And might those quantum superpositions then show up in the ways neurons are triggered to communicate via electrical signals?

Maybe, says Penrose, our ability to sustain seemingly incompatible mental states is no quirk of perception, but a real quantum effect.

Perhaps quantum mechanics is involved in consciousness

After all, the human brain seems able to handle cognitive processes that still far exceed the capabilities of digital computers. Perhaps we can even carry out computational tasks that are impossible on ordinary computers, which use classical digital logic.

Penrose first proposed that quantum effects feature in human cognition in his 1989 book The Emperor's New Mind. The idea is called Orch-OR, which is short for "orchestrated objective reduction". The phrase "objective reduction" means that, as Penrose believes, the collapse of quantum interference and superposition is a real, physical process, like the bursting of a bubble.

Orch-OR draws on Penrose's suggestion that gravity is responsible for the fact that everyday objects, such as chairs and planets, do not display quantum effects. Penrose believes that quantum superpositions become impossible for objects much larger than atoms, because their gravitational effects would then force two incompatible versions of space-time to coexist.

Penrose developed this idea further with American physician Stuart Hameroff. In his 1994 book Shadows of the Mind, he suggested that the structures involved in this quantum cognition might be protein strands called microtubules. These are found in most of our cells, including the neurons in our brains. Penrose and Hameroff argue that vibrations of microtubules can adopt a quantum superposition.

But there is no evidence that such a thing is remotely feasible.

It has been suggested that the idea of quantum superpositions in microtubules is supported by experiments described in 2013, but in fact those studies made no mention of quantum effects.

Besides, most researchers think that the Orch-OR idea was ruled out by a study published in 2000. Physicist Max Tegmark calculated that quantum superpositions of the molecules involved in neural signaling could not survive for even a fraction of the time needed for such a signal to get anywhere.

Other researchers have found evidence for quantum effects in living beings

Quantum effects such as superposition are easily destroyed, because of a process called decoherence. This is caused by the interactions of a quantum object with its surrounding environment, through which the "quantumness" leaks away.

Decoherence is expected to be extremely rapid in warm and wet environments like living cells.

Nerve signals are electrical pulses, caused by the passage of electrically-charged atoms across the walls of nerve cells. If one of these atoms was in a superposition and then collided with a neuron, Tegmark showed that the superposition should decay in less than one billion billionth of a second. It takes at least ten thousand trillion times as long for a neuron to discharge a signal.

As a result, ideas about quantum effects in the brain are viewed with great skepticism.

However, Penrose is unmoved by those arguments and stands by the Orch-OR hypothesis. And despite Tegmark's prediction of ultra-fast decoherence in cells, other researchers have found evidence for quantum effects in living beings. Some argue that quantum mechanics is harnessed by migratory birds that use magnetic navigation, and by green plants when they use sunlight to make sugars in photosynthesis.

Besides, the idea that the brain might employ quantum tricks shows no sign of going away. For there is now another, quite different argument for it.

In a study published in 2015, physicist Matthew Fisher of the University of California at Santa Barbara argued that the brain might contain molecules capable of sustaining more robust quantum superpositions. Specifically, he thinks that the nuclei of phosphorus atoms may have this ability.

Phosphorus atoms are everywhere in living cells. They often take the form of phosphate ions, in which one phosphorus atom joins up with four oxygen atoms.

Such ions are the basic unit of energy within cells. Much of the cell's energy is stored in molecules called ATP, which contain a string of three phosphate groups joined to an organic molecule. When one of the phosphates is cut free, energy is released for the cell to use.

Cells have molecular machinery for assembling phosphate ions into groups and cleaving them off again. Fisher suggested a scheme in which two phosphate ions might be placed in a special kind of superposition called an "entangled state".

Phosphorus spins could resist decoherence for a day or so, even in living cells

The phosphorus nuclei have a quantum property called spin, which makes them rather like little magnets with poles pointing in particular directions. In an entangled state, the spin of one phosphorus nucleus depends on that of the other.

Put another way, entangled states are really superposition states involving more than one quantum particle.

Fisher says that the quantum-mechanical behaviour of these nuclear spins could plausibly resist decoherence on human timescales. He agrees with Tegmark that quantum vibrations, like those postulated by Penrose and Hameroff, will be strongly affected by their surroundings "and will decohere almost immediately". But nuclear spins do not interact very strongly with their surroundings.

All the same, quantum behaviour in the phosphorus nuclear spins would have to be "protected" from decoherence.

This might happen, Fisher says, if the phosphorus atoms are incorporated into larger objects called "Posner molecules". These are clusters of six phosphate ions, combined with nine calcium ions. There is some evidence that they can exist in living cells, though this is currently far from conclusive.

I decided... to explore how on earth the lithium ion could have such a dramatic effect in treating mental conditions

In Posner molecules, Fisher argues, phosphorus spins could resist decoherence for a day or so, even in living cells. That means they could influence how the brain works.

The idea is that Posner molecules can be swallowed up by neurons. Once inside, the Posner molecules could trigger the firing of a signal to another neuron, by falling apart and releasing their calcium ions.

Because of entanglement in Posner molecules, two such signals might thus in turn become entangled: a kind of quantum superposition of a "thought", you might say. "If quantum processing with nuclear spins is in fact present in the brain, it would be an extremely common occurrence, happening pretty much all the time," Fisher says.

He first got this idea when he started thinking about mental illness.

"My entry into the biochemistry of the brain started when I decided three or four years ago to explore how on earth the lithium ion could have such a dramatic effect in treating mental conditions," Fisher says.

At this point, Fisher's proposal is no more than an intriguing idea

Lithium drugs are widely used for treating bipolar disorder. They work, but nobody really knows how.

"I wasn't looking for a quantum explanation," Fisher says. But then he came across a paper reporting that lithium drugs had different effects on the behaviour of rats, depending on what form or "isotope" of lithium was used.

On the face of it, that was extremely puzzling. In chemical terms, different isotopes behave almost identically, so if the lithium worked like a conventional drug the isotopes should all have had the same effect.

But Fisher realised that the nuclei of the atoms of different lithium isotopes can have different spins. This quantum property might affect the way lithium drugs act. For example, if lithium substitutes for calcium in Posner molecules, the lithium spins might "feel" and influence those of phosphorus atoms, and so interfere with their entanglement.

We do not even know what consciousness is

If this is true, it would help to explain why lithium can treat bipolar disorder.

At this point, Fisher's proposal is no more than an intriguing idea. But there are several ways in which its plausibility can be tested, starting with the idea that phosphorus spins in Posner molecules can keep their quantum coherence for long periods. That is what Fisher aims to do next.

All the same, he is wary of being associated with the earlier ideas about "quantum consciousness", which he sees as highly speculative at best.

Physicists are not terribly comfortable with finding themselves inside their theories. Most hope that consciousness and the brain can be kept out of quantum theory, and perhaps vice versa. After all, we do not even know what consciousness is, let alone have a theory to describe it.

We all know what red is like, but we have no way to communicate the sensation

It does not help that there is now a New Age cottage industry devoted to notions of "quantum consciousness", claiming that quantum mechanics offers plausible rationales for such things as telepathy and telekinesis.

As a result, physicists are often embarrassed to even mention the words "quantum" and "consciousness" in the same sentence.

But setting that aside, the idea has a long history. Ever since the "observer effect" and the mind first insinuated themselves into quantum theory in the early days, it has been devilishly hard to kick them out. A few researchers think we might never manage to do so.

In 2016, Adrian Kent of the University of Cambridge in the UK, one of the most respected "quantum philosophers", speculated that consciousness might alter the behaviour of quantum systems in subtle but detectable ways.

Kent is very cautious about this idea. "There is no compelling reason of principle to believe that quantum theory is the right theory in which to try to formulate a theory of consciousness, or that the problems of quantum theory must have anything to do with the problem of consciousness," he admits.

Every line of thought on the relationship of consciousness to physics runs into deep trouble

But he says that it is hard to see how a description of consciousness based purely on pre-quantum physics can account for all the features it seems to have.

One particularly puzzling question is how our conscious minds can experience unique sensations, such as the colour red or the smell of frying bacon. With the exception of people with visual impairments, we all know what red is like, but we have no way to communicate the sensation and there is nothing in physics that tells us what it should be like.

Sensations like this are called "qualia". We perceive them as unified properties of the outside world, but in fact they are products of our consciousness and that is hard to explain. Indeed, in 1995 philosopher David Chalmers dubbed it "the hard problem" of consciousness.

"Every line of thought on the relationship of consciousness to physics runs into deep trouble," says Kent.

This has prompted him to suggest that "we could make some progress on understanding the problem of the evolution of consciousness if we supposed that consciousnesses alters (albeit perhaps very slightly and subtly) quantum probabilities."

"Quantum consciousness" is widely derided as mystical woo, but it just will not go away

In other words, the mind could genuinely affect the outcomes of measurements.

It does not, in this view, exactly determine "what is real". But it might affect the chance that each of the possible actualities permitted by quantum mechanics is the one we do in fact observe, in a way that quantum theory itself cannot predict. Kent says that we might look for such effects experimentally.

He even bravely estimates the chances of finding them. "I would give credence of perhaps 15% that something specifically to do with consciousness causes deviations from quantum theory, with perhaps 3% credence that this will be experimentally detectable within the next 50 years," he says.

If that happens, it would transform our ideas about both physics and the mind. That seems a chance worth exploring.

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The strange link between the human mind and quantum physics

Quantum theory is the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level.The nature and behavior of matter and energy at that level is sometimes referred to as quantum physics and quantum mechanics. Organizations in several countries have devoted significant resources to the development of quantum computing, which uses quantum theory to drastically improve computing capabilities beyond what is possible using today's classical computers.

In 1900, physicist Max Planck presented his quantum theory to the German Physical Society. Planck had sought to discover the reason that radiation from a glowing body changes in color from red, to orange, and, finally, to blue as its temperature rises. He found that by making the assumption that energy existed in individual units in the same way that matter does, rather than just as a constant electromagnetic wave - as had been formerly assumed - and was therefore quantifiable, he could find the answer to his question. The existence of these units became the first assumption of quantum theory.

Planck wrote a mathematical equation involving a figure to represent these individual units of energy, which he called quanta. The equation explained the phenomenon very well; Planck found that at certain discrete temperature levels (exact multiples of a basic minimum value), energy from a glowing body will occupy different areas of the color spectrum. Planck assumed there was a theory yet to emerge from the discovery of quanta, but, in fact, their very existence implied a completely new and fundamental understanding of the laws of nature. Planck won the Nobel Prize in Physics for his theory in 1918, but developments by various scientists over a thirty-year period all contributed to the modern understanding of quantum theory.

The two major interpretations of quantum theory's implications for the nature of reality are the Copenhagen interpretation and the many-worlds theory. Niels Bohr proposed the Copenhagen interpretation of quantum theory, which asserts that a particle is whatever it is measured to be (for example, a wave or a particle), but that it cannot be assumed to have specific properties, or even to exist, until it is measured. In short, Bohr was saying that objective reality does not exist. This translates to a principle called superposition that claims that while we do not know what the state of any object is, it is actually in all possible states simultaneously, as long as we don't look to check.

To illustrate this theory, we can use the famous and somewhat cruel analogy of Schrodinger's Cat. First, we have a living cat and place it in a thick lead box. At this stage, there is no question that the cat is alive. We then throw in a vial of cyanide and seal the box. We do not know if the cat is alive or if the cyanide capsule has broken and the cat has died. Since we do not know, the cat is both dead and alive, according to quantum law - in a superposition of states. It is only when we break open the box and see what condition the cat is that the superposition is lost, and the cat must be either alive or dead.

The second interpretation of quantum theory is the many-worlds (or multiverse theory. It holds that as soon as a potential exists for any object to be in any state, the universe of that object transmutes into a series of parallel universes equal to the number of possible states in which that the object can exist, with each universe containing a unique single possible state of that object. Furthermore, there is a mechanism for interaction between these universes that somehow permits all states to be accessible in some way and for all possible states to be affected in some manner. Stephen Hawking and the late Richard Feynman are among the scientists who have expressed a preference for the many-worlds theory.

Although scientists throughout the past century have balked at the implications of quantum theory - Planck and Einstein among them - the theory's principles have repeatedly been supported by experimentation, even when the scientists were trying to disprove them. Quantum theory and Einstein's theory of relativity form the basis for modern physics. The principles of quantum physics are being applied in an increasing number of areas, including quantum optics, quantum chemistry, quantum computing, and quantum cryptography.

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What is quantum theory? - Definition from WhatIs.com