Category Archives: Quantum Physics

The contemporary computer processor at only half the size of a penny possesses the extraordinary capacity to carry out 11 trillion operations per second, with the assistance of an impressive assembly of 16 billion transistors.[1] This feat starkly contrasts the early days of transistor-based machines, such as the Manchester Transistor Computer, which had an estimated 100,000 operations per second, using 92 transistors and having a dimension of a large refrigerator. For comparison, while the Manchester Transistor Computer could take several seconds or minutes to calculate the sum of two large numbers, the Apple M1 chip can calculate it almost instantly. Such a rapid acceleration of processing capabilities and device miniaturization is attributable to the empirical observation known as Moores Law, named after the late Gordon Moore, the co-founder of Intel. Moores Law posits that the number of transistors integrated into a circuit is poised to double approximately every two years.[2]

In their development, these powerful processors have paved the way for advancements in diverse domains, including the disruptive field of artificial intelligence (AI). Nevertheless, as we confront the boundaries of Moores Law due to the physical limits of transistor miniaturization,[3] the horizons of the field of computing are extended into the enigmatic sphere of quantum physics the branch of physics that studies the behavior of matter and energy at the atomic and subatomic scales. It is within this realm that the prospect of quantum computing arises, offering immense potential for exponential growth in computational performance and speed, thereby heralding a transformative era in AI.

In this article, we scrutinize the captivating universe of quantum computing and its prospective implications on the development of AI and examine the legal measures adopted by leading tech companies to protect their innovations within this rapidly advancing field, particularly through patent law.

Qubits: The Building Blocks of Quantum Computing

In classical computing, the storage and computation of information are entrusted to binary bits, which assume either a 0 or 1 value. For example, a classical computer can have a specialized storage device called a register that can store a specific number at a time using bits. Each bit is like a slot that can be either empty (0) or occupied (1), and together they can represent numbers, such as the number 2 (with a binary representation of 010). In contrast, quantum computing harnesses the potential of quantum bits (infinitesimal particles, such as electrons or photons, defined by their respective quantum properties, including spin or polarization), commonly referred to as qubits.

Distinct from their classical counterparts, qubits can coexist in a superposition of states, signifying their capacity to represent both 0 and 1 simultaneously. This advantage means that, unlike bits with slots that are either empty or occupied, each qubit can be both empty and occupied at the same time, allowing each register to represent multiple numbers concurrently. While a bit register can only represent the number 2 (010), a qubit register can represent both the numbers 2 and 4 (010 and 100) simultaneously.

This superposition of states enables the parallel processing of information since multiple numbers in a qubit register can be processed at one time. For example, a classical computer may use two different bit registers to first add the number 2 to the number 4 (010 +100) and then add the number 4 to the number 1 (100+001), performing the calculations one after the other. In contrast, qubit registers, since they can hold multiple numbers at once, can perform both operationsadding the number 2 to the number 4 (010 + 100) and adding the number 4 to the number 1 (100 + 001)simultaneously.

Moreover, qubits employ the singular characteristics of entanglement and interference to execute intricate computations with a level of efficiency unattainable by classical computers. For instance, entanglement facilitates instant communication and coordination, which increases computational efficiency. At the same time, interference involves performing calculations on multiple possibilities at once and adjusting probability amplitudes to guide the quantum system toward the optimal solution. Collectively, these attributes equip quantum computers with the ability to confront challenges that would otherwise remain insurmountable for conventional computing systems, thereby radically disrupting the field of computing and every field that depends on it.

Quantum Computing

Quantum computing embodies a transformative leap for AI, providing the capacity to process large data sets and complex algorithms at unprecedented speeds. This transformative technology has far-reaching implications in fields like cryptography,[4] drug discovery,[5] financial modeling,[6] and numerous other disciplines, as it offers unparalleled computational power and efficacy. For example, a classical computer using a General Number Field Sieve (GNFS) algorithm might take several months or even years to factorize a 2048-bit number. In contrast, a quantum computer using Shors algorithm (a quantum algorithm) could potentially accomplish this task in a matter of hours or days. This capability can be used to break the widely used RSA public key encryption system, which would take conventional computers tens or hundreds of millions of years to break, jeopardizing the security of encrypted data, communications, and transactions across industries such as finance, healthcare, and government. Leveraging the unique properties of qubitsincluding superposition, entanglement, and interference quantum computers are equipped to process vast amounts of information in parallel. This capability enables them to address intricate problems and undertake calculations at velocities that, in certain but not all cases,[7] surpass those of classical computers by orders of magnitude.

The augmented computational capacity of quantum computing is promising to significantly disrupt various AI domains, encompassing quantum machine learning, natural language processing (NLP), and optimization quandaries. For instance, quantum algorithms can expedite the training of machine learning models by processing extensive datasets with greater efficiency, enhancing performance, and accelerating model development. Furthermore, quantum-boosted natural language processing algorithms may yield more precise language translation, sentiment analysis, and information extraction, fundamentally altering how we engage with technology.

Patent Applications Related to Quantum Computers

While quantum computers remain in their nascent phase, to date, the United States Patent and Trademark Office has received more than 6,000 applications directed to quantum computers, with over 1,800 applications being granted a United States patent. Among these applications and patents, IBM emerges as the preeminent leader, trailed closely by various companies, including Microsoft, Google, and Intel, which are recognized as significant contributors to the field of AI. For instance, Microsoft is a major investor in OpenAI (the developer of ChatGPT) and has developed Azure AI (a suite of AI services and tools for implementing AI into applications or services) and is integrating ChatGPT into various Microsoft products like Bing and Microsoft 365 Copilot. Similarly, Google has created AI breakthroughs such as AlphaGo (AI that defeated the world champion of the board game Go), hardware like tensor processing units (TPUs) (for accelerating machine learning and deep learning tasks), and has released its own chatbot called Bard (also known as LaMDA).

Patents Covering Quantum Computing

The domain of quantum computing is progressing at a remarkable pace, as current research seeks to refine hardware, create error correction methodologies, and investigate novel algorithms and applications. IBM and Microsoft stand at the forefront of this R&D landscape in quantum computing. Both enterprises have strategically harnessed their research findings to secure early patents encompassing quantum computers. Notwithstanding, this initial phase may merely represent the inception of a competitive endeavor to obtain patents in this rapidly evolving field. A few noteworthy and recent United States patents that have been granted thus far include:

Conclusion

Quantum computing signifies a monumental leap forward for AI, offering unparalleled computational strength and efficiency. As we approach the limits of Moores Law, the future of AI is contingent upon harnessing qubits distinctive properties, such as superposition, entanglement, and interference. The cultivation of quantum machine learning, along with its applications in an array of AI domains, including advanced machine learning, NLP, and optimization, portends a revolution in how we address complex challenges and engage with technology.

Prominent tech companies like IBM and Microsoft have demonstrated their commitment to this burgeoning field through investments and the construction of patent portfolios that encompass this technology. The evident significance of quantum computing in shaping the future of AI suggests that we may be witnessing the onset of a competitive patent race within the sphere of quantum computing.

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The Quantum Frontier: Disrupting AI and Igniting a Patent Race - Lexology

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Digital displays comprising organic materials have brought about a new era in consumer electronics, helping to mass produce brighter screens that hold numerous advantages over those made of regular crystalline materials. These organic light-emitting diodes, or OLEDs, can, for example, enable the manufacture of foldable phones that double their screen size when opened.

Yet even the most advanced OLED displays in production today waste about half of the light they emita shortfall that had seemed unavoidable because it stems from the physics of light. A new study, led by a Weizmann Institute of Science researcher, Prof. Binghai Yan of the Condensed Matter Physics Department, may lead to a change in the way future devices light up their OLED screens.

In this collaborative study, Yan and colleagues discovered a new method for controlling a key property of light. This technique, which involves new material and device designs, paves the way to making screens that are twice as brightor twice as energy efficientas the ones currently on the market. It may also lead to far faster data transmission capabilities than those existing today, applications that showcase the huge potential of next-generation organic semiconductors.

To understand why state-of-the-art displays have a brightness cutoff, we must first consider the property of light known as handedness, or chirality, a term derived from the Greek word for "hand." Its meaning depends on the context. In physics, chirality refers to the self-rotation of particles in relation to their motion. When photons or electrons flow, they move in space, but they also spin. When these particles spin in the same direction in which they travel, as a bullet does, we call their chirality right-handed; when they spin against that direction, they have left-handed chirality.

In biology and chemistry, chirality refers to objects that are mirror images of each other, like two hands. For example, DNA, proteins and most other naturally occurring organic molecules are termed right-handed. And there is considerable interplay between different types of chirality. For instance, the geometric chirality of molecules in an organic material determines the chirality of particles passing through them.

This is relevant to many display applications because these displays have a transparent outer layer made of a chiral material, which allows only one-handed lightsay, right-handedto pass in and out, blocking the entry of photons of the other chirality. It does this to neutralize incoming ambient light, whose chirality is mixed; if allowed to pass through, this light would lower the screen's contrast, making it difficult to view in daylight.

The one-handed transparent layer is essential for operating displays in bright light (try using your smartphone to navigate at high noon without it), but it's wasteful. When the diodes of modern screens emit lightwhich generally has a mixed chiralitytoward the screen's surface, half of this light's photons cannot reach the viewer, as their chirality doesn't match that of the transparent outer layer, which is fixed to neutralize ambient light.

But this may be about to change.

In the new study, Yan and his team proposed controlling the chirality of photons in ways previously deemed impossible. The proposal involves diodes that will predominantly emit light of one chiralitythe one that matches the chirality of the transparent outer layer. This can be achieved by creating diodes that simultaneously emit light in opposite directionsone facing forward, the other backwardand are outfitted with a back panel coated with a polymer containing a chiral organic material.

Half of the diode's light, the one that has a chirality matching the transparent layer, traverses this layer unhindered. But the remaining half is not lost. Rather, it bounces back and forth until hitting the back polymer panel of the diode, which flips its chirality. This polymer is engineered in such a way that the chirality information it contains is efficiently converted into the rotation of electrons, and then into the chirality of light, leading to strongly polarized light emission.

The study began with experimental results that initially appeared to be downright bizarre.

Dr. Li Wan, then a postdoctoral fellow at Linkping University in Sweden, found what we now know to be a method for controlling and amplifying the chirality of light in organic devices.

"These findings ran so counter to everything that was known in this field, other scientists had a hard time believing Wan's results. They said that something was probably wrong with his experiments," recalls Yan.

Wan and his Ph.D. supervisor, Prof. Alasdair Campbell, had shown that they could flip the chirality of an electron flow in their experimental installation by changing the polarity of the battery generating the electric current. Each time they flipped the polarity of the power supply, the chirality of the electron flow changed consistently. As they didn't change the materials, this finding was contrary to all textbook knowledge at the time.

Campbell was convinced they were on to something important, but he passed away in 2021, before Wan could back up his findings theoretically. Following Campbell's death, Wan sought out Yan, whose online lecture on chirality he had heard. In that lecture, Yan talked about his theory which, using concepts of quantum physics, explained how the chirality of a material determines the chirality of an electron flow.

Yan started analyzing Wan's experiments with Wan and two other scientists, Dr. Yizhou Liu of Weizmann's Condensed Matter Physics Department and Prof. Matthew J. Fuchter of Imperial College London. Yan had to extend his theory of chirality so that it would explain Wan's results, but Yan ended up showing that these findings were actually an inevitable outcome of his own theory. Moreover, the scientists found they could also control the chirality of light emitted by the electron flow by making sure that the photons fly out along the same trajectory as the flow, thus preserving their bullet-like spinning.

"We've revealed an intriguing unity between seemingly unrelated aspects of chirality: the structural geometry of a material, the handedness of an electron flow and finally, the handedness of light," Yan says, summing up the new study.

Apart from improving the efficiency of our screens, the study's findings could also be applied to achieving speedy data transmission. They could, for instance, be used to create optical switches that will work vastly faster than any mechanical ones, flipping the chirality of the photon flowsay, right-handed to denote 0, and left-handed, 1by switching the electric polarity.

And last but not least, yet another outcome of this research is that textbooks will need to be updated to account for Yan's theory of chirality.

The findings are published in the journal Nature Photonics.

More information: Li Wan et al, Anomalous circularly polarized light emission in organic light-emitting diodes caused by orbitalmomentum locking, Nature Photonics (2022). DOI: 10.1038/s41566-022-01113-9

Journal information: Nature Photonics

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A collaborative study of a key property of light may help double screen luminescence - Phys.org

Taylor says that the course and Harnishs senior thesis, a play she wrote about the course material, This is Your Computer on Drugswhich she is also directing on April 29 and 30 at Columbiarepresent the culmination of their three-year collaborative relationship.

Harnish took her first class with Taylor, Philosophy of Religion, during the spring semester of her freshman year, after which she decided to become a religion major instead of the double major she had declared in philosophy and theater. This was also when COVID hit, right when Harnish was writing her midterm paper, so the course was completed over Zoom. She then enrolled in two more courses with Taylor during the fall 2020 semester, Theory and Recovering Place, because he had hinted at retirement. Both classes were conducted virtually.

It was the depths of the pandemic, and Harnish, who had returned to Indiana, where she grew up, was having a hard time. She was living alone in a government-subsidized apartment for artists in Indianapolis, working two jobs, taking 16 course credit hours, and trying to cope with life during COVID.

Come midterms, she emailed Taylor to alert him that she was planning on withdrawing from Columbia for the rest of the semester because of her difficulty managing everything. He offered to Zoom with her later that day.

He talked me into staying in school, said Harnish, and its a good thing he did, because my final project for Recovering Place was my first full-length play, The Foundation of Roses.

The 60-page script is a ghost story about her challenging childhood experiences, said Taylor. It was so remarkable that I nominated it for the Religion Departments Peter Awn Award, which is given annually to the most outstanding undergraduate paper or project in the department. My colleagues agreed with my assessment, and Alethea won the award in 2021.

Harnish has since written four more plays. One of them, Phantasmagoria, a one-person, autobiographical show, made its Off-Broadway debut in June 2022 when she performed it at the Downtown Urban Arts Festival, where it won second place for the Best Play Award. The work was about leaving her rural roots in Indiana to attend college in New York.

According to Harnish, she was the first person from her high school to get into an Ivy League university, and traveling halfway across the country to a big city was a culture shock. Meeting Taylor, who became a mentor, was very beneficial for her.

Over time, the relationship has morphed from a mentor-mentee one into something more reciprocal, said Harnish.

Taylor, who started teaching at Williams College in 1973, and arrived full-time at Columbia in 2007, said that early on he detected something very special about Alethea. It was not just her exceptional intelligence, interest, maturity, and determination, but also a rare imaginative creativity.

Once campus came back to life in fall 2021, at the start of Harnishs junior year, the two continued their conversations in person, and Harnish started sending Taylor examples of her writing. They met regularly during Taylors office hours to discuss her work. One day, she asked him what he was working on for his next book. Hegel and quantum mechanics, he said.

In one of those strange moments the theoretical physicist Wolfgang Pauli and the psychologist Carl Jung labeled synchronicity, said Taylor, Alethea said, Thats weird because I want to write and produce a play for my senior thesis about quantum physics and New Age spirituality.

Out of that convergence came the course theyre now co-teaching. They started by delving deeper into their shared interest in the material through reading and further discussion. Few people realize that personal computers, the Internet, the World Wide Web, and the Metaverse all trace their origins to hippies and the drug culture of the 1960s, said Taylor.

The more I thought about it, the clearer it became that this would be the perfect subject for my last course, he continued. My professional career spanned precisely the half-century from the 1960s to the present.

When Taylor asked her to co-teach the course, Harnish was initially terrified. We had spent almost two years in conversation by that point, and I knew that this would be the opportunity of a lifetime, she said. His insisting that he was also learning from me gave me the confidence to take on such a role.

Although Harnish has fully embraced her leadership role with the course this semester, she is not sure if she will pursue a career in higher education. Her immediate plans after graduation are to travel to Greece this summer with a Brooklyn-based theater company, providing administrative support for its apprentice program. She then wants to spend a year in New York, completing the applications for various playwriting fellowships and other writing programs.

Back in the classroom, the next time Hippie Physics meets, Harnish, dressed in a jean shirt, long, pleated skirt, and cowboy boots, leads the discussion on the assigned readings from The Book by Alan Watts and Zen Mind, Beginners Mind by Shunryu Suzuki. One of her touches has been to start every session spending a few moments listening to one of the eras classic rock songs, and then opening the floor to a parsing of the songs meaning. Todays selection is Led Zeppelins Stairway to Heaven.

After she stops the music, she says, What is the implication philosophically of there being a stairway to heaven for us? Were down here, and we have to get up there.

As he watches her effortlessly command the classroom, Taylor says, Strangely, the success of this course makes it both easier and more difficult for me to stop teaching. We hear much, perhaps too much, today about the problems with higher education, and especially with the humanities. But as I watch Alethea teach and her fellow undergraduates respond to her, I have hope for the future.

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A Student Graduates, a Professor Retires, but They Will Stay in Touch - Columbia University

Erwin Schrdinger has been recognized as "the father of quantum mechanics," which deals with subatomic particles. At this level of scale, the normal laws of physics begin to break down, which is why quantum physics is now considered a separate school of thought from classical physics. Famously, Schrdinger once presented a thought experiment to illustrate a paradox inherent in the principle of quantum superposition, which provides that a system can exist in multiple states until its observation leads to the result: There is a cat inside a box, and the cat is both alive and dead until the box is opened, which is an interesting concept to make an allusion to on "Mrs. Davis."

It is hard to deny the similarities between Arthur Schroedinger on "Mrs. Davis" and the Nobel Prize-winning physicist. Besides the cat, Arthur claims to be a scientist himself, and both of them wear glasses. While Arthur is possibly a descendant of Schrdinger, who died in the 1960s, the zaniness of "Mrs. Davis" allows for the possibility that he may be Schrdinger himself in a different state. Either way, it will be interesting to see where the character fits into the equation and why he was missing for ten years.

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Mrs. Davis Episode 1: The Crucial Clue To The Stranded Man's ... - Looper

IISER partners with international collaborators for breakthrough in the field of Quantum Communication  The Financial Express

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IISER partners with international collaborators for breakthrough in the field of Quantum Communication - The Financial Express

'QBism': quantum mechanics is not a description of objective reality it reveals a world of genuine free will  The Conversation

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'QBism': quantum mechanics is not a description of objective reality it reveals a world of genuine free will - The Conversation

Scientists think it will be particularly useful for problems that involve many variables, such as analyzing financial risk, encrypting data, and studying the properties of materials.

Researchers doubt that individuals will own personal quantum computers in near future. Instead, theyll be housed at academic institutions and private companies where they can be accessed through a cloud service.

Quantum computers use fundamental units of information similar to the bits used in classical computing. These are called qubits.

However, unlike conventional computer bitswhich convey information as a 0 or 1qubits convey information through a combination of quantum states, which are unique conditions found only on the subatomic scale.

For example, one quantum state that could be used to encode information is a property called spin, which is the intrinsic angular momentum of an electron. Spin can be thought of like a tiny compass needle that points either up or down. Researchers can manipulate that needle to encode information into the electrons themselves, much like they would with conventional bitsbut in this case, the information is encoded in a combination of possible states. Qubits are not either 0 or 1, but rather both and neither, in a quantum phenomenon called superposition.

This allows quantum computers to process information in a wholly different way than their conventional counterparts, and therefore they can solve certain types of problems that would take even the largest supercomputers decades to complete. These are problems like factoring large numbers or solving complex logistics calculations (see the traveling salesman problem). Quantum computers would be especially useful for cryptography as well as discovering new types of pharmaceutical drugs or new materials for solar cells, batteries, or other technologies.

But to unlock that potential, a quantum computer must be able to process a large number of qubitsmore than any single machine can manage at the moment. That is, unless several quantum computers could be joined through the quantum internet and their computational power pooled, creating a far more capable system.

There are several different types of qubits in development, and each comes with distinct advantages and disadvantages. The most common qubits being studied today are quantum dots, ion traps, superconducting circuits, and defect spin qubits.

Like many scientific advances, we wont understand everything the quantum internet can do until its been fully developed.

Few could imagine 60 years ago that a handful of interconnected computers would one day spawn the sprawling digital landscape we know today. The quantum internet presents a similar unknown, but a number of applications have been theorized and some have already been demonstrated.

Thanks to qubits unique quantum properties, scientists think the quantum internet will greatly improve information security, making it nearly impossible for quantum encrypted messages to be intercepted and deciphered. Quantum key distribution, or QKD, is a process by which two parties share a cryptographic key over a quantum network that cannot be intercepted. Several private companies already offer the process, and it has even been used to secure national elections.

At the same time, quantum computers pose a threat to traditional encrypted communication. RSA, the current standard for protecting sensitive digital information, is nearly impossible for modern computers to break; however, quantum computers with enough processing power could get past RSA encryption in a matter of minutes or seconds.

A fully-realized quantum network could significantly improve the precision of scientific instruments used to study certain phenomena. The impact of such a network would be wide-ranging, but early interest has centered on gravitational waves from black holes, microscopy, and electromagnetic imaging.

Creating a purely quantum internet would also relieve the need for quantum information to transition between classical and quantum systems, which is a considerable hurdle in current systems. Instead, it would allow a set of individual quantum computers to process information as one conglomerate machine, giving them far greater computational power than any single system could command on its own.

"The quantum internet represents a paradigm shift in how we think about secure global communication," said David Awschalom, the Liew Family Professor in Molecular Engineering and Physics at the University of Chicago, director of the Chicago Quantum Exchange, and director of Q-NEXT, a Department of Energy Quantum Information Science Center at Argonne. "Being able to create an entangled network of quantum computers would allow us to send unhackable encrypted messages, keep technology in perfect sync across long distances using quantum clocks, and solve complex problems that one quantum computer might struggle with alone--and those are just some of the applications we know about right now. The future is likely to hold surprising and impactful discoveries using quantum networks."

To date, no one has been able to successfully create a sustained quantum network on a large scale, but there have been major advances.

In 2017 researchers at the University of Science and Technology of China used lasers to successfully transmit entangled photons between a satellite in orbit and ground stations more than 700 miles below. The experiment showed the possibility of using satellites to form part of a quantum network, but the system was only able to recover one photon out of every 6 milliontoo few to be used for reliable communication.

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What is the quantum internet? | University of Chicago News

Yesterday, data was simply stored and managed. Today, data is an essential differentiator. At Quantum, we believe it's time to shift the focus from accumulating data to making it work much harder. Its a new data reality thats endlessly alive. Its massively growing, widely distributed, unstructured, and its gaining value at every turn. Your video and unstructured data not only needs to be fully protected, but it is also full of possibility. Quantum partners with you so you can shape it, use it, and transform it into the information you need to drive forward. With Quantum, you can enrich, orchestrate, protect, and archive your video and unstructured data, securely and at scalenow and for decades to come.

Its not only about managing data. Its about making sure you can extract value from it to gain a competitive edge. Between 80-90% of data collected today is unstructured. Locked inside these video and audio files, photos, security camera footage, sensor data, scientific data, and satellite imagery is a wealth of information that holds the key to informed decision-making.

We enable a world where data is alive. We make it right-time, right-place data so its available, discoverable, and safe. With Quantum, you have the insights you need to drive new opportunities, explore new paths, or accelerate the next groundbreaking discovery. Our bold, innovative, end-to-end data solutions allow forward-thinking organizationslike yoursto harness the enriched world of living data.

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This isnt inflexible, one-size-fits-all data management. Its innovative technology that supports your business, your needs, and your budget through the entire lifecyclefrom where data is captured to where its stored to where its used. From the worlds fastest file system for video to OPEX-friendly software subscriptions and as-a-Service options, Quantum solutions support your business every step of the way. Whether your business is helping to keep the world safe, making breakthrough discoveries, or creating entertainment, our end-to-end data solutions are built for living data.

The Tools You Need to Add Value to Your Data

Quantum builds in data enrichment at the foundation of our solutions, so getting valuable information from your data is not an afterthought. With complete, ecosystem-friendly solutions, you can store as much data as you neednow and in the futureand leverage rich information about your business. Quantum solutions allow you to avoid overprovisioning your data infrastructure through scalable on-prem solutions and subscription-based models. So, with Quantum, your data works for you.

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About Quantum | Quantum

Yoram AlhassidFrederick Phineas Rose Professor of PhysicsSPL 50yoram.alhassid@yale.edu203-432-6922Research Website Theorist

Current Projects:

The nuclear many-body problem;Femtoscience and nanoscience: nuclei quantum dots and nanoparticles;Cold atomic Fermi gases

Current Projects:

Quadratic Echo Line-Narrowing, Imaging Hard and Soft Solids, Advancing Spectral Reconstruction with Undersampled Data Sets, Custom NMR/MRI Probe Design and Construction

Current Projects:

Ultracold atomic physics in optical lattices

Current Projects:

Optomechanics: Radiation Pressure - Radiation pressure in the quantum engine, Optical control of microstructures, Mechanical control of nonclassical light and Persistent Current - Microcantilevers and probes of closed mesoscopic systems, In-situ electron thermometry, Persistent currents in normal-metal rings

Current Projects:

Haloscope At Yale Sensitive to Axion CDM (HAYSTAC), Electric dipole moment, Casimir effect

Current Projects:

Cryogenic Underground Observatory for Rare Events (CUORE), IceCube Neutrino Obervatory, CUORE Upgrade with Particle IDentification (CUPID), ATLAS, COSINE-100, DM-Ice, Haloscope At Yale Sensitive To Axion CDM (HAYSTAC)

Current Projects:

Quantum error correction when the noise is biased, Scalable fault-tolerant quantum error correction with bosonic qubits

Current Projects:

Exciton Transport & Diffusion; Time-Dependent Phenomena; Heterojunctions, Interfaces and Substrates; Defects

Current Projects:

The study of problems at the interface of optical and condensed matter physics

Current Projects:

Quantum transport phenomena in disordered media, mesoscopic electron physics, non-linear and chaotic dynamics, quantum and wave chaos, quantum measurement and quantum computing. Laser physics, non-linear optics, microcavity and random lasers.

Current Projects:

Quantum transductionfrom microwave to optical photons,Quantum networksand quantum communications,Superconducting quantum detectors

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Quantum Physics | Department of Physics - Yale University

Origin of Quantum Theory

In the 1900s, the field of Physics seemed, for the briefest time, to be at a halt. We were, however, at the brink of the discovery of one of the most revolutionary theories proposed to date: quantum physics. This theory was developed by a German physicist named Max Planck: he proposed that the energy of electromagnetic waves, unlike previously thought, was not a continuum, but rather, that there was a minimal, unbreakable, quantifiable unit of energy, that we call quanta. Plank's theory was shortly thereafter extended by Einstein, who found that the quantization of radiation provided an explanation for the photoelectric effect.

A lot of experiments, including the double-slit experiment by the famous mathematician Thomas Young, and Einstein's aforementioned photoelectric effect, provided extensive proof that waves and particles were not two different physical objects, but rather, that at a small enough scale, particles exhibit wave-like behavior, and electromagnetic waves (that is, light) behave as if they were tiny massless particles made of units of energy: the famous quanta. Wener Heisenberg would further build on this idea of particle-wave duality and postulate in 1927 one of the main axioms of quantum mechanics: the uncertainty principle. This theorem tells us that, for subatomic particles, we cannot exactly measure simultaneously their position and their velocity, giving a fundamental limit to measurements, a property that is based on the wave-like nature of particles.

Finally, it was Paul Dirac and Erwin Schrodinger who formulated the mathematical framework that tied together atomic theory with quantum mechanics. They developed the Schrodinger equation, which allows us to compute the wavefunction of a quantum system, and the more general, relativistic version, called the Dirac equation. Their work ultimately led to both of them winning a Nobel prize in Physics in 1933.

The fundamental postulates of quantum theory are:

In simpler terms, a wavefunction is a probabilistic description of a system. Many times it is said that a quantum system can be in a superposition of different states, and indeed, the wavefunction represents all of the possible states on which you can find a quantum particle (for example, all of the different possible positions) and their associated probability.

$$i hbar frac{partial}{partial t}Psi(t,x) = left( - frac{hbar ^2} {2m} frac{partial^2}{partial x^2 } + V(t,x) right) Psi(t,x) $$

This equation appears difficult at first sight, but it can be broken down into pieces in the following way: the left-hand side of the equation indicates the time evolution. {eq}hbar {/eq} is the plank constant, which gives us a sense of the energy scale of the system we are working with. On the right-hand side, we find two different terms, the first one involving the velocity of the particle, and thus corresponding to the kinetic energy, and the second one, {eq}V(t,x) {/eq}, corresponding to the potential energy.

When we measure a particle, the wavefunction is said to "collapse" - that is, the particle will not be in a superposition of states with associated probabilities anymore, but in a definite single state, corresponding to the measured quantity.

These principles have many consequences and have been used to derive many important theorems, but two of them are the most notable: Heisenberg's uncertainty principle and the existence of entanglement.

As mentioned before, Heisenberg's uncertainty principle states that one cannot know with perfect accuracy both the position and the velocity of a quantum particle. Plainly said, there is a fundamental limit on the information one can extract out of a quantum system, and this is because when we measure a particle and the wavefunction collapses, there is a loss of information happening during that collapse. Another way to understand this principle is to think about it in practice: Let's say that we have an electron and that we wish to measure its location. For that, we would need to look at the electron, either by shining a laser at it or by taking a photograph. Both processes are invasive and disrupt the state of the electron, causing a change in its internal energy, since we would be bombarding it with a ray of light. This change of energy, which is needed to determine the position, will affect the velocity of the electron. Therefore, we cannot know with exactitude the speed of the electron anymore. the same happens if we try to measure the velocity: in that case, it will be the position of the electron the one we would not be able to determine exactly.

Entanglement is a different phenomenon that occurs when two quantum particles interact. Sometimes, two interacting quantum particles can stay connected - in quantum terms this means that instead of there being two different wavefunctions, one representing each particle, there is a bigger, single wavefunction representing both of them at the same time. The result is that both of these particles stay connected, and can influence each other even if they are thousands of miles apart. The coolest (and most spooky!) thing is that, because we know that measurements affect the state of a quantum system, that means that if you separate two entangled particles and then you measure the state of one of them, the state of the other one will immediately be affected as well, no matter how far it is located.

Let's try to clarify all of these ideas with a famous example: Schrodinger's Cat.

This is a thought experiment that is aimed at illustrating the concept of superposition. Let's say we have a hypothetical cat, and that we put it inside of a box with poison, and then we close the box. We will also assume that the cat has a 50/50 chance of eating the poison. Therefore, until we open the box, we do not know with certainty if the cat will be dead or alive - there is a 50/50 chance of him being either. At that stage, if we imagine that the cat is a quantum particle, we can write the cat's wavefunction, for example, to be something like this:

$$Psi = 0.5 |text{dead}> + 0.5 |text{alive}> $$

This means that the cat is in a state which is a superposition of dead and alive: it is dead with a 50% chance, and alive with a 50% chance. Let's say that we now open the box, and find that the kitty is alive. The measurement, or the act of opening the box, has made the wavefunction collapse, and now we find the cat in a state of 100% aliveness.

Another spooky and plain amazing phenomenon that quantum particles can exhibit is that of quantum tunneling.

In the classical world, when you throw a ball against a wall, you know exactly what will happen. The wall acts as a barrier that is impenetrable, and the ball will certainly bounce back. However, this is no longer true for quantum particles. Given that quantum particles can be in a superposition of position states, they sometimes exhibit really spooky characteristics. When you throw a quantum particle against a barrier, there might be a small probability of finding the particle on the other side of the barrier. This means that, if you repeat the experiment again and again measuring the position of the particle right after hitting the barrier, while most of the times you will find that the quantum particle bounced back, a small portion of the times you will find the particle on the other side of the barrier: this is called quantum tunneling.

Today we learned that Quantum Theory is the branch of physics that studies atomic and subatomic particles, and their associated phenomena. It was developed in the early 1900s by Max Plank, and the theory was extended by many physicists including Einstein, Heisenberg, Dirac, and Schrodinger.

Quantum particles are described by a wavefunction, and when we observe them (that is when we measure them) we can alter their state. Quantum particles can be found in a superposition of states, but we do not know which one until we measure them: this is best exemplified by the hypothetical Schrodinger's cat, a thought experiment consisting of putting a cat on a box with poison, which results in the cat being in a superposition of dead and alive, with the observer not knowing until they open the box.

Some important principles of Quantum theory include the Heisenberg uncertainty principle, which indicates that we cannot know with perfect accuracy both the position and the velocity of a quantum particle, and the existence of entanglement, a long-range interaction effect that interacting quantum particles can have on one another.

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