Monthly Archives: January 2021

UK Research and Innovation (UKRI) is investing 31 million into seven projects to show how quantum technologies could solve some of the greatest mysteries of the universe such as dark matter and black holes.

A project led by the University of Nottingham aims to provide insights to the physics of the early universe and black holes that cannot be tested in a laboratory.

The team will use quantum simulators to simulate the conditions of the early universe and black holes with sufficient accuracy to confirm some of Einsteins predictions on general relativity.

A team led by Royal Holloway, University of London, will develop new quantum sensors which can be used to search for dark matter.

The projects are supported through the Quantum Technologies for Fundamental Physics programme, delivered by the Science and Technology Facilities Council (STFC) and the Engineering and Physical Sciences Research Council (EPSRC) as part of UKRIs Strategic Priorities Fund. The programme is part of the National Quantum Technologies Programme.

STFC is proud to support these projects that utilise cutting-edge quantum technologies for novel and exciting research into fundamental physics.

Major scientific discoveries often arise from the application of new technologies and techniques. With the application of emerging quantum technologies, I believe we have an opportunity to change the way we search for answers to some of the biggest mysteries of the universe.

These include exploring what dark matter is made of, finding the absolute mass of neutrinos and establishing how quantum mechanics fits with Einsteins theory of relativity.

I believe strongly that this exciting new research programme will enable the UK to take the lead in a new way of exploring profound questions in fundamental physics.

The National Quantum Technologies Programme has successfully accelerated the first wave of quantum technologies to a maturity where they can be used to make advances in both fundamental science and industrial applications.

The investments UKRI is making through the Quantum Technologies for Fundamental Physics programme allows us to bring together the expertise of EPSRC and STFC to apply the latest advances in quantum science and technology to explore, and answer, long-standing research questions in fundamental physics.

This is a hugely exciting programme and we look forward to delivering these projects and funding further work in this area as well as exploring opportunities for exploiting quantum technologies with other UKRI partners.

As we build back better from the pandemic, its critical that we throw our weight behind new transformative technologies that could help to unearth new scientific discoveries and cement the UKs status as a science superpower.

Todays funding will enable some of the UKs most ambitious quantum researchers to develop state of art technologies that could help us solve important unanswered questions about our universe, from proving Einsteins theory of relativity to understanding the mysterious behaviour of black holes.

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New quantum technology projects to solve mysteries of the universe - Open Access Government

A collaboration of scientists from across the UK are working on a new project to detect hidden particles, the discovery of which could open up a new frontier in fundamental physics.

The project, Quantum Sensing for the Hidden Sector (QSHS), is led by scientists at the University of Sheffield and involves the Universities of Cambridge, Lancaster, Liverpool, Oxford, Royal Holloway and University College London and the National Physical Laboratory.

Funded by the Science and Technology Facilities Council (STFC), as part of UK Research and Innovation (UKRI), the project is the best supported and largest UK effort in hidden sector physics to date, and involves scientists from a range of disciplines within physics.

QSHS aims to solve some of the most fundamental mysteries in modern physics using new technologies being developed for the rapidly expanding field of quantum measurement science.

Working with the Axion Dark Matter Experiment (ADMX) collaboration in the US, but also developing pioneering quantum electronics and novel experiment designs in the UK. The group aims to shed new light on the particles of the hidden sector which could provide new insights into fundamental mysteries, most importantly the dark matter problem, which is the observation that galaxies and the observable Universe are heavier than their observed constituents - stars, planets, dust and gas.

The extra matter making up the difference could be made up wholly or partly of ultra-light particles, so-called hidden sector particles that have so far evaded detection. The signatures of these particles are signals so faint that the world's most sensitive measurement devices will be developed by our team for the search.

It's high risk, high reward science. You might see nothing or you might on the other hand make a massive discovery. Nobody knows which, but the discovery of hidden sector particles would open up a completely new frontier in fundamental physics.

Professor Ed Daw

Professor of dark matter and gravitational wave physics at the University of Sheffield

Professor Ed Daw, Professor of dark matter and gravitational wave physics at the University of Sheffield, and principal investigator for the project, said: Hidden sector particles, if they exist, may be the so-far unidentified dark matter, and may in addition solve important outstanding problems with the theory that we have developed governing quarks and the atomic nucleus. The hidden sector may even provide critical insights into the inflationary phase thought to occur very shortly after the big bang.

It's high risk, high reward science. You might see nothing or you might on the other hand make a massive discovery. Nobody knows which, but the discovery of hidden sector particles would open up a completely new frontier in fundamental physics. It would be like the invention of the particle beam accelerator, a whole new way of doing science.

Hidden sector particles may play other significant roles in physics, including in early Universe cosmology and the evolution of the Universe in the moments after it came into existence. We are excited to be embarking on this journey of discovery, and we hope the British public will share in this excitement as we start this research project.

The discovery of hidden sector particle dark matter would be a momentous event in fundamental physics. The dark matter problem is now over 50 years old, but in addition a new set of light particles would be bound to solve some of the persistent problems with the standard model of particle physics.

Professor Stafford Withington, Co-Investigator and Senior Project Scientist on QSHS from the University of Cambridge, said: In recent years, the UK has invested heavily in establishing the laboratory infrastructure needed to develop a new generation of ultra-low-noise electronics and associated control systems. The new electronics operate in a fundamentally different way to the conventional electronics with which we are all familiar. It exploits the mysterious behaviour of quantum mechanics to yield sensitivities that are limited only by the fluctuations inherent in the fundamental nature of space-time. The electronic devices are based on a range of superconducting materials, and work at temperatures of around 10mK, where thermal fluctuations are essentially eliminated.

The team will develop this technology to a high level of sophistication, and deploy it to search for the lowest-mass particles detected to date. These particles are predicted to exist theoretically, but have not yet been discovered experimentally. Our ability to probe the particulate nature of the physical world with sensitivities that push at the limits imposed by quantum uncertainty will open up a new frontier in physics.

This new window will allow physicists to to explore the nature of physical reality at the most fundamental level, and it is extremely exciting that the UK will be playing a major international role in this new generation of science.

The detection of these hidden particles requires technology of unprecedented sensitivity. The team are aiming to develop new and world-leading devices which could also be applied to make critical progress in other areas of physics such as quantum computing and quantum systems engineering.

The UK research team will form a collaboration with the US based ADMX collaboration, who operate the most sensitive detector for a particular variety of hidden sector particle, the axion.

The full QSHS team consists of The University of Sheffield (lead institution, principal investigator Prof. E Daw), University of Cambridge (co-I and senior project scientist Prof. Stafford Withington), Lancaster University (co-Is Prof. Yuri Pashkin, Dr. Ian Bailey, Dr. Ed Laird) The University of Liverpool (co-I DR. Ed Hardy), The National Physical Laboratory (co-Is Prof. Ling Hao, Prof. John Gallop), University of Oxford (co-Is Dr. Peter Leek, Prof. Gianluca Gregori, Prof. John March-Russell, Prof. Subir Sarkar, Dr. Boon-Kok Tan) , Royal Holloway - University of London (co-Is . Prof. Phil Meeson, Dr. Stephen West), and University College London (co-I Dr. Ed Romans).

With almost 29,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the worlds leading universities.

A member of the UKs prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

Sheffield is the only university to feature in The Sunday Times 100 Best Not-For-Profit Organisations to Work For 2018 and for the last eight years has been ranked in the top five UK universities for Student Satisfaction by Times Higher Education.

Sheffield has six Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, GlaxoSmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.

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University of Sheffield to lead multi-million pound project which could open up a new frontier in physics - University of Sheffield News

One of my all-time favorite plays is Copenhagen by Michael Frayn. The 1998 Tony Award winner tries to untangle the mysteries of a night in 1941 when German physicist Werner Heisenberg visited his mentor Niels Bohr at his home in the Danish capital. Bohr and Heisenberg had worked together to deduce the rules of quantum physics (known as the "Copenhagen model"), but now Heisenberg had a new boss, Adolf Hitler, who wanted an atomic bomb.

After a dinner prepared by Bohr's wife, Margarethe, Bohr and Heisenberg went for a walk in the garden. But instead of wandering for hours, as they often did while working on difficult problems, they quickly returned to the house. Heisenberg thanked Margarethe and showed himself out.

Soon after, the Bohrs fled Nazi-occupied Denmark in the middle of the night. They made their way to America, where Niels Bohr worked on the Manhattan Project. Meanwhile, Heisenberg became the head of the Nazi bomb project, which never even came close to producing a working weapon. Neither man ever revealed what they talked about that night. Did Heisenberg try to recruit Bohr for the Nazi bomb project? Was he there to ask his old mentor to check his math? Or did he carry a warning to Bohr? The three people present went to their graves keeping the secret. Frayn's play explores the possibilities, with the ghosts of the three people present reliving all the different interpretations of the events.

Kemp Powers' 2013 play, One Night in Miami, tries something similar. On February 25, 1964, Cassius Clay beat Sonny Liston to claim the heavyweight boxing title. In the crowd that night were Malcolm X, Sam Cooke, and Jim Brown. After the fight, instead of hitting the legendary Miami party circuit, the soon-to-be Muhammad Ali retreated to Malcolm X's hotel room, where they were later joined by Cooke and Brown. It was an unprecedented gathering of Black talent, and the weightiness of the evening was not apparent at the time. No one knows what they really talked about, but Powers' script imagines an evening that is equal parts celebratory and foreboding.

Actress Regina King chose to adapt One Night in Miami for her directorial debut after winning the Academy Award for Best Supporting Actress for 2018's If Beale Street Could Talk. King's first task was casting four of the most recognizable people in 20th-century history. It's hard to say who had the hardest job. Kingsley Ben-Adir, who recently played Barack Obama in The Comey Rule, portrays Malcolm X which means he's in the shadow of Denzel Washington's astounding performance in Spike Lee's biopic. Ballers' Eli Goree is Ali, a role that even the likes of Will Smith couldn't pull off convincingly. Aldis Hodge, MC Ren from Straight Outta Compton, plays Jim Brown, a man considered by some to be the greatest player in NFL history and who went on to a 50-year career in film and television. As Sam Cooke, Leslie Odom Jr. at least has the advantage of a great singing voice, since he originated the role of Aaron Burr in Hamilton on Broadway.

Crafting these performances to perfection is clearly where King's head is at and rightly so. All four of her leads turn out to be stellar. Goree's Ali is, improbably, the best of the bunch. He can both deliver the legendary bombast and reveal a thoughtful vulnerability in private. Ben-Adir's Malcolm X is on the receiving end of most of that vulnerability. In Powers' script, Malcolm X is the most morally ambivalent character, who intends to use the publicity surrounding his friend's historic championship to launch his schism with the Nation of Islam. But it is Malcolm who convinces Sam Cooke to stop devoting his talent to sappy love songs and push socially conscious works like "A Change is Gonna Come."

One Night in Miami lacks Copenhagen's experimental streak, but it functions beautifully as a four-handed character sketch of some of the most important Black men of the 20th century. (It's undoubtedly more entertaining when I saw Copenhagen performed live, half the audience left during intermission.) King's cameras pace restlessly around the room, finding framing that keeps all four actors in view, as they would appear onstage. This is a film that carefully doles out close-ups, and more directors should heed King's example. The film loses momentum when the group breaks up, and each character gets a little exposition designed to educate the audience on their historical importance. But when the four legends are together in the same room, One Night in Miami crackles with the fire of life.

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The Greatest: Four Legends Gather in One Night in Miami - Memphis Flyer

LONDON, Jan. 13, 2021 /PRNewswire/ --Raytheon UK, a unit of Raytheon Technologies (NYSE: RTX), alongside strategic partner Capita, received a contract award to provide the Royal Navy with transformative technology, training and learning solutions over the next 12 years.

The contract, which will be led by Capita, has an initial contract value of 200 million to Raytheon UK and will ensure the Royal Navy offers best-in-class training to all its service personnel. It will accelerate the use of new technology, processes and learning solutions, aligning with the Royal Navy's transformation agenda and positioning it to thrive in the 21st century.

"This announcement allows the team to begin efforts to transform the Royal Navy's training and learning solutions, and to modernise and transform the way training is delivered across the Armed Forces," said Jeff Lewis, chief executive of Raytheon UK. "Our extensive experience in leading large and complex transformative change programmes around the world will provide the Royal Navy with tailored, digitally enabled training, fit for the future."

Raytheon UK will play a key role in modernising and transforming the Royal Navy's training analysis, design, delivery, assurance, and management/support services, helping to make the UK Armed Forces more agile and adaptable than ever to tackle future challenges.

"We are committed to investing in the UK and helping to keep the country secure and our Armed Forces equipped with the best affordable sovereign solutions, creating highly skilled jobs across the UK," Lewis said. "We look forward to delivering these solutions to the Royal Navy over the coming years."

Rear Adm. Phil Hally MBE, the Royal Navy's director of people and training, said, "The award of this 12-year contract marks a major milestone for Navy transformation. It will see the modernisation of the RN training system at scale to deliver the operational capabilities of the future, unlock more opportunities for our people, and get better trained people to the frontline, quicker."

About Raytheon UKWith facilities in Broughton, Waddington, Glenrothes, Harlow, Gloucester and Manchester, Raytheon UK is invested in the British workforce and the development of UK technology. Across the country the company employs 1,700 people. As a prime contractor and major supplier to the U.K. Ministry of Defence, Raytheon UK continues to invest in research and development, supporting innovation and technological advances across the country.

Raytheon UK is a unit of Raytheon Technologies and sits within the Raytheon Intelligence & Space business.

About Raytheon TechnologiesRaytheon Technologies Corporation is an aerospace and defense company that provides advanced systems and services for commercial, military and government customers worldwide. With four industry-leading businesses Collins Aerospace Systems, Pratt & Whitney, Raytheon Intelligence & Space and Raytheon Missiles & Defense the company delivers solutions that push the boundaries in avionics, cybersecurity, directed energy, electric propulsion, hypersonics, and quantum physics. The company, formed in 2020 through the combination of Raytheon Company and the United Technologies Corporation aerospace businesses, is headquartered inWaltham, Massachusetts.

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Raytheon UK part of team transforming the Royal Navy's technology, training and learning solutions - PRNewswire

Abstract

Optical trapping and manipulation have been widely applied to biological systems, and their cutting-edge techniques are creating current trends in nanomaterial sciences. The resonant absorption of materials induces not only the energy transfer from photons to quantum mechanical motion of electrons but also the momentum transfer between them, resulting in dissipative optical forces that drive the macroscopic mechanical motion of the particles. However, optical manipulation, according to the quantum mechanical properties of individual nanoparticles, is still challenging. Here, we demonstrate selective transportation of nanodiamonds with and without nitrogen-vacancy centers by balancing resonant absorption and scattering forces induced by two different-colored lasers counterpropagating along a nanofiber. Furthermore, we propose a methodology for precisely determining the absorption cross sections for single nanoparticles by monitoring the optically driven motion, which is called as optical force spectroscopy. This method provides a novel direction in optical manipulation technology toward development of functional nanomaterials and quantum devices.

Nanoparticles and nanomaterialssuch as quantum dots, nanocrystals, carbon nanomaterials, molecular aggregates, and metal nanoparticleshave attracted great attention owing to their unique mechanical and quantum mechanical properties and have been used in various photonic, electronic, mechanical, and biomedical devices, such as light emitters, solar cells, photocatalysts, molecular electronics, structural materials, drug delivery, and bioimaging (16). Because these properties of nanoparticles/nanomaterials are strongly influenced by the surrounding environment and are significantly different from the bulk properties, such as quantum size effect, the characterization of individual nanoparticles provides important knowledge for advancing nanomaterial and quantum material sciences. Furthermore, the selection and sorting of single nanoparticles according to their characteristics are essential and desired for the precise design of functional nanostructures and development of single-quantum sensors, single-photon sources, and quantum information devices (7, 8).

Optical trapping and manipulation based on optical forces are promising tools for positioning, transporting, and aligning fine particles without mechanical contacts (9, 10). Optical tweezers proposed by Ashkin et al. have been used in various research fields, such as biophysics, cell biology, microfluidics, total analytical systems, and micromechanics (11, 12). Optical sorting of dielectric objects has been developed using holographic optics, flow cytometry, interference technology, and near field photonics (1315). Metal nanoparticles can also be separated by optical forces based on the surface plasmon resonances (16). However, these techniques are limited to the particle selection by the size and refractive index. The optical gradient and scattering forces exerted on small particles and their dependences on the diameter, wavelength, and relative refractive index are determined by the Mie theory. Furthermore, the reported methods are applicable only to the sorting of submicrometer or larger-sized dielectric particles. Trapping and manipulation of smaller-sized particles remain challenging because the optical force becomes weaker in proportion to the particle volume.

In this study, we demonstrate the optical selection and sorting of nanoparticles according to their quantum mechanical properties. Semiconductor quantum dots exhibit characteristic optoelectronic properties due to the quantum confinement of the electron-hole pairs in the nanovolume (1, 2). Diamond nanoparticles exhibit quantum resonances of point defects (17, 18). The optical forces reflect these quantum mechanical properties of nanoparticles and their optical characteristics (19, 20). The interaction between light and nanomaterials induces not only an energy transfer from the photons to the quantum mechanical motion of the electrons but also a momentum transfer between them. The change in the photon momentum give rise to optical forces, which drive the macroscopic mechanical motion of the nanoparticles. We note that there are three types of optical forces: (i) gradient force arising from the inhomogeneous intensity distribution of the electric field, (ii) dissipative scattering force caused by the real part of the refractive index, and (iii) quantum resonant absorption force exerted on nanomaterials. Therefore, we can realize the characterization and selective manipulation of single nanoparticles having various properties by monitoring and controlling the particle motions. This methodology provides a new direction in optical force technology toward advances in nanomaterial sciences.

To realize the sorting of individual nanoparticles, we use counterpropagating different-colored lasers that can extract the resonant absorption force by cancelling out the scattering forces. The counterpropagating beam systems were constructed using a pair of lenses with large numerical aperture placed opposite to each other (21) and the inversely directed evanescent waves (16). However, it is difficult to exclude the influence of the gradient force that easily negates the small effect of the quantum resonance force. Thus, we focused on tapered optical fibers, i.e., nanofibers (22, 23). We prepared a nanofiber with a diameter of several hundred nanometers and length of several millimeters (24), which exhibited the characteristics of single-mode propagation, thereby forming an intense evanescent field around the fiber and enabling long-distance propagation while maintaining a tightly focused beam of light. Using these characteristics, a uniform electric field distribution could be generated along the fiber by which the particle motion was restricted to one dimension. In addition, the optical gradient force and thermophoretic force, arising from the temperature gradient (e.g., Soret effect), were exerted in a direction perpendicular to the fiber axis such that the particle motion along the nanofiber was driven only by the resonant absorption and scattering forces. Furthermore, because the momentum of the photons in a waveguide depends on the propagation constants of the individual modes, the single-mode wave in our nanofiber had the constant photon momentum; this provides an ideal platform for analyzing the optical forces exerted on the nanoparticles. On the basis of the balance of the absorption and scattering forces induced by the different-colored lasers counterpropagating along the nanofiber, we succeeded in achieving the selective transportation of single nanoparticles according to the quantum resonant absorption (Fig. 1A).

(A) Concept of optical force absorption spectroscopy. By monitoring the mechanical motion of a single nanoparticle driven by optical forces, the resonant absorption properties can be analyzed with high sensitivity. Using two different-colored lasers counterpropagating along a nanofiber, a nanoparticle is trapped by the gradient force and transported by the absorption and scattering forces. The laser powers are adjusted to cancel out the scattering forces such that the particle moves depending on the absorption cross section. (B) Experimental setup. GR and NIR diode lasers are introduced from both ends of a nanofiber. The laser powers are measured by photodiodes (PD1 and PD2) and controlled by rotational neutral density filters to balance the forces. To record the motion of nanoparticles, a weak red laser is used, and its scattered light is monitored using a microscope-attached charge-coupled device (CCD) camera with filters to cut the strong scattered light of the GR and NIR lasers.

In addition to the selection and sorting, the proposed system can precisely determine the resonant absorption cross sections of single nanoparticles. Fluorescence and photothermal spectroscopies have been widely used for characterizing single nanoparticles and nanomaterials because of their high sensitivity at the level of single-molecule detection (25, 26). However, these methods probe the relaxation processes emitting a photon and thermal energy, which are regarded as indirect absorption measurements. When the excited states of the materials irreversibly transit to other states without undergoing relaxation processes, such as photochemical reactions, these techniques can no longer observe the resonant absorption. Absorption spectroscopy, which directly measures the excitation processes, is an indispensable tool for analyzing the interaction strengths between light and matter. In particular, the absolute values of the absorption cross sections of single nanoparticles/nanomaterials are essential for experimental physics in material science and are crucial for designing nanostructured materials at a single-quantum state level (27). However, it is still challenging to detect extremely small absorption signals of single nanoparticles and nanomaterials. In our method, accurate measurement of quantum resonant absorption is realized by precisely observing the optical forcedriven motions of the nanoparticles, called as optical force spectroscopy. This spectroscopy based on the optical momentum change instead of the energy change is conceptually different from the conventional techniques.

Figure 1B illustrates the experimental setup. A nanofiber with a diameter of 400 nm was fabricated from a commercial single-mode optical fiber (24). The diameter is constant in the waist part of the fiber over a length of several hundred micrometers. The nanofiber was soaked in an aqueous solution of diamond nanoparticles, i.e., nanodiamonds (NDs). Because nitrogen-vacancy centers (NVCs) in NDs have superior properties, such as no photobleaching, high sensitivity to the surrounding environment, and sharp zero phonon line absorption, they have been gaining attention as luminescent and magnetic-responsive nanomaterials that can be used for biological imaging, sensing, and single-photon source (17, 18). Thus, selection and sorting of NDs with and without NVCs are highly desirable. We prepared two types of NDs; one contained NVCs (>300 per particle), i.e., quantum resonant ND (r-ND), and the other was almost free from the NVCs, i.e., nonresonant ND (n-ND). The diameters of both r-NDs and n-NDs were 50 15 nm. Continuous-wave green (GR; 532 nm) and near-infrared (NIR; 1064 nm) diode lasers were launched from both ends of the nanofiber. The NVCs exhibit absorption at the GR region but not at the NIR region (28, 29). Furthermore, we introduce a weak red laser in the fiber as a probe light (690 nm, 0.1 mW) to monitor the motion of the NDs, which was recorded by an optical microscope equipped with a charge-coupled device (CCD) camera.

Figure 2A depicts the trapping and transportation of a single r-ND, where only the GR laser (70 mW) is incident from the left end of the fiber and the motion of the r-ND is observed in the waist part of the fiber. The result shows that the r-ND is attracted by the gradient force of the evanescent field and moves along the fiber because of the dissipative forces. The particle speed is constant at 110 m/s (see a trajectory in fig. S1). We evaluate the force exerted on the r-ND as 89 fN by considering the balance between the optical force and viscous drag using the Faxen formula for correcting the effect of the fiber surface [(23) and see the Supplementary Materials). When the NIR laser is simultaneously incident from the other end of the fiber (from the right), where the NIR laser power is fixed at 250 mW, and the GR laser power is varied from 70 to 0 mW, we achieve the motion control of a single r-ND (Fig. 2B). At the GR laser power of 70 mW, the r-ND moves toward the propagation direction of the GR laser (from left to right). As the GR laser power decreases, the motion decelerates and subsequently stops (~8 s). On further decreasing the GR laser power, the r-ND moves toward the opposite direction. The motion control experiment for an n-ND is illustrated in the Supplementary Materials (fig. S3).

(A) Time-sequential images of the r-ND observed at 2-s intervals. The GR laser is incident from the left end (70 mW). A single r-ND is trapped and transported along the nanofiber at the velocity of 110 m/s. (B) Time-sequential images of the r-ND observed at 4-s interval. The GR laser is incident from the left end of a nanofiber and the NIR laser from the opposite end. The power of the NIR laser is fixed at 250 mW, and the GR laser power is changed from 70 to 0 mW. At approximately 8 s, the optical forces exerted by the two lasers balance each other. The white bar indicates a scale of 100 m. The dotted line represents the nanofiber position.

The dissipative optical force exerted on an r-ND along a nanofiber is composed of two components, namely, absorption and scattering forces (Fabs, Fsca), which are represented by the absorption and scattering cross sections (abs, sca), as followsF=Fabs+Fsca=neffIc(abs+sca)(1)where I and c represent the intensity and velocity of light in a vacuum, respectively, and neff is the effective refractive index of the nanofiber (neff = 1.354 at 532 nm). The scattering cross section for Rayleigh particles is theoretically given bysca=1285n2V234(n12n22n122n22)2(2)where n1 and n2 are the refractive indices of diamond and surrounding water, respectively, is the incident laser wavelength in vacuum, and V is the volume of the particle. In the case of r-NDs including NVCs, abs is given by the transition dipole strength of an NVC and the number of NVCs in r-ND. The NIR laser induces only the scattering force, as NVCs exhibit no absorption at 1064 nm.

We perform a motion control experiment for an n-ND without NVCs to measure the balanced powers of the GR and NIR lasers for restricting the motion of the particle. The NIR laser power was fixed at 160 mW, corresponding to the intensity of 108 MW/cm2 estimated from the mode profile of the nanofiber, while the observed balanced power of the GR laser was 7.61 mW (intensity, 6.06 MW/cm2). As Fabs is not exerted on the n-ND, scattering forces (Fsca) by the GR and NIR lasers balance each other. Moreover, sca strongly depends on the wavelength (Eq. 2), which is compensated by the large difference between the intensities of the GR and NIR lasers. As sca is proportional to the square of the particle volume, the scattering force also changes significantly depending on the particle size. Fortunately, the ratio of the scattering forces at 532 and 1064 nm is constant for any particle size. This is because the volume dependence of sca is the same (V2) for both wavelengths. Thus, it is noted that the balanced powers of the two counterpropagating lasers remain unchanged for n-NDs of any size.

Furthermore, we demonstrate the selective transportation of r-NDs and n-NDs (Fig. 3 and movie S1). The same experimental setup and nanofiber were used, and the NIR laser power was 160 mW. The GR laser power was adjusted to 7.40 mW to drive different motions of the r-NDs and n-NDs. This value is slightly lower than the balanced power of the n-ND such that the scattering force exerted by the NIR laser is stronger for n-NDs than that by the GR laser, whereas the resonant absorption force on the r-NDs by the GR laser reverses the force strength relation. By switching the probe laser on and off, we can measure the emission from the NVCs and thus distinguish between the r-NDs and n-NDs. The two particles at both ends are r-NDs (numbered 1 and 4) and the other two particles are n-NDs (numbered 2 and 3). Scattered light spots of four NDs have nearly the same intensities when the probe laser is off, while the spots of r-NDs are brighter than the spots of n-NDs in Fig. 3 because the NVC emission is added to the scattered light. The r-NDs slowly move to the right (along the propagation direction of the GR laser), whereas the n-NDs move in the opposite direction (see trajectories in fig. S2). This result clearly demonstrates the selective transportation of NDs according to the quantum resonant absorption of NVCs by using the optical forces.

Time-sequential images observed at 2-s intervals. Numbers indicate individual NDs. Particles 1 and 4 represent r-NDs, and particles 2 and 3 represent n-NDs, which is confirmed by the emission of the NVCs. The powers of GR and NIR lasers are set at 7.40 and 160 mW, respectively. The r-NDs move to the right (direction of GR laser propagation), whereas the n-NDs move toward the opposite direction. The white bar indicates a scale of 100 m. The dashed line represents the nanofiber position.

Next, we analyze the absorption cross section (abs) of a single r-ND. We prepared the same experimental conditions and used the same nanofiber that was used for the balanced power measurement of an n-ND. At the NIR laser power of 160 mW, the balanced power of the GR lasers for an r-ND was measured to be 6.75 mW (intensity, 5.37 MW/cm2). Then, by turning the NIR laser off, the motion of r-NDs driven by the GR laser was observed to determine the strength of the optical force. On the basis of the balance with the viscous drag, the optical force composed of Fabs and Fsca was calculated as 6.30 fN. As a reference, the data of the n-ND were used for the present absorption analysis. By comparing the balanced powers of the GR laser for the r-ND (Pr-ND = 6.75 mW) and n-ND (Pn-ND = 7.61 mW), we obtain the ratio of Fabs and Fsca exerted on the r-ND as (Pn-ND Pr-ND):Pr-ND (Fig. 4) such that the measured optical force on the r-ND (F = 6.30 fN) can be decomposed into Fabs = 0.71 fN and Fsca = 5.59 fN. This result demonstrates that the absorption and scattering forces exerted on a single r-ND can be separately determined with subfemtonewton order accuracy. Thus, from Eq. 1, we evaluate the abs to be 2.9 1014 cm2. We repeated the measurements for 10 different r-NDs using the same nanofiber to perform the experiments under the same conditions. The average and SD of the evaluated abs were 3.3 1014 and 1.1 1014 cm2, respectively. The deviations in abs can be attributed to the variations in the number of NVCs contained in the r-NDs with different sizes and defect densities. The detailed distribution of abs and estimated number of NVCs are shown in the Supplementary Materials (see fig. S4).

The sum of the absorption and scattering forces exerted on the r-ND under GR laser irradiation (1 = 532 nm) with the power Pr-ND being balanced by the scattering force exerted by the NIR (2 = 1064 nm) laser. For the n-ND having no absorbers, the scattering forces exerted by the GR laser with Pn-ND and the NIR laser with constant power balance each other. From these balances, the ratio of the absorption and scattering forces on the ND can be determined as (Pn-ND Pr-ND):Pr-ND.

Here, we emphasize that the present method can detect the absorption cross section in the order of a square nanometer, which is close to those of single molecules (typically as large as 1015 cm2). Under the diffraction-limited illumination condition, this absorption cross section corresponds to a transmittance of ~106. Recently, Kukura et al. (30) and Celebrano et al. (31) succeeded in measuring the extremely small absorption using highly sensitive detectors, and the accuracy of their method is comparable with that of our method. However, in their technique, the Rayleigh scattering caused by nanoparticles and nanomaterials attenuates the transmitted light intensity as well such that the absorption signals cannot be extracted separately from the scattering components. In contrast, our proposed optical force spectroscopy can separately determine the absorption and scattering cross sections of single nanoparticles from the momentum change. The sensitivity is not limited by the signal-to-noise ratio of light intensity detection but restricted by the accuracy of the motion detection. Although nanometer-level position sensing techniques are available, the random thermal motion is the main factor that determines the accuracy. If the experiment is performed using superfluid helium at the cryogenic temperature, then the detection accuracy will be ultimately improved.

We demonstrated the selective transportation of single nanoparticles based on the relation between the quantum mechanical properties of nanomaterials and their macroscopic motion driven by the quantum resonant optical forces. This selective transportation is applicable to the precise sorting of nanocrystals, quantum dots, and molecular nanoparticles according to their resonant absorption properties. Optical force spectroscopy directly and sensitively measures the interaction between light and nanoparticles separately from the scattering effects based on the photon momentum change and not the energy change. It is noted that even if the reference nanoparticle having the same parent material but without absorbers is unavailable, the proposed absorption detection can still be achieved (see Materials and Methods). Although we focus on NDs as the samples for the first demonstration, note that other kinds of nanoparticles can be equally interesting targets. Size-selective optical transport of semiconductor quantum dots has been successfully demonstrated (32). Furthermore, it was reported that organic dye-doped nanoparticles have unique optical trapping characteristics according to their quantum resonance properties (33, 34). Applying the present technique to these nanomaterials will be our future endeavor. In conclusion, we believe that our scheme can enable a new class of optical force methodologies to investigate the characteristics of advanced nanomaterials and quantum materials and develop state-of-the-art nanodevices.

We used commercially available NDs having a mean diameter of 50 nm (r-NDs, FND Biotech Inc.; n-NDs, Microdiamant Japan. The absorption of NVCs appears at 532 nm after proton irradiation for fabricating r-NDs; contrarily, n-NDs exhibit no absorption at 532 nm. These were dispersed in pure water with 0.1 weight % surfactant. The concentration was adjusted such that a single ND is trapped by a nanofiber during the experiment.

A commercially available single-mode optical fiber (780HP, Thorlabs) was used to fabricate a nanofiber. It was heated with a ceramic heater at ~1400C and stretched at both ends. The waist diameter of the nanofiber used in this study was 400 nm, which remained constant (variation of <2%) over a length of several hundred micrometers. From the mode dispersion curve obtained by the fiber mode analysis, the single-mode propagation is valid when the wavelength of incident light is longer than 360 nm. The fiber was fixed on a glass slide using ultraviolet glue and soaked in a cell filled with an ND-dispersed aqueous solution.

Continuous-wave GR (532 nm) and NIR (1064 nm) diode lasers were introduced from both ends of the fabricated nanofiber. The laser powers were controlled using rotational neutral density filters. To record the motions of the NDs, we introduced a weak red laser (690 nm), and its light, scattered light from the particles, was monitored using a CCD camera. When nanoparticles other than the observed particles are trapped on the fiber, their scattering reduces the laser intensity irradiated on the particle. To avoid this disturbance, the experiments were performed after ensuring no change in the transmitted laser power.

When the reference nanoparticle having the same parent material but containing no absorbers is unavailable, the proposed absorption detection can still be realized by the following method: The measurement of the balanced laser powers for the reference particle is replaced by the calculation of the ratio of the scattering cross sections at two different wavelengths (using Eq. 2). When the refractive index of the parent material is constant at two laser wavelengths, the ratio of the scattering cross sections can be obtained using the inverse fourth power law. Using this value, we can determine the balanced laser powers for the virtual nonabsorbing particle. We analyzed the same data for 10 r-NDs as the abovementioned experiments but without using the data for n-NDs; consequently, the absorption cross sections were determined as (3.8 1.0) 1014 cm2. The variation from the above value [(3.3 1.1) 1014 cm2] would have been caused by a deviation from the Rayleigh scattering theory (Eq. 2) owing to the shape, size, and refractive index of the particles, as well as the random and systematic errors in the measurements.

Acknowledgments: Funding: The authors acknowledge the funding received from JSPS KAKENHI (grant numbers JP16H06504, JP16H06506, JP18H03882, JP18H05205, JP17K05016, and JP19H04529) and the Cooperative Research Program of Network Joint Research Center for Materials and Devices. Author contributions: H.I. and K.S. developed the concept and supervised the experiments. K.Y., H.F., and K.S. conducted the experiments. H.I. and T.W. theoretically elucidated the phenomena. H.F., K.Y., T.W., H.I., and K.S. participated in discussion of the results. H.F., H.I., and K.S. prepared the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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Optical selection and sorting of nanoparticles according to quantum mechanical properties - Science Advances