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  • 07 May

    QT/ Evading the uncertainty principle in quantum physics

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Fri, May 7, 2021 5:27 PM by Paradigm Fund

QT/ Evading the uncertainty principle in quantum physics

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Quantum news biweekly vol.3, 23rd April — 7th MayTL;DRIn quantum mechanics, the Heisenberg uncertainty principle dictates that the position and speed of an object cannot both be known fully precisely at the same time. Researchers now show that two vibrating drumheads, the size of a human hair, can be prepared in a quantum state which evades the uncertainty principle.Researchers have big ideas for the potential of quantum technology, from unhackable networks to earthquake sensors. But all these things depend on a major technological feat: being able to build and control systems of quantum particles, which are among the smallest objects in the universe. That goal is now a step closer with the publication of a new method by University of Chicago scientists. Published in Nature, the paper shows how to bring multiple molecules at once into a single quantum state — one of the most important goals in quantum physics.Quantum systems consisting of several particles can be used to measure magnetic or electric fields more precisely. A young physicist at the University of Basel has now proposed a new scheme for such measurements that uses a particular kind of correlation between quantum particles.Scientists characterized how the electronic states in a compound containing iron, tellurium, and selenium depend on local chemical concentrations. They discovered that superconductivity (conducting electricity without resistance), along with distinct magnetic correlations, appears when the local concentration of iron is sufficiently low; a coexisting electronic state existing only at the surface (topological surface state) arises when the concentration of tellurium is sufficiently high. Reported in Nature Materials, their findings point to the composition range necessary for topological superconductivity. Topological superconductivity could enable more robust quantum computing, which promises to deliver exponential increases in processing power.Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, the University of Chicago and scientific institutes and universities in Japan, Korea and Hungary have established guidelines that will be an invaluable resource for the discovery of new defect-based quantum systems.Scientists from the University of Bristol’s Quantum Engineering Technology Labs (QETLabs) have developed an algorithm that provides valuable insights into the physics underlying quantum systems — paving the way for significant advances in quantum computation and sensing, and potentially turning a new page in scientific investigation.The ability to turn on and off a physical process with just one photon is a fundamental building block for quantum photonic technologies. Realizing this in a chip-scale architecture is important for scalability, which amplifies a breakthrough by City College of New York researchers led by physicist Vinod Menon. They’ve demonstrated for the first time the use of “Rydberg states” in solid state materials (previously shown in cold atom gases) to enhance nonlinear optical interactions to unprecedented levels in solid state systems. This feat is a first step towards realizing chip-scale scalable single photon switches.Researchers have developed a method that allows for simulation and visualization of magnetic-field-induced electron currents inside gold nanoparticles. The method facilitates accurate analysis of magnetic field effects inside complex nanostructures in nuclear magnetic resonance measurements and establishes quantitative criteria for aromaticity of nanoparticles.The future of particle acceleration has begun. Awake is a promising concept for a completely new method with which particles can be accelerated even over short distances. The basis for this is a plasma wave that accelerates electrons and thus brings them to high energies. A team led by the Max Planck Institute for Physics now reports a breakthrough in this context. For the first time, they were able to precisely time the production of the proton microbunches that drive the wave in the plasma. This fulfills an important prerequisite for using the Awake technology for collision experiments.And more!Quantum Computing MarketAccording to the recent market research report ‘Quantum Computing Market with COVID-19 impact by Offering (Systems and Services), Deployment (On Premises and Cloud Based), Application, Technology, End-use Industry and Region — Global Forecast to 2026’, published by MarketsandMarkets, the Quantum Computing market is expected to grow from USD 472 million in 2021 to USD 1,765 million by 2026, at a CAGR of 30.2%. The early adoption of quantum computing in the banking and finance sector is expected to fuel the growth of the market globally. Other key factors contributing to the growth of the quantum computing market include rising investments by governments of different countries to carry out research and development activities related to quantum computing technology. Several companies are focusing on the adoption of QCaaS post-COVID-19. This, in turn, is expected to contribute to the growth of the quantum computing market. However, stability and error correction issues are expected to restrain the growth of the market.According to ‘Quantum Computing Market Research Report: By Offering, Deployment Type, Application, Technology, Industry — Industry Share, Growth, Drivers, Trends and Demand Forecast to 2030’ report, the quantum computing market is projected to reach $64,988 million by 2030. Machine learning (ML) is expected to progress at the highest CAGR, during the forecast period, among all application categories, owing to the fact that quantum computing is being integrated in ML for improving the latter’s use case.By 2030, Europe and North America are expected to account for more than 78.0% in the quantum computing market, as Canada, the U.S., the U.K., Germany, and Russia are witnessing heavy investments in the field.Latest ResearchesQuantum mechanics–free subsystem with mechanical oscillatorsby Laure Mercier de Lépinay, Caspar F. Ockeloen-Korppi, Matthew J. Woolley, Mika A. Sillanpää in ScienceThe uncertainty principle, first introduced by Werner Heisenberg in the late 1920’s, is a fundamental concept of quantum mechanics. In the quantum world, particles like the electrons that power all electrical product can also behave like waves. As a result, particles cannot have a well-defined position and momentum simultaneously. For instance, measuring the momentum of a particle leads to a disturbance of position, and therefore the position cannot be precisely defined.In recent research, published in Science, a team led by Prof. Mika Sillanpää at Aalto University in Finland has shown that there is a way to get around the uncertainty principle. The team included Dr. Matt Woolley from the University of New South Wales in Australia, who developed the theoretical model for the experiment.Instead of elementary particles, the team carried out the experiments using much larger objects: two vibrating drumheads one-fifth of the width of a human hair. The drumheads were carefully coerced into behaving quantum mechanically.“In our work, the drumheads exhibit a collective quantum motion. The drums vibrate in an opposite phase to each other, such that when one of them is in an end position of the vibration cycle, the other is in the opposite position at the same time. In this situation, the quantum uncertainty of the drums’ motion is cancelled if the two drums are treated as one quantum-mechanical entity,” explains the lead author of the study, Dr. Laure Mercier de Lepinay.This means that the researchers were able to simultaneously measure the position and the momentum of the two drumheads — which should not be possible according to the Heisenberg uncertainty principle. Breaking the rule allows them to be able to characterize extremely weak forces driving the drumheads.“One of the drums responds to all the forces of the other drum in the opposing way, kind of with a negative mass,” Sillanpää says.Furthermore, the researchers also exploited this result to provide the most solid evidence to date that such large objects can exhibit what is known as quantum entanglement. Entangled objects cannot be described independently of each other, even though they may have an arbitrarily large spatial separation. Entanglement allows pairs of objects to behave in ways that contradict classical physics, and is the key resource behind emerging quantum technologies. A quantum computer can, for example, carry out the types of calculations needed to invent new medicines much faster than any supercomputer ever could.In macroscopic objects, quantum effects like entanglement are very fragile, and are destroyed easily by any disturbances from their surrounding environment. Therefore, the experiments were carried out at a very low temperature, only a hundredth a degree above absolute zero at -273 degrees.In the future, the research group will use these ideas in laboratory tests aiming at probing the interplay of quantum mechanics and gravity. The vibrating drumheads may also serve as interfaces for connecting nodes of large-scale, distributed quantum networks.Atomic Bose-Einstein condensate to molecular Bose-Einstein condensate transitionby Zhang, Chen, Yao and Chin in NatureResearchers have big ideas for the potential of quantum technology, from unhackable networks to earthquake sensors. But all these things depend on a major technological feat: being able to build and control systems of quantum particles, which are among the smallest objects in the universe.That goal is now a step closer with the publication of a new method by University of Chicago scientists. The paper shows how to bring multiple molecules at once into a single quantum state — one of the most important goals in quantum physics.“People have been trying to do this for decades, so we’re very excited,” said senior author Cheng Chin, a professor of physics at UChicago who said he has wanted to achieve this goal since he was a graduate student in the 1990s. “I hope this can open new fields in many-body quantum chemistry. There’s evidence that there are a lot of discoveries waiting out there.”One of the essential states of matter is called a Bose-Einstein condensate: When a group of particles cooled to nearly absolute zero share a quantum state, the entire group starts behaving as though it were a single atom. It’s a bit like coaxing an entire band to march entirely in step while playing in tune — difficult to achieve, but when it happens, a whole new world of possibilities can open up.Scientists have been able to do this with atoms for a few decades, but what they’d really like to do is to be able to do it with molecules. Such a breakthrough could serve as the underpinning for many forms of quantum technology.But because molecules are larger than atoms and have many more moving parts, most attempts to harness them have dissolved into chaos. “Atoms are simple spherical objects, whereas molecules can vibrate, rotate, carry small magnets,” said Chin. “Because molecules can do so many different things, it makes them more useful, and at the same time much harder to control.”Chin’s group wanted to take advantage of a few new capabilities in the lab that had recently become available. Last year, they began experimenting with adding two conditions.The first was cooling the entire system down even further — down to 10 nanokelvins, a split hair above absolute zero. Then they packed the molecules into a crawl space so that they were pinned flat. “Typically, molecules want to move in all directions, and if you allow that, they are much less stable,” said Chin. “We confined the molecules so that they are on a 2D surface and can only move in two directions.”The result was a set of virtually identical molecules — lined up with exactly the same orientation, the same vibrational frequency, in the same quantum state.The scientists described this molecular condensate as like a pristine sheet of new drawing paper for quantum engineering. “It’s the absolute ideal starting point,” Chin said. “For example, if you want to build quantum systems to hold information, you need a clean slate to write on before you can format and store that information.”So far, they’ve been able to link up to a few thousand molecules together in such a state, and are beginning to explore its potential.“In the traditional way to think about chemistry, you think about a few atoms and molecules colliding and forming a new molecule,” Chin said. “But in the quantum regime, all molecules act together, in collective behavior. This opens a whole new way to explore how molecules can all react together to become a new kind of molecule. “This has been a goal of mine since I was a student,” he added, “so we’re very, very happy about this result.”Metrological complementarity reveals the Einstein-Podolsky-Rosen paradoxby Benjamin Yadin, Matteo Fadel, Manuel Gessner in Nature CommunicationsQuantum systems consisting of several particles can be used to measure magnetic or electric fields more precisely. A young physicist at the University of Basel has now proposed a new scheme for such measurements that uses a particular kind of correlation between quantum particles.In quantum information, the fictitious agents Alice and Bob are often used to illustrate complex communication tasks. In one such process, Alice can use entangled quantum particles such as photons to transmit or “teleport” a quantum state — unknown even to herself — to Bob, something that is not feasible using traditional communications.However, it has been unclear whether the team Alice-Bob can use similar quantum states for other things besides communication. A young physicist at the University of Basel has now shown how particular types of quantum states can be used to perform measurements with higher precision than quantum physics would ordinarily allow.Quantum steering at a distanceTogether with researchers in Great Britain and France, Dr. Matteo Fadel, who works at the Physics Department of the University of Basel, has thought about how high-precision measurement tasks can be tackled with the help of so-called quantum steering.Quantum steering describes the fact that in certain quantum states of systems consisting of two particles, a measurement on the first particle allows one to make more precise predictions about possible measurement results on the second particle than quantum mechanics would allow if only the measurement on the second particle had been made. It is just as if the measurement on the first particle had “steered” the state of the second one.This phenomenon is also known as the EPR paradox, named after Albert Einstein, Boris Podolsky and Nathan Rosen, who first described it in 1935. What is remarkable about it is that it works even if the particles are far apart because they are quantum-mechanically entangled and can feel each other at a distance. This is also what allows Alice to transmit her quantum state to Bob in quantum teleportation.“For quantum steering, the particles have to be entangled with each other in a very particular fashion,” Fadel explains. “We were interested in understanding whether this could be used for making better measurements.” The measurement procedure he proposes consists of Alice’s performing a measurement on her particle and transmitting the result to Bob.Thanks to quantum steering, Bob can then adjust his measurement apparatus such that the measurement error on his particle is smaller than it would have been without Alice’s information. In this way, Bob can measure, for instance, magnetic or electric fields acting on his particles with high precision.Systematic study of steering-enhanced measurementsThe study of Fadel and his colleagues now makes it possible to systematically study and demonstrate the usefulness of quantum steering for metrological applications. “The idea for this arose from an experiment we already did in 2018 in the laboratory of Professor Philipp Treutlein at the University of Basel,” says Fadel.“In that experiment, we were able to measure quantum steering for the first time between two clouds containing hundreds of cold atoms each. After that, we asked ourselves whether it might be possible to do something useful with that.” In his work, Fadel has now created a solid mathematical basis for realizing real-life measurement applications that use quantum steering as a resource.“In a few simple cases, we already knew that there was a connection between the EPR paradox and precision measurements,” Treutlein says. “But now we have a general theoretical framework, based on which we can also develop new strategies for quantum metrology.” Researchers are already working on demonstrating Fadel’s ideas experimentally. In the future, this could result in new quantum-enhanced measurement devices.Electronic properties of the bulk and surface states of Fe1 yTe1−xSexby Yangmu Li, Nader Zaki, Vasile O. Garlea, Andrei T. Savici, David Fobes, Zhijun Xu, Fernando Camino, Cedomir Petrovic, Genda Gu, Peter D. Johnson, John M. Tranquada, Igor A. Zaliznyak in Nature MaterialsScientists characterized how the electronic states in a compound containing iron, tellurium, and selenium depend on local chemical concentrations. They discovered that superconductivity (conducting electricity without resistance), along with distinct magnetic correlations, appears when the local concentration of iron is sufficiently low; a coexisting electronic state existing only at the surface (topological surface state) arises when the concentration of tellurium is sufficiently high.Their findings point to the composition range necessary for topological superconductivity. Topological superconductivity could enable more robust quantum computing, which promises to deliver exponential increases in processing power.“Quantum computing is still in its infancy, and one of the key challenges is reducing the error rate of the computations,” said first author Yangmu Li, a postdoc in the Neutron Scattering Group of the Condensed Matter Physics and Materials Science (CMPMS) Division at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory. Errors arise as qubits, or quantum information bits, interact with their environment. However, unlike trapped ions or solid-state qubits such as point defects in diamond, topological superconducting qubits are intrinsically protected from part of the noise. Therefore, they could support computation less prone to errors. The question is, where can we find topological superconductivity?In this study, the scientists narrowed the search in one compound known to host topological surface states and part of the family of iron-based superconductors. In this compound, topological and superconducting states are not distributed uniformly across the surface. Understanding what’s behind these variations in electronic states and how to control them is key to enabling practical applications like topologically protected quantum computing.From previous research, the team knew modifying the amount of iron could switch the material from a superconducting to nonsuperconducting state. For this study, physicist Gendu Gu of the CMPMS Division grew two types of large single crystals, one with slightly more iron relative to the other. The sample with the higher iron content is nonsuperconducting; the other sample is superconducting.To understand whether the arrangement of electrons in the bulk of the material varied between the superconducting and nonsuperconducting samples, the team turned to spin-polarized neutron scattering. The Spallation Neutron Source (SNS), located at DOE’s Oak Ridge National Laboratory, is home to a one-of-a-kind instrument for performing this technique.“Neutron scattering can tell us the magnetic moments, or spins, of electrons and the atomic structure of a material,” explained corresponding author, Igor Zaliznyak, a physicist in the CMPMS Division Neutron Scattering Group who led the Brookhaven team that helped design and install the instrument with collaborators at Oak Ridge. “In order to single out the magnetic properties of electrons, we polarize the neutrons using a mirror that reflects only one specific spin direction.”To their surprise, the scientists observed drastically different patterns of electron magnetic moments in the two samples. Therefore, the slight alteration in the amount of iron caused a change in electronic state.“After seeing this dramatic change, we figured we should look at the distribution of electronic states as a function of local chemical composition,” said Zaliznyak.At Brookhaven’s Center for Functional Nanomaterials (CFN), Li, with support from CFN staff members Fernando Camino and Gwen Wright, determined the chemical composition across representative smaller pieces of both sample types through energy-dispersive x-ray spectroscopy. In this technique, a sample is bombarded with electrons, and the emitted x-rays characteristic of different elements are detected. They also measured the local electrical resistance — which indicates how coherently electrons can transport charge — with microscale electrical probes. For each crystal, Li defined a small square grid (100 by 100 microns). In total, the team mapped the local composition and resistance at more than 2,000 different locations.“Through the experiments at the CFN, we characterized the chemistry and overall conduction properties of the electrons,” said Zaliznyak. “But we also need to characterize the microscopic electronic properties, or how electrons propagate in the material, whether in the bulk or on the surface. Superconductivity induced in electrons propagating on the surface can host topological objects called Majorana modes, which are in theory one of the best ways to perform quantum computations. Information on bulk and surface electronic properties can be obtained through photoemission spectroscopy.”For the photoemission spectroscopy experiments, Zaliznyak and Li reached out to Peter Johnson, leader of the CMPMS Division Electron Spectroscopy Group, and Nader Zaki, a scientific associate in Johnson’s group. By measuring the energy and momentum of electrons ejected from the samples (using the same spatial grid) in response to light, they quantified the strengths of the electronic states propagating on the surface, in the bulk, and forming the superconducting state. They quantitatively fit the photoemission spectra to a model that characterizes the strengths of these states.Then, the team mapped the electronic state strengths as a function of local composition, essentially building a phase diagram.“This phase diagram includes the superconducting and topological phase transitions and points to where we could find a useful chemical composition for quantum computation materials,” said Li. “For certain compositions, no coherent electronic states exist to develop topological superconductivity. In previous studies, people thought instrument failure or measurement error were why they weren’t seeing features of topological superconductivity. Here we show that it’s due to the electronic states themselves.”“When the material is close to the transition between the topological and nontopological state, you can expect fluctuations,” added Zaliznyak. “For topology to arise, the electronic states need to be well-developed and coherent. So, from a technological perspective, we need to synthesize materials away from the transition line.”Next, the scientists will expand the phase diagram to explore the compositional range in the topological direction, focusing on samples with less selenium and more tellurium. They are also considering applying neutron scattering to understand an unexpected energy gap (an energy range where no electrons are allowed) opening in the topological surface state of the same compound. Johnson’s group recently discovered this gap and hypothesized it was caused by surface magnetism.Quantum guidelines for solid-state spin defectsby Wolfowicz, G., Heremans, F.J., Anderson, C.P. et al. in Nat Rev MaterClaiming that something has a defect normally suggests an undesirable feature. That’s not the case in solid-state systems, such as the semiconductors at the heart of modern classical electronic devices. They work because of defects introduced into the rigidly ordered arrangement of atoms in crystalline materials like silicon. Surprisingly, in the quantum world, defects also play an important role. Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, the University of Chicago and scientific institutes and universities in Japan, Korea and Hungary have established guidelines that will be an invaluable resource for the discovery of new defect-based quantum systems.Such systems have possible applications in quantum communications, sensing and computing and thereby could have a transformative effect on society. Quantum communications could distribute quantum information robustly and securely over long distances, making a quantum internet possible. Quantum sensing could achieve unprecedented sensitivities for measurements with biological, astronomical, technological and military interest. Quantum computing could reliably simulate the behavior of matter down to the atomic level and possibly simulate and discover new drugs.The team derived their design guidelines based on an extensive review of the vast body of knowledge acquired over the last several decades on spin defects in solid-state materials.“The defects that interest us here are isolated distortions in the orderly arrangement of atoms in a crystal,” explained Joseph Heremans, a scientist in Argonne’s Center for Molecular Engineering and Materials Science division, as well as the University of Chicago Pritzker School of Molecular Engineering.Such distortions might include holes or vacancies created by the removal of atoms or impurities added as dopants. These distortions, in turn, can trap electrons within the crystal. These electrons have a property called spin, which acts as an isolated quantum system.“Spin being a key quantum property, spin defects can hold quantum information in a form that physicists call quantum bits, or qubits, in analogy with the bit of information in classical computing,” added Gary Wolfowicz, assistant scientist in Argonne’s Center for Molecular Engineering and Materials Science division, along with the University of Chicago Pritzker School of Molecular Engineering.For several decades, scientists have been studying these spin defects to create a broad array of proof-of-concept devices. However, previous research has only focused on one or two leading candidate qubits.“Our field has had a somewhat narrow focus for many years,” said Christopher Anderson, a postdoctoral scholar in the University of Chicago Pritzker School of Molecular Engineering. “It was like we only had a few horses in the quantum race. But now we understand that there are many other quantum horses to back, and exactly what to look for in those horses.”The team’s guidelines encompass the properties of both the defects and the material selected to host them. The key defect properties are spin, optical (for example, how light interacts with the spin of the trapped electrons), and charge state of the defect.Possible solid-state materials include not only the already well-studied few like silicon, diamond and silicon carbide but other more recent entries like various oxides. All these materials have different advantages and disadvantages laid out in the guidelines. For example, diamond is clear and hard, but expensive. On the other hand, silicon is easy to make devices with at low cost, but is more affected by free charges and temperature.“Our guidelines are there for quantum scientists and engineers to assess the interplay between the defect properties and the selected host material in designing new qubits tailored to some specific application,” Heremans noted.“Spin defects have a central role to play in creating new quantum devices, whether they be small quantum computers, the quantum internet, or nanoscale quantum sensors,” continued Anderson. “By drawing upon the extensive knowledge on spin defects to derive these guidelines, we have laid the groundwork so that the quantum workforce — now and in the future — can design from the ground up the perfect qubit for a specific use.”“We are especially proud of our guidelines because intended users extend from veteran quantum scientists to researchers in other fields and graduate students hoping to join the quantum workforce,” said Wolfowicz.The work also establishes the groundwork for designing scalable semiconductor quantum devices and dovetails well with Q-NEXT, a DOE-funded quantum information science research center led by Argonne. Q-NEXT’s goal includes establishing a semiconductor quantum “foundry” for developing quantum interconnects and sensors.“Our team’s guidelines will act as a blueprint to help direct the Q-NEXT mission in designing the next generation of quantum materials and devices,” said David Awschalom, senior scientist in Argonne’s Materials Science division, Liew Family Professor of Molecular Engineering at the University of Chicago Pritzker School of Molecular Engineering, and director of both the Chicago Quantum Exchange and Q-NEXT. “When it comes to quantum technologies with spins, this work sets the stage and informs the field how to move forward.”Learning models of quantum systems from experimentsby Antonio A. Gentile, Brian Flynn, Sebastian Knauer, Nathan Wiebe, Stefano Paesani, Christopher E. Granade, John G. Rarity, Raffaele Santagati & Anthony Laing in Nature PhysicsScientists from the University of Bristol’s Quantum Engineering Technology Labs (QETLabs) have developed an algorithm that provides valuable insights into the physics underlying quantum systems — paving the way for significant advances in quantum computation and sensing, and potentially turning a new page in scientific investigation.In physics, systems of particles and their evolution are described by mathematical models, requiring the successful interplay of theoretical arguments and experimental verification. Even more complex is the description of systems of particles interacting with each other at the quantum mechanical level, which is often done using a Hamiltonian model. The process of formulating Hamiltonian models from observations is made even harder by the nature of quantum states, which collapse when attempts are made to inspect them.In the paper, Learning models of quantum systems from experiments, quantum mechanics from Bristol’s QET Labs describe an algorithm which overcomes these challenges by acting as an autonomous agent, using machine learning to reverse engineer Hamiltonian models.The team developed a new protocol to formulate and validate approximate models for quantum systems of interest. Their algorithm works autonomously, designing and performing experiments on the targeted quantum system, with the resultant data being fed back into the algorithm. It proposes candidate Hamiltonian models to describe the target system, and distinguishes between them using statistical metrics, namely Bayes factors.Excitingly, the team were able to successfully demonstrate the algorithm’s ability on a real-life quantum experiment involving defect centres in a diamond, a well-studied platform for quantum information processing and quantum sensing.The algorithm could be used to aid automated characterisation of new devices, such as quantum sensors. This development therefore represents a significant breakthrough in the development of quantum technologies.“Combining the power of today’s supercomputers with machine learning, we were able to automatically discover structure in quantum systems. As new quantum computers/simulators become available, the algorithm becomes more exciting: first it can help to verify the performance of the device itself, then exploit those devices to understand ever-larger systems,” said Brian Flynn from the University of Bristol’s QETLabs and Quantum Engineering Centre for Doctoral Training.“This level of automation makes it possible to entertain myriads of hypothetical models before selecting an optimal one, a task that would be otherwise daunting for systems whose complexity is ever increasing,” said Andreas Gentile, formerly of Bristol’s QETLabs, now at Qu & Co.“Understanding the underlying physics and the models describing quantum systems, help us to advance our knowledge of technologies suitable for quantum computation and quantum sensing,” said Sebastian Knauer, also formerly of Bristol’s QETLabs and now based at the University of Vienna’s Faculty of Physics.Anthony Laing, co-Director of QETLabs and Associate Professor in Bristol’s School of Physics, and an author on the paper, praised the team: “In the past we have relied on the genius and hard work of scientists to uncover new physics. Here the team have potentially turned a new page in scientific investigation by bestowing machines with the capability to learn from experiments and discover new physics. The consequences could be far reaching indeed.”The next step for the research is to extend the algorithm to explore larger systems, and different classes of quantum models which represent different physical regimes or underlying structures.Enhanced nonlinear interaction of polaritons via excitonic Rydberg states in monolayer WSe2by Jie Gu, Valentin Walther, Lutz Waldecker, Daniel Rhodes, Archana Raja, James C. Hone, Tony F. Heinz, Stéphane Kéna-Cohen, Thomas Pohl, Vinod M. Menon in Nature CommunicationsThe ability to turn on and off a physical process with just one photon is a fundamental building block for quantum photonic technologies. Realizing this in a chip-scale architecture is important for scalability, which amplifies a breakthrough by City College of New York researchers led by physicist Vinod Menon. They’ve demonstrated for the first time the use of “Rydberg states” in solid state materials (previously shown in cold atom gases) to enhance nonlinear optical interactions to unprecedented levels in solid state systems. This feat is a first step towards realizing chip-scale scalable single photon switches.In solid state systems, exciton-polaritons, half-light half-matter quasiparticles, which result from the hybridization of electronic excitations (excitons) and photons, are an attractive candidate to realize nonlinearities at the quantum limit. “Here we realize these quasiparticles with Rydberg excitons (excited states of excitons) in atomically thin semiconductors (2D materials),” said Menon, chair of physics in City College’s Division of Science. “Excited states of excitons owing to their larger size, show enhanced interactions and therefore hold promise for accessing the quantum domain of single-photon nonlinearities, as demonstrated previously with Rydberg states in atomic systems.”According to Menon, the demonstration of Rydberg exciton-polaritons in two-dimensional semiconductors and their enhanced nonlinear response presents the first step towards the generation of strong photon interactions in solid state systems, a necessary building block for quantum photonic technologies.Jie Gu, a graduate student working under Menon’s supervision, was the first author of the study. The team also included scientists from Stanford, Columbia, Aarhus and Montreal Polytechnic universities.The research of Professor Menon and his co-workers could have a tremendous impact on Army goals for ultra-low energy information processing and computing for mobile Army platforms such as unmanned systems,” said Dr. Michael Gerhold, program manager at the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory. “Optical switching and nonlinearities used in future computing paradigms that use photonics would benefit from this advancement. Such strong coupling effects would reduce energy consumption and possibly aid computing performance.a Schematic illustration of the sample structure. b Optical image after the multilayer hBN-WSe2 stacking was transferred on top of the DBR. The area where three WSe2 layers overlap is marked with the white arrow. c Angle resolved differential reflection of multilayer structure on DBR at room temperature. Absorption features can be observed at the energies of the 1 s and 2 s exciton and are marked by the white arrows.Magnetically induced currents and aromaticity in ligand-stabilized Au and AuPt superatomsby Omar López-Estrada, Bernardo Zuniga-Gutierrez, Elli Selenius, Sami Malola, Hannu Häkkinen in Nature CommunicationsResearchers in the Nanoscience Center of University of Jyvaskyla, in Finland and in the Guadalajara University in Mexico developed a method that allows for simulation and visualization of magnetic-field-induced electron currents inside gold nanoparticles. The method facilitates accurate analysis of magnetic field effects inside complex nanostructures in nuclear magnetic resonance measurements and establishes quantitative criteria for aromaticity of nanoparticles.According to the classical electromagnetism, a charged particle moving in an external magnetic field experiences a force that makes the particle’s path circular. This basic law of physics is used, e.g., in designing cyclotrons that work as particle accelerators. When nanometer-size metal particles are placed in a magnetic field, the field induces a circulating electron current inside the particle. The circulating current in turn creates an internal magnetic field that opposes the external field. This physical effect is called magnetic shielding.The strength of the shielding can be investigated by using nuclear magnetic resonance (NMR) spectroscopy. The internal magnetic shielding varies strongly in an atomic length scale even inside a nanometer-size particle. Understanding these atom-scale variations is possible only by employing quantum mechanical theory of the electronic properties of each atom making the nanoparticle.Now, the research group of Professor Hannu Häkkinen in the University of Jyväskylä, in collaboration with University of Guadalajara in Mexico, developed a method to compute, visualize, and analyze the circulating electron currents inside complex 3D nanostructures. The method was applied to gold nanoparticles with a diameter of only about one nanometer. The calculations shed light onto unexplained experimental results from previous NMR measurements in the literature regarding how magnetic shielding inside the particle changes when one gold atom is replaced by one platinum atom.A new quantitative measure to characterize aromaticity inside metal nanoparticles was also developed based on the total integrated strength of the shielding electron current.“Aromaticity of molecules is one of the oldest concepts in chemistry, and it has been traditionally connected to ring-like organic molecules and to their delocalized valence electron density that can develop circulating currents in an external magnetic field. However, generally accepted quantitative criteria for the degree of aromaticity have been lacking. Our method yields now a new tool to study and analyze electron currents at the resolution of one atom inside any nanostructure, in principle. The peer reviewers of our work considered this as a significant advancement in the field,” says Professor Häkkinen who coordinated the research.a [HAu9(PPh3)8]2+ (cluster 1 in text) and (b) [HPtAu8(PPh3)8]+ (cluster 2). Characteristic distances in metal cores are labeled (dN and dNa,b, N = 1–4). Au: yellow, P: orange, C: grey, core-hydrogen: white. Some PPh3 ligands and protons in the phenyl rings are omitted for clarity.Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasmaby P. Wiwattananon, J. Wolfenden, B. Woolley, G. Xia, M. Zepp, G. Zevi Della Porta in Physical Review LettersThe future of particle acceleration has begun. Awake is a promising concept for a completely new method with which particles can be accelerated even over short distances. The basis for this is a plasma wave that accelerates electrons and thus brings them to high energies. A team led by the Max Planck Institute for Physics now reports a breakthrough in this context. For the first time, they were able to precisely time the production of the proton microbunches that drive the wave in the plasma. This fulfills an important prerequisite for using the Awake technology for collision experiments.How do you create a wave for electrons? The carrier substance for this is a plasma (i.e., an ionized gas in which positive and negative charges are separated). Directing a proton beam through the plasma creates a wave on which electrons ride and are accelerated to high energies.The proton source of Awake is the SPS ring at Cern, a pre-accelerator for the 27-kilometer circumference ring of the Large Hadron Collider (LHC). It produces proton bunches about 10-cm long. “However, in order to generate a large amplitude plasma wave, the proton bunch length must be much shorter — in the millimeter range,” explains Fabian Batsch, PhD student at the Max Planck Institute for Physics.The scientists take advantage of self-modulation, a “natural” interaction between the bunch and plasma. “In the process, the longer proton bunch is split into high-energy proton microbunches of only a few millimeters in length, building the train beam,” says Batsch. “This process forms a plasma wave, which propagates with the train travelling through the plasma field.”Precise timing allows ideal electron accelerationHowever, a stable and reproducible field is required to accelerate electrons and bring them to collision. This is exactly what the team has found a solution for now. “If a sufficiently large electric field is applied when the long proton bunch is injected and the self-modulation is thus immediately set in motion.”“Since the plasma is formed right away, we can exactly time the phase of the short proton microbunches,” says Patric Muggli, head of the Awake working group at the Max Planck Insstitute for Physics. “This allows us to set the pace for the train. Thus, the electrons are caught and accelerated by the wave at the ideal moment.”First research projects in sightThe Awake technology is still in the early stages of development. However, with each step toward success, the chances of this accelerator technology actually being used in the coming decades increase. The first proposals for smaller accelerator projects (e.g., for example to study the fine structure of protons) are to be made as early as 2024.According to Muggli, the advantages of the novel accelerator technology — plasma wakefield acceleration — are obvious: “With this technology, we can reduce the distance needed to accelerate electrons to peak energy by a factor of 20. The accelerators of the future could therefore be much smaller. This means: Less space, less effort, and therefore lower costs.”Schematic of the experimental setup showing the main components used for measurements presented here. Inset 1: RIF in the middle of the proton bunch (tRIF=0ps). Inset 2: streak camera image of a modulated proton bunch, laser reference signal at t=0ps (red circle).MISC — @cambridgecqc — @quantumjournalSubscribe to Paradigm!Medium. Twitter. Telegram. Telegram Chat. Reddit. LinkedIn.Main sourcesResearch articlesAdvanced Quantum TechnologiesPRX QuantumScience DailySciTechDailyQuantum NewsNatureQT/ Evading the uncertainty principle in quantum physics was originally published in Paradigm on Medium, where people are continuing the conversation by highlighting and responding to this story.

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