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CAMPUS CLOSED, EVENT POSTPONED

Exponential Quantum Advantage in Approximate Optimization of Hard Constraint Satisfaction Problems

Abstract: A huge range of important problems in computer science–including task optimization, formal logic, encryption, and machine learning–can be solved by finding the sequence of binary variables that optimizes a cost function defined by a series of few-variable constraint relationships. Many of these problems are in the complexity class NP, and are in the worst case, and often the typical case, exponentially hard in the number of variables for all known methods. This hardness applies both to exact and approximate optimization, e.g. finding configurations with a value within a defined fraction of the global optimum. Fundamentally, the lack of any guided local minimum escape method ensures the hardness of both exact and approximate optimization classically, but the intuitive mechanism for approximation hardness in quantum algorithms based on Hamiltonian time evolution is not well understood. In this work, using the prototypically hard MAX-3-XORSAT problem class, we explore this question. We conclude that the mechanisms for quantum exact and approximation hardness are fundamentally distinct. We qualitatively identify why traditional methods such as high depth quantum adiabatic optimization algorithms are not reliably good approximation algorithms. We propose a new spectral folding optimization method that does not suffer from these issues and study it analytically and numerically. We consider random rank-3 hypergraphs including extremal planted solution instances, where the ground state satisfies an anomalously high fraction of constraints compared to truly random problems. We show that, if we define the energy to be E = N_unsat-N_sat, then spectrally folded quantum optimization will return states with energy E ≤ AE_GS (where E_GS is the ground state energy) in polynomial time, where conservatively, A ≃ 0.6. We thoroughly benchmark variations of spectrally folded quantum optimization for random classically approximation-hard (planted solution) instances in simulation, and find performance consistent with this prediction. We do not claim that this approximation guarantee holds for all possible hypergraphs, though our algorithm’s mechanism can likely generalize widely. These results suggest that quantum computers are more powerful for approximate optimization than had been previously assumed.

The preprint on this is on arxiv: https://arxiv.org/abs/2312.06104

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Hunting for High-Energy Cosmic Radiation: The Coherent Radio Technique

Abstract: Cosmic rays and neutrinos provide a unique window into observations of the most violent physical phenomena in the universe. At the highest energies, the flux of these particles at Earth is incredibly low, making direct detection challenging. For neutrinos, the problem is further compounded by their miniscule interaction probabilities. By measuring emission from particle cascades sourced from cosmic ray or neutrino interactions, it is possible to cost-effectively instrument large detection volumes and improve the chances of detection. In this talk, I will introduce the method of indirect detection of these cosmic particles through the measurement of coherent radio emission, highlighting the strengths and weaknesses of the technique. I will describe many of the active experimental efforts which hunt for neutrinos using radio observations and where they fit within the landscape of high-energy multi-messenger astronomy.

Bio: Austin is a postdoctoral scholar at The Pennsylvania State University, associated with the Institute for Gravitation and the Cosmos and the Departments of Astronomy and Astrophyiscs. He previously obtained his B.S. in Engineering Physics and M.S. in Applied Physics at The Colorado School of Mines and his Ph.D in Astroparticle Physics at Gran Sasso Science Institute in L’Aquila, Italy. Austin is engaged in a wide array of unique experiments which aim to add high energy neutrinos to the emerging picture of multi-messenger astrophysics. His current work includes the modeling of neutrino propagation and interactions at the highest energies, parameterizing the optical and radio emission from extensive air showers, and optimizing the next generation neutrino telescopes. Outside of his studies, Austin likes running, riding motorcycles, and playing D&D.

Superconducting technologies have been developed and employed with great success by the quantum information science community.
More and more, these technologies show promise for fundamental physics. I want to sketch some of their possible advantages in the context of the Ricochet and Project 8 neutrino experiments.

Project 8 aims to measure the neutrino mass using the observation of cyclotron radiation from tritium decay electrons. To collect and detect this attowatt power signal, we investigate the quantum-limited readout of resonant cavities using Travelling Wave Parametric Amplifiers (TWPA) at MIT. These amplifiers are appropriate for broadband microwave amplification with a high dynamic range that could suit both Project 8 and Ricochet.

The Ricochet experiment aims to detect coherent elastic neutrino-nucleus scattering at the nuclear research reactor in Grenoble, France. The experiment will start data-taking in 2024 with two complementary detector technologies, both employing cryogenic calorimeters.

One of the two detector technologies envisaged by Ricochet has a target mass consisting of superconducting crystals. When a neutrino interacts coherently with a nucleus in a superconducting crystal lattice, the recoil energy produces phonons and excites cooper pairs into Bogoliubov quasiparticles. The milli-electronvolt-scale bandgap of superconductors might enable a significantly lower nuclear recoil energy threshold. To sense the energy in the phonon and quasiparticle systems, a trapping and thermalisation layer is connected with transition edge sensors for ultra-sensitive heat to current conversion. Several detectors are envisaged to be frequency multiplexed into the microwave band using SQUIDs and resonators at cryogenic temperatures.

Exponential Quantum Advantage in Approximate Optimization of Hard Constraint Satisfaction Problems

Abstract: A huge range of important problems in computer science–including task optimization, formal logic, encryption, and machine learning–can be solved by finding the sequence of binary variables that optimizes a cost function defined by a series of few-variable constraint relationships. Many of these problems are in the complexity class NP, and are in the worst case, and often the typical case, exponentially hard in the number of variables for all known methods. This hardness applies both to exact and approximate optimization, e.g. finding configurations with a value within a defined fraction of the global optimum. Fundamentally, the lack of any guided local minimum escape method ensures the hardness of both exact and approximate optimization classically, but the intuitive mechanism for approximation hardness in quantum algorithms based on Hamiltonian time evolution is not well understood. In this work, using the prototypically hard MAX-3-XORSAT problem class, we explore this question. We conclude that the mechanisms for quantum exact and approximation hardness are fundamentally distinct. We qualitatively identify why traditional methods such as high depth quantum adiabatic optimization algorithms are not reliably good approximation algorithms. We propose a new spectral folding optimization method that does not suffer from these issues and study it analytically and numerically. We consider random rank-3 hypergraphs including extremal planted solution instances, where the ground state satisfies an anomalously high fraction of constraints compared to truly random problems. We show that, if we define the energy to be E = N_unsat-N_sat, then spectrally folded quantum optimization will return states with energy E ≤ AE_GS (where E_GS is the ground state energy) in polynomial time, where conservatively, A ≃ 0.6. We thoroughly benchmark variations of spectrally folded quantum optimization for random classically approximation-hard (planted solution) instances in simulation, and find performance consistent with this prediction. We do not claim that this approximation guarantee holds for all possible hypergraphs, though our algorithm’s mechanism can likely generalize widely. These results suggest that quantum computers are more powerful for approximate optimization than had been previously assumed.

The preprint on this is on arxiv: https://arxiv.org/abs/2312.06104

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Generating High-Intensity, Ultrashort Optical Pulses

With the invention of lasers, the intensity of a light wave was increased by orders of magnitude over what had been achieved with a light bulb or sunlight. This much higher intensity led to new phenomena being observed, such as violet light coming out when red light went into the material. After Gérard Mourou and I developed chirped pulse amplification, also known as CPA, the intensity again increased by more than a factor of 1,000 and it once again made new types of interactions possible between light and matter. We developed a laser that could deliver short pulses of light that knocked the electrons off their atoms. This new understanding of laser-matter interactions, led to the development of new machining techniques that are used in laser eye surgery or micromachining of glass used in cell phones.

Bio: Donna Strickland is a professor in the Department of Physics and Astronomy at the University of Waterloo and is one of the recipients of the Nobel Prize in Physics 2018 for developing chirped pulse amplification with Gérard Mourou, her PhD supervisor at the time. They published this Nobel-winning research in 1985 when Strickland was a PhD student at the University of Rochester in New York state. Together they paved the way toward the most intense laser pulses ever created. The research has several applications today in industry and medicine — including the cutting of a patient’s cornea in laser eye surgery, and the machining of small glass parts for use in cell phones. Strickland was a research associate at the National Research Council Canada, a physicist at Lawrence Livermore National Laboratory and a member of technical staff at Princeton University. In 1997, she joined the University of Waterloo, where her ultrafast laser group develops high-intensity laser systems for nonlinear optics investigations. She is a recipient of a Sloan Research Fellowship, a Premier’s Research Excellence Award and a Cottrell Scholar Award. She served as the president of the Optical Society (OSA) in 2013 and is a fellow of OSA, the Royal Society of Canada, and SPIE (International Society for Optics and Photonics). Strickland is an honorary fellow of the Canadian Academy of Engineering as well as the Institute of Physics. She received the Golden Plate Award from the Academy of Achievement and holds numerous honorary doctorates. Strickland earned a PhD in optics from the University of Rochester and a B.Eng. from McMaster University.

Hybrid presentation brought to you by the Mines Physics Department, The Chipps Colloquium Series, The Payne Institute for Public Policy, Society of Physics Students, and Society of Women in Physics.

https://mines.zoom.us/j/95251534507

Lecture and reception afterward will be held in Friedhoff Hall.

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Revealing Unknown Nuclear Properties with Next-Gen Precision Technique

Radioactive ion beam facilities offer unique access to unexplored regions of the nuclear chart. Due to short half-lives and low production yields of the most promising regions of the nuclear chart, next-generation high-precision techniques are crucial for characterizing fundamental nuclear properties. This talk presents recent developments in ion trapping and laser spectroscopy techniques of radioactive isotopes that have enabled pioneering precision measurements of neutron-rich indium isotopes in the direct vicinity of the doubly-magic 100Sn(N=Z=50) at CERN/ISOLDE. Using precision mass measurements, we resolved a discrepancy in the β-decay energy of 100Sn, thereby providing an updated atomic mass value for 100Sn via its direct β-decay into 100In [Nature Phys. 17, 1099 (2021)]. Furthermore, using precision laser spectroscopy of the same indium isotopes, we shed light on 100Sn’s doubly magic character through the evolution of nuclear deformation across the indium isotopic chain. [arXiv:2310.15093; under review with Nature Phys.] The impact of these measurements is further demonstrated through an assessment of state-of-the-art density-functional and ab initio nuclear theory approaches. Lastly, I will introduce a new experiment in which both techniques are combined into a quantum-sensing setup capable of precision measurements of fundamental symmetries and unknown effects of the nuclear electroweak structure [arXiv:2310.11192; under review with Phys. Rev. Lett.]. In particular, utilizing a two-level superposition in single trapped molecular ions allows for vast amplification of unknown parity-violating effects such as the nuclear anapole moment. The tremendous leverage offered by radioactive molecules is discussed.

Bio
Undergraduate research at the Max-Planck-Institute for Nuclear Physics in trapped cluster research under Prof. Klaus Blaum
Master’s and doctorate research at CERN’s radioactive ion beam facility ISOLDE in precision mass spectrometry also under Prof. Klaus Blaum
Implemented the next-generation mass spectrometry technique called “phase-imaging” and employed in exotic isotopes around 100Sn and 132Sn
Graduated “Summa Cum Laude” in only 2.5 yrs (50% German average) and awarded with three dissertation awards: Heidelberg University, German Physical Society, European Physical Society
Postdoctoral research at MIT in precision laser spectroscopy of radionuclides under Prof Ronald Garcia Ruiz
Key person to build new laser spec setup at the new FRIB facility at MSU with three accepted proposals as spokesperson
Awarded with Humboldt Research Fellowship and Young Scientist Award of GSI facility to create and lead a new quantum-sensing experiment to study fundamental symmetry violation and electroweak effects.

Individual Rare Earth Ions in Nanophotonic Structures for Quantum Networks Applications

Abstract: Single erbium ions in crystalline hosts are attractive candidates for solid-state spin-photon interfaces thanks to long-lived spin states and optical transitions in the telecom band, promising a clear advantage for long-distance quantum network applications. These ions can be incorporated into a wide range of host materials, which influence their spin and optical coherence properties through the concentration of other magnetic spins and the erbium site symmetry. Using silicon photonic crystal cavities, we can isolate single erbium ions and investigate their optical and spin properties using resonance fluorescence and optically detected magnetic resonance. In this talk, I will show our recent work on erbium ions implanted into CaWO4, which enabled the observation of the high indistinguishability of subsequently emitted photons in the Hong-Ou-Mandel experiment [1]. This represents a notable step towards the construction of telecom band quantum repeater networks with single erbium ions. I will also discuss our recent progress on generating spin-photon and spin-spin entanglement. [1] S. Ourari*, Ł. Dusanowski*, S.P. Horvath*, M.T. Uysal*, C.M. Phenicie, P. Stevenson, M. Raha, S. Chen, R.J. Cava, N.P. de Leon, and J.D. Thompson, Indistinguishable telecom band photons from a single Er ion in the solid state, Nature 620, 977 (2023).

Bio: Lukasz Dusanowski is an Associate Research Scholar at the Department of Electrical and Computer Engineering at Princeton University. He obtained his Ph.D. in Physics at Wroclaw University of Science and Technology in Poland. Before joining Princeton, he was a Humboldt postdoctoral fellow at the University of Wurzburg in Germany, where he worked on developing different single photon emitter platforms integrated with on-chip photonic circuits. Currently, his research is focused on utilizing rare earth ion dopants in crystalline hosts as single photon sources and quantum memories for quantum network applications.

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PAUL DENHOLM

The Physics of the Power Grid: What is the Role of Inertia and its Alternatives in the Clean Energy Grid of the Future?

Abstract: The existing power grid relies heavily on physical inertia provided by thermal and hydropower generators to maintain a nearly constant frequency. But the inverters used by wind and solar do not inherently provide physical inertia, and there is concern that replacing conventional generators with renewable resources could compromise grid stability. In this talk, we will discuss the role of inertia in maintaining reliable electricity, and what alternatives might be used in a grid relying largely on inverter-based resources.

Bio: Paul Denholm is a member of the Transmission Group in the Grid Planning and Analysis Center and also a senior research fellow—the highest technical position at NREL—leading research in grid applications for energy storage and solar energy. He pioneered a variety of research methods for understanding the technical, economic, and environmental benefits and impacts of the large scale deployment of renewable electricity generation. He has delivered over 100 invited presentations to agencies including the National Science Foundation, the World Bank, and the International Energy Agency. He has co-authored over 100 articles related to renewable energy integration. While his official title is principal analyst, he is still an engineer at heart and in his free time he likes to build contraptions of dubious functionality, like a concentrating solar marshmallow cooker.

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DR. LAURA KIM

UCLA

Nanophotonic Interfaces to Control Plasmons and Spins for Next-Generation Quantum Technologies

Abstract: Light-matter interactions mediated by photonic quasiparticles play a crucial role in unlocking phenomena that are not accessible with free-space photons and providing efficient interfaces for quantum systems. In the first part of the presentation, I will present the first experimental demonstration of a mid-infrared light-emitting mechanism originating from an ultrafast coupling of optically excited carriers into hot plasmon excitations in graphene. Such excitations show gate-tunable, non-Planckian emission characteristics due to the atom-level confinement of the electromagnetic states. These findings for plasmon emission in photo-inverted graphene open a new path for the exploration of mid-infrared emission processes, and this mechanism can potentially be exploited for both far-field and near-field applications for strong optical field generation. In the second part of the presentation, I will present a resonant metasurface that mediates efficient spin-photon interactions and enables a new type of quantum imaging hardware. This quantum metasurface containing nitrogen-vacancy (NV) spin ensembles coherently encodes information about the local magnetic field on spin-dependent phase and amplitude changes of near-telecom light. The central challenge with NV sensing remains in suboptimal optical readout due to the inefficient spin-photon interface, limiting its achievable sensitivity. In this presentation, I will discuss that nanophotonic strategies provide opportunities to achieve near-unity optical spin readout fidelity for absorption-based readout. This resonant surface is designed to readily couple with external radiation and allow shot-noise-limited sensing with a standard camera, eliminating the need of single-photon detectors. This quantum optical imaging system paves the way for a new type of quantum micro(nano)scopy. The projected performance makes the studied quantum imaging metasurface appealing for the most demanding applications such as imaging through scattering tissues and spatially resolved chemical NMR detection.

Biography: Laura Kim is an assistant professor in the Department of Materials Science and Engineering at UCLA. Prior to joining UCLA, she completed her IC Postdoctoral Fellowship in the Quantum Photonics Laboratory at the Massachusetts Institute of Technology. She received her B.S. and Ph.D. degrees from the California Institute of Technology. She was named a 2020 EECS Rising Star and a recipient of the IC Postdoctoral Fellowship, Gary Malouf Foundation Award, and National Science Foundation Graduate Research Fellowship. She serves on the Early Career Editorial Advisory Board of Applied Physics Letters. Her current research interests include enhancing photonic-quasiparticle-driven light-matter interactions and developing nanoscale quantum sensing technologies.

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DR. TIANYU WANG

Boston University

Optical Neural Networks: Neuromorphic Computing and Sensing in the Optical Domain

Dr. Rahul Nandkishore

University of Colorado @ Boulder

Ergodicity Breaking in Quantum Dynamics

Abstract: When can isolated many body quantum systems fail to go to equilibrium under their own dynamics, and how robust can this `ergodicity breaking’ be? This question has been a central theme of research in quantum dynamics over the past decade, and I will share with you some highlights, focusing on three key developments: many body localization, dynamics with multipolar symmetries, and dynamics with higher form symmetries. I will present the rich and exotic phenomena that arise in these three regimes, and how they may be realized experimentally. I will then discuss some key open directions for the field.

Bio: Rahul Nandkishore is a theoretical physicist interested in a broad range of problems, from non-equilibrium quantum dynamics, to exotic phases of matter, to effects arising from interplay of interactions and disorder in both solid state and synthetic quantum systems. He received his PhD in 2012 from MIT, then spent three years at the Princeton Center for Theoretical Science as a postdoctoral fellow, before moving to a faculty position at the University of Colorado Boulder, where he has been ever since. He is Associate Professor of Physics at Boulder, and Director of the Boulder Center for Theory of Quantum Matter. He is known for his work on graphene and Dirac semimetals, on many body localization, on fracton phases of matter, and on constrained quantum dynamics. His research has been recognized by numerous awards including Young Investigator awards from the U.S. Department of Defense, a Sloan Research Fellowship, and a Simons Fellowship in Theoretical Physics.

Dr. Kamil Ciesielski

Colorado School of Mines, Physics

Thermal and electronic properties of complex ternary antimonides

Abstract: Applications of thermoelectric materials span from powering space missions through waste heat recovery, up to cooling medical products in remote environments. Furthermore, this field is a remarkable platform for exploring functionality of ideas appearing within condensed-matter physics. The thermoelectric community has recently been focused on exotic phenomena, which can lead to extreme reduction of phonon propagation. While the number of notable experimental observations in a few past years has been significant, the connection between crystal structure and transport properties is frequently still under-discussed. In the first part of this seminar, I will address one of the difficulties in this area, namely I will discuss the significance of rattling in the context of phonon transport. The original approach in the literature was correlating the rattling behavior with low reported values of lattice thermal conductivity. Further research undermined this concept, as it turned out that rattling in the conventional clathrates is localized in narrow frequency range, hence its overall effect on bulk properties must be limited. We show, that some of the unconventional (pnictide-based) clathrates can be built from a variety of cavities in its crystal structure, spanning to sizes much bigger than observed ever before. As shown by phonon dispersion, such crystal structure leads to dense ladder of flat, ultra-low lying optical modes that significantly contribute to scattering of acoustic phonons; i.e. we have shown that rattling can have a vital influence on some materials. Proper understanding of the thermal transport in structurally complex materials will be crucial for developing the next generation of thermoelectrics and other functional materials. In the second part of the talk, I will show that zinc-antimonides can also be fascinating from electronic and magnetic perspective. The 2019 discovery in Toberer lab has revealed Kagome compounds AV₃Sb₅ (A = K, Cs, Rb), that intertwine complex quantum phenomena: topological band structures, charge density waves, and superconductivity. The curious properties seem to emerge from Kagome net of vanadium atoms. We recently obtained a new grant focused on exploration of broad chemical space for novel materials with frustrated vanadium nets and emergent electronic effects. I will describe our research plan therein, combining experiments with state-of-the-art calculations, and discuss our first findings.

Bio: Kamil Ciesielski is a Research Associate at Physics Department, Colorado School of Mines. He obtained his B.S. and M.E. from Gdansk University of Technology in Poland and PhD from Institute of Low Temperature and Structure Research, Polish Academy of Sciences. His work focuses primarily on thermoelectricity and crystallographic disorder. Chemical systems he studied span from half-Heusler phases, binary chalcogenides, clathrates and other Zintl phases, as well as various intermetallics. In 2021 he received Graduate Student Award from International Thermoelectric Society. Currently, he is working on the application of his expertise in thermal transport  to novel functional materials, including solid-state electrolytes.

Dr. Kyle Leach

Colorado School of Mines, Physics

Hunting for Ghosts using Rare-Isotope Doped Superconducting and Optomechanical Sensors

Abstract: Nuclear beta and electron capture (EC) decay serve as sensitive probes of the structure and symmetries at the microscopic scale of our Universe. As such, precision measurements of the final-state products in these processes can be used as powerful laboratories to search for new physics from the meV to TeV scale, as well as addressing fundamental questions of quantum mechanics at the subatomic scale. Significant advances in “rare isotope” availability and quality, coupled with decades of sensing technique development from the AMO community have led us into a new era of fundamental tests of nature using unstable nuclei. For the past few years, we have taken the approach of embedding radioisotopes in thin-film superconducting tunnel junctions (STJs) to precisely measure the recoiling atom that gets an eV-scale “kick” from the neutrino following EC decay. These recoils are encoded with the fundamental quantum information of the neutrino and decay process, as well as carrying unique signatures of weakly coupled beyond standard model (BSM) physics; including neutrino mass, exotic weak currents, and potential “dark” particles created within the energy-window of the decay. These measurements provide a complimentary and (crucially) model-independent portal to the dark sector with sensitivities that push towards synergy between laboratory and cosmological probes. In this talk, I will discuss the broad program we have developed to provide leading limits in these areas as well as the technological advances across several sub-disciplines of science required to enable this work, including subatomic physics, quantum engineering, atomic theory, and materials science. Finally, I will discuss future prospects of extending this work using macroscopic amounts of harvested exotic atoms from the Facility for Rare Isotope Beams (FRIB) in optically levitated nanospheres for direct momentum measurements of the decay recoils.