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Journal articleBulmer JFF, Bell BA, Chadwick RS, et al., 2022,
The boundary for quantum advantage in Gaussian boson sampling
, Science Advances, Vol: 8, ISSN: 2375-2548Identifying the boundary beyond which quantum machines provide a computational advantage over their classical counterparts is a crucial step in charting their usefulness. Gaussian boson sampling (GBS), in which photons are measured from a highly entangled Gaussian state, is a leading approach in pursuing quantum advantage. State-of-the-art GBS experiments that run in minutes would require 600 million years to simulate using the best preexisting classical algorithms. Here, we present faster classical GBS simulation methods, including speed and accuracy improvements to the calculation of loop hafnians. We test these on a ∼100,000-core supercomputer to emulate GBS experiments with up to 100 modes and up to 92 photons. This reduces the simulation time for state-of-the-art GBS experiments to several months, a nine–orders of magnitude improvement over previous estimates. Last, we introduce a distribution that is efficient to sample from classically and that passes a variety of GBS validation methods
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Conference paperSvela A, Enzian G, Freisem L, et al., 2022,
Single- and Multi-Phonon Subtraction to a Mechanical Thermal State via Optomechanics
By heralding events of single- and multi-phonon subtraction to a mechanical thermal state in a Brillouin optomechanical system and using heterodyne tomography, we observe non-Gaussianity in the s-parameterised Wigner phase-space distribution.
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Conference paperMoroney N, Del Bino L, Zhang S, et al., 2022,
All-optical Kerr Polarization Controller
We demonstrate an all-optical polarization controller in a high-finesse Fabry-Pérot microresonator. Kerr-nonlinearity-induced symmetry breaking splits linear polarized input light into left- and right-circular polarized components, enabling all-optical polarization control with mW-level threshold.
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Conference paperMaimaris M, Pettipher AJ, Azzouzi M, et al., 2022,
Sub-10fs Photocurrent and Photoluminescence Action Spectroscopies of Organic Optoelectronic Devices Reveals Ultrafast Formation of Bound Excitonic States
We apply ultrafast pump-push-photocurrent and pump-push-photoluminescence spectroscopies to polyfluorene organic diode to track in time the bound exciton formation. ‘Cold’-excitons become bound within 10-fs while ‘hot’-excitons can dissociate spontaneously within 50-fs before acquiring bound character.
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Conference paperEnzian G, Freisem L, Price JJ, et al., 2022,
Brillouin optomechanics: From strong coupling to single-phonon-level operations
, Conference on Optical and Quantum Sensing and Precision Metrology II, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X -
Journal articleCorfield O, Lishman J, Lee C, et al., 2021,
Certifying multilevel coherence in the motional state of a trapped ion
, PRX Quantum, Vol: 2, ISSN: 2691-3399Quantum coherence is the foundation of almost all departures from classical physics and is exhibited when a quantum system is in a superposition of different basis states. Here, the coherent superposition of three motional Fock states of a single trapped ion is experimentally certified, with a procedure that does not produce false positives. As the motional state cannot be directly interrogated, our scheme uses an interference pattern generated by projective measurement of the coupled qubit state. The minimum number of coherently superposed states is inferred from a series of threshold values based on analysis of the interference pattern. This demonstrates that high-level coherence can be verified and investigated with simple nonideal control methods that are well suited to noisy intermediate-scale quantum devices.
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Journal articleBarontini G, Blackburn L, Boyer V, et al., 2021,
Measuring the stability of fundamental constants with a network of clocks
The detection of variations of fundamental constants of the Standard Modelwould provide us with compelling evidence of new physics, and could lift theveil on the nature of dark matter and dark energy. In this work, we discuss howa network of atomic and molecular clocks can be used to look for suchvariations with unprecedented sensitivity over a wide range of time scales.This is precisely the goal of the recently launched QSNET project: A network ofclocks for measuring the stability of fundamental constants. QSNET will includestate-of-the-art atomic clocks, but will also develop next-generation molecularand highly charged ion clocks with enhanced sensitivity to variations offundamental constants. We describe the technological and scientific aims ofQSNET and evaluate its expected performance. We show that in the range ofparameters probed by QSNET, either we will discover new physics, or we willimpose new constraints on violations of fundamental symmetries and a range oftheories beyond the Standard Model, including dark matter and dark energymodels.
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Journal articleEnzian G, Freisem L, Price JJ, et al., 2021,
Non-Gaussian Mechanical Motion via Single and Multiphonon Subtraction from a Thermal State
, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007- Author Web Link
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- Citations: 9
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Journal articleMukherjee R, Kuros A, Sacha K, et al., 2021,
Controlled preparation of phases in two-dimensional time crystals
, Physical Review Research, Vol: 3, ISSN: 2643-1564The study of phases is useful for understanding novel states of matter. One such state of matter aretime crystals which constitute periodically driven interacting many-body systems that spontaneouslybreak time translation symmetry. Time crystals with arbitrary periods (and dimensions) can berealized using the model of Bose-Einstein condensates bouncing on periodically-driven mirror(s). Inthis work, we identify the different phases that characterize the two-dimensional time crystal. Bydetermining the optimal initial conditions and value of system parameters, we provide a practicalroute to realize a specific phase of the time crystal. These different phases can be mapped tothe many-body states existing on a two-dimensional Hubbard lattice model, thereby opening upinteresting opportunities for quantum simulation of many-body physics in time lattices.
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Journal articleToninelli C, Gerhardt I, Clark AS, et al., 2021,
Single organic molecules for photonic quantum technologies
, NATURE MATERIALS, Vol: 20, Pages: 1615-1628, ISSN: 1476-1122- Author Web Link
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- Citations: 50
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Journal articleKanari-Naish LA, Clarke J, Vanner MR, et al., 2021,
Can the displacemon device test objective collapse models?
, AVS QUANTUM SCIENCE, Vol: 3 -
Journal articleSmith AWR, Khosla KE, Self CN, et al., 2021,
Qubit readout error mitigation with bit-flip averaging
, Science Advances, Vol: 7, Pages: 1-10, ISSN: 2375-2548Quantum computers are becoming increasingly accessible, and may soonoutperform classical computers for useful tasks. However, qubit readout errorsremain a significant hurdle to running quantum algorithms on current devices.We present a scheme to more efficiently mitigate these errors on quantumhardware and numerically show that our method consistently gives advantage overprevious mitigation schemes. Our scheme removes biases in the readout errorsallowing a general error model to be built with far fewer calibrationmeasurements. Specifically, for reading out $n$-qubits we show a factor of$2^n$ reduction in the number of calibration measurements without sacrificingthe ability to compensate for correlated errors. Our approach can be combinedwith, and simplify, other mitigation methods allowing tractable mitigation evenfor large numbers of qubits.
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Journal articleDriver T, Bachhawat N, Pipkorn R, et al., 2021,
Proteomic Database Search Engine for Two-Dimensional Partial Covariance Mass Spectrometry
, ANALYTICAL CHEMISTRY, Vol: 93, Pages: 14946-14954, ISSN: 0003-2700- Author Web Link
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- Citations: 3
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Journal articleEnzian G, Freisem L, Price J, et al., 2021,
Non-Gaussian mechanical motion via single and multi-phonon subtraction from a thermal state
, Physical Review Letters, ISSN: 0031-9007Quantum optical measurement techniques offer a rich avenue for quantum control of mechanical oscillators via cavity optomechanics. In particular, a powerful yet little explored combination utilizes optical measurements to perform heralded non-Gaussian mechanical state preparation followed by tomography to determine the mechanical phase-space distribution. Here, we experimentally perform heralded single- and multi-phonon subtraction via photon counting to a laser-cooled mechanical thermal state with a Brillouin optomechanical system at room temperature, and use optical heterodyne detection to measure the s-parameterized Wigner distribution of the non-Gaussian mechanical states generated. The techniques developed here advance the state-of-the-art for optics-based tomography of mechanical states and will be useful for a broad range of applied and fundamental studies that utilize mechanical quantum-state engineering and tomography.
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Journal articleMa Y, Kim MS, Stickler BA, 2021,
Torque-free manipulation of nanoparticle rotations via embedded spins
, Physical Review B: Condensed Matter and Materials Physics, Vol: 104, ISSN: 1098-0121Spin angular momentum and mechanical rotation both contribute to the total angular momentum of rigid bodies, leading to spin-rotational coupling via the Einstein–de Haas and Barnett effects. Here, we show that the revolutions of symmetric nanorotors can be strongly affected by a small number of intrinsic spins. The resulting dynamics are observable with freely rotating nanodiamonds with embedded nitrogen-vacancy centers and persist for realistically shaped near-symmetric particles, opening the door to torque-free schemes to control their rotations at the quantum level.
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Journal articleHaug T, Bharti K, Kim MS, 2021,
Capacity and quantum geometry of parametrized quantum circuits
, PRX Quantum, Vol: 2, Pages: 1-14, ISSN: 2691-3399To harness the potential of noisy intermediate-scale quantum devices, it is paramount to find the best type of circuits to run hybrid quantum-classical algorithms. Key candidates are parametrized quantum circuits that can be effectively implemented on current devices. Here, we evaluate the capacity and trainability of these circuits using the geometric structure of the parameter space via the effective quantum dimension, which reveals the expressive power of circuits in general as well as of particular initialization strategies. We assess the expressive power of various popular circuit types and find striking differences depending on the type of entangling gates used. Particular circuits are characterized by scaling laws in their expressiveness. We identify a transition in the quantum geometry of the parameter space, which leads to a decay of the quantum natural gradient for deep circuits. For shallow circuits, the quantum natural gradient can be orders of magnitude larger in value compared to the regular gradient; however, both of them can suffer from vanishing gradients. By tuning a fixed set of circuit parameters to randomized ones, we find a region where the circuit is expressive but does not suffer from barren plateaus, hinting at a good way to initialize circuits. We show an algorithm that prunes redundant parameters of a circuit without affecting its effective dimension. Our results enhance the understanding of parametrized quantum circuits and can be immediately applied to improve variational quantum algorithms.
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Journal articleGersema P, Voges KK, Borgloh MMZA, et al., 2021,
Probing Photoinduced Two-Body Loss of Ultracold Nonreactive Bosonic <SUP>23</SUP>Na<SUP>87</SUP>Rb and <SUP>23</SUP>Na<SUP>39</SUP>K Molecules
, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007 -
Journal articleZhao H, Smith A, Mintert F, et al., 2021,
Orthogonal Quantum Many-Body Scars
, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007- Author Web Link
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- Citations: 20
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Conference paperBarontini G, Boyer V, Calmet X, et al., 2021,
QSNET, a network of clock for measuring the stability of fundamental constants
, Proceedings Volume 11881, Quantum Technology: Driving Commercialisation of an Enabling Science II, Publisher: SPIE, Pages: 1-4The QSNET consortium is building a UK network of next-generation atomic and molecular clocks that will achieve unprecedented sensitivity in testing variations of the fine structure constant, α, and the electron-to-proton mass ratio, μ. This in turn will provide more stringent constraints on a wide range of fundamental and phenomenological theories beyond the Standard Model and on dark matter models.
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Journal articleBray AC, Maxwell AS, Kissin Y, et al., 2021,
Polarization in strong-field ionization of excited helium
, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 54, ISSN: 0953-4075- Author Web Link
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- Citations: 4
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Journal articleAlauze X, Lim J, Trigatzis MA, et al., 2021,
An ultracold molecular beam for testing fundamental physics
, Quantum Science and Technology, Vol: 6, ISSN: 2058-9565We use two-dimensional transverse laser cooling to produce an ultracold beam of YbF molecules. Through experiments and numerical simulations, we study how the cooling is influenced by the polarization configuration, laser intensity, laser detuning and applied magnetic field. The ultracold part of the beam contains more than 2 × 105 molecules per shot and has a temperature below 200 μK, and the cooling yields a 300-fold increase in the brightness of the beam. The method can improve the precision of experiments that use molecules to test fundamental physics. In particular, the beam is suitable for measuring the electron electric dipole moment with a statistical precision better than 10−30 e cm.
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Journal articleVovrosh J, Khosla KE, Greenaway S, et al., 2021,
Simple mitigation of global depolarizing errors in quantum simulations.
, Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 104, Pages: 1-8, ISSN: 1539-3755To get the best possible results from current quantum devices error mitigation is essential. In this work we present a simple but effective error mitigation technique based on the assumption that noise in a deep quantum circuit is well described by global depolarizing error channels. By measuring the errors directly on the device, we use an error model ansatz to infer error-free results from noisy data. We highlight the effectiveness of our mitigation via two examples of recent interest in quantum many-body physics: entanglement measurements and real-time dynamics of confinement in quantum spin chains. Our technique enables us to get quantitative results from the IBM quantum computers showing signatures of confinement, i.e., we are able to extract the meson masses of the confined excitations which were previously out of reach. Additionally, we show the applicability of this mitigation protocol in a wider setting with numerical simulations of more general tasks using a realistic error model. Our protocol is device-independent, simply implementable, and leads to large improvements in results if the global errors are well described by depolarization.
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Journal articleDhar HS, Zuo Z, Rodrigues JD, et al., 2021,
Quest for vortices in photon condensates
, PHYSICAL REVIEW A, Vol: 104, ISSN: 2469-9926- Author Web Link
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- Citations: 1
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Journal articleBarillot T, Alexander O, Cooper B, et al., 2021,
Correlation-driven transient hole dynamics resolved in space and time in the isopropanol molecule
, Physical Review X, Vol: 11, Pages: 1-15, ISSN: 2160-3308The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or, hole)dynamics prior to significant structural change was first recognized more than 20 years ago andtermed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specifichole within the molecule. We report an investigation of the dynamics of inner valence hole states inisopropanol where we use an x-ray pump/x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an abinitio theoretical treatment. We record the signature of transient hole dynamics and make the firsttentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify thatthe effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localizedin space and time in molecules and thus to charge transfer phenomena that are fundamental inchemical and material physics.
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Journal articleBohman M, Grunhofer V, Smorra C, et al., 2021,
Sympathetic cooling of a trapped proton mediated by an LC circuit
, NATURE, Vol: 596, Pages: 514-+, ISSN: 0028-0836- Author Web Link
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- Citations: 8
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Journal articleDriver T, Averbukh V, Frasiński LJ, et al., 2021,
Two-dimensional partial covariance mass spectrometry for the top-down analysis of intact proteins.
, Analytical Chemistry, Vol: 93, Pages: 10779-10788, ISSN: 0003-2700Two-dimensional partial covariance mass spectrometry (2D-PC-MS) exploits the inherent fluctuations of fragment ion abundances across a series of tandem mass spectra, to identify correlated pairs of fragment ions produced along the same fragmentation pathway of the same parent (e.g., peptide) ion. Here, we apply 2D-PC-MS to the analysis of intact protein ions in a standard linear ion trap mass analyzer, using the fact that the fragment-fragment correlation signals are much more specific to the biomolecular sequence than one-dimensional (1D) tandem mass spectrometry (MS/MS) signals at the same mass accuracy and resolution. We show that from the distribution of signals on a 2D-PC-MS map it is possible to extract the charge state of both parent and fragment ions without resolving the isotopic envelope. Furthermore, the 2D map of fragment-fragment correlations naturally separates the products of the primary decomposition pathways of the molecular ions from those of the secondary ones. We access this spectral information using an adapted version of the Hough transform. We demonstrate the successful identification of highly charged, intact protein molecules bypassing the need for high mass resolution. Using this technique, we also perform the in silico deconvolution of the overlapping fragment ion signals from two co-isolated and co-fragmented intact proteins, demonstrating a viable new method for the concurrent mass spectrometric identification of a mixture of intact protein ions from the same fragment ion spectrum.
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Journal articleLee S-W, Im D-G, Kim Y-H, et al., 2021,
Quantum teleportation is a reversal of quantum measurement
, Physical Review Research, Vol: 3, Pages: 1-16, ISSN: 2643-1564We introduce a generalized concept of quantum teleportation in the framework of quantum measurement and reversing operation. Our framework makes it possible to find an optimal protocol for quantum teleportation enabling a faithful transfer of unknown quantum states with maximum success probability up to the fundamental limit of the no-cloning theorem. Moreover, an optimized protocol in this generalized approach allows us to overcome noise in quantum channel beyond the reach of existing teleportation protocols without requiring extra qubit resources. Our proposed framework is applicable to multipartite quantum communications and primitive functionalities in scalable quantum architectures.
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Journal articleStickler BA, Hornberger K, Kim MS, 2021,
Quantum rotations of nanoparticles
, NATURE REVIEWS PHYSICS, Vol: 3, Pages: 589-597- Author Web Link
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- Citations: 34
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Journal articleMori T, Zhao H, Mintert F, et al., 2021,
Rigorous Bounds on the Heating Rate in Thue-Morse Quasiperiodically and Randomly Driven Quantum Many-Body Systems
, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007- Author Web Link
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- Citations: 10
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Journal articleSelf CN, Khosla KE, Smith AWR, et al., 2021,
Variational quantum algorithm with information sharing
, npj Quantum Information, Vol: 7, ISSN: 2056-6387We introduce an optimisation method for variational quantum algorithms and experimentally demonstrate a 100-fold improvement in efficiency compared to naive implementations. The effectiveness of our approach is shown by obtaining multi-dimensional energy surfaces for small molecules and a spin model. Our method solves related variational problems in parallel by exploiting the global nature of Bayesian optimisation and sharing information between different optimisers. Parallelisation makes our method ideally suited to the next generation of variational problems with many physical degrees of freedom. This addresses a key challenge in scaling-up quantum algorithms towards demonstrating quantum advantage for problems of real-world interest.
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