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Journal articleTaylor A, Bressanini G, Kwon H, et al., 2024,
Quantum error cancellation in photonic systems: undoing photon losses
, Physical Review A, Vol: 110, ISSN: 2469-9926Real photonic devices are subject to photon losses that can decohere quantum information encoded in the system. In the absence of full fault tolerance, quantum error mitigation techniques have been introduced to help manage errors in noisy quantum devices. In this paper, we introduce an error mitigation protocol inspired by probabilistic error cancellation (a popular error mitigation technique in discrete variable systems) for continuous variable systems. We show that our quantum error cancellation protocol can undo photon losses in expectation value estimation tasks. To do this, we analytically derive the (nonphysical) inverse photon loss channel and decompose it into a sum over physically realizable channels with potentially negative coefficients. The bias of our ideal expectation value estimator can be made arbitrarily small at the cost of increasing the sampling overhead. The protocol requires a noiseless amplification followed by a series of photon subtractions. While these operations can be implemented probabilistically, for certain classes of initial state one can avoid the burden of carrying out the amplification and photon subtractions by leveraging Monte Carlo methods to give an unbiased estimate of the ideal expectation value. We validate our proposed mitigation protocol by simulating the scheme on squeezed vacuum states, cat states, and entangled coherent states.
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Journal articleAthanasakis-Kaklamanakis M, Wilkins SG, Lassegues P, et al., 2024,
Radiative lifetime of the <i>A</i> <SUP>2</SUP>Π <sub>1 / 2</sub> state in RaF with relevance to laser cooling
, PHYSICAL REVIEW A, Vol: 110, ISSN: 2469-9926 -
Journal articleXiao X, Yang JJ, Millard TS, et al., 2024,
Nanofocusing in critically coupled nanogap waveguide resonators
, ACS Photonics, Vol: 11, Pages: 2836-2842, ISSN: 2330-4022Coupling between optical antenna resonances is a powerful way to control the distribution of light in nanoscale systems. When the strength of coupling is fine-tuned against resonance loss, a critical coupling condition is often met, where energy can be efficiently directed between the system’s components. In this work, we use this concept to nanofocus optical energy into the 50 nm gap of a waveguide resonator, which on its own cannot be excited by external illumination. Light couples to the waveguide antenna via Fano interference with a bar antenna dimer. As a composite antenna, the shifting of the dimer relative to the waveguide resonator enables the precise tuning of their mutual coupling. We find a critical coupling condition where light is maximally focused into the waveguide’s gap corresponding to unity coupling cooperativity. Our interpretation of critical-coupling-induced nanofocusing is supported by the simultaneous maximization of both second and third harmonic generation at the critical condition.
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Journal articleWill C, Wiesinger M, Micke P, et al., 2024,
Image-Current Mediated Sympathetic Laser Cooling of a Single Proton in a Penning Trap Down to 170 mK Axial Temperature
, PHYSICAL REVIEW LETTERS, Vol: 133, ISSN: 0031-9007 -
Journal articleJae J, Lee J, Kim MS, et al., 2024,
Contextual quantum metrology
, npj Quantum Information, Vol: 10, ISSN: 2056-6387We demonstrate that the contextuality of measurement selection can enhance the precision of quantum metrology with a simple linear optical experiment. Contextuality is a nonclassical property known as a resource for various quantum information processing tasks. Recent studies show that contextuality by anomalous weak values can be utilized to enhance metrological precision, unraveling the role of contextuality in quantum metrology. Our contextual quantum metrology (coQM) scheme can elevate the precision of the optical polarimetry as much as 6 times the precision limit given by the Quantum Fisher Information. We achieve the contextuality-enabled enhancement with two mutually complementary measurements, whereas, in the conventional method, some optimal measurements to achieve the precision limit are either theoretically challenging to find or experimentally infeasible to realize. These results highlight that the contextuality of measurement selection is applicable in practice for quantum metrology.
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Journal articleMichniewicz J, Kim MS, 2024,
Leveraging off-the-shelf silicon chips for quantum computing
, APPLIED PHYSICS LETTERS, Vol: 124, ISSN: 0003-6951 -
Journal articleHaug T, Lee S, Kim MS, 2024,
Efficient quantum algorithms for stabilizer entropies
, Physical Review Letters, Vol: 132, ISSN: 0031-9007Stabilizer entropies (SEs) are measures of nonstabilizerness or “magic” that quantify the degree to whicha state is described by stabilizers. SEs are especially interesting due to their connections to scrambling,localization and property testing. However, applications have been limited so far as previously knownmeasurement protocols for SEs scale exponentially with the number of qubits. Here, we efficiently measureSEs for integer R´enyi index n > 1 via Bell measurements. The SE of N-qubit quantum states can bemeasured with OðnÞ copies and OðnNÞ classical computational time, where for even n we additionallyrequire the complex conjugate of the state. We provide efficient bounds of various nonstabilizernessmonotones that are intractable to compute beyond a few qubits. Using the IonQ quantum computer, wemeasure SEs of random Clifford circuits doped with non-Clifford gates and give bounds for the stabilizerfidelity, stabilizer extent, and robustness of magic. We provide efficient algorithms to measure Clifford averaged 4n-point out-of-time-order correlators and multifractal flatness. With these measures we study thescrambling time of doped Clifford circuits and random Hamiltonian evolution depending on nonstabilizer ness. Counterintuitively, random Hamiltonian evolution becomes less scrambled at long times, which wereveal with the multifractal flatness. Our results open up the exploration of nonstabilizerness with quantumcomputers.
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Journal articleZhu R, Pike-Burke C, Mintert F, 2024,
Active learning for quantum mechanical measurements
, PHYSICAL REVIEW A, Vol: 109, ISSN: 2469-9926 -
Journal articleHanks M, Lee S, Kim MS, 2024,
Noise-Tailored Constructions for Spin Wigner Function Kernels
, ADVANCED PHYSICS RESEARCH, Vol: 3, ISSN: 2751-1200 -
Journal articleMok W-K, Zhang H, Haug T, et al., 2024,
Rigorous noise reduction with quantum autoencoders
, AVS QUANTUM SCIENCE, Vol: 6 -
Journal articlePopa S, Schaller S, Fielicke A, et al., 2024,
Understanding Inner-Shell Excitations in Molecules through Spectroscopy of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>4</mml:mn><mml:mi>f</mml:mi></mml:math> Hole States of YbF
, Physical Review X, Vol: 14<jats:p>Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multiphoton ionization spectroscopy. We investigate the excited states of lowest energy, 8474, 9013, and <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>9090</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:msup><a:mrow><a:mi>cm</a:mi></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn></a:mrow></a:msup></a:math> above the ground state, all corresponding to the configuration <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mn>4</c:mn><c:msup><c:mrow><c:mi>f</c:mi></c:mrow><c:mrow><c:mn>13</c:mn></c:mrow></c:msup><c:mn>6</c:mn><c:msup><c:mrow><c:mi>s</c:mi></c:mrow><c:mrow><c:mn>2</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:mtext> </c:mtext><c:msub><c:mrow><c:mmultiscripts><c:mrow><c:mi>F</c:mi></c:mrow><c:mprescripts/><c:none/><c:mrow><c:mn>2</c:mn></c:mrow></c:mmultiscripts></c:mrow><c:mrow><c:mn>7</c:mn><c:mo>/</c:mo><c:mn>2</c:mn></c:mrow></c:msub></c:mrow></c:math> of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msup>&l
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Journal articleWalraven EF, Tarbutt MR, Karman T, 2024,
Scheme for deterministic loading of laser-cooled molecules into optical tweezers
, Physical Review Letters, Vol: 132, ISSN: 0031-9007We propose to repeatedly load laser-cooled molecules into optical tweezers, and transfer them to storage states that are rotationally excited by two additional quanta. Collisional loss of molecules in these storage states is suppressed, and a dipolar blockade prevents the accumulation of more than one molecule. Applying three cycles loads tweezers with single molecules at an 80% success rate, limited by residual collisional loss. This improved loading efficiency reduces the time needed for rearrangement of tweezer arrays, which would otherwise limit the scalability of neutral molecule quantum computers.
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Journal articleCornish SL, Tarbutt MR, Hazzard KRA, 2024,
Quantum computation and quantum simulation with ultracold molecules
, NATURE PHYSICS, Vol: 20, Pages: 730-740, ISSN: 1745-2473 -
Journal articleShi B, Mintert F, 2024,
Quantum simulations of time-dependent Hamiltonians beyond the quasistatic approximation
, Physical Review Research, Vol: 6, ISSN: 2643-1564Existing approaches to analogue quantum simulations of time-dependent quantum systems relyon perturbative corrections to quantum simulations of time-independent quantum systems. Weovercome this restriction to perturbative treatments with an approach based on flow equations anda multi-mode Fourier expansion. The potential of the quantum simulations that can be achievedwith our approach is demonstrated with the pedagogical example of a Lambda-system and thequench in finite time through a quantum phase transition of a Chern insulator in a driven noninteracting Hubbard system. The example of the Lambda-system demonstrates the ability of ourapproach to describe situations beyond the validity of adiabatic approximations.
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Journal articleTang Y, Dhar HS, Oulton RF, et al., 2024,
Breakdown of Temporal Coherence in Photon Condensates
, PHYSICAL REVIEW LETTERS, Vol: 132, ISSN: 0031-9007 -
Journal articleGuo Z, Driver T, Beauvarlet S, et al., 2024,
Experimental demonstration of attosecond pump-probe spectroscopy with an X-ray free-electron laser
, NATURE PHOTONICS, ISSN: 1749-4885 -
Journal articleLi W, Brown D, Vylegzhanin A, et al., 2024,
Atom-light interactions using optical nanofibres—a perspective
, JPhys Photonics, Vol: 6Complete control of light-matter interactions at a single quantum level is critical for quantum science applications such as precision measurement and information processing. Nanophotonic devices, developed with recent advancements in nanofabrication techniques, can be used to tailor the interactions between single photons and atoms. One example of such a nanophotonic device is the optical nanofibre, which provides an excellent platform due to the strongly confined transverse light fields, long interaction length, low loss, and diverse optical modes. This facilitates a strong interaction between atoms and guided light, revealing chiral atom-light processes and the prospect of waveguide quantum electrodynamics. This paper highlights recent advances, experimental techniques, and future perspectives of the optical nanofibre-atom hybrid quantum platform.
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Journal articleCheng C, Frasinski LJ, Allum F, et al., 2024,
Multiparticle cumulant mapping for Coulomb explosion imaging: Calculations and algorithm
, PHYSICAL REVIEW A, Vol: 109, ISSN: 2469-9926 -
Journal articlePopa S, Schaller S, Fielicke A, et al., 2024,
Understanding inner-shell excitations in molecules through spectroscopy of the 4f hole states of YbF
, Physical Review X, Vol: 14, ISSN: 2160-3308Molecules containing a lanthanide atom have sets of electronic states arising from excitation of an inner-shell electron. These states have received little attention, but are thought to play an important role in laser cooling of such molecules and may be a useful resource for testing fundamental physics. We study a series of inner-shell excited states in YbF using resonance-enhanced multi-photon ionisation spectroscopy. We investigate the excited states of lowest energy, 8474, 9013 and 9090 cm⁻¹ above the ground state, all corresponding to the configuration 4f¹³6s² ²F₇⁄₂ of the Yb⁺ ion. They are metastable, since they have no electric dipole allowed transitions to the ground state. We also characterize a state at 31050 cm¯¹ that is easily excited from both the ground and metastable states, which makes it especially useful for this spectroscopic study. Finally, we study two states at 48720 cm¯¹ and 48729 cm¯¹, which are above the ionization limit and feature strong auto-ionizing resonances that prove useful for efficient detection of the molecules and for identifying the rotational quantum number of each line in the spectrum. We resolve the rotational structures of all these states and find that they can all be described by a very simple model based on Hund’s case (c). Our study provides information necessary for laser slowing and magneto-optical trapping of YbF, which is an important species for testing fundamental physics. We also consider whether the low-lying inner-shell states may themselves be useful as probes of the electron’s electric dipole moment or of varying fundamental constants, since they are long-lived states in a laser-coolable molecule featuring closely-spaced levels of opposite parity.
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Journal articleTang Y, Dhar HS, Oulton RF, et al., 2024,
Photon-photon correlation of condensed light in a microcavity
, Physical Review A (atomic, molecular, and optical physics and quantum information), Vol: 109, ISSN: 2469-9926The study of temporal coherence in a Bose-Einstein condensate of photons can be challenging, especially in the presence of correlations between the photonic modes. In this work, we use a microscopic, multimode model of photonic condensation inside a dye-filled microcavity and the quantum regression theorem to derive an analytical expression for the equation of motion of the photon-photon correlation function. This allows us to derive the coherence time of the photonic modes and identify a nonmonotonic dependence of the temporal coherence of the condensed light with the cutoff frequency of the microcavity.
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Journal articleAlaa El-Din K, Alexander O, Frasinski L, et al., 2024,
Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning
, Scientific Reports, Vol: 14, ISSN: 2045-2322X-ray free-electron lasers are sources of coherent, high-intensity X-rays with numerous applications in ultra-fast measurements and dynamic structural imaging. Due to the stochastic nature of the self-amplified spontaneous emission process and the difficulty in controlling injection of electrons, output pulses exhibit significant noise and limited temporal coherence. Standard measurement techniques used for characterizing two-coloured X-ray pulses are challenging, as they are either invasive or diagnostically expensive. In this work, we employ machine learning methods such as neural networks and decision trees to predict the central photon energies of pairs of attosecond fundamental and second harmonic pulses using parameters that are easily recorded at the high-repetition rate of a single shot. Using real experimental data, we apply a detailed feature analysis on the input parameters while optimizing the training time of the machine learning methods. Our predictive models are able to make predictions of central photon energy for one of the pulses without measuring the other pulse, thereby leveraging the use of the spectrometer without having to extend its detection window. We anticipate applications in X-ray spectroscopy using XFELs, such as in time-resolved X-ray absorption and photoemission spectroscopy, where improved measurement of input spectra will lead to better experimental outcomes.
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Journal articleGreenaway S, Petiziol F, Zhao H, et al., 2024,
Variational quantum gate optimization at the pulse level
, SciPost Physics, Vol: 16, ISSN: 2542-4653We experimentally investigate the viability of a variational quantum gate optimizationprotocol informed by the underlying physical Hamiltonian of fixed-frequency transmonqubits. Through the successful experimental optimization of two and three qubit quan-tum gates the utility of the scheme for obtaining gates based on static effective Hamilto-nians is demonstrated. The limits of such a strategy are investigated through the opti-mization of a time-dependent, Floquet-engineered gate, however parameter drift is iden-tified as a key limiting factor preventing the implementation of such a scheme which thevariational optimization protocol is unable to overcome.
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Journal articleYu S, Liu W, Tao S-J, et al., 2024,
A von-Neumann-like photonic processor and its application in studying quantum signature of chaos
, LIGHT-SCIENCE & APPLICATIONS, Vol: 13, ISSN: 2095-5545 -
Journal articleWang Z, Wang F, Vovrosh J, et al., 2024,
Quantum simulation of hadronic states with Rydberg-dressed atoms
, PHYSICAL REVIEW A, Vol: 109, ISSN: 2469-9926 -
Journal articleTang H, Shang X-W, Shi Z-Y, et al., 2024,
Simulating photosynthetic energy transport on a photonic network
, npj Quantum Information, Vol: 10, ISSN: 2056-6387Quantum effects in photosynthetic energy transport in nature, especially for the typical Fenna-Matthews-Olson (FMO) complexes, are extensively studied in quantum biology. Such energy transport processes can be investigated as open quantum systems that blend the quantum coherence and environmental noise, and have been experimentally simulated on a few quantum devices. However, the existing experiments always lack a solid quantum simulation for the FMO energy transport due to their constraints to map a variety of issues in actual FMO complexes that have rich biological meanings. Here we successfully map the full coupling profile of the seven-site FMO structure by comprehensive characterisation and precise control of the evanescent coupling of the three-dimensional waveguide array. By applying a stochastic dynamical modulation on each waveguide, we introduce the base site energy and the dephasing term in coloured noise to faithfully simulate the power spectral density of the FMO complexes. We show our photonic model well interprets the phenomena including reorganisation energy, vibrational assistance, exciton transfer and energy localisation. We further experimentally demonstrate the existence of an optimal transport efficiency at certain dephasing strength, providing a window to closely investigate environment-assisted quantum transport.
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Journal articleStray B, Ennis O, Hedges S, et al., 2024,
Centralized design and production of the ultra-high vacuum and laser-stabilization systems for the AION ultra-cold strontium laboratories
, AVS Quantum Science, Vol: 6, ISSN: 2639-0213This paper outlines the centralized design and production of the ultra-high-vacuum sidearm and laser-stabilization systems for the AION Ultra-Cold Strontium Laboratories. Commissioning data on the residual gas and steady-state pressures in the sidearm chambers, on magnetic field quality, on laser stabilization, and on the loading rate for the 3D magneto-optical trap are presented. Streamlining the design and production of the sidearm and laser stabilization systems enabled the AION Collaboration to build and equip in parallel five state-of-the-art Ultra-Cold Strontium Laboratories within 24 months by leveraging key expertise in the collaboration. This approach could serve as a model for the development and construction of other cold atom experiments, such as atomic clock experiments and neutral atom quantum computing systems, by establishing dedicated design and production units at national laboratories.
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Journal articleGreenaway S, Smith A, Mintert F, et al., 2024,
Analogue Quantum Simulation with Fixed-Frequency Transmon Qubits
, QUANTUM, Vol: 8, ISSN: 2521-327X -
Journal articleSchwickert D, Przystawik A, Diaman D, et al., 2024,
Coupled electron-nuclear dynamics induced and monitored with femtosecond soft X-ray pulses in the amino acid glycine
, The Journal of Physical Chemistry A: Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; Theory, Vol: 128, Pages: 989-995, ISSN: 1089-5639The coupling of electronic and nuclear motion in polyatomic molecules is at the heart of attochemistry. The molecular properties, transient structures, and reaction mechanism of these many-body quantum objects are defined on the level of electrons and ions by molecular wave functions and their coherent superposition, respectively. In the present contribution, we monitor nonadiabatic quantum wave packet dynamics during molecular charge motion by reconstructing both the oscillatory charge density distribution and the characteristic time-dependent nuclear configuration coordinate from time-resolved Auger electron spectroscopic data recorded in previous studies on glycine molecules [Schwickert et al. Sci. Adv. 2022, 8, eabn6848]. The electronic and nuclear motion on the femtosecond time scale was induced and probed in kinematically complete soft X-ray experiments at the FLASH free-electron laser facility. The detailed analysis of amplitude, instantaneous phase, and instantaneous frequency of the propagating many-body wave packet during its lifecycle provides unprecedented insight into dynamical processes beyond the Born-Oppenheimer approximation. We are confident that the refined experimental data evaluation helps to develop new theoretical tools to describe time-dependent molecular wave functions in complicated but ubiquitous non-Born-Oppenheimer photochemical conditions.
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Journal articlePetiziol F, Wimberger S, Eckardt A, et al., 2024,
Nonperturbative Floquet engineering of the toric-code Hamiltonian and its ground state
, PHYSICAL REVIEW B, Vol: 109, ISSN: 2469-9950 -
Journal articleBressanini G, Kwon H, Kim MS, 2024,
Gaussian boson sampling with click-counting detectors
, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 109, ISSN: 1050-2947Gaussian boson sampling constitutes a prime candidate for an experimental demonstration of quantum advantage within reach with current technological capabilities. The original proposal employs photon-number-resolving detectors, however, these are not widely available. Nevertheless, inexpensive threshold detectors can be combined into a single click-counting detector to achieve approximate photon-number resolution. We investigate the problem of sampling from a general multimode Gaussian state using click-counting detectors and show that the probability of obtaining a given outcome is related to a matrix function which is dubbed as the Kensingtonian. We show how the Kensingtonian relates to the Torontonian and the Hafnian, thus bridging the gap between known Gaussian boson sampling variants. We then prove that, under standard complexity-theoretical conjectures, the model cannot be simulated efficiently.
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