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  • Journal article
    Ling Y, Qvarfort S, Mintert F, 2023,

    Fast optomechanical photon blockade

    , Physical Review Research, Vol: 5, Pages: 1-14, ISSN: 2643-1564

    The photon blockade effect is commonly exploited in the development of single-photon sources. While the photon blockade effect could be used to prepare high-fidelity single-photon states in idealized regimes, practical implementations in optomechanical systems suffer from an interplay of competing processes. Here we derive a control scheme that exploits destructive interference of Fock state amplitudes of more than one photon. The resulting preparation time for photon-blockaded quantum states is limited only by the optomechanical interaction strength and can thus be orders of magnitude shorter than in existing schemes that achieve photon blockade in the steady state.

  • Journal article
    Bergmann K, Eberly JH, Halfmann T, Knight PL, Vitanov NVet al., 2023,

    Editorial note for the J. Phys. B. special issue 'Coherent Control: Photons, Atoms and Molecules' honoring the life and work of Bruce W Shore

    , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 56, ISSN: 0953-4075
  • Journal article
    Ruberti M, Averbukh V, 2023,

    Advances in modeling attosecond electron dynamics in molecular photoionization

    , WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE, ISSN: 1759-0876
  • Journal article
    Guo N-J, Li S, Liu W, Yang Y-Z, Zeng X-D, Yu S, Meng Y, Li Z-P, Wang Z-A, Xie L-K, Ge R-C, Wang J-F, Li Q, Xu J-S, Wang Y-T, Tang J-S, Gali A, Li C-F, Guo G-Cet al., 2023,

    Coherent control of an ultrabright single spin in hexagonal boron nitride at room temperature.

    , Nat Commun, Vol: 14

    Hexagonal boron nitride (hBN) is a remarkable two-dimensional (2D) material that hosts solid-state spins and has great potential to be used in quantum information applications, including quantum networks. However, in this application, both the optical and spin properties are crucial for single spins but have not yet been discovered simultaneously for hBN spins. Here, we realize an efficient method for arraying and isolating the single defects of hBN and use this method to discover a new spin defect with a high probability of 85%. This single defect exhibits outstanding optical properties and an optically controllable spin, as indicated by the observed significant Rabi oscillation and Hahn echo experiments at room temperature. First principles calculations indicate that complexes of carbon and oxygen dopants may be the origin of the single spin defects. This provides a possibility for further addressing spins that can be optically controlled.

  • Journal article
    Grell G, Guo Z, Driver T, Decleva P, Plesiat E, Picon A, Gonzalez-Vazquez J, Walter P, Marangos JP, Cryan JP, Marinelli A, Palacios A, Martin Fet al., 2023,

    Effect of the shot-to-shot variation on charge migration induced by sub-fs x-ray free-electron laser pulses

    , PHYSICAL REVIEW RESEARCH, Vol: 5
  • Journal article
    Yang Y-Z, Zhu T-X, Li Z-P, Zeng X-D, Guo N-J, Yu S, Meng Y, Wang Z-A, Xie L-K, Zhou Z-Q, Li Q, Xu J-S, Gao X-Y, Liu W, Wang Y-T, Tang J-S, Li C-F, Guo G-Cet al., 2023,

    Laser Direct Writing of Visible Spin Defects in Hexagonal Boron Nitride for Applications in Spin-Based Technologies

    , ACS Applied Nano Materials, Vol: 6, Pages: 6407-6414, ISSN: 2574-0970
  • Journal article
    Coste N, Gundin M, Fioretto DA, Thomas SE, Millet C, Mehdi E, Somaschi N, Morassi M, Pont M, Lemaitre A, Belabas N, Krebs O, Lanco L, Senellart Pet al., 2023,

    Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation

    , QUANTUM SCIENCE AND TECHNOLOGY, Vol: 8, ISSN: 2058-9565
  • Journal article
    Shah R, Barrett TJ, Colcelli A, Oručević F, Trombettoni A, Krüger Pet al., 2023,

    Probing the Degree of Coherence through the Full 1D to 3D Crossover.

    , Phys Rev Lett, Vol: 130

    We experimentally study a gas of quantum degenerate ^{87}Rb atoms throughout the full dimensional crossover, from a one-dimensional (1D) system exhibiting phase fluctuations consistent with 1D theory to a three-dimensional (3D) phase-coherent system, thereby smoothly interpolating between these distinct, well-understood regimes. Using a hybrid trapping architecture combining an atom chip with a printed circuit board, we continuously adjust the system's dimensionality over a wide range while measuring the phase fluctuations through the power spectrum of density ripples in time-of-flight expansion. Our measurements confirm that the chemical potential μ controls the departure of the system from 3D and that the fluctuations are dependent on both μ and the temperature T. Through a rigorous study we quantitatively observe how inside the crossover the dependence on T gradually disappears as the system becomes 3D. Throughout the entire crossover the fluctuations are shown to be determined by the relative occupation of 1D axial collective excitations.

  • Journal article
    Lee C, Webster SC, Toba JM, Corfield O, Porter G, Thompson RCet al., 2023,

    Measurement-based ground-state cooling of a trapped-ion oscillator

    , PHYSICAL REVIEW A, Vol: 107, ISSN: 2469-9926
  • Journal article
    Cheng C, Frasinski LJ, Mogol G, Allum F, Howard AJ, Rolles D, Bucksbaum PH, Brouard M, Forbes R, Weinacht Tet al., 2023,

    Multiparticle Cumulant Mapping for Coulomb Explosion Imaging

    , PHYSICAL REVIEW LETTERS, Vol: 130, ISSN: 0031-9007
  • Journal article
    Haug T, Self CN, Kim MS, 2023,

    Quantum machine learning of large datasets using randomized measurements

    , Machine Learning: Science and Technology, Vol: 4, Pages: 1-17, ISSN: 2632-2153

    Quantum computers promise to enhance machine learning for practical applications. Quantum machine learning for real-world data has to handle extensive amounts of high-dimensional data. However, conventional methods for measuring quantum kernels are impractical for large datasets as they scale with the square of the dataset size. Here, we measure quantum kernels using randomized measurements. The quantum computation time scales linearly with dataset size and quadratic for classical post-processing. While our method scales in general exponentially in qubit number, we gain a substantial speed-up when running on intermediate-sized quantum computers. Further, we efficiently encode high-dimensional data into quantum computers with the number of features scaling linearly with the circuit depth. The encoding is characterized by the quantum Fisher information metric and is related to the radial basis function kernel. Our approach is robust to noise via a cost-free error mitigation scheme. We demonstrate the advantages of our methods for noisy quantum computers by classifying images with the IBM quantum computer. To achieve further speedups we distribute the quantum computational tasks between different quantum computers. Our method enables benchmarking of quantum machine learning algorithms with large datasets on currently available quantum computers.

  • Journal article
    Thomas SE, Sagona-Stophel S, Schofield Z, Walmsley IA, Ledingham PMet al., 2023,

    Single-photon-compatible telecommunications-band quantum memory in a hot atomic gas

    , Physical Review Applied, Vol: 19, Pages: 1-6, ISSN: 2331-7019

    The efficient storage and on-demand retrieval of quantum optical states that are compatible with the telecommunications band is a requirement for future terrestrial-based quantum optical networking. Spectrum in the telecommunications band minimizes optical fiber-propagation losses, and broad optical bandwidth facilitates high-speed networking protocols. Here we report on a telecommunications-wavelength- and bandwidth-compatible quantum memory. Using the Off-Resonant Cascaded Absorption protocol in hot 87Rb vapor, we demonstrate a total internal memory efficiency of 20.90(1)% with a Doppler-limited storage time of 1.10(2) ns. We characterize the memory performance with weak coherent states and measure a signal-to-noise ratio of 1.9(1)×104 for an average input photon number of 0.084.

  • Journal article
    Ho C, Lim J, Sauer B, Tarbutt Met al., 2023,

    Measuring the nuclear magnetic quadrupole moment in heavy polar molecules

    , Frontiers in Physics, Vol: 11, Pages: 1-10, ISSN: 2296-424X

    Theories that extend the Standard Model of particle physics often introduce new interactions that violate charge-parity (CP) symmetry. CP-violating effects within an atomic nucleus can be probed by measuring its nuclear magnetic quadrupole moment (MQM). The sensitivity of such a measurement is enhanced when using a heavy polar molecule containing a nucleus with quadrupole deformation. We determine how the energy levels of a molecule are shifted by the MQM and how those shifts can be measured. The measurement scheme requires molecules in a superposition of magnetic sub-levels that differ by many units of angular momentum. We develop a generic scheme for preparing these states. Finally, we consider the sensitivity that can be reached, showing that this method can reduce the current uncertainties on several CP-violating parameters.

  • Journal article
    Lee J, Park J, Kim J, Kim MS, Nha Het al., 2023,

    Non-Gaussian entanglement criteria for atomic homodyne detection

    , Physical Review A, Vol: 107, ISSN: 2469-9926

    Homodyne measurement is a crucial tool widely used to address continuous variables for bosonic quantum systems. While an ideal homodyne detection provides a powerful analysis, e.g., to effectively measure quadrature amplitudes of light in quantum optics, it relies on the use of a strong reference field, the so-called local oscillator, typically in a coherent state. Such a strong coherent local oscillator may not be readily available, particularly for a massive quantum system like a Bose-Einstein condensate, posing a substantial challenge in dealing with continuous variables appropriately. It is necessary to establish a practical framework that includes the effects of nonideal local oscillators for a rigorous assessment of various quantum tests and applications. We here develop entanglement criteria beyond a Gaussian regime applicable for this realistic homodyne measurement that do not require assumptions on the state of local oscillators. We discuss the working conditions of homodyne detection to effectively detect non-Gaussian quantum entanglement under various states of local oscillators.

  • Journal article
    Haug T, Kim M, 2023,

    Scalable measures of magic for quantum computers

    , PRX Quantum, Vol: 4, ISSN: 2691-3399

    Nonstabilizerness or magic resource characterizes the amount of non-Clifford operations needed to prepare quantum states. It is a crucial resource for quantum computing and a necessary condition for quantum advantage. However, quantifying magic resource beyond a few qubits has been a major challenge. Here, we introduce efficient measures of magic resource for pure quantum states with a sampling cost that is independent of the number of qubits. Our method uses Bell measurements over two copies of a state, which we implement in experiment together with a cost-free error-mitigation scheme. We show the transition of classically simulable stabilizer states into intractable quantum states on the IonQ quantum computer. For applications, we efficiently distinguish stabilizer and nonstabilizer states with low measurement cost even in the presence of experimental noise. Further, we propose a variational quantum algorithm to maximize our measure via the shift rule. Our algorithm can be free of barren plateaus even for highly expressible variational circuits. Finally, we experimentally demonstrate a Bell-measurement protocol for the stabilizer Rényi entropy as well as the Wallach-Meyer entanglement measure. Our results pave the way to understanding the nonclassical power of quantum computers, quantum simulators, and quantum many-body systems.

  • Conference paper
    Pearce E, Flórez J, Gemmell NR, Karzazi MA, Ma Y, Bressanini G, Battle RA, Murray RT, Kim MS, Phillips CC, Oulton RF, Clark ASet al., 2023,

    Enhancing Nonlinear Interferometers for Imaging with Undetected Photons: Seeding and High-Gain

    Infrared (IR) imaging and spectroscopy is invaluable to many disciplines for its ability to probe molecular responses, from material analysis to diagnostic medicine. However, these applications are often limited by inefficient, noisy detectors. Non-degenerate nonlinear interferometers (NLIs) offer an alternative route through a technique known as imaging with undetected photons [1]. For an NLI producing visible-IR photon pairs, a change in the IR due to an object can be observed as a change to the interference of the visible photons. The IR does not need to be detected, bypassing the need for IR detectors completely.

  • Conference paper
    Sun B, Sotirova A, Dela Cruz V, Ballance C, Mer E, Patel RB, Walmsley IA, Booth MJet al., 2023,

    Ultrafast Laser Written Waveguide Chips for Quantum Applications

    Ultrafast laser micro-fabrication has found a wide range of applications in the past decades. In particular, it is possible to create advanced photonics chips based on three-dimensional optical waveguides. Significant potential has been demonstrated in areas such as topological photonics[1] and quantum technologies[2]. Traditional fabrication methods create optical waveguides by focusing ultrafast laser into transparent materials, such as fused silica or borosilicate glass, producing localized refractive index modification. Here, we demonstrate that our recently reported Spherical Phase Induced Multi-Core Waveguides (SPIM-WGs)[3] overcome some constraints of traditional waveguide fabrication techniques, enabling new functionalities in quantum applications.

  • Journal article
    Alexander OG, Marangos JP, Ruberti M, Vacher Met al., 2023,

    Attosecond electron dynamics in molecular systems

    , Advances in Atomic Molecular and Optical Physics, Vol: 72, Pages: 183-251, ISSN: 1049-250X

    In this paper we review the topic of attosecond electron dynamics in molecular systems. We present a digest of recent research on this topic conducted by ourselves and other researchers with the intention of providing an accessible, but rigorous, account of the current state of this intriguing field of research. A short account of the background quantum theory is given before discussing recent theoretical advances on understanding correlation driven electron dynamics and electron nuclear coupling in molecules undergoing fast photoionization. We then review experimental advances, using both high harmonic generation and XFEL based ultrafast x-ray pulses, and provide three recent case studies from our own work to illustrate this. The final sections look forward to the next steps in this field: we discuss the prospect for controlling attochemistry as well as extending attosecond measurement methods to electron dynamics in larger molecules and condensed phase systems.

  • Journal article
    Hanks M, Kim MS, 2022,

    Fault tolerance in qudit circuit design

    , PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926
  • Journal article
    Fasoulakis A, Major KDD, Hoggarth RAA, Burdekin P, Bogusz DPP, Schofield RCC, Clark ASSet al., 2022,

    Uniaxial strain tuning of organic molecule single photon sources

    , NANOSCALE, Vol: 15, Pages: 177-184, ISSN: 2040-3364
  • Journal article
    Raii O, Mintert F, Burgarth D, 2022,

    Scalable quantum control and non-Abelian anyon creation in the Kitaev honeycomb model

    , PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926
  • Journal article
    Alonso I, Alpigiani C, Altschul B, Araujo H, Arduini G, Arlt J, Badurina L, Balaz A, Bandarupally S, Barish BC, Barone M, Barsanti M, Bass S, Bassi A, Battelier B, Baynham CFA, Beaufils Q, Berge J, Bernabeu J, Bertoldi A, Bingham R, Bize S, Blas D, Bongs K, Bouyer P, Braitenberg C, Brand C, Braxmaier C, Bresson A, Buchmueller O, Budker D, Bugalho L, Burdin S, Cacciapuoti L, Callegari S, Calmet X, Calonico D, Canuel B, Caramete L-I, Carraz O, Cassettari D, Chakraborty P, Chattopadhyay S, Chauhan U, Chen X, Chen Y-A, Chiofalo ML, Coleman J, Corgier R, Cotter JP, Cruise AM, Cui Y, Davies G, De Roeck A, Demarteau M, Derevianko A, Di Clemente M, Djordjevic GS, Donadi S, Dore O, Dornan P, Doser M, Drougakis G, Dunningham J, Easo S, Eby J, Elertas G, Ellis J, Evans D, Examilioti P, Fadeev P, Fani M, Fassi F, Fattori M, Fedderke MA, Felea D, Feng C-H, Ferreras J, Flack R, Flambaum VV, Forsberg R, Fromhold M, Gaaloul N, Garraway BM, Georgousi M, Geraci A, Gibble K, Gibson V, Gill P, Giudice G, Goldwin J, Gould O, Grachov O, Graham PW, Grasso D, Griffin P, Guerlin C, Gupta RK, Haehnelt M, Hawkins L, Hees A, Henderson VA, Herr W, Herrmann S, Hird T, Hobson R, Hock V, Hogan JM, Holst B, Holynski M, Israelsson U, Jeglic P, Jetzer P, Juzeliunas G, Kaltenbaek R, Kamenik JF, Kehagias A, Kirova T, Kiss-Toth M, Koke S, Kolkowitz S, Kornakov G, Kovachy T, Krutzik M, Kumar M, Kumar P, Lammerzahl C, Landsberg G, Le Poncin-Lafitte C, Leibrandt DR, Leveque T, Lewicki M, Li R, Lipniacka A, Lisdat C, Liu M, Lopez-Gonzalez JL, Loriani S, Louko J, Luciano GG, Lundblad N, Maddox S, Mahmoud MA, Maleknejad A, March-Russell J, Massonnet D, McCabe C, Meister M, Meznarsic T, Micalizio S, Migliaccio F, Millington P, Milosevic M, Mitchell J, Morley GW, Muller J, Murphy E, Mustecaplioglu OE, O'Shea V, Oi DKL, Olson J, Pal D, Papazoglou DG, Pasatembou E, Paternostro M, Pawlowski K, Pelucchi E, dos Santos FP, Peters A, Pikovski I, Pilaftsis A, Pinto A, Prevedelli M, Puthiya-Veettil V, Quenby J, Rafelskiet al., 2022,

    Cold atoms in space: community workshop summary and proposed road-map

    , EPJ QUANTUM TECHNOLOGY, Vol: 9, ISSN: 2662-4400
  • Journal article
    Haug T, Kim MS, 2022,

    Natural parametrized quantum circuit

    , PHYSICAL REVIEW A, Vol: 106, ISSN: 2469-9926
  • Journal article
    Barnard J, Lee J, Alexander O, Jarosch S, Garratt D, Picciuto R, Kowalczyk K, Ferchaud C, Gregory A, Matthews M, Marangos Jet al., 2022,

    Delivery of stable ultra-thin liquid sheets in vacuum for biochemical spectroscopy

    , Frontiers in Molecular Biosciences, Vol: 9, ISSN: 2296-889X

    The development of ultra-thin flat liquid sheets capable of running in vacuum has provided an exciting new target for X-ray absorption spectroscopy in the liquid and solution phases. Several methods have become available for delivering in-vacuum sheet jets using different nozzle designs. We compare the sheets produced by two different types of nozzle; a commercially available borosillicate glass chip using microfluidic channels to deliver colliding jets, and an in-house fabricated fan spray nozzle which compresses the liquid on an axis out of a slit to achieve collision conditions. We find in our tests that both nozzles are suitable for use in X-ray absorption spectroscopy with the fan spray nozzle producing thicker but more stable jets than the commercial nozzle. We also provide practical details of how to run these nozzles in vacuum.

  • Journal article
    Schwickert D, Ruberti M, Kolorenc P, Przystawik A, Skruszewicz S, Sumfleth M, Braune M, Bocklage L, Carretero L, Czwalinna MK, Diaman D, Duesterer S, Kuhlmann M, Palutke S, Roehlsberger R, Roensch-Schulenburg J, Toleikis S, Usenko S, Viefhaus J, Vorobiov A, Martins M, Kip D, Averbukh V, Marangos JP, Laarmann Tet al., 2022,

    Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy

    , STRUCTURAL DYNAMICS-US, Vol: 9
  • Journal article
    Bellini M, Kwon H, Biagi N, Francesconi S, Zavatta A, Kim MSet al., 2022,

    Demonstrating quantum microscopic reversibility using coherent states of light

    , Physical Review Letters, Vol: 129, Pages: 1-6, ISSN: 0031-9007

    The principle of microscopic reversibility lies at the core of fluctuation theorems, which have extended our understanding of the second law of thermodynamics to the statistical level. In the quantum regime, however, this elementary principle should be amended as the system energy cannot be sharply determined at a given quantum phase space point. In this Letter, we propose and experimentally test a quantum generalization of the microscopic reversibility when a quantum system interacts with a heat bath through energy-preserving unitary dynamics. Quantum effects can be identified by noting that the backward process is less likely to happen in the existence of quantum coherence between the system’s energy eigenstates. The experimental demonstration has been realized by mixing coherent and thermal states in a beam splitter, followed by heterodyne detection in an optical setup. We verify that the quantum modification for the principle of microscopic reversibility is critical in the low-temperature limit, while the quantum-to-classical transition is observed as the temperature of the thermal field gets higher.

  • Journal article
    Tarrant J, Khokhlova M, Averbukh V, 2022,

    Interferometry of quantum revivals (vol 157, 054304, 2022)

    , JOURNAL OF CHEMICAL PHYSICS, Vol: 157, ISSN: 0021-9606
  • Journal article
    Koukoulekidis N, Kwon H, Jee HH, Jennings D, Kim MSet al., 2022,

    Faster Born probability estimation via gate merging and frame optimisation

    , Quantum, Vol: 6, Pages: 838-838, ISSN: 2521-327X

    Outcome probability estimation via classical methods is an important task for validating quantum computing devices. Outcome probabilities of any quantum circuit can be estimated using Monte Carlo sampling, where the amount of negativity present in the circuit frame representation quantifies the overhead on the number of samples required to achieve a certain precision. In this paper, we propose two classical sub-routines: circuit gate merging and frame optimisation, which optimise the circuit representation to reduce the sampling overhead. We show that the runtimes of both sub-routines scale polynomially in circuit size and gate depth. Our methods are applicable to general circuits, regardless of generating gate sets, qudit dimensions and the chosen frame representations for the circuit components. We numerically demonstrate that our methods provide improved scaling in the negativity overhead for all tested cases of random circuits with Clifford+T and Haar-random gates, and that the performance of our methods compares favourably with prior quasi-probability simulators as the number of non-Clifford gates increases.

  • Journal article
    Koukoulekidis N, Jee H, Jennings D, Kim M, Kwon Het al., 2022,

    Faster Born probability estimation via gate merging and frame optimisation

    , Quantum, Vol: 6, Pages: 838-838, ISSN: 2521-327X

    Outcome probability estimation via classical methods is an important task for validating quantum computing devices. Outcome probabilities of any quantum circuit can be estimated using Monte Carlo sampling, where the amount of negativity present in the circuit frame representation quantifies the overhead on the number of samples required to achieve a certain precision. In this paper, we propose two classical sub-routines: circuit gate merging and frame optimisation, which optimise the circuit representation to reduce the sampling overhead. We show that the runtimes of both sub-routines scale polynomially in circuit size and gate depth. Our methods are applicable to general circuits, regardless of generating gate sets, qudit dimensions and the chosen frame representations for the circuit components. We numerically demonstrate that our methods provide improved scaling in the negativity overhead for all tested cases of random circuits with Clifford+T and Haar-random gates, and that the performance of our methods compares favourably with prior quasi-probability simulators as the number of non-Clifford gates increases.

  • Journal article
    Bressanini G, Kwon H, Kim MS, 2022,

    Noise thresholds for classical simulability of nonlinear boson sampling

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 106, Pages: 1-9, ISSN: 1050-2947

    Boson sampling, a computational problem conjectured to be hard to simulate on a classical machine, is a promising candidate for an experimental demonstration of quantum advantage using bosons. However, inevitable experimental noise and imperfections, such as loss in the interferometer and random counts at the detectors, could challenge the sampling task from entering the regime where quantum advantage is achievable. In this work we introduce higher-order nonlinearities as a means to enhance the computational complexity of the problem and the protocol's robustness against noise, i.e., to increase the noise threshold that allows us to perform an efficient classical simulation of the problem. Using a phase-space method based on the negativity volume of the relevant quasiprobability distributions, we establish a necessary nonclassicality condition that any experimental proof of quantum advantage must satisfy. Our results indicate that the addition of single-mode Kerr nonlinearity at the input-state preparation level, while retaining a linear-optical evolution, makes the boson-sampling protocol more robust against noise and consequently relaxes the constraints on the noise parameters required to show quantum advantage.

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