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  • Journal article
    Smith AWR, Gray J, Kim MS, 2021,

    Efficient quantum state sample tomography with basis-dependent neural networks

    , PRX Quantum, Vol: 2, Pages: 1-15, ISSN: 2691-3399

    We use a metalearning neural-network approach to analyze data from a measured quantum state. Once our neural network has been trained, it can be used to efficiently sample measurements of the state in measurement bases not contained in the training data. These samples can be used to calculate expectation values and other useful quantities. We refer to this process as “state sample tomography.” We encode the state’s measurement outcome distributions using an efficiently parameterized generative neural network. This allows each stage in the tomography process to be performed efficiently even for large systems. Our scheme is demonstrated on recent IBM Quantum devices, producing a model for a six-qubit state’s measurement outcomes with a predictive accuracy (classical fidelity) greater than 95% for all test cases using only 100 random measurement settings as opposed to the 729 settings required for standard full tomography using local measurements. This reduction in the required number of measurements scales favorably, with training data in 200 measurement settings, yielding a predictive accuracy greater than 92% for a ten-qubit state where 59 049 settings are typically required for full local measurement-based quantum state tomography. A reduction in the number of measurements by a factor, in this case, of almost 600 could allow for estimations of expectation values and state fidelities in practicable times on current quantum devices.

  • Journal article
    Petiziol F, Sameti M, Carretta S, Wimberger S, Mintert Fet al., 2021,

    Quantum Simulation of Three-Body Interactions in Weakly Driven Quantum Systems

    , PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
  • Journal article
    Fitch N, Tarbutt M, 2021,

    Laser-cooled molecules

    , Advances in Atomic Molecular and Optical Physics, ISSN: 1049-250X
  • Journal article
    Driver T, Bachhawat N, Frasinski L, Marangos J, Averbukh V, Edelson-Averbukh Met al., 2021,

    Chimera spectrum diagnostics for peptides using two-dimensional partial covariance mass spectrometry

    , Molecules, Vol: 26, ISSN: 1420-3049

    The rate of successful identification of peptide sequences by tandem mass spectrometry (MS/MS) is adversely affected by the common occurrence of co-isolation and co-fragmentation of two or more isobaric or isomeric parent ions. This results in so-called `chimera spectra’, which feature peaks of the fragment ions from more than a single precursor ion. The totality of the fragment ion peaks in chimera spectra cannot be assigned to a single peptide sequence, which contradicts a fundamental assumption of the standard automated MS/MS spectra analysis tools, such as protein database search engines. This calls for a diagnostic method able to identify chimera spectra to single out the cases where this assumption is not valid. Here, we demonstrate that, within the recently developed two-dimensional partial covariance mass spectrometry (2D-PC-MS), it is possible to reliably identify chimera spectra directly from the two-dimensional fragment ion spectrum, irrespective of whether the co-isolated peptide ions are isobaric up to a finite mass accuracy or isomeric. We introduce ‘3-57 chimera tag’ technique for chimera spectrum diagnostics based on 2D-PC-MS and perform numerical simulations to examine its efficiency. We experimentally demonstrate the detection of a mixture of two isomeric parent ions, even under conditions when one isomeric peptide is at one five-hundredth of the molar concentration of the second isomer.

  • Journal article
    Thomas SE, Billard M, Coste N, Wein SC, Priya, Ollivier H, Krebs O, Tazairt L, Harouri A, Lemaitre A, Sagnes I, Anton C, Lanco L, Somaschi N, Loredo JC, Senellart Pet al., 2021,

    Bright Polarized Single-Photon Source Based on a Linear Dipole

    , PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
  • Journal article
    Kissin Y, Ruberti M, Kolorenc P, Averbukh Vet al., 2021,

    Attosecond pump-attosecond probe spectroscopy of Auger decay

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 23, Pages: 12376-12386, ISSN: 1463-9076
  • Journal article
    Toros M, Van De Kamp TW, Marshman RJ, Kim MS, Mazumdar A, Bose Set al., 2021,

    Relative acceleration noise mitigation for nanocrystal matter-wave interferometry: Applications to entangling masses via quantum gravity

    , Physical Review Special Topics: Physics Education Research, Vol: 3, Pages: 1-14, ISSN: 1554-9178

    Matter-wave interferometers with large momentum transfers, irrespective of specific implementations, will face a universal dephasing due to relative accelerations between the interferometric mass and the associated apparatus. Here we propose a solution that works even without actively tracking the relative accelerations: putting both the interfering mass and its associated apparatus in a freely falling capsule, so that the strongest inertial noise components vanish due to the equivalence principle. In this setting, we investigate two of the most important remaining noise sources: (a) the noninertial jitter of the experimental setup and (b) the gravity-gradient noise. We show that the former can be reduced below desired values by appropriate pressures and temperatures, while the latter can be fully mitigated in a controlled environment. We finally apply the analysis to a recent proposal for testing the quantum nature of gravity [S. Bose et al., Phys. Rev. Lett. 119, 240401 (2017)] through the entanglement of two masses undergoing interferometry. We show that the relevant entanglement witnessing is feasible with achievable levels of relative acceleration noise.

  • Working paper
    Sturges TJ, McDermott T, Buraczewski A, Clements WR, Renema JJ, Nam SW, Gerrits T, Lita A, Kolthammer WS, Eckstein A, Walmsley IA, Stobinska Met al., 2021,

    Quantum simulations with multiphoton Fock states

    , Publisher: NATURE RESEARCH
  • Journal article
    Im D-G, Lee C-H, Kim Y, Nha H, Kim MS, Lee S-W, Kim Y-Het al., 2021,

    Optimal teleportation via noisy quantum channels without additional qubit resources

    , npj Quantum Information, Vol: 7, Pages: 1-7, ISSN: 2056-6387

    Quantum teleportation exemplifies how the transmission of quantum information starkly differs from that of classical information and serves as a key protocol for quantum communication and quantum computing. While an ideal teleportation protocol requires noiseless quantum channels to share a pure maximally entangled state, the reality is that shared entanglement is often severely degraded due to various decoherence mechanisms. Although the quantum noise induced by the decoherence is indeed a major obstacle to realizing a near-term quantum network or processor with a limited number of qubits, the methodologies considered thus far to address this issue are resource-intensive. Here, we demonstrate a protocol that allows optimal quantum teleportation via noisy quantum channels without additional qubit resources. By analyzing teleportation in the framework of generalized quantum measurement, we optimize the teleportation protocol for noisy quantum channels. In particular, we experimentally demonstrate that our protocol enables to teleport an unknown qubit even via a single copy of an entangled state under strong decoherence that would otherwise preclude any quantum operation. Our work provides a useful methodology for practically coping with decoherence with a limited number of qubits and paves the way for realizing noisy intermediate-scale quantum computing and quantum communication.

  • Conference paper
    Schofield RC, Boissier S, Jin L, Ovvyan A, Nur S, Koppens FHL, Toninelli C, Pernice WHP, Major KD, Hinds EA, Clark ASet al., 2021,

    Coupling a Single Molecule to an Interrupted Nanophotonic Waveguide

    Single organic molecules have recently seen increased interest for use as single photon sources [1]. They emit photons with high efficiency and at favourable wavelengths for coupling to other quantum systems. While the excitation of molecules and their subsequent radiative emission is efficient [2] , the generated photons can be difficult to efficiently collect. There is therefore a large amount of ongoing work on coupling organic molecules to nanophotonic structures to modify their emission. Evanescent coupling to nanophotonic [3] , [4] and hybrid plasmonic [5] waveguides has shown promise but has limitations; the molecules must be very close to the waveguide to be in the evanescent field of the guided mode which can cause the molecules to become unstable. Here I will present our recent work on coupling organic molecules to interrupted waveguides using on chip micro-capillaries [6].

  • Journal article
    Thekkadath GS, Sempere-Llagostera S, Bell BA, Patel RB, Kim MS, Walmsley IAet al., 2021,

    Single-shot discrimination of coherent states beyond the standard quantum limit

    , OPTICS LETTERS, Vol: 46, Pages: 2565-2568, ISSN: 0146-9592
  • Journal article
    Sameti M, Lishman J, Mintert F, 2021,

    Strong-coupling quantum logic of trapped ions

    , PHYSICAL REVIEW A, Vol: 103, ISSN: 2469-9926
  • Journal article
    Ashfold M, Chergui M, Fischer I, Ge L, Grell G, Ivanov M, Kirrander A, Kornilov O, Krishnan SR, Kupper J, Kuttner C, Makhija V, Martin F, Matsika S, Minns RS, Natan A, Neumark DM, Palacios A, Pratt S, Roder A, Rost JM, Ruberti M, Stolow A, Titov E, Young Let al., 2021,

    Time-resolved ultrafast spectroscopy: general discussion

    , FARADAY DISCUSSIONS, Vol: 228, Pages: 329-348, ISSN: 1359-6640
  • Conference paper
    Enzian G, Price JJ, Freisem L, Szczykulska M, Nunn J, Walmsley IA, Silver J, Bino LD, Zhang S, Del'Haye P, Janousek J, Buchler BC, Koy Lam P, Vanner MRet al., 2021,

    Brillouin optomechanics in whispering-gallery-mode microresonators: From strong coupling to single-phonon addition and subtraction

    We experimentally explore backward Brillouin scattering with high-frequency acoustic fields for optomechanics applications. We (i) demonstrate strong coupling between the optical and acoustic fields and (ii) perform single-phonon addition and subtraction operations.

  • Journal article
    Nyman RA, Dhar HS, Rodrigues JD, Mintert Fet al., 2021,

    Phase transitions of light in a dye-filled microcavity: observations and simulations

    , Journal of Physics: Conference Series, Vol: 1919, Pages: 012006-012006, ISSN: 1742-6588

    <jats:title>Abstract</jats:title> <jats:p>Photon thermalisation and condensation in dye-filled microcavities is a growing area of scientific interest, at the intersection of photonics, quantum optics and statistical physics. We give here a short introduction to the topic, together with an explanation of some of our more important recent results. A key result across several projects is that we have a model based on a detailed physical description which has been used to accurately describe experimental observations. We present a new open-source package in Python called PyPBEC which implements this model. The aim is to enable the reader to readily simulate and explore the physics of photon condensates themselves, so this article also includes a working example code which can be downloaded from the GitHub repository.</jats:p>

  • Journal article
    Ruberti M, 2021,

    Quantum electronic coherences by attosecond transient absorption spectroscopy: <i>ab initio</i> B-spline RCS-ADC study

    , FARADAY DISCUSSIONS, Vol: 228, Pages: 286-311, ISSN: 1359-6640
  • Journal article
    Li S, Driver T, Alexander O, Cooper B, Garratt D, Marinelli A, Cryan JP, Marangos JPet al., 2021,

    Time-resolved pump-probe spectroscopy with spectral domain ghost imaging

    , FARADAY DISCUSSIONS, Vol: 228, Pages: 488-501, ISSN: 1359-6640
  • Journal article
    Danson CN, White M, Barr JRM, Bett T, Blyth P, Bowley D, Brenner C, Collins RJ, Croxford N, Dangor AEB, Devereux L, Dyer PE, Dymoke-Bradshaw A, Edwards CB, Ewart P, Ferguson AI, Girkin JM, Hall DR, Hanna DC, Harris W, Hillier DI, Hooker CJ, Hooker SM, Hopps N, Hull J, Hunt D, Jaroszynski DA, Kempenaars M, Kessler H, Knight PL, Knight S, Knowles A, Lewis CLS, Lipton KS, Littlechild A, Littlechild J, Maggs P, Malcolm GPA, Mangles SPD, Martin W, McKenna P, Moore RO, Morrison C, Najmudin Z, Neely D, New GHC, Norman MJ, Paine T, Parker AW, Penman RR, Pert GJ, Pietraszewski C, Randewich A, Rizvi NH, Seddon N, Sheng Z-M, Slater D, Smith RA, Spindloe C, Taylor R, Thomas G, Tisch JWG, Wark JS, Webb C, Wiggins SM, Willford D, Winstone Tet al., 2021,

    A history of high-power laser research and development in the United Kingdom

    , High Power Laser Science and Engineering, Vol: 9, Pages: 1-86, ISSN: 2095-4719

    The first demonstration of laser action in ruby was made in 1960 by T. H. Maiman of Hughes Research Laboratories, USA. Many laboratories worldwide began the search for lasers using different materials, operating at different wavelengths. In the UK, academia, industry and the central laboratories took up the challenge from the earliest days to develop these systems for a broad range of applications. This historical review looks at the contribution the UK has made to the advancement of the technology, the development of systems and components and their exploitation over the last 60 years.

  • Journal article
    Tao S-J, Wang Q-Q, Chen Z, Pan W-W, Yu S, Chen G, Xu X-Y, Han Y-J, Li C-F, Guo G-Cet al., 2021,

    Experimental optimal generation of hybrid entangled states in photonic quantum walks

    , OPTICS LETTERS, Vol: 46, Pages: 1868-1871, ISSN: 0146-9592
  • Journal article
    Rodrigues JD, Dhar HS, Walker BT, Smith JM, Oulton RF, Mintert F, Nyman RAet al., 2021,

    Learning the Fuzzy Phases of Small Photonic Condensates

    , PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
  • Journal article
    Jurgilas S, Chakraborty A, Rich CJH, Caldwell L, Williams HJ, Fitch NJ, Sauer BE, Frye MD, Hutson JM, Tarbutt MRet al., 2021,

    Collisions between Ultracold Molecules and Atoms in a Magnetic Trap

    , PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
  • Journal article
    Chevalier H, Paige AJ, Kwon H, Kim MSet al., 2021,

    Violating the Leggett-Garg inequalities with classical light

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 103, Pages: 1-9, ISSN: 1050-2947

    In an endeavor to better define the distinction between classical macroscopic and quantum microscopic regimes, the Leggett-Garg inequalities were established as a test of macroscopic-realistic theories, which are commonly thought to be a suitable class of descriptions for classical dynamics. The relationship between their violation and nonclassicality is however not obvious. We show that classical states of light, which in the quantum optical sense are any convex sums of coherent states, may not satisfy the Leggett-Garg inequalities. After introducing a simple Mach-Zehnder setup and showing how to obtain a violation with a single photon using negative measurements, we focus on classical states of light, in particular those of low average photon number. We demonstrate how one can still perform negative measurements with an appropriate assignment of variables, and show that the inequalities are violable with coherent states. Finally, we abandon the initial phase reference and demonstrate that the violation is still possible, in particular with thermal states of light, and we investigate the effect of intermediate dephasing.

  • Journal article
    Thomas S, Senellart P, 2021,

    The race for the ideal single-photon source is on

    , NATURE NANOTECHNOLOGY, Vol: 16, Pages: 367-368, ISSN: 1748-3387
  • Journal article
    Caldwell L, Tarbutt M, 2021,

    General approach to state-dependent optical tweezer traps for polar molecules

    , Physical Review Research, Vol: 3, ISSN: 2643-1564

    State-dependent optical tweezers can be used to trap a pair of molecules with a separation much smaller than the wavelength of the trapping light, greatly enhancing the dipole-dipole interaction between them. Here we describe a general approach to producing these state-dependent potentials using the tensor part of the ac Stark shift and show how it can be used to carry out two-qubit gates between pairs of molecules. The method is applicable to broad classes of molecules including bialkali molecules produced by atom association and those amenable to direct laser cooling.

  • Journal article
    Joseph D, Callison A, Ling C, Mintert Fet al., 2021,

    Two quantum Ising algorithms for the shortest-vector problem

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 103, Pages: 1-12, ISSN: 1050-2947

    Quantum computers are expected to break today's public key cryptography within a few decades. New cryptosystems are being designed and standardized for the postquantum era, and a significant proportion of these rely on the hardness of problems like the shortest-vector problem to a quantum adversary. In this paper we describe two variants of a quantum Ising algorithm to solve this problem. One variant is spatially efficient, requiring only O(Nlog2N) qubits, where N is the lattice dimension, while the other variant is more robust to noise. Analysis of the algorithms' performance on a quantum annealer and in numerical simulations shows that the more qubit-efficient variant will outperform in the long run, while the other variant is more suitable for near-term implementation.

  • Journal article
    Koukoulekidis N, Alexander R, Hebdige T, Jennings Det al., 2021,

    The geometry of passivity for quantum states and a novel elementary derivation of the Gibbs state

    , Quantum: the open journal for quantum science, Vol: 5, Pages: 1-24, ISSN: 2521-327X

    Passivity is a fundamental concept that constitutes a necessary condition for any quantum system to attain thermodynamic equilibrium, and for a notion of temperature to emerge. While extensive work has been done that exploits this, the transition from passivity at a single-shot level to the completely passive Gibbs state is technically clear but lacks a good over-arching intuition. Here, we reformulate passivity for quantum systems in purely geometric terms. This description makes the emergence of the Gibbs state from passive states entirely transparent. Beyond clarifying existing results, it also provides novel analysis for non-equilibrium quantum systems. We show that, to every passive state, one can associate a simple convex shape in a 2-dimensional plane, and that the area of this shape measures the degree to which the system deviates from the manifold of equilibrium states. This provides a novel geometric measure of athermality with relations to both ergotropy and β--athermality.

  • Journal article
    Simsek S, Mintert F, 2021,

    Quantum control with a multi-dimensional Gaussian quantum invariant

    , Quantum, Vol: 5, Pages: 1-12, ISSN: 2521-327X

    The framework of quantum invariants is an elegant generalization of adiabatic quantum control to control fields that do not need to change slowly. Due to the unavailability of invariants for systems with more than one spatial dimension, the benefits of this framework have not yet been exploited in multi-dimensional systems. We construct a multi-dimensional Gaussian quantum invariant that permits the design of time-dependent potentials that let the ground state of an initial potential evolve towards the ground state of a final potential. The scope of this framework is demonstrated with the task of shuttling an ion around a corner which is a paradigmatic control problem in achieving scalability of trapped ion quantum information technology.

  • Journal article
    Lie SH, Kwon H, Kim MS, Jeong Het al., 2021,

    Quantum one-time tables for unconditionally secure qubit- commitment

    , Quantum, Vol: 5, Pages: 1-17, ISSN: 2521-327X

    The commodity-based cryptography is an alternative approach to realize conventionally impossible cryptographic primitives such as unconditionally secure bit-commitment by consuming pre-established correlation between distrustful participants. A unit of such classical correlation is known as the one-time table (OTT). In this paper, we introduce a new example besides quantum key distribution in which quantum correlation is useful for cryptography. We propose a scheme for unconditionally secure qubit-commitment, a quantum cryptographic primitive forbidden by the recently proven no-masking theorem in the standard model, based on the consumption of the quantum generalization of the OTT, the bipartite quantum state we named quantum one-time tables (QOTT). The construction of the QOTT is based on the newly analyzed internal structure of quantum masker and the quantum secret sharing schemes. Our qubit-commitment scheme is shown to be universally composable. We propose to measure the randomness cost of preparing a (Q)OTT in terms of its entropy, and show that the QOTT with superdense coding can increase the security level with half the cost of OTTs for unconditionally secure bit-commitment. The QOTT exemplifies an operational setting where neither maximally classically correlated state nor maximally entangled state, but rather a well-structured partially entangled mixed state is more valuable resource.

  • Journal article
    Ollivier H, Thomas SE, Wein SC, Wenniger IMDB, Coste N, Loredo JC, Somaschi N, Harouri A, Lemaitre A, Sagnes I, Lanco L, Simon C, Anton C, Krebs O, Senellart Pet al., 2021,

    Hong-Ou-Mandel Interference with Imperfect Single Photon Sources

    , PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
  • Journal article
    Neveu P, Clarke J, Vanner MR, Verhagen Eet al., 2021,

    Preparation and verification of two-mode mechanical entanglement through pulsed optomechanical measurements

    , NEW JOURNAL OF PHYSICS, Vol: 23, ISSN: 1367-2630

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