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  • Journal article
    Caldwell L, Tarbutt MR, 2020,

    Enhancing dipolar interactions between molecules using state-dependent optical tweezer traps

    , Physical Review Letters, Vol: 125, Pages: 243201 – 1-243201 – 6, ISSN: 0031-9007

    We show how state-dependent optical potentials can be used to trap a pair of molecules in different internal states at a separation much smaller than the wavelength of the trapping light. This close spacing greatly enhances thedipole-dipole interaction and we show how it can be used to implement two-qubit gates between molecules that are 100 times faster than existing protocols and than rotational coherence times already demonstrated. We analyze complications due to hyperfine structure, tensor light shifts, photon scattering and collisional loss, and conclude that none is a barrier to implementing the scheme.

  • Journal article
    Jia Z-A, Zhai R, Yu S, Wu Y-C, Guo G-Cet al., 2020,

    Hierarchy of genuine multipartite quantum correlations

    , Quantum Information Processing, Vol: 19, ISSN: 1570-0755
  • Journal article
    Dhar HS, Rodrigues JD, Walker BT, Oulton RF, Nyman RA, Mintert Fet al., 2020,

    Transport and localization of light inside a dye-filled microcavity

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 102, Pages: 1-9, ISSN: 1050-2947

    The driven-dissipative nature of light-matter interaction inside a multimode, dye-filled microcavity makes it an ideal system to study nonequilibrium phenomena, such as transport. In this work, we investigate how light is efficiently transported inside such a microcavity, mediated by incoherent absorption and emission processes. In particular, we show that there exist two distinct regimes of transport, viz. conductive and localized, arising from the complex interplay between the thermalizing effect of the dye molecules and the nonequilibrium influence of driving and loss. The propagation of light in the conductive regime occurs when several localized cavity modes undergo dynamical phase transitions to a condensed, or lasing, state. Furthermore, we observe that, while such transport is robust for weak disorder in the cavity potential, strong disorder can lead to localization of light even under good thermalizing conditions. Importantly, the exhibited transport and localization of light is a manifestation of the nonequilibrium dynamics rather than any coherent interference in the system.

  • Journal article
    Oh C, Kwon H, Jiang L, Kim MSet al., 2020,

    Field-gradient measurement using a Stern-Gerlach atomic interferometer with butterfly geometry

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 102, Pages: 053321 – 1-053321 – 8, ISSN: 1050-2947

    Atomic interferometers have been studied as a promising device for precise sensing of external fields. Among various configurations, a particular configuration with a butterfly-shaped geometry has been designed to sensitively probe field gradients. We introduce a Stern-Gerlach (SG) butterfly interferometer by incorporating magnetic field in the conventional butterfly-shaped configuration. Atomic trajectories of the interferometer can be flexibly adjusted by controlling magnetic fields to increase the sensitivity of the interferometer, while the conventional butterfly interferometer using Raman transitions can be understood as a special case. We also show that the SG interferometer can keep high contrast against a misalignment in position and momentum caused by the field gradient.

  • Journal article
    Jennings D, Cirstoiu C, Korzekwa K, 2020,

    Robustness of Noether's principle: maximal disconnects between conservation laws and symmetries in quantum theory

    , Physical Review X, Vol: 10, Pages: 041035 – 1-041035 – 41, ISSN: 2160-3308

    To what extent does Noether’s principle apply to quantum channels? Here, we quantify the degreeto which imposing a symmetry constraint on quantum channels implies a conservation law, and showthat this relates to physically impossible transformations in quantum theory, such as time-reversaland spin-inversion. In this analysis, the convex structure and extremal points of the set of quantumchannels symmetric under the action of a Lie group G becomes essential. It allows us to derivebounds on the deviation from conservation laws under any symmetric quantum channel in terms ofthe deviation from closed dynamics as measured by the unitarity of the channel E. In particular,we investigate in detail the U(1) and SU(2) symmetries related to energy and angular momentumconservation laws. In the latter case, we provide fundamental limits on how much a spin-jA systemcan be used to polarise a larger spin-jB system, and on how much one can invert spin polarisationusing a rotationally-symmetric operation. Finally, we also establish novel links between unitarity,complementary channels and purity that are of independent interest.

  • Journal article
    Mukherjee R, Xie H, Mintert F, 2020,

    Bayesian Optimal Control of Greenberger-Horne-Zeilinger States in Rydberg Lattices

    , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
  • Journal article
    Wan KH, Neville A, Kolthammer WS, 2020,

    Memory-assisted decoder for approximate Gottesman-Kitaev-Preskill codes

    , Physical Review Research, Vol: 2, ISSN: 2643-1564

    We propose a quantum error correction protocol for continuous-variable finite-energy, approximate Gottesman-Kitaev-Preskill (GKP) states undergoing small Gaussian random displacement errors, based on the scheme of Glancy and Knill [Phys. Rev. A 73, 012325 (2006)]. We show that combining multiple rounds of error-syndrome extraction with Bayesian estimation offers enhanced protection of GKP-encoded qubits over comparible single-round approaches. Furthermore, we show that the expected total displacement error incurred in multiple rounds of error followed by syndrome extraction is bounded by 2√π. By recompiling the syndrome-extraction circuits, we show that all squeezing operations can be subsumed into auxiliary state preparation, reducing them to beamsplitter transformations and quadrature measurements.

  • Journal article
    Holmes Z, Mintert F, Anders J, 2020,

    Gibbs mixing of partially distinguishable photons with a polarising beamsplitter membrane

    , NEW JOURNAL OF PHYSICS, Vol: 22, ISSN: 1367-2630
  • Journal article
    Meng Y, Yu S, Jia Z-A, Wang Y-T, Ke Z-J, Liu W, Li Z-P, Yang Y-Z, Wang H, Wu Y-C, Tang J-S, Li C-F, Guo G-Cet al., 2020,

    Environment-induced sudden change of coherence in quantum systems

    , PHYSICAL REVIEW A, Vol: 102, ISSN: 2469-9926
  • Journal article
    Burdekin P, Grandi S, Newbold R, Hoggarth RA, Major KD, Clark ASet al., 2020,

    Single-Photon-Level Sub-Doppler Pump-Probe Spectroscopy of Rubidium

    , PHYSICAL REVIEW APPLIED, Vol: 14, ISSN: 2331-7019
  • Journal article
    Thekkadath GS, Mycroft ME, Bell BA, Wade CG, Eckstein A, Phillips DS, Patel RB, Buraczewski A, Lita AE, Gerrits T, Nam SW, Stobinska M, Lvovsky AI, Walmsley IAet al., 2020,

    Quantum-enhanced interferometry with large heralded photon-number states

  • Journal article
    Tardiff E, Fan X, Gabrielse G, Grzonka D, Hamley C, Hessels EA, Jones N, Khatri G, Kolthammer WS, Martinez Zambrano D, Meisenhelder C, Morrison T, Nottet E, Novitski E, Storry CHet al., 2020,

    Two-symmetry Penning-Ioffe trap for antihydrogen cooling and spectroscopy

    , Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 977, Pages: 1-17, ISSN: 0168-9002

    High-accuracy spectroscopic comparisons of trapped antihydrogen atoms (H) and hydrogen atoms (H) promiseto stringently test the fundamental CPT symmetry invariance of the standard model of particle physics. ATRAP’snested Penning-Ioffe trap was developed for such studies. The first of its unique features is that its magneticIoffe trap forHatoms can be switched between quadrupole and octupole symmetries. The second is that itallows laser and microwave access perpendicular to the central axis of the traps.

  • Journal article
    Xie J, Zhang A, Cao N, Xu H, Zheng K, Poon Y-T, Sze N-S, Xu P, Zeng B, Zhang Let al., 2020,

    Observing Geometry of Quantum States in a Three-Level System

    , Physical Review Letters, Vol: 125, ISSN: 0031-9007
  • Journal article
    Nehra R, Eaton M, Gonzalez-Arciniegas C, Kim MS, Gerrits T, Lita A, Nam SW, Pfister Oet al., 2020,

    Generalized overlap quantum state tomography

  • Journal article
    Driver T, Cooper B, Ayers R, Pipkorn R, Patchkovskii S, Averbukh V, Klug D, Marangos J, Frasinski L, Edelson-Averbukh Met al., 2020,

    Two-dimensional partial covariance mass spectrometry of large molecules based on fragment correlations

    , Physical Review X, Vol: 10, Pages: 041004 – 1-041004 – 13, ISSN: 2160-3308

    Covariance mapping [L. J. Frasinski, K. Codling, and P. A. Hatherly, Science 246, 1029 (1989)] is a well-established technique used for the study of mechanisms of laser-induced molecular ionization and decomposition. It measures statistical correlations between fluctuating signals of pairs of detected species (ions, fragments, electrons). A positive correlation identifies pairs of products originating from the same dissociation or ionization event. A major challenge for covariance-mapping spectroscopy is accessing decompositions of large polyatomic molecules, where true physical correlations are overwhelmed by spurious signals of no physical significance induced by fluctuations in experimental parameters. As a result, successful applications of covariance mapping have so far been restricted to low-mass systems, e.g., organic molecules of around 50 daltons (Da). Partial-covariance mapping was suggested to tackle the problem of spurious correlations by taking into account the independently measured fluctuations in the experimental conditions. However, its potential has never been realized for the decomposition of large molecules, because in these complex situations, determining and continuously monitoring multiple experimental parameters affecting all the measured signals simultaneously becomes unfeasible. We introduce, through deriving theoretically and confirming experimentally, a conceptually new type of partial-covariance mapping—self-correcting partial-covariance spectroscopy—based on a parameter extracted from the measured spectrum itself. We use the readily available total ion count as the self-correcting partial-covariance parameter, thus eliminating the challenge of determining experimental parameter fluctuations in covariance measurements of large complex systems. The introduced self-correcting partial covariance enables us to successfully resolve correlations of molecules as large as

  • Journal article
    Liu W, Wang Y-T, Li Z-P, Yu S, Ke Z-J, Meng Y, Tang J-S, Li C-F, Guo G-Cet al., 2020,

    An ultrastable and robust single-photon emitter in hexagonal boron nitride

    , Physica E: Low-dimensional Systems and Nanostructures, Vol: 124, Pages: 114251-114251, ISSN: 1386-9477
  • Journal article
    Khokhlova M, Bahmanpour L, Bachhawat N, Cooper B, Averbukh Vet al., 2020,

    Interatomic coulombic decay rate in endohedral complexes

  • Journal article
    Kuroś A, Mukherjee R, Golletz W, Sauvage F, Giergiel K, Mintert F, Sacha Ket al., 2020,

    Phase diagram and optimal control for n-tupling discrete time crystal

    , New Journal of Physics, Vol: 22, Pages: 1-13, ISSN: 1367-2630
  • Journal article
    Kwon H, Paige AJ, Kim MS, 2020,

    Condition on the Rényi entanglement entropy under stochastic local manipulation

    , Physical Review Letters, Vol: 125, Pages: 100502 – 1-100502 – 7, ISSN: 0031-9007

    The Rényi entanglement entropy (REE) is an entanglement quantifier considered as a natural generalization of the entanglement entropy. When it comes to stochastic local operations and classical communication (SLOCC), however, only a limited class of the REEs satisfy the monotonicity condition, while their statistical properties beyond mean values have not been fully investigated. Here, we establish a general condition that the probability distribution of the REE of any order obeys under SLOCC. The condition is obtained by introducing a family of entanglement monotones that contain the higher-order moments of the REEs. The contribution from the higher-order moments imposes a strict limitation on entanglement distillation via SLOCC. We find that the upper bound on success probabilities for entanglement distillation exponentially decreases as the amount of raised entanglement increases, which cannot be captured from the monotonicity of the REE. Based on the strong restriction on entanglement transformation under SLOCC, we design a new method to estimate entanglement in quantum many-body systems from experimentally observable quantities.

  • Journal article
    Hunter-Gordon M, Szabo Z, Nyman RA, Mintert Fet al., 2020,

    Quantum simulation of the dephasing Anderson model

    , Physical Review A: Atomic, Molecular and Optical Physics, Vol: 102, Pages: 022407 – 1-022407 – 4, ISSN: 1050-2947

    The interplay of Anderson localization and decoherence results in intricate dynamics that is notoriously difficult to simulate on classical computers. We develop the framework for a quantum simulation of such an open quantum system making use of time-varying randomized gradients, and show that even an implementation with limited experimental resources results in accurate simulations.

  • Journal article
    O'Neal JT, Champenois EG, Oberli S, Obaid R, Al-Haddad A, Barnard J, Berrah N, Coffee R, Duris J, Galinis G, Garratt D, Glownia JM, Haxton D, Ho P, Li S, Li X, MacArthur J, Marangos JP, Natan A, Shivaram N, Slaughter DS, Walter P, Wandel S, Young L, Bostedt C, Bucksbaum PH, Picon A, Marinelli A, Cryan JPet al., 2020,

    Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses

    , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
  • Journal article
    Yu S, Meng Y, Patel RB, Wang Y-T, Ke Z-J, Liu W, Li Z-P, Yang Y-Z, Zhang W-H, Tang J-S, Li C-F, Guo G-Cet al., 2020,

    Experimental Observation of Coherent-Information Superadditivity in a Dephrasure Channel

    , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
  • Journal article
    Weaver B, Greening D, Tisch J, Marangos J, Larsen E, Pettipher A, Walke Det al., 2020,

    Generation and measurement of isolated attosecond pulses with enhanced flux using a two colour synthesized laser field

    , Optics Express, Vol: 28, Pages: 23329-23337, ISSN: 1094-4087

    We have generated isolated attosecond pulses and performed attosecond streaking measurements using a two-colour synthesized laser field consisting of a strong near-infrared few-cycle pulse and a weaker multi-cycle pulse centred at 400 nm. An actively stabilized interferometer was used to coherently combine the two pulses. Using attosecond streaking we characterised the electric fields of the two pulses and accurately retrieved the spectrum of the multi-cycle pulse. We demonstrated a two-fold increase in the flux of isolated attosecond pulses produced and show that their duration was minimally affected by the presence of the weaker field due to spectral filtering by a multilayer mirror.

  • Journal article
    Ke Z-J, Wang Y-T, Yu S, Liu W, Meng Y, Li Z-P, Wang H, Li Q, Xu J-S, Xiao Y, Tang J-S, Li C-F, Guo G-Cet al., 2020,

    Detection and quantification of entanglement with measurement-device-independent and universal entanglement witness*

    , Chinese Physics B, Vol: 29, Pages: 080301-080301, ISSN: 1674-1056

    <jats:p>Entanglement is the key resource in quantum information processing, and an entanglement witness (EW) is designed to detect whether a quantum system has any entanglement. However, prior knowledge of the target states should be known first to design a suitable EW, which weakens this method. Nevertheless, a recent theory shows that it is possible to design a universal entanglement witness (UEW) to detect negative-partial-transpose (NPT) entanglement in unknown bipartite states with measurement-device-independent (MDI) characteristic. The outcome of a UEW can also be upgraded to be an entanglement measure. In this study, we experimentally design and realize an MDI UEW for two-qubit entangled states. All of the tested states are well-detected without any prior knowledge. We also show that it is able to quantify entanglement by comparing it with concurrence estimated through state tomography. The relation between them is also revealed. The entire experimental framework ensures that the UEW is MDI.</jats:p>

  • Journal article
    Crespo H, Witting T, Canhota M, Miranda M, Tisch Jet al., 2020,

    In-situ temporal measurement of ultrashort laser pulses at full power during high-intensity laser-matter interactions

    , Optica, Vol: 7, Pages: 995-1002, ISSN: 2334-2536

    In laser-matter interaction experiments it is of paramount importance to be able tocharacterise the laser pulse on target (in-situ) and at full power. This allows pulse optimisationand meaningful comparison with theory, and can shed fundamental new light on pulse distortionsoccurring in or on the target. Here we introduce and demonstrate a new technique based ondispersion scan using the concurrent third harmonic emission from the target that permits the full(amplitude and phase), in-situ, in-parallel characterisation of ultrashort laser pulses in a gas orsolid target over a very wide intensity range that encompasses the1013−1015W cm−2regime ofhigh harmonic generation and other important strong field phenomena, with possible extensionto relativistic intensities also presently inaccessible to other diagnostics.

  • Journal article
    Ma Y, Khosla K, Stickler B, Kim Met al., 2020,

    Quantum persistent tennis racket dynamics of nanorotors

    , Physical Review Letters, Vol: 125, ISSN: 0031-9007

    Classical rotations of asymmetric rigid bodies are unstable around the axis of intermediate moment of inertia, causing a flipping of rotor orientation. This effect, known as the tennis racket effect, quickly averages to zero in classical ensembles since the flipping period varies significantly upon approaching the separatrix. Here, we explore the quantum rotations of rapidly spinning thermal asymmetric nanorotors and show that classically forbidden tunnelling gives rise to persistent tennis racket dynamics, in stark contrast to the classical expectation. We characterise this effect, demonstrating that quantum coherent flipping dynamics can persist even in the regime where millions of angular momentum states are occupied. This persistent flipping offers a promising route for observing and exploiting quantum effects in rotational degrees of freedom for molecules and nanoparticles.

  • Journal article
    Meng C, Brawley GA, Bennett JS, Vanner MR, Bowen WPet al., 2020,

    Mechanical Squeezing via Fast Continuous Measurement

    , PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
  • Journal article
    Lishman J, Mintert F, 2020,

    Trapped-ion entangling gates robust against qubit frequency errors

  • Journal article
    Zhang W-H, Zhang C, Chen Z, Peng X-X, Xu X-Y, Yin P, Yu S, Ye X-J, Han Y-J, Xu J-S, Chen G, Li C-F, Guo G-Cet al., 2020,

    Experimental Optimal Verification of Entangled States Using Local Measurements.

    , Phys Rev Lett, Vol: 125

    The initialization of a quantum system into a certain state is a crucial aspect of quantum information science. While a variety of measurement strategies have been developed to characterize how well the system is initialized, for a given one, there is in general a trade-off between its efficiency and the accessible information of the quantum state. Conventional quantum state tomography can characterize unknown states while requiring exponentially expensive time-consuming postprocessing. Alternatively, recent theoretical breakthroughs show that quantum state verification provides a technique to quantify the prepared state with significantly fewer samples, especially for multipartite entangled states. In this Letter, we modify the original proposal to be robust to practical imperfections, and experimentally implement a scalable quantum state verification on two-qubit and four-qubit entangled states with nonadaptive local measurements. For all the tested states, the estimated infidelity is inversely proportional to the number of samples, which illustrates the power to characterize a quantum state with a small number of samples. Compared to the globally optimal strategy which requires nonlocal measurements, the efficiency in our experiment is only worse by a small constant factor (<2.5). We compare the performance difference between quantum state verification and quantum state tomography in an experiment to characterize a four-photon Greenberger-Horne-Zeilinger state, and the results indicate the advantage of quantum state verification in both the achieved efficiency and precision.

  • Journal article
    Hiemstra T, Parker TF, Humphreys P, Tiedau J, Beck M, Karpinski M, Smith BJ, Eckstein A, Kolthammer WS, Walmsley IAet al., 2020,

    Pure single photons from scalable frequency multiplexing

    , Physical Review Applied, Vol: 14, ISSN: 2331-7019

    We demonstrate multiphoton interference using a resource-efficient frequency multiplexing scheme, suitable for quantum information applications that demand multiple indistinguishable and pure single photons. In our source, frequency-correlated photon pairs are generated over a wide range of frequencies by pulsed parametric down conversion. Indistinguishable single photons of a predetermined frequency are prepared using frequency-resolved detection of one photon to control an electro-optic frequency shift applied to its partner. Measured photon statistics show multiplexing increases the probability of delivering a single photon, without a corresponding increase to multiphoton events. Interference of consecutive outputs is used to bound the modal purity and demonstrate the nonclassical nature of the emitted light.

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