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  • 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.

  • Journal article
    Garces GT, Chrzanowski HM, Daryanoosh S, Thiel V, Marchant AL, Patel RB, Humphreys PC, Datta A, Walmsley IAet al., 2020,

    Quantum-enhanced stimulated emission detection for label-free microscopy

    , APPLIED PHYSICS LETTERS, Vol: 117, ISSN: 0003-6951
  • Journal article
    Mukherjee R, Sauvage F, Xie H, Loew R, Mintert Fet al., 2020,

    Preparation of ordered states in ultra–cold gases using Bayesian optimization

    , New Journal of Physics, Vol: 22, ISSN: 1367-2630

    Ultra-cold atomic gases are unique in terms of the degree of controllability, both for internal and external degrees of freedom. This makes it possible to use them for the study of complex quantum many-body phenomena. However in many scenarios, the prerequisite condition of faithfully preparing a desired quantum state despite decoherence and system imperfections is not always adequately met. To path the way to a specific target state, we explore quantum optimal control framework based on Bayesian optimization. The probabilistic modeling and broad exploration aspects of Bayesian optimization is particularly suitable for quantum experiments where data acquisition can be expensive. Using numerical simulations for the superfluid to Mott- insulator transition for bosons in a lattice as well for the formation of Rydberg crystals as explicit examples, we demonstrate that Bayesian optimization is capable of finding better control solutions with regards to finite and noisy data compared to existing methods of optimal control.

  • Journal article
    Schofield RC, Bogusz DP, Hoggarth RA, Nur S, Major KD, Clark ASet al., 2020,

    Polymer-encapsulated organic nanocrystals for single photon emission

    , Optical Materials Express, Vol: 10, Pages: 1586-1586, ISSN: 2159-3930

    We demonstrate an emulsion-polymerisation technique to embed dibenzoterrylene-doped anthracene nanocrystals in polymethyl methacrylate (PMMA) nanocapsules. The nanocapsules require no further protection after fabrication and are resistant to sublimation compared to unprotected anthracene. The room temperature emission from single dibenzoterrylene molecules is stable and when cooled to cryogenic temperatures we see no change in their excellent optical properties compared to existing growth methods. We also show emission from nanocapsules embedded in a thin layer of titanium dioxide, highlighting their potential for integration into hybrid nanophotonic devices.

  • Journal article
    Clarke J, Sahium P, Khosla K, Pikovski I, Kim M, Vanner Met al., 2020,

    Generating mechanical and optomechanical entanglement via pulsed interaction and measurement

    , New Journal of Physics, Vol: 22, Pages: 1-32, ISSN: 1367-2630

    Entanglement generation at a macroscopic scale o ers an exciting avenue to de-velop new quantum technologies and study fundamental physics on a tabletop.Cavity quantum optomechanics provides an ideal platform to generate and exploitsuch phenomena owing to the precision of quantum optics combined with recent ex-perimental advances in optomechanical devices. In this work, we propose schemesoperating outside the resolved-sideband regime, to prepare and verify both optical-mechanical and mechanical-mechanical entanglement. Our schemes employ pulsedinteractions with a duration much less than the mechanical period and, togetherwith homodyne measurements, can both generate and characterize these types ofentanglement. To improve the performance of our schemes, a precooling stagecomprising prior pulses can be utilized to increase the amount of entanglementprepared, and local optical squeezers may be used to provide resilience againstopen-system dynamics. The entanglement generated by our schemes is quanti edusing the logarithmic negativity and is analysed with respect to the strength of thepulsed optomechanical interactions for realistic experimental scenarios includingmechanical decoherence and optical loss. Two separate schemes for mechanicalentanglement generation are introduced and compared: one scheme based on anoptical interferometric design, and the other comprising sequential optomechani-cal interactions. The pulsed nature of our protocols provides more direct access tothese quantum correlations in the time domain, with applications including quan-tum metrology and tests of quantum decoherence. By considering a parameter setbased on recent experiments, the feasibility to generate signi cant entanglementwith our schemes, even with large optical losses, is demonstrated.

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

    Experimental Investigation of State Distinguishability in Parity-Time Symmetric Quantum Dynamics

    , PHYSICAL REVIEW LETTERS, Vol: 124, ISSN: 0031-9007
  • Journal article
    Kolorenc P, Averbukh V, 2020,

    Fano-ADC(2,2) method for electronic decay rates

    , JOURNAL OF CHEMICAL PHYSICS, Vol: 152, ISSN: 0021-9606
  • Journal article
    Hughes M, Frye MD, Sawant R, Bhole G, Jones JA, Cornish SL, Tarbutt MR, Hutson JM, Jaksch D, Mur-Petit Jet al., 2020,

    Robust entangling gate for polar molecules using magnetic and microwave fields

    , Physical Review A, Vol: 101, Pages: 062308-1-062308-12, ISSN: 2469-9926

    Polar molecules are an emerging platform for quantum technologies based on their long-range electric dipole–dipole interactions, which open new possibilities for quantum information processing and the quantum simulation of strongly correlated systems. Here, we use magnetic and microwave fields to design a fast entangling gate with >0.999 fidelity and which is robust with respect to fluctuations in the trapping and control fields and to small thermal excitations. These results establish the feasibility to build a scalable quantum processor with a broad range of molecular species in optical-lattice and optical-tweezers setups.

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

    Enhanced energy transfer to an optomechanical piston from indistinguishable photons

    , Physical Review Letters, Vol: 124, Pages: 210601-1-210601-6, ISSN: 0031-9007

    Thought experiments involving gases and pistons, such as Maxwell’s demon and Gibbs’ mixing, are central to our understanding of thermodynamics. Here we present a quantum thermodynamic thought experiment in which the energy transfer from two photonic gases to a piston membrane grows quadratically with the number of photons for indistinguishable gases, while linearly for distinguishable gases. This signature of Bosonic bunching may be observed in optomechanical experiments, highlighting the potential of these systems for the realization of thermodynamic thought experiments in the quantum realm.

  • Journal article
    Ma Y, Armata F, Khosla KE, Kim MSet al., 2020,

    Optical squeezing for an optomechanical system without quantizing the mechanical motion

    , Physical Review & Research International, Vol: 2, ISSN: 2231-1815

    Witnessing quantumness in mesoscopic objects is an important milestone for both quantum technologies and foundational reasons. Cavity optomechanics offers the ideal system to achieve this by combing high-precision optical measurements with mechanical oscillators. However, mechanical quantumness can only be established if the behavior is incompatible with any classical description of an oscillator. After explicitly considering classical and hybrid quantum-classical descriptions of an optomechanical system, we rule out squeezing of the optical field as such a witness by showing it is also predicted without quantizing the mechanical oscillator.

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