133 results found
Zhao H, Knolle J, Moessner R, et al., 2022, Suppression of Interband Heating for Random Driving, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007
Sauvage F, Mintert F, 2022, Optimal Control of Families of Quantum Gates, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007
Joseph D, Martinez AJ, Ling C, et al., 2022, Quantum mean-value approximator for hard integer-value problems, PHYSICAL REVIEW A, Vol: 105, ISSN: 2469-9926
Corfield O, Lishman J, Lee C, et al., 2021, Certifying multilevel coherence in the motional state of a trapped ion, PRX Quantum, Vol: 2, ISSN: 2691-3399
Quantum coherence is the foundation of almost all departures from classical physics and is exhibited when a quantum system is in a superposition of different basis states. Here, the coherent superposition of three motional Fock states of a single trapped ion is experimentally certified, with a procedure that does not produce false positives. As the motional state cannot be directly interrogated, our scheme uses an interference pattern generated by projective measurement of the coupled qubit state. The minimum number of coherently superposed states is inferred from a series of threshold values based on analysis of the interference pattern. This demonstrates that high-level coherence can be verified and investigated with simple nonideal control methods that are well suited to noisy intermediate-scale quantum devices.
Mukherjee R, Kuros A, Sacha K, et al., 2021, Controlled preparation of phases in two-dimensional time crystals, Physical Review Research, Vol: 3, ISSN: 2643-1564
The study of phases is useful for understanding novel states of matter. One such state of matter aretime crystals which constitute periodically driven interacting many-body systems that spontaneouslybreak time translation symmetry. Time crystals with arbitrary periods (and dimensions) can berealized using the model of Bose-Einstein condensates bouncing on periodically-driven mirror(s). Inthis work, we identify the different phases that characterize the two-dimensional time crystal. Bydetermining the optimal initial conditions and value of system parameters, we provide a practicalroute to realize a specific phase of the time crystal. These different phases can be mapped tothe many-body states existing on a two-dimensional Hubbard lattice model, thereby opening upinteresting opportunities for quantum simulation of many-body physics in time lattices.
Mori T, Zhao H, Mintert F, et al., 2021, Rigorous Bounds on the Heating Rate in Thue-Morse Quasiperiodically and Randomly Driven Quantum Many-Body Systems, PHYSICAL REVIEW LETTERS, Vol: 127, ISSN: 0031-9007
Self CN, Khosla KE, Smith AWR, et al., 2021, Variational quantum algorithm with information sharing, npj Quantum Information, Vol: 7, ISSN: 2056-6387
We introduce an optimisation method for variational quantum algorithms and experimentally demonstrate a 100-fold improvement in efficiency compared to naive implementations. The effectiveness of our approach is shown by obtaining multi-dimensional energy surfaces for small molecules and a spin model. Our method solves related variational problems in parallel by exploiting the global nature of Bayesian optimisation and sharing information between different optimisers. Parallelisation makes our method ideally suited to the next generation of variational problems with many physical degrees of freedom. This addresses a key challenge in scaling-up quantum algorithms towards demonstrating quantum advantage for problems of real-world interest.
Ling Y, Mintert F, 2021, Deterministic preparation of nonclassical states of light in cavity optomechanics, Physical Review Research, Vol: 3, ISSN: 2643-1564
Cavity-optomechanics is an ideal platform for the generation non-Gaussian quantum states due to the anharmonic interaction between the light field and the mechanical oscillator, but it is exactly this interaction that also impedes the preparation of pure states of the light field. In this paper we derive a driving protocol that helps to exploit the anharmonic interaction for state preparation and that ensures that the state of the light field remains close to pure. This shall enable the deterministic preparation of photon Fock states or coherent superpositions thereof.
The accurate implementation of quantum gates is essential for the realisation of quantum algorithms and digital quantum simulations. This accuracy may be increased on noisy hardware through the variational optimisation of gates, however the experimental realisation of such a protocol is impeded by the large effort required to estimate the fidelity of an implemented gate. With a hierarchy of approximations we find a faithful approximation to the quantum process fidelity that can be estimated experimentally with reduced effort. Its practical use is demonstrated with the optimisation of a three-qubit quantum gate on a commercially available quantum processor.
Petiziol F, Sameti M, Carretta S, et al., 2021, Quantum Simulation of Three-Body Interactions in Weakly Driven Quantum Systems, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
Sameti M, Lishman J, Mintert F, 2021, Strong-coupling quantum logic of trapped ions, PHYSICAL REVIEW A, Vol: 103, ISSN: 2469-9926
Nyman RA, Dhar HS, Rodrigues JD, et 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>
Rodrigues JD, Dhar HS, Walker BT, et al., 2021, Learning the Fuzzy Phases of Small Photonic Condensates, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
Joseph D, Callison A, Ling C, et 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.
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.
Zhao H, Mintert F, Moessner R, et al., 2021, Random Multipolar Driving: Tunably Slow Heating through Spectral Engineering, PHYSICAL REVIEW LETTERS, Vol: 126, ISSN: 0031-9007
Sauvage F, Mintert F, 2020, Optimal Quantum Control with Poor Statistics, PRX QUANTUM, Vol: 1
Dhar HS, Rodrigues JD, Walker BT, et 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.
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
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
Kuroś A, Mukherjee R, Golletz W, et 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
Hunter-Gordon M, Szabo Z, Nyman RA, et 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.
Lishman J, Mintert F, 2020, Trapped-ion entangling gates robust against qubit frequency errors, PHYSICAL REVIEW RESEARCH, Vol: 2
Mukherjee R, Sauvage F, Xie H, et 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.
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.
Newman D, Mintert F, Nazir A, 2020, Quantum limit to nonequilibrium heat-engine performance imposed by strong system-reservoir coupling, PHYSICAL REVIEW E, Vol: 101, ISSN: 2470-0045
Rath Y, Mintert F, 2020, Prominent interference peaks in the dephasing Anderson model, PHYSICAL REVIEW RESEARCH, Vol: 2
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