99 results found
Marques Rodrigues J, Walker BT, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Nature Communications, Vol: 11, ISSN: 2041-1723
While equilibrium phase transitions are easily described by order parameters and free-energylandscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here,we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. Wequench the system to a far-from-equilibrium state and find delayed condensation close to a criticalexcitation energy, a transient equivalent of critical slowing down. Besides number fluctuations nearthe critical excitation energy, we show that transient phase transitions exhibit timing jitter in thecondensate formation. This jitter is a manifestation of the randomness associated with spontaneousemission, showing that condensation is a stochastic, rather than deterministic process. Despite thenon-equilibrium character of this phase transition, we construct an effective free-energy landscapethat describes the formation jitter and allows, in principle, its generalization to a wider class ofprocesses.
Walker BT, Rodrigues JD, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation.
While equilibrium phase transitions are easily described by order parameters and free-energy landscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. We quench the system to a far-from-equilibrium state and find delayed condensation close to a critical excitation energy, a transient equivalent of critical slowing down. Besides number fluctuations near the critical excitation energy, we show that transient phase transitions exhibit timing jitter in the condensate formation. This jitter is a manifestation of the randomness associated with spontaneous emission, showing that condensation is a stochastic, rather than deterministic process. Despite the non-equilibrium character of this phase transition, we construct an effective free-energy landscape that describes the formation jitter and allows, in principle, its generalization to a wider class of processes.
Petiziol F, Arimondo E, Giannelli L, et al., 2020, Optimized three-level quantum transfers based on frequency-modulated optical excitations., Sci Rep, Vol: 10
The difficulty in combining high fidelity with fast operation times and robustness against sources of noise is the central challenge of most quantum control problems, with immediate implications for the realization of quantum devices. We theoretically propose a protocol, based on the widespread stimulated Raman adiabatic passage technique, which achieves these objectives for quantum state transfers in generic three-level systems. Our protocol realizes accelerated adiabatic following through the application of additional control fields on the optical excitations. These act along frequency sidebands of the principal adiabatic pulses, dynamically counteracting undesired transitions. The scheme facilitates experimental control, not requiring new hardly-accessible resources. We show numerically that the method is efficient in a very wide set of control parameters, bringing the timescales closer to the quantum speed limit, also in the presence of environmental disturbance. These results hold for complete population transfers and for many applications, e.g., for realizing quantum gates, both for optical and microwave implementations. Furthermore, extensions to adiabatic passage problems in more-level systems are straightforward.
Holmes Z, Mingo EH, Chen CYR, et al., 2020, Quantifying athermality and quantum induced deviations from classical fluctuation relations, Entropy: international and interdisciplinary journal of entropy and information studies, Vol: 22, Pages: 1-29, ISSN: 1099-4300
In recent years a quantum information theoretic framework has emerged forincorporating non-classical phenomena into fluctuation relations. Here weelucidate this framework by exploring deviations from classical fluctuationrelations resulting from the athermality of the initial thermal system andquantum coherence of the system's energy supply. In particular we developCrooks-like equalities for an oscillator system which is prepared either inphoton added or photon subtracted thermal states and derive a Jarzynski-likeequality for average work extraction. We use these equalities to discuss theextent to which adding or subtracting a photon increases the informationalcontent of a state thereby amplifying the suppression of free energy increasingprocess. We go on to derive a Crooks-like equality for an energy supply that isprepared in a pure binomial state, leading to a non-trivial contribution fromenergy and coherence on the resultant irreversibility. We show how the binomialstate equality fits in relation to a previously derived coherent state equalityand offers a richer feature-set.
Tranter A, Love P, Mintert F, et al., 2019, Ordering of Trotterization: impact on errors in quantum simulation of electronic structure, Entropy: international and interdisciplinary journal of entropy and information studies, Vol: 21, ISSN: 1099-4300
Trotter–Suzuki decompositions are frequently used in the quantum simulation of quantum chemistry. They transform the evolution operator into a form implementable on a quantum device, while incurring an error—the Trotter error. The Trotter error can be made arbitrarily small by increasing the Trotter number. However, this increases the length of the quantum circuits required, which may be impractical. It is therefore desirable to find methods of reducing the Trotter error through alternate means. The Trotter error is dependent on the order in which individual term unitaries are applied. Due to the factorial growth in the number of possible orderings with respect to the number of terms, finding an optimal strategy for ordering Trotter sequences is difficult. In this paper, we propose three ordering strategies, and assess their impact on the Trotter error incurred. Initially, we exhaustively examine the possible orderings for molecular hydrogen in a STO-3G basis. We demonstrate how the optimal ordering scheme depends on the compatibility graph of the Hamiltonian, and show how it varies with increasing bond length. We then use 44 molecular Hamiltonians to evaluate two strategies based on coloring their incompatibility graphs, while considering the properties of the obtained colorings. We find that the Trotter error for most for systems involving heavy atoms, using a reference magnitude ordering, is less than 1 kcal/mol. Relative to this, the difference between ordering schemes can be substantial, being approximately on the order of millihartrees. The coloring-based ordering schemes are reasonably promising—particularly for systems involving heavy atoms—however further work is required to increase dependence on the magnitude of terms. Finally, we consider ordering strategies based on the norm of the Trotter error operator, including an iterative method for generating the new error operator terms added upon insertion of a term into an ordered Hamil
Zhao H, Knolle J, Mintert F, 2019, Engineered nearest-neighbor interactions with doubly modulated optical lattices, Publisher: AMER PHYSICAL SOC
Walker BT, Hesten HJ, Nyman RA, et al., 2019, Collective excitation profiles and the dynamics of photonic condensates, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 100, Pages: 1-7, ISSN: 1050-2947
Photonic condensates are complex systems exhibiting phase transitions due to the interaction with their molecular environment. Given the macroscopic number of molecules that form a reservoir of excitations, numerical simulations are expensive, even for systems with few cavity modes. We present a systematic construction of molecular excitation profiles with a clear hierarchical ordering, such that only modes in the lowest order in the hierarchy directly affect the cavity photon dynamics. In addition to a substantial gain in computational efficiency for simulations of photon dynamics, the explicit spatial shape of the mode profiles offers a clear physical insight into the competition among the cavity modes for access to molecular excitations.
Walker BT, Hesten HJ, Dhar HS, et al., 2019, Non-critical slowing down of photonic condensation, Physical Review Letters, Vol: 123, ISSN: 0031-9007
We investigate the response of a photonic gas interacting with a reservoir ofpumped dye-molecules to quenches in the pump power. In addition to the expecteddramatic critical slowing down of the equilibration time around phasetransitions we find extremely slow equilibration even far away from phasetransitions. This non-critical slowing down can be accounted for quantitativelyby fierce competition among cavity modes for access to the molecularenvironment, and we provide a quantitative explanation for this non-criticalslowing down.
Zhao H, Mintert F, Knolle J, 2019, Floquet time spirals and stable discrete-time quasicrystals in quasiperiodically driven quantum many-body systems, Publisher: AMER PHYSICAL SOC
Petiziol F, Dive B, Carretta S, et al., 2019, Accelerating adiabatic protocols for entangling two qubits in circuit QED, PHYSICAL REVIEW A, Vol: 99, ISSN: 2469-9926
Holmes Z, Weidt S, Jennings D, et al., 2019, Coherent fluctuation relations: from the abstract to the concrete, Quantum, Vol: 3, ISSN: 2521-327X
Recent studies using the quantum information theoretic approach to thermodynamics show that the presence of coherence in quantum systems generates corrections to classical fluctuation theorems. To explicate the physical origins and implications of such corrections, we here convert an abstract framework of an autonomous quantum Crooks relation into quantum Crooks equalities for well-known coherent, squeezed and cat states. We further provide a proposal for a concrete experimental scenario to test these equalities. Our scheme consists of the autonomous evolution of a trapped ion and uses a position dependent AC Stark shift.
Walker BT, Flatten LC, Hesten HJ, et al., 2018, Driven-dissipative non-equilibrium Bose-Einstein condensation of less than ten photons, Nature Physics, Vol: 14, Pages: 1173-1177+, ISSN: 1745-2473
In a Bose–Einstein condensate, bosons condense in the lowest-energy mode available and exhibit high coherence. Quantum condensation is inherently a multimode phenomenon, yet understanding of the condensation transition in the macroscopic limit is hampered by the difficulty in resolving populations of individual modes and the coherences between them. Here, we report non-equilibrium Bose–Einstein condensation of 7 ± 2 photons in a sculpted dye-filled microcavity, where the extremely small particle number and large mode spacing of the condensate allow us to measure occupancies and coherences of the individual energy levels of the bosonic field. Coherence of the individual modes is found to generally increase with increasing photon number. However, at the break-down of thermal equilibrium we observe phase transitions to a multimode condensate regime wherein coherence unexpectedly decreases with increasing population, suggesting the presence of strong intermode phase or number correlations despite the absence of a direct nonlinearity. Experiments are well-matched to a detailed non-equilibrium model. We find that microlaser and Bose–Einstein statistics each describe complementary parts of our data and are limits of our model in appropriate regimes, providing elements to inform the debate on the differences between the two concepts1,2.
Tranter A, Love PJ, Mintert F, et al., 2018, A Comparison of the Bravyi-Kitaev and Jordan-Wigner Transformations for the Quantum Simulation of Quantum Chemistry, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, Vol: 14, Pages: 5617-5630, ISSN: 1549-9618
Petiziol F, Dive B, Mintert F, et al., 2018, Fast adiabatic evolution by oscillating initial Hamiltonians, PHYSICAL REVIEW A, Vol: 98, ISSN: 2469-9926
Verdeny A, Puig J, Mintert F, 2018, Quasi-Periodically Driven Quantum Systems, ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES, Vol: 71, Pages: 897-907, ISSN: 0932-0784
Latmiral L, Mintert F, 2018, Deterministic preparation of highly non-classical macroscopic quantum states, npj Quantum Information, Vol: 4, ISSN: 2056-6387
We present a scheme to deterministically prepare non-classical quantum states of a massive mirror including highly non-Gaussian states exhibiting sizeable negativity of the Wigner function. This is achieved by exploiting the non-linear light–matter interaction in an optomechanical cavity by driving the system with optimally designed frequency patterns. Our scheme reveals to be resilient against mechanical and optical damping, as well as mechanical thermal noise and imperfections in the driving scheme. Our proposal thus opens a promising route for table-top experiments to explore and exploit macroscopic quantum phenomena.
Dive B, Pitchford A, Burgarth D, et al., 2018, In situ upgrade of quantum simulators to universal computers, Quantum, Vol: 2, Pages: 80-80, ISSN: 2521-327X
Quantum simulators, machines that can replicate the dynamics of quantum systems, are being built as useful devices and are seen as a stepping stone to universal quantum computers. A key difference between the two is that computers have the ability to perform the logic gates that make up algorithms. We propose a method for learning how to construct these gates efficiently by using the simulator to perform optimal control on itself. This bypasses two major problems of purely classical approaches to the control problem: the need to have an accurate model of the system, and a classical computer more powerful than the quantum one to carry out the required simulations. Strong evidence that the scheme scales polynomially in the number of qubits, for systems of up to 9 qubits with Ising interactions, is presented from numerical simulations carried out in different topologies. This suggests that this in situ approach is a practical way of upgrading quantum simulators to computers.
Hesten HJ, Nyman RA, Mintert F, 2018, Decondensation in Nonequilibrium Photonic Condensates: When Less Is More, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
Kaufman AM, Tichy MC, Mintert F, et al., 2018, The Hong-Ou-Mandel Effect With Atoms, ADVANCES IN ATOMIC, MOLECULAR, AND OPTICAL PHYSICS, VOL 67, Editors: Arimondo, DiMauro, Yelin, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: 377-427
Krimer DO, Hartl B, Mintert F, et al., 2017, Optimal control of non-Markovian dynamics in a single-mode cavity strongly coupled to an inhomogeneously broadened spin ensemble, PHYSICAL REVIEW A, Vol: 96, ISSN: 2469-9926
Quantum optics is the study of the intrinsically quantum properties of light. During the second part of the 20th century experimental and theoretical progress developed together; nowadays quantum optics provides a testbed of many fundamental aspects of quantum mechanics such as coherence and quantum entanglement. Quantum optics helped trigger, both directly and indirectly, the birth of quantum technologies, whose aim is to harness non-classical quantum effects in applications from quantum key distribution to quantum computing. Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies. In this review, we celebrate the work of Sir Peter Knight and present an overview of the development of quantum optics and its impact on quantum technologies research. We describe the core theoretical tools developed to express and study the quantum properties of light, the key experimental approaches used to control, manipulate and measure such properties and their application in quantum simulation, and quantum computing.
Newman D, Mintert F, Nazir A, 2017, Performance of a quantum heat engine at strong reservoir coupling, Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 95, ISSN: 1539-3755
We study a quantum heat engine at strong coupling between the system and the thermal reservoirs. Exploiting a collective coordinate mapping, we incorporate system-reservoir correlations into a consistent thermodynamic analysis, thus circumventing the usual restriction to weak coupling and vanishing correlations. We apply our formalism to the example of a quantum Otto cycle, demonstrating that the performance of the engine is diminished in the strong coupling regime with respect to its weakly coupled counterpart, producing a reduced net work output and operating at a lower energy conversion efficiency. We identify costs imposed by sudden decoupling of the system and reservoirs around the cycle as being primarily responsible for the diminished performance, and we define an alternative operational procedure which can partially recover the work output and efficiency. More generally, the collective coordinate mapping holds considerable promise for wider studies of thermodynamic systems beyond weak reservoir coupling.
Witt B, Rudnicki L, Tanimura Y, et al., 2017, Exploring complete positivity in hierarchy equationsof motion, New Journal of Physics, Vol: 19, ISSN: 1367-2630
We derive a purely algebraic framework for the identi cation of hierarchyequations of motion that induce completely positive dynamics and demonstrate the applicability of our approach with several examples. We nd bounds on the violation of complete positivity for microscopically derived hierarchy equations of motion and construct well-behaved phenomenological models with strongly non-Markovian revivals of quantum coherence.
Haddadfarshi F, Mintert, 2016, High fidelity quantum gates of trapped ions mediated by a dissipative bus mode, New Journal of Physics, Vol: 18, ISSN: 1367-2630
We describe entangling quantum gates for trapped ions mediated bya dissipative bus mode and show that suitably designed, polychromatic controlpulses decrease ion-phonon entanglement substantially while maintaining the mediatedinteraction. In particular for multi-qubit gates this yields a signi cant improvement ingate performance.
Haddadfarshi F, Mintert F, 2016, High fidelity quantum gates of trapped ions in the presence of motional heating, NEW JOURNAL OF PHYSICS, Vol: 18, ISSN: 1367-2630
Nyman RA, Marelic J, Zajiczek LF, et al., 2016, Spatiotemporal coherence of non-equilibrium multimode photon condensates, New Journal of Physics, Vol: 18, ISSN: 1367-2630
We report on the observation of quantum coherence of Bose–Einstein condensed photons in an optically pumped, dye-filled microcavity. We find that coherence is long-range in space and time above condensation threshold, but short-range below threshold, compatible with thermal-equilibrium theory. Far above threshold, the condensate is no longer at thermal equilibrium and is fragmented over non-degenerate, spatially overlapping modes. A microscopic theory including cavity loss, molecular structure and relaxation shows that this multimode condensation is similar to multimode lasing induced by imperfect gain clamping.
Dive B, Burgarth D, Mintert F, 2016, Isotropy and control of dissipative quantum dynamics, PHYSICAL REVIEW A, Vol: 94, ISSN: 2469-9926
Verdeny A, Mintert F, 2015, Tunable Chern insulator with optimally shaken lattices, PHYSICAL REVIEW A, Vol: 92, ISSN: 1050-2947
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