Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F28: Quantum Computing with Open Quantum Systems |
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Sponsoring Units: DQI Chair: Camille Lombard Latune, University of KwaZulu-Natal Room: BCEC 161 |
Tuesday, March 5, 2019 11:15AM - 11:27AM |
F28.00001: Dynamics of Quantum Photocells Driven by Periodic or Stochastic Photon Pulses Sangchul Oh We investigate the dynamics of a quantum photocell as a quantum heat engine, driven by external photon pulses. The photocell is assumed to be only in thermal contact with a cold reservoir, and the stream of work sources from a work or hot reservoir is represented by repeated photon pulses. The interaction between photon pulses and the photocell is described by the pumping term in a Lindblad master equation. By solving the Lindblad master equation, we study numerically the dynamics of a photocell driven by periodic, random, and Poisson photon pulses. We find that the fluctuations in power output of the photocell change dramatically, depending on the statistics of photon pulses and the parameters of the photocell. At low power output, the level occupation probabilities change somewhat smoothly over a long-period of time, even if the photocell is driven by random photon pulses. We analyze how the fluctuation in photon pulses affects the fluctuation in power output for various photon pulses and the parameters of the photocell. |
Tuesday, March 5, 2019 11:27AM - 11:39AM |
F28.00002: Coherent fluctuation relations: from the abstract to the concrete Zoe Holmes, Sebastian Weidt, David Jennings, Janet Anders, Florian Mintert 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. |
Tuesday, March 5, 2019 11:39AM - 11:51AM |
F28.00003: How nonequlibriumness influences macroscopic realism through Leggett-Garg inequality? Kun Zhang, Jin Wang We study the macroscopic realism through Leggett-Garg inequality (LGI) for a two-qubit quantum system coupled with two environments characterized by either the bosonic (thermal and photonic) baths or fermionic (electronic) baths with different temperatures or chemical potentials respectively. Analytical form of LGI and the maximal values of LGI based on the quantum master equation beyond secular approximation are derived. We found that the nonequilibriumness quantified by the temperature difference or chemical potential difference can lead to the LGI violation or the increase of the maximal value of LGI, restoring the quantum nature from certain equilibrium cases where LGI is preserved giving classical realism. Our results shed light on the nature of the macroscopic realism and the relationship between the nonequilibriumness and quantum temporal correlation. Our finding of nonequilibrium promoted LGI violation suggests a new strategy for the design of quantum information processing and quantum computational devices to maintain the quantum nature and quantum correlations for long. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F28.00004: Discord vs Distortion: Classical vs Quantum Barry C Sanders, Wei-Wei Zhang, Yuval R Sanders, Nigum Arshed Quantum discord is a popular quantum-resource measure but a nonzero value does not necessarily imply quantumness; nonzero classical discord arises if local measurements disturb the stochastic information state [V. Gheorghiu, M. C. de Oliveira and B. C. Sanders, Phys. Rev. Lett. 115, 030403 (2015)]. The classical interpretation of discord breaks down if and only if entanglement of formation for the informational state is nonzero, thereby creating a tight link between entanglement and genuine quantum discord. Here we present mathematical relations, and specifically monotonicity between discord and channel-distortion measures such as mean-squared distortion and Kullback-Leibler divergence. Whereas the previous result showed discord can be nonzero for stochastic information, our new results demonstrate a tight link between classical discord and other information-theoretic measures of noisy channels. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F28.00005: Information-theoretic aspects of the generalized amplitude damping channel Sumeet Khatri, Kunal Sharma, Mark M Wilde In this work, we provide an information-theoretic characterization and analysis of the generalized amplitude damping channel (GADC), which is the qubit analogue of the bosonic thermal loss channel. This channel can be used to model the disspation in a qubit system in the presence of an environment at a finite temperature, and it arises in the study of spin chains. The purpose of our work is to provide bounds on the fundamental limits of the GADC for communicating classical, quantum, and private information. Using the notion of approximate degradability, we provide upper bounds on the quantum and private capacities of this channel. We also provide upper bounds based on data processing inequalities by exploiting the mathematical decomposition of the GADC into channels for which the quantum capacity is known exactly. Using a similar decomposition technique, we are able to provide upper and lower bounds on the classical capacity of the GADC. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F28.00006: Superadditivity and boosting coherent information using useless channels Vikesh Siddhu Superadditivity of the coherent information makes it hard to understand and compute the quantum capacity of a quantum channel, a central quantity in quantum information. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F28.00007: Consequences of measurement back-action from quantum monitoring:
non-standard speed limits and spontaneous symmetry breaking Luis Pedro Garcia-Pintos, Diego Tielas, Adolfo del Campo The information acquired during the monitoring of a quantum system provides a state description that can differ greatly from the description given by agents ignorant of the outcomes. While the lack of information in the later results in a mixed density matrix following open system dynamics, the measurement back-action in the former case provides a more accurate description. We present consequences of such measurement back-action to two problems in quantum theory: the limits to the speed of evolution, and the process of spontaneous symmetry breaking. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F28.00008: Characterizing Initial Correlations via Spectroscopy Parth Jatakia, Sai Vinjanampathy, Kasturi Saha In the presence of initial correlations, quantum evolution cannot be described in terms of completely positive trace preserving maps. Such initial correlations can arise due to strong coupling between the system and environment and inform the applicability of important results in physics, such as the quantum regression formula. Therefore it is vital to characterize these correlations for a better understanding of the system and proper quantum control. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F28.00009: Quantum Forking for Open Quantum Systems Simulation June-Koo(KEVIN) RHEE, Ilya Sinayskiy, Daniel Kyungdeock Park, Francesco Petruccione Many quantum information processing tasks spend non-negligible computational costs for preparing an input quantum state. However, a quantum input state prepared for a specific algorithm cannot be reused for another task once measured by the postulate of the quantum measurement. Moreover, the quantum state cannot be cloned. Hence, in general, one is forced to repeat the state preparation routine per algorithm, even when individual algorithms receive the same input. Meanwhile, many quantum algorithms demand repetitions for sampling the answer. Thus while information processing tasks have the potential to benefit from laws of quantum mechanics, they also impose unavoidable redundancy. Here we introduce quantum information forking that allows an array of qubits to undergo independent processes in superposition to reduce the number of the state initialization procedure. As an example, we demonstrate the application of quantum forking to quantum Monte-Carlo sampling. In this case, quantum forking allows for the implementation of the independent propagation of the quantum trajectories, while maintaining the constant cost of initial state preparation. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F28.00010: Experimental Test of Decoherence Theory using Electron Matter Waves Peter Beierle, Liyun Zhang, Zilin Chen, Hans Peter Wagner, Herman Batelaan A controlled decoherence environment is studied experimentally by free electron interaction as it travels over a [semi]conducting plates. The results are compared with physical models based on decoherence theory to investigate the quantum-classical transition. The experiment is consistent with decoherence theory and rules out established coulomb interaction models in favor of plasmonic excitation models. In contrast to previous decoherence experiments, the present experimental setup may be sensitive to the onset of decoherence[1]. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F28.00011: Using a Shot Noise Junction to Characterize a Josepheson Travelling Wave Parametric Amplifier Jacob Epstein, Kyle McElroy, Lafe Spietz, Timothy M Sweeney, Jose Aumentado, Joan A Hoffmann The Josepheson Travelling Wave Parametric Amplifier (JTWPA) is a solution for a broad band amplifier with near quantum limited noise characteristics. Reported techniques using AC Stark shifts to characterize the noise of a JTWPA show excellent noise characteristics but are inherently narrow band. Using a shot noise tunnel junction (SNTJ) allows for broadband characterization of the noise temperature of the JTWPA. Techniques for optimizing the TWPA for different measurement uses will also be discussed. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F28.00012: Stabilization of cavity Hilbert subspaces in cavity quantum electrodynamics by measurement-based quantum feedback Yves Berube-Lauziere, Rémi Azouit Measurement-based quantum feedback (MBQFB) for actively preparing and stabilizing Fock number states in a cavity quantum electrodynamics (CQED) set-up has been achieved by Haroche et al. The approach relies on injecting, after each weak dispersive measurement of the cavity state using Rydberg atoms flying through the cavity as sensors, a low average photon number classical coherent field to steer the cavity towards the targeted number state. Preparing and stabilizing a superposition of Fock states using MBQFB is more challenging since the superposition must be an eigenstate of the quantum measurement operators. This condition requires that each Fock state composing the superposition be an eigenstate with the same eigenvalue for each measurement operator. Owing to the special form of the measurement operators in the dispersive regime, this constrains the phase shift per photon to specific values and leads to the stabilization of subspaces. Results from realistic simulations taking into account decoherence and imperfections in a CQED set-up will be presented. These support the validity of the underlying theory that generalizes the previous theory for preparing Fock number states. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F28.00013: Ground state cooling in the strong-coupling regime Chung Kow, Hakan Tureci, Anja Metelmann, Archana Kamal Strong coupling between quantum systems, whereby the coupling strength greatly exceeds the decay rates, is a mainstay in quantum information platforms. Notably, this regime is explored in hybrid quantum systems involving entanglement between a microscopic and a macroscopic degree of freedom. Nonetheless, in certain instances it can be a liability; for instance, active cooling of a system to its ground state in the strong coupling regime leads to hybridization of the system and the bath modes. Here we present a novel approach using dissipation engineering that mitigates normal-mode splitting between the system and the bath, while preserving strong coupling between the two. Specifically, we employ an optomechanical setup where the mechanical mode is cooled without hybridizing with the optical bath. The connection of such dissipation-engineered cooling with the physics of exceptional points will also be discussed. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F28.00014: Engineered Dissipation as Your Side-kick: A Hybrid Scheme for Quantum Error Correction. Lasse Bjørn Kristensen, Morten Kjærgaard, Christian Kraglund Andersen, Nikolaj T Zinner The main adversary when trying to harness the power of quantum computation is the ever-present occurrence of errors and decoherence. These effects constantly conspire to alter the state of the quantum bits of your quantum computer, thereby slowly corrupting the stored information and messing up the output of your beautiful quantum algorithms. Luckily, a plethora of quantum error correcting codes have been invented to help mitigate this problem. One interesting branch of this field is the study of autonomous error correction codes that attempt to fight fire with fire by engineering dynamics and dissipation of systems so that they become able to detect and correct errors on their own, without relying on an external experimenter doing costly measurement- and correction-steps. In this talk, we present a scheme that combine these ideas with traditional measurement-based error correction into a 6-qubit hybrid scheme capable of protecting qubits from photon-loss and dephasing errors, achieving 10-fold improvements in dephasing times and 5-fold improvements to relaxation times for realistic superconducting-qubit parameters and noise while employing only relatively simple local 2-qubit interactions. |
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