Assessing the quantumness of a damped two-level system

Friedenberger, Alexander; Lutz, Eric

doi:10.1103/physreva.95.022101

Cited by 33 publications

(37 citation statements)

References 73 publications

(96 reference statements)

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“…Quantum Otto cycles have previously been studied in the weak coupling regime [3,4,9,13,17,18] with various results ranging from those analogous to classical thermodynamic bounds [9], to interesting violations thereof [8]. An advantage of the Otto cycle is that it allows energetic changes to be distinguished by means of separate strokes where either work is extracted from (or done on) the system, or energy is exchanged between the system and the reservoirs.…”

Section: Otto Cycle Modelmentioning

confidence: 99%

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Performance of a quantum heat engine at strong reservoir coupling

2017

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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 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.

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Section: Otto Cycle Modelmentioning

confidence: 99%

“…Typically, quantum mechanical models of heat engines are restricted to the weak coupling regime [3,4,9,13,[16][17][18]. That is, they assume the interaction strength between the working system and each reservoir to be negligible in comparison to their respective self-energies.…”

Section: Introductionmentioning

confidence: 99%

Performance of a quantum heat engine at strong reservoir coupling

2017

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“…For a damped qubit in a Markovian thermal reservoir, it has been then seen that the envelope of the quantum witness, defined according to the usual intermediate and final measurements Π b ± of Eq. (19), indeed coincides with the coherence monotone [58]. However, for a generic open (nonisolated) quantum system, the behavior of the quantum witness is more subtle [62]: it is not guaranteed that it reaches the upper bound by usual projective blind measurements and optimization procedures may be required.…”

Section: Quantum Witness Optimizationmentioning

confidence: 99%

Validating and controlling quantum enhancement against noise by the motion of a qubit

2020

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Experimental validation and control of quantum traits for an open quantum system are important for any quantum information purpose. We consider a traveling atom qubit as a quantum memory with adjustable velocity inside a leaky cavity, adopting a quantum witness as a figure of merit for quantumness assessment. We show that this model constitutes an inherent physical instance where the quantum witness does not work properly if not suitably optimized. We then supply the optimal intermediate blind measurements which make the quantum witness a faithful tester of quantum coherence. We thus find that larger velocities protect quantumness against noise, leading to lifetime extension of hybrid qubit-photon entanglement and to higher phase estimation precision. Control of qubit motion thus reveals itself as a quantum enhancer. arXiv:1911.07146v1 [quant-ph]

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“…We evaluate the quantum witness (6) for a damped two-level system with M=2 in the following way. We assume that the system is initially prepared in the eigenstate +ñ = ñ + ñ | (| | ) 2 of the operator s x at t=0 [34,35]. At time t=τ/2 a nonselective generalized measurement in the σ x -basis is performed, or not, whereas at t=τ the projector P = +ñá+ + | | is measured.…”

Section: Witness Of a Damped Qubitmentioning

confidence: 99%

Quantum witness of a damped qubit with generalized measurements

2019

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We evaluate the quantum witness based on the no-signaling-in-time condition of a damped two-level system for nonselective generalized measurements of varying strength. We explicitly compute its dependence on the measurement strength for a generic example. We find a vanishing derivative for weak measurements and an infinite derivative in the limit of projective measurements. The quantum witness is hence mostly insensitive to the strength of the measurement in the weak measurement regime and displays a singular, extremely sensitive dependence for strong measurements. We finally relate this behavior to that of the measurement disturbance defined in terms of the fidelity between pre-measurement and post-measurement states.

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Assessing the quantumness of a damped two-level system

Cited by 33 publications

References 73 publications

Performance of a quantum heat engine at strong reservoir coupling

Performance of a quantum heat engine at strong reservoir coupling

Validating and controlling quantum enhancement against noise by the motion of a qubit

Quantum witness of a damped qubit with generalized measurements

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