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International Conference on Quantum Information

Non-Markov Control of Quantum Thermodynamics in Multipartite Systems

Gershon Kurizki, Nir Bar‐Gill, Noam Erez A, Goren Gordon

Published Jan 1, 2008• 0 citations
Publisher

Abstract

We predict [1] drastic deviations from ordinary thermodynamic trends, which are monotonic approach to thermal equilibrium and positive entropy production, when qubits coupled to bosonic baths are probed on non-Markovian time scales by quantum nondemolition measurements, as well as coherently modulated. The resulting changes in the temperature, entropy and state-purity of both the system and the bath only depend on the rate of measurement, without any rapport to thermodynamic laws. These effects in principle allow much faster cooling and state purification than other methods. Generalizations of these effects to entangled multipartite systems [2] controlled by local measurements and modulations bring about surprising dynamic changes in the entanglement. Collective bosonic states coupled to a bath are shown to obey similar principles [3].

DOI
10.1364/icqi.2008.qtuc1

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We study deviations from thermal equilibrium between two-level systems (TLS) and a bath by frequent and brief quantum measurements of the TLS energy-states. The resulting entropy and temperature of both the system and the bath are found to be completely determined by the measurement rate, and unrelated to what is expected by standard thermodynamical rules that hold for Markovian baths. These anomalies allow for very fast control heating, cooling and state-purification (entropy reduction) of quantum systems much sooner than their thermal equilibration time.
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We study the relationship between a (non-)Markovian evolution and the entropy production rate. We consider a system qubit in contact with a thermal bath and in addition the system is strongly coupled to an ancillary qubit. We examine the steady state properties finding that the coupling leads to effective temperatures emerging in the composite system, and show that this is related to the creation of correlations between the qubits. By establishing the conditions under which the system reaches thermal equilibrium with the bath despite undergoing a non-Markovian evolution, we examine the entropy production rate, showing that its transient negativity is a sufficient sign of non-Markovianity.
Accurate temperature estimation in the quantum and cryogenic regimes remains a fundamental challenge. Here, we investigate nonequilibrium quantum thermometry using a single-qubit probe coupled to a bosonic bath through noncommuting interaction operators, which unify pure dephasing and dissipative dynamics within a spin-boson model. We show that the interference between these two coupling channels induces strong non-Markovian feedback between populations and coherences, leading to coherence trapping and enhanced thermal sensitivity. Remarkably, by tuning the coupling structure, the probe's temperature sensitivity exhibits a quadratic low-temperature scaling, even under weak coupling. Moreover, while coherence-based measurements are formally suboptimal, they become the most informative in the early nonequilibrium regime, where memory effects dominate. Our findings identify noncommutative system-bath couplings as a practical and tunable resource for achieving high-precision quantum thermometry in realistic open-system architectures.