Non-Markovian dynamics of a quantum heat engine: out-of-equilibrium operation and thermal coupling control

Abstract

Real quantum heat engines lack the separation of time and length scales that is characteristic for classical engines. They must be understood as open quantum systems in non-equilibrium with timecontrolled coupling to thermal reservoirs as integral part. Here, we present a systematic approach to describe a broad class of engines and protocols beyond conventional weak coupling treatments starting from a microscopic modeling. For the four stroke Otto engine the full dynamical range down to low temperatures is explored and the crucial role of the work associated with the coupling/decoupling to/from reservoirs as an integral part in the energy balance is revealed. Quantum correlations turn out to be instrumental to enhance the efficiency which opens new ways for optimal control techniques. OPEN ACCESS RECEIVED

Speed-Ups to Isothermality: Enhanced Quantum Thermal Machines through Control of the System-Bath Coupling

“…These processes can then be sped up by increasing the system-environment coupling, which naturally reduces τ eq . However, modifying the interaction also induces additional dissipation, which prohibits the nonphysical possibility of performing an isothermal process arbitrarily quickly [2][3][4][5] (note that increasing the coupling can lead to power output enhancements [2,3,6]). Given this nontrivial trade-off, the goal of this article is to develop quantum-thermodynamic protocols that smoothly modify the system-bath interaction in order to speed up an isothermal process while keeping the overall dissipation constant.…”

Non-Markovian quantum Otto refrigerator

“…that contain sums over bosonic modes that become infinite in the continuum limit. The renormalization coefficients μ c/h , related to the static reservoir response [22,24], ensure that only the dynamical impact of the medium-reservoir coupling contributes to the microscopic dynamics. With quantum reservoir correlation functions…”

“…with a parametric-type driving ω(t). The above formulation also allows to treat anharmonic and higher dimensional systems [22], but already the one-dimensional linear problem reveals the highly non-trivial features of the underlying dynamics. The operating principle of the quantum Otto refrigerator, as depicted in Fig.…”

“…In a recent publication [22], we presented a nonperturbative simulation platform that allows to operate a quantum Otto cycle with harmonic/anharmonic oscillator as working medium in a fully dynamical, finite-time protocol with explicit cyclic modulation of the system-reservoir coupling. We were thereby able to observe the engine's operation during its cyclic dynamics as an open quantum system with consecutive de-/coupling phases to/from the hot/cold reservoirs as integral parts of the net energy.…”

State leakage during fast decay and control of a superconducting transmon qubit

“…However, environmental engineering should not be restricted to weak coupling only. In particular, quantum heat engines and simulators may need relatively strong coupling to the bath 1,[12][13][14] . Considerable attention has recently been focused on strong coupling regions in the context of fast qubit initialization with engineered and tunable environments [15][16][17][18] .…”