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Entanglement in a quantum heat engine

Harald Öhrn

Published Jan 1, 2020• 0 citations
OpenAlex

Abstract

In 2015 Jonatan Bohr Brask et al. showed that steady-state entanglement could be generated in two interacting qubits incoherently coupled to thermal baths of different temperatures [1]. This thesis is an attempt to re-evaluate their findings with the hope that a slightly different approach and system can help further our understanding of this not yet well understood phenomena. A Lindblad master equation approach is taken to study a two-qubit thermal machine interacting with bosonic thermal reservoirs. It is found that the steady-state entanglement behaves similarly using the Lindblad approach, the main difference being that a larger amount of entanglement can be generated than initially found in Ref. [1].

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In 2015 Jonatan Bohr Brask et al. showed that steady-state entanglement could be generated in two interacting qubits incoherently coupled to thermal baths of different temperatures [1]. This thesis is an attempt to re-evaluate their findings with the hope that a slightly different approach and system can help further our understanding of this not yet well understood phenomena. A Lindblad master equation approach is taken to study a two-qubit thermal machine interacting with bosonic thermal reservoirs. It is found that the steady-state entanglement behaves similarly using the Lindblad approach, the main difference being that a larger amount of entanglement can be generated than initially found in Ref. [1].
We discuss a simple quantum thermal machine for the generation of steady-state entanglement between two interacting qubits. The machine is autonomous in the sense that it uses only incoherent interactions with thermal baths, but no source of coherence or external control. By weakly coupling the qubits to thermal baths at different temperatures, inducing a heat current through the system, steady-state entanglement is generated far from thermal equilibrium. Finally, we discuss two possible implementations, using superconducting flux qubits or a semiconductor double quantum dot. Experimental prospects for steady-state entanglement are promising in both systems.
We discuss a simple quantum thermal machine for the generation of steady-state entanglement between two interacting qubits. The machine is autonomous in the sense that it uses only incoherent interactions with thermal baths, but no source of coherence or external control. By weakly coupling the qubits to thermal baths at different temperatures, inducing a heat current through the system, steady-state entanglement is generated far from thermal equilibrium. Finally, we discuss two possible implementations, using superconducting flux qubits or a semiconductor double quantum dot. Experimental prospects for steady-state entanglement are promising in both systems.
Autonomous entanglement engines have recently been proposed to generate steady-state bipartite and multipartite entanglement exploiting only incoherent interactions with thermal baths at different temperatures. In this work, we investigate the interplay between heat current and entanglement in a two-qubit entanglement engine, deriving a critical heat current for successful operation of the engine, i.e. a cut-off above which entanglement is present. The heat current can thus be seen as a witness to the presence of entanglement. In the regime of weak-inter qubit coupling, we also investigate the effect of two experimentally relevant parameters for the qubits, the energy detuning and tunnelling, on the entanglement production. Finally, we show that the regime of strong inter-qubit coupling provides no clear advantage over the weak regime, in the context of out-of-equilibrium entanglement engines.
Abstract Autonomous entanglement engines have recently been proposed to generate steady-state bipartite and multipartite entanglement exploiting only incoherent interactions with thermal baths at different temperatures. In this work, we investigate the interplay between heat current and entanglement in a two-qubit entanglement engine, deriving a critical heat current for successful operation of the engine, i.e. a cut-off above which entanglement is present. The heat current can thus be seen as a witness to the presence of entanglement. In the regime of weak-inter-qubit coupling, we also investigate the effect of two experimentally relevant parameters for the qubits, the energy detuning and tunnelling, on the entanglement production. Finally, we show that the regime of strong inter-qubit coupling provides no clear advantage over the weak regime, in the context of out-of-equilibrium entanglement engines.
Abstract We study the entanglement generated in the steady state of two interacting qubits coupled to thermal reservoirs. We show that the amount of steady-state entanglement can be enhanced by the presence of a third thermal reservoir which is common to both qubits. Specifically, we find that entanglement can be enhanced as long as the temperature of the common reservoir is below the thermalisation temperature of the qubits, whenever a single temperature can be assigned to the steady state of the qubits in the absence of the common reservoir. Moreover, the amount of entanglement generated with the common reservoir present can be significantly larger than that which can be obtained without it for any temperature of the individual reservoirs. From the perspective of thermodynamics, we find that enhancement of entanglement is associated with heat absorption by the common reservoir. We propose a possible implementation of our scheme in superconducting circuits and find that a significant enhancement of steady-state entanglement should be observable under experimentally realistic conditions.
Entanglement is a fundamental feature of quantum physics and a key resource for quantum communication, computing, and sensing. Entangled states are fragile and maintaining coherence is a central challenge in quantum information processing. Nevertheless, entanglement can be generated and stabilized through dissipative processes. In fact, entanglement has been shown to exist in the steady state of certain interacting quantum systems subject solely to incoherent coupling to thermal baths. This has been demonstrated in a range of bi- and multipartite settings using systems of finite dimension. Here we focus on the steady state of infinite-dimensional bosonic systems. Specifically, we consider any set of bosonic modes undergoing excitation-number-preserving interactions of arbitrary strength and divided between an arbitrary number of parties that each couple weakly to thermal baths at different temperatures. We show that a unique steady state is always separable.