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arXiv:1508.03803 · Physical review. B./Physical review. B

Maxwell's demon based on a single qubit

Jukka P Pekola, Dmitry S. Golubev, D. V. Averin

Published Jan 5, 2016• 40 citations
arXivHTMLPDF

Abstract

We propose and analyze Maxwell's demon based on a single qubit with avoided level crossing. Its operation cycle consists of adiabatic drive to the point of minimum energy separation, measurement of the qubit state, and conditional feedback. We show that the heat extracted from the bath at temperature $T$ can ideally approach the Landauer limit of ${k}_{B}T\phantom{\rule{0.16em}{0ex}}ln2$ per cycle even in the quantum regime. Practical demon efficiency is limited by the interplay of Landau-Zener transitions and coupling to the bath. We suggest that an experimental demonstration of the demon is fully feasible using one of the standard superconducting qubits.

DOI
10.1103/physrevb.93.024501

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We propose and analyze Maxwell's demon based on a single qubit with avoided level crossing. Its operation cycle consists of adiabatic drive to the point of minimum energy separation, measurement of the qubit state, and conditional feedback. We show that the heat extracted from the bath at temperature TTT can ideally approach the Landauer limit of kBTln2{k}_{B}T\phantom{\rule{0.16em}{0ex}}ln2kB​Tln2 per cycle even in the quantum regime. Practical demon efficiency is limited by the interplay of Landau-Zener transitions and coupling to the bath. We suggest that an experimental demonstration of the demon is fully feasible using one of the standard superconducting qubits.
In apparent contradiction to the laws of thermodynamics, Maxwell's demon is able to cyclically extract work from a system in contact with a thermal bath, exploiting the information about its microstate. The resolution of this paradox required the insight that an intimate relationship exists between information and thermodynamics. Here, we realize a Maxwell demon experiment that tracks the state of each constituent in both the classical and quantum regimes. The demon is a microwave cavity that encodes quantum information about a superconducting qubit and converts information into work by powering up a propagating microwave pulse by stimulated emission. Thanks to the high level of control of superconducting circuits, we directly measure the extracted work and quantify the entropy remaining in the demon's memory. This experiment provides an enlightening illustration of the interplay of thermodynamics with quantum information.
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We investigated coupled-qubit-based thermal machines powered by quantum measurements and feedback. We considered two different versions of the machine: (1) a quantum Maxwell's demon, where the coupled-qubit system is connected to a detachable single shared bath, and (2) a measurement-assisted refrigerator, where the coupled-qubit system is in contact with a hot and cold bath. In the quantum Maxwell's demon case, we discuss both discrete and continuous measurements. We found that the power output from a single qubit-based device can be improved by coupling it to the second qubit. We further found that the simultaneous measurement of both qubits can produce higher net heat extraction compared to two setups operated in parallel where only single-qubit measurements are performed. In the refrigerator case, we used continuous measurement and unitary operations to power the coupled-qubit-based refrigerator. We found that the cooling power of a refrigerator operated with swap operations can be enhanced by performing suitable measurements.
During the last years, with the evolution of technology enabling the control of nano-mesoscopic systems, the possibility of experimentally implementing a Maxwell’s demon has aroused much interest. Its classical version has already been implemented, in photonic and electronic systems, and currently its quantum version is being broadly studied. In this context, the purpose of this work is the development of a protocol for the implementation of the quantum version of an autonomous Maxwell’s demon in a system of superconducting qubits. The system is composed of an Asymmetrical Single-Cooper-Pair Transistor, ASCPT, which has its extremities in contact with heat baths, such that the left one has a lower temperature than the right one. And of a device of two interacting Cooper-Pair Boxes, CPB’s, named as an ECPB, for Extended Cooper-Pair Box. The ECPB is also in contact with a heat bath and possess a genuine quantum feature, entanglement, being described by its antisymmetric and symmetric states, that couple capacitively to the ASCPT with different strengths. A specific operating regime was found where the spontaneous dynamics of the tunneling of Cooper pairs through the ASCPT, will led to a heat transport from the bath in contact with the left extremity of the ASCPT to the bath at the right. And so, as in Maxwell’s original thought experiment, the demon, which is composed by the ECPB and the island of the ASCPT, mediates a heat flux from a cold to a hot bath, without the expense of work. However as expected, the violation of the 2nd law of thermodynamics does not occur, as during the dynamics heat is also released to the bath in contact with the ECPB, compensating the decrease of entropy that occurs in the baths in contact with the ASCPT.
A quantum mechanical Maxwell demon is proposed in a quantum dot setting. The demon avoids continuous-measurement induced decoherence by exploiting an undetailed charge detector. The control of coherent tunneling via Landau-Zener-Stückelberg-Majorana driving allows for efficient feedback operations with no work invested. The local violation of the second law achieves simultaneous power generation and cooling. We discuss the response current fluctuations, and the demon backaction deriving from failures, finding optimal performance in the nonadiabatic regime.
The essence of both classical and quantum engines is to extract useful energy (work) from stochastic energy sources, e.g., thermal baths. In Maxwell's demon engines, work extraction is assisted by a feedback control based on measurements performed by a demon, whose memory is erased at some nonzero energy cost. Here we propose a new type of quantum Maxwell's demon engine where work is directly extracted from the measurement channel, such that no heat bath is required. We show that in the Zeno regime of frequent measurements, memory erasure costs eventually vanish. Our findings provide a new paradigm to analyze quantum heat engines and work extraction in the quantum world.