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Edited by Steven M. Girvin, Yale University, New Haven, CT, and approved June 5, 2017 (received for review March 23, 2017)
Significance
Maxwell’s demon plays a central role in thermodynamics of quantum information, yet a full experimental characterization is still missing in the quantum regime. Here we use superconducting circuits to realize a quantum Maxwell demon in which all thermodynamic quantities can be controlled and measured. Using power detection resolved at the single microwave photon level and unprecedented tomography techniques, we directly measure the extracted work while tracking the qubit and cavity entropies and energies. We are thus able to fully characterize the demon’s memory after the work extraction and show that it takes full part in the thermodynamic process. The experiment establishes superconducting circuits as a testbed well suited to perform quantum thermodynamics experiments.
Abstract
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.
Footnotes
↵1N.C. and S.J. contributed equally to this work.
- ↵2To whom correspondence should be addressed. Email: benjamin.huard{at}ens-lyon.fr.
Author contributions: N.C., S.J., L.B., P.C.-I., A.A., and B.H. designed research; N.C., S.J., Q.F., and B.H. performed research; N.C., S.J., R.A., P.R., and B.H. analyzed data; and N.C., S.J., L.B., J.A., and B.H. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1704827114/-/DCSupplemental.
Observing a quantum Maxwell demon at work
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