Maxwell’s Demon Meets Nonequilibrium Quantum Thermodynamics

Abstract

Maxwell's demon explores the role of information in physical processes. Employing information about microscopic degrees of freedom, this "intelligent observer" is capable of compensating entropy production (or extracting work), apparently challenging the second law of thermodynamics. In a modern standpoint, it is regarded as a feedback control mechanism and the limits of thermodynamics are recast incorporating information-to-energy conversion. We derive a trade-off relation between information-theoretic quantities empowering the design of an efficient Maxwell's demon in a quantum system. The demon is experimentally implemented as a spin-1=2 quantum memory that acquires information, and employs it to control the dynamics of another spin-1=2 system, through a natural interaction. Noise and imperfections in this protocol are investigated by the assessment of its effectiveness. This realization provides experimental evidence that the irreversibility in a nonequilibrium dynamics can be mitigated by assessing microscopic information and applying a feed-forward strategy at the quantum scale. DOI: 10.1103/PhysRevLett.117.240502 Connections between thermodynamics and information theory have been producing important insights and useful applications in the past few years, which has turned out to be a dynamic field [1][2][3][4]. Its genesis traces back to the famous Maxwell's demon gedanken experiment [5][6][7][8][9]. In 1867, Maxwell conceived a "neat fingered being," which has the ability to gather information about the microscopic state of a gas and use this information to transfer fast particles to a hot medium and slow particles to a cold one, engendering an apparent conflict with the second law of thermodynamics. Several approaches and developments concerning this conundrum had been put forward [5][6][7][8][9], but only after more than a century, in 1982, Bennett [10] realized that the apparent contradiction with the second law could be puzzled out by considering the Landauer's erasure principle [11][12][13][14].Theoretical endeavors to incorporate information into thermodynamics acquire a pragmatic applicability within the recent technological progress, where information just started to be manipulated at the micro-and nanoscale. A modern framework for these endeavors has been provided by explicitly taking into account the change, introduced in the statistical description of the system, due to the assessment of its microscopic information [15]. This outlines an illuminating paradigm for Maxwell's demon, where the information-to-energy conversion is governed by fluctuation theorems, which hold for small systems arbitrarily far from equilibrium [16][17][18][19][20]. Generalizations of the second law in the presence of feedback control can be obtained from this framework, establishing bounds for information-based work extraction [21]. Notwithstanding its fundamental relevance, these relations do not provide a clear recipe for building a demon in a laboratory setting. Owing to the challenges associated with a high prec...

DFT-inspired methods for quantum thermodynamics

“…The thermodynamic description of quantum many-body systems is significant for understanding the limits of the emerging quantum technology [1][2][3][4][5][6] . Fluctuation theorems [7][8][9][10][11][12][13][14] have been key tools to describe the unavoidable fluctuations in the non-equilibrium dynamics and related experiments have been performed for small, non-interacting systems [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] , in both the classical and quantum domain. When we turn to the case of systems composed of interacting particles ('many-body systems'), complex behavior arises as a consequence of the interactions.…”