{
  "id": "2008.02818",
  "version": "v1",
  "published": "2020-08-06T18:00:38.000Z",
  "updated": "2020-08-06T18:00:38.000Z",
  "title": "Time's Arrow of a Quantum Superposition of Thermodynamic Evolutions",
  "authors": [
    "Giulia Rubino",
    "Gonzalo Manzano",
    "Časlav Brukner"
  ],
  "comment": "14 pages, 7 figures",
  "categories": [
    "quant-ph"
  ],
  "abstract": "A priori, there exists no preferential temporal direction as microscopic physical laws are time-symmetric. Still, the second law of thermodynamics allows one to associate the `forward' temporal direction to a positive entropy variation in a thermodynamic process, and a negative variation with its `time-reversal' counterpart. This definition of a temporal axis is normally considered to apply in both classical and quantum contexts. Yet, quantum physics admits also superpositions between forward and time-reversal processes, thereby seemingly eluding conventional definitions of time's arrow. In this work, we demonstrate that a quantum measurement of entropy can distinguish the two temporal directions, effectively projecting such superpositions of thermodynamic processes onto the forward (time-reversal) time-direction when large positive (negative) values are measured. Remarkably, for small values (of the order of plus or minus one), the amplitudes of forward and time-reversal processes can interfere, giving rise to entropy distributions featuring a more or less reversible process than either of the two components individually, or any classical mixture thereof. Finally, we extend these concepts to the case of a thermal machine running in a superposition of the heat engine and the refrigerator mode, illustrating how such interference effects can be employed to reduce undesirable fluctuations.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-08-06T18:00:38.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "times arrow",
      "thermodynamic evolutions",
      "quantum superposition",
      "time-reversal processes",
      "thermodynamic process"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}