Quantum Thermodynamics and Macroscopic Quantum Phenomena
Almost all branches of physics can be placed in the Quantum-Classical and the micro-Macro matrix, the underlying disciplines being quantum and statistical physics. Macro-Classical and micro-Quantum have been the natural pairings which have dictated the way we looked at Nature. The new challenge is the cross-mixing of Macroscopic with Quantum: Are there systems which show quantum features at a macroscopic scale? Superconductivity, Bose-Einstein condensates and certain nanoelectro- quantum opto-mechanical systems are familiar examples. The key feature is the high degree of quantum coherence. Asking such a question for general quantum many-body systems [1] poses a greater conceptual challenge -- what conditions would permit quantum features to survive at a macroscopic scale? How would the innate quantum features of each microscopic particle change as we increase the number of particles to what we would call macroscopic? What is Macroscopic? Is macroscopic defined by sheer size and number? What if the constituent particles are weakly coupled, strongly coupled? How does quantum correlation enter the picture? How do the quantum entanglement between constituents and that between levels of structure affect the overall quantum properties of a macroscopic object? [2] Sharing the concern of these issues is the new field of quantum thermodynamics [3] which should not be construed as the quantum version, much less the quantization, of classical thermodynamics. Rather, it studies the thermodynamics of a quantum many-body system, whose thermodynamic limit may not even exist, especially for small quantum systems. The four laws of classical thermodynamics need be scrutinized one by one, because the basic assumptions and hypotheses may no longer hold. Even quantum statistical mechanics is grossly lacking in the face of this challenge: quantum coherence and entanglement are completely left out. In this talk I will try to highlight the many facets of these two newly emergent fields by laying out the fundamental issues which need be addressed clearly for us to ask the right questions. I will summarize our recent work on finding pathways to better understand macroscopic quantum phenomena and deconstructing the cause of “hot entanglement” [4,5]. Wrestling with the complexity of these issues in this fascinating kaleidoscope will not only challenge the keenly inquisitive mind, their fruits of labor borne can benefit the brave new world of “quantum engineering” where coherent, entangled, collective features and fluctuations of small quantum systems will remake the rules of the game.
[1] C H Chou, B L Hu, Y Subasi in: J. Phys.: Conf. Ser., 306, 012002 (2011) [arXiv:1106.0556]; 330, 012003 (2011) [arXiv:1107.3008] which contain references to some recent experiments in MQP.
[2] C H Chou, B L Hu, Y Subasi, Macroscopic Quantum Phenomena from the Coupling Pattern and Entanglement Structure Perspective [arXiv:1308.4225] B L Hu, Y Subasi, Pathways toward understanding Macroscopic Quantum Phenomena, in J. Phys.: Conf. Ser. 442, 012010 (2013) [arXiv:1304.7839] .
[3] See, e.g., J. Gemmer, M. Michel and G. Mahler, Quantum Thermodynamics. Springer, Berlin (2004)
[4] V. Vedral, “Quantum Physics: Hot Entanglement” Nature 468, 769 (2010). F. Galve, L.A. Pachon and D. Zueco, "Bringing entanglement to the high temperature limit", Phys. Rev. Lett. 105, 180501 (2010).
[5]J. T. Hsiang and B. L. Hu, “Hot Entanglement”? -- A Nonequilibrium Quantum Field Theory Scrutiny Phys. Lett. B 750, 396 (2015) [arXiv:1506.02941] “Quantum Entanglement at High Temperatures? -- Bosonic Systems in Nonequilibrium Steady State”, JHEP 11(2015) 090[arXiv:1503.03587 ]
