Does an Isolated Many Body Quantum System Relax?
Professor Jörg Schmiedmayer
Vienna Center for Quantum Science and Technology (VCQ), Atominstitut, TUWien, Austria
3:30 pm, Friday 1 May 2015, EN102 Lecture Theatre (EN Building), Hawthorn.
Interfering two isolated onedimensional quantum gases we study how the coherence created between the two many body systems by the splitting process slowly degrades by coupling to the many internal degrees of freedom available [1]. Two distinct regimes are clearly visible: for short length scales the system is characterized by spin diffusion, for long length scales by spin decay [2]. For a sudden quench the system approaches a prethermalized state [3], which is characterized by thermal like correlation functions in the observed interference fringes with an effective temperature over five times lower than the kinetic temperature of the initial system. A detailed study of the time evolution of the correlation functions reveals that these thermallike properties emerge locally in their final form and propagate through the system in a lightconelike evolution [4]. Furthermore we demonstrate that the prethermalized state for a general quench is described by a generalized Gibbs ensemble [5]. This is verified through a detailed study of the full nontranslation invariant phase correlation functions up to 10th order. Finally we show two distinct ways for subsequent evolution away from the prethermalized state. One proceeds by further dephasing, the other by higher order phonon scattering processes. In both cases the final state is indistinguishable from a thermally relaxed state. We conjecture that our experiments points to a universal way through which relaxation in isolated many body quantum systems proceeds if the low energy dynamics is dominated by long lived excitations (quasi particles).
Supported by the Wittgenstein Prize, the Austrian Science Foundation (FWF) SFB FoQuS: F40P10 and the EU through the ERCAdG QuantumRelax
[1] S. Hofferberth et al. Nature, 449, 324 (2007).
[2] M. Kuhnert et al., Phys. Rev. Lett, 110, 090405 (2013).
[3] M. Gring et al., Science, 337, 1318 (2012); D. Adu Smith et al. NJP, 15, 075011 (2013).
[4] T. Langen et al., Nature Physics, 9, 640–643 (2013).
[5] T. Langen et al., Science (2015) arXiv:1411.7185.
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