Środowiskowe Seminarium z Informacji i Technologii Kwantowych

One of the core questions of quantum physics is how to reconcile the unitary evolution of quantum states, which is information-preserving and time-reversible, with evolution following the second law of thermodynamics, which, in general, is neither. The resolution to this paradox is to recognize that global unitary evolution of a multi-partite quantum state causes the state of local subsystems to evolve towards maximum-entropy states [1-3]. In this work, we experimentally demonstrate this effect in linear quantum optics by simultaneously showing the convergence of local quantum states to a generalized Gibbs ensemble constituting a maximum-entropy state under precisely controlled conditions, while using a new, efficient certification method to demonstrate that the state retains global purity [4]. Our quantum states are manipulated by a programmable integrated photonic quantum processor, which simulates arbitrary non-interacting Hamiltonians, demonstrating the universality of this phenomenon. Our results show the potential of photonic devices for quantum simulations involving non-Gaussian states.

[1] Popescu, S., Short, A., & Winter, A. (2006). Entanglement and the foundations of statistical mechanics. Nature Physics, 2(11), 754–758.
[2] Cramer, M., Flesch, A., McCulloch, I. P., Schollwöck, U., & Eisert, J. (2008). Exploring Local Quantum Many-Body Relaxation by Atoms in Optical Superlattices, 101(6), 063001. http://doi.org/10.1103/PhysRevLett.101.063001
[3] Linden, N., Popescu, S., Short, A. J., & Winter, A. (2009). Quantum mechanical evolution towards thermal equilibrium. Physical Review E, 79(6), 061103. http://doi.org/10.1103/PhysRevE.79.061103
[4] Somhorst, F. H. B., van der Meer, R., Anguita, M. C., Schadow, R., Snijders, H. J., de Goede, M., et al. (2021). Quantum photo-thermodynamics on a programmable photonic quantum processor. arXiv:2201.00049