A quantum Newton's cradle

Abstract

It is a fundamental assumption of statistical mechanics that a closed system with many degrees of freedom ergodically samples all equal energy points in phase space. To understand the limits of this assumption, it is important to find and study systems that are not ergodic, and thus do not reach thermal equilibrium. A few complex systems have been proposed that are expected not to thermalize because their dynamics are integrable. Some nearly integrable systems of many particles have been studied numerically, and shown not to ergodically sample phase space. However, there has been no experimental demonstration of such a system with many degrees of freedom that does not approach thermal equilibrium. Here we report the preparation of out-of-equilibrium arrays of trapped one-dimensional (1D) Bose gases, each containing from 40 to 250 (87)Rb atoms, which do not noticeably equilibrate even after thousands of collisions. Our results are probably explainable by the well-known fact that a homogeneous 1D Bose gas with point-like collisional interactions is integrable. Until now, however, the time evolution of out-of-equilibrium 1D Bose gases has been a theoretically unsettled issue, as practical factors such as harmonic trapping and imperfectly point-like interactions may compromise integrability. The absence of damping in 1D Bose gases may lead to potential applications in force sensing and atom interferometry.

Non-equilibrium dynamics of an unstable quantum pendulum explored in a spin-1 Bose–Einstein condensate

“…In future work, we intend to further investigate the damping of the spin dynamics and its connection to thermalization of isolated quantum systems subject to loss. Similar investigations are ongoing using one-dimensional condensate systems [30][31][32][33] , and it will be interesting to explore the similarities and differences in these completely different systems.…”

Rare‐region effects and dynamics near the many‐body localization transition

“…The ETH states that the eigenstates of a generic many-body quantum system are locally "thermal," in the sense that the reduced density matrix of a sufficiently small subsystem is the same when the full system is in an eigenstate as when the full system is in any other thermal equilibrium state, such as the Boltzmann distribution. Numerical evidence supports the ETH in a variety of quantum systems [1,4,5], although it is known to fail in certain experimentally relevant special cases, e.g., a one-dimensional Bose (or Fermi) gas with short-range interactions [1,4,6]. Such special cases, corresponding to integrable (and thus non-chaotic) dynamics, were thought to be fine-tuned points rather than stable dynamical phases.…”

“…That such questions can be probed experimentally at all is the result of advances in preparing, controlling and measuring such systems in a variety of platforms, including ultracold atomic [14,15], trapped ion systems [16,17], superconducting qubit arrays [18], NV-centers [19] etc. These developments bring the investigation of outof-equilibrium many-body quantum dynamics within experimental reach; and, indeed, both the failure of thermalization in integrable one-dimensional quantum systems [6,20,21] and the presence of MBL regimes have been experimentally demonstrated [22][23][24][25][26][27].…”

Stationary behaviour of observables after a quantum quench in the spin-1/2 Heisenberg XXZ chain

“…Nonequilibrium dynamics in closed quantum systems, and in particular quantum quenches, have attracted much experimental [1][2][3][4][5][6] and theoretical attention in recent years. There is a growing consensus that integrable models exhibit important differences in behaviour as compared to non-integrable ones 41 .…”