A quantum Newton's cradle.

Area of Science:

• Statistical Mechanics
• Quantum Gases
• Many-Body Physics

Background:

• Statistical mechanics assumes systems with many degrees of freedom ergodically sample phase space, reaching thermal equilibrium.
• Non-ergodic systems that do not thermalize are crucial for understanding the limits of this fundamental assumption.
• Previous studies proposed complex systems with integrable dynamics as non-ergodic, but experimental evidence was lacking.

Purpose of the Study:

• To experimentally investigate the ergodicity and thermalization of many-body quantum systems.
• To explore systems that deviate from the standard assumptions of statistical mechanics.
• To provide the first experimental demonstration of a many-degrees-of-freedom system that does not approach thermal equilibrium.

Main Methods:

• Preparation of out-of-equilibrium arrays of trapped one-dimensional (1D) Bose gases.
• Utilizing rubidium-87 ((87)Rb) atoms, with each gas containing 40 to 250 atoms.
• Observing the time evolution of these systems over thousands of collisions to assess equilibration.

Main Results:

• The prepared one-dimensional Bose gases showed no noticeable equilibration, even after extended periods.
• The observed non-ergodic behavior is consistent with the known integrability of homogeneous 1D Bose gases with point-like interactions.
• This experimental result addresses the unsettled theoretical issue of 1D Bose gas time evolution under realistic conditions.

Conclusions:

• The experiment provides the first direct evidence of non-thermalizing dynamics in a many-body quantum system.
• The findings validate theoretical predictions about the integrability of 1D Bose gases and their deviation from ergodicity.
• The absence of damping in these 1D Bose gases suggests potential applications in precision measurement technologies like force sensing and atom interferometry.