Metastable order protected by destructive many-body interference

Abstract

The phenomenon of metastability shapes dynamical processes ranging from radioactive decay to chemical reactions. Here, we present a mechanism for metastability in which a quantum gas selfstabilizes against relaxation towards thermal equilibrium by establishing a transient ordered state. In this state, the direct relaxation channel is suppressed by destructive interference, which derives from the chiral order of the transient state. In particular, we consider the dynamical evolution of an ultracold bosonic gas in an optical lattice, that is quenched into a higher band of the lattice, which triggers the dynamical evolution. Following this quench, the self-stabilization phenomenon manifests itself in three stages of relaxation, subsequent to the preparation of the incoherent excited state. In the first stage, the gas develops coherence resulting in the ordered state, during the second stage the gas forms a long-lived state with inhibited relaxation and slow loss of coherence, followed by the third stage of fast relaxation to the thermal ground state. We demonstrate this mechanism experimentally and theoretically, and discuss its broader implications.

Orbital many-body dynamics of bosons in the second Bloch band of an optical lattice

“…We use a tight-binding model including all nearest-and next-nearest-neighbour hopping terms as well as on-site interaction terms, for details see Ref. [30]. Along the xand y-direction we use periodic boundary conditions and a discretized harmonic trap in the z-direction.…”

“…A and Ref. [30]. Finally, ∆V and V 0 are ramped up in 0.3 ms to final values ∆V f ∈ [0.55, 0.75] × V 0,f and V 0,f = 7.2 E rec .…”

“…B and Ref. [30]. We initialize the c-field propagation from a thermal ensemble of temperature T using Monte Carlo sampling with parameters V 0,i = 4.3 E rec and ∆V i = −1.23 V 0,i .…”

Quantum degenerate Fermi gas in an orbital optical lattice

“…In Ref. [42], it has been shown that specific parameter configurations can be found, where different scattering processes destructively interfere with the result of remarkably long lifetimes on the order of several 100 ms. In the following, we explore the band decay dynamics after exciting a large fraction of fermionic atoms to the 2 nd band.…”

“…For modeling band relaxation, only band-index changing collisions are relevant. We assume that, similarly as found for bosons in the same lattice potential [26,42], the dominant collisional process leading to loss of 2 nd band population, is associated with a transfer of pairs of colliding spin-up and a spin-down atoms to the 1 st band. Thereby, in fulfillment of energy-momentum conservation, an energy per particle of approximately the band gap between the 1 st and 2 nd bands is deposited into motion along the z-axis.…”