Observing non-ergodicity due to kinetic constraints in tilted Fermi-Hubbard chains

Abstract

The thermalization of isolated quantum many-body systems is deeply related to fundamental questions of quantum information theory. While integrable or many-body localized systems display non-ergodic behavior due to extensively many conserved quantities, recent theoretical studies have identified a rich variety of more exotic phenomena in between these two extreme limits. The tilted one-dimensional Fermi-Hubbard model, which is readily accessible in experiments with ultracold atoms, emerged as an intriguing playground to study non-ergodic behavior in a clean disorder-free system. While non-ergodic behavior was established theoretically in certain limiting cases, there is no complete understanding of the complex thermalization properties of this model. In this work, we experimentally study the relaxation of an initial charge-density wave and find a remarkably long-lived initial-state memory over a wide range of parameters. Our observations are well reproduced by numerical simulations of a clean system. Using analytical calculations we further provide a detailed microscopic understanding of this behavior, which can be attributed to emergent kinetic constraints.

Observation of unconventional many-body scarring in a quantum simulator

“…The connected component of the Hilbert space contains only certain types of two-site configurations (20,11,12, 02, 01), while all other two-site configurations are forbidden (22,21,10,00). If we consider the configuration 20 to be an excitation, all allowed configurations can be mapped to those of the PXP model as follows:…”

“…Such behavior hinders the scrambling of information encoded in the initial state and suppresses the spreading of quantum entanglement, allowing a many-body system to display persistent quantum revivals. Many-body scarring was first observed in the Rydberg atom experimental platform [9,10] and subsequent observations of weak ergodicity breaking phenomena have attracted much attention [11][12][13]. On the other hand, theoretical works have unearthed universal scarring mechanisms [14][15][16][17], pointing to the ubiquity of scarring phenomena in periodically-driven systems [18][19][20] and in the presence of disorder [21,22].…”

Many-body localization in a quantum gas with long-range interactions and linear external potential

“…In general, our findings significantly extend the class of systems, where the transitions between the localized and chaotic many-body regimes can be studied in detail by accessing relevant observables in cold-atom experiments [20]. The systems under study are completely disorder free and quasi translationally invariant in the sense that the shift operator commutes with the Hamiltonians up to a constant.…”

“…Such an experimentally-relevant observable (see, e.g., Ref. [20]), which is especially convenient for our quench protocol, is the even-odd site occupation imbalance (or the so-called amplitude of the charge-density wave). It is defined as a difference between the number of particles on even and odd sites of the lattice ( and , respectively), normalized by the total number of particles ,…”

“…[16], where one required artificial disorder produced by quasiperiodic potentials or other means. Recently, it was shown that analogous systems with only short-range interactions and disorder-free (linear or harmonic) potentials can exhibit localized behavior in a wide range of Hamiltonian parameters, which was named as the Stark (or Bloch) localization [17][18][19] and was also observed experimentally [20].…”