Abstract
Periodic driving has emerged as a powerful tool in the quest to engineer new and exotic quantum phases. While driven many-body systems are generically expected to absorb energy indefinitely and reach an infinite-temperature state, the rate of heating can be exponentially suppressed when the drive frequency is large compared to the local energy scales of the system -- leading to long-lived 'prethermal' regimes. In this work, we experimentally study a bosonic cloud of ultracold atoms in a driven optical lattice and identify such a prethermal regime in the Bose-Hubbard model. By measuring the energy absorption of the cloud as the driving frequency is increased, we observe an exponential-in-frequency reduction of the heating rate persisting over more than 2 orders of magnitude. The tunability of the lattice potentials allows us to explore one- and two-dimensional systems in a range of different interacting regimes. Alongside the exponential decrease, the dependence of the heating rate on the frequency displays features characteristic of the phase diagram of the Bose-Hubbard model, whose understanding is additionally supported by numerical simulations in one dimension. Our results show experimental evidence of the phenomenon of Floquet prethermalization, and provide insight into the characterization of heating for driven bosonic systems.
Highlights
The study of out-of-equilibrium dynamics in Floquet systems is an exciting new frontier in quantum physics [1,2,3,4,5]
The dependence of the heating rate on the frequency displays features characteristic of the phase diagram of the Bose-Hubbard model, whose understanding is supported by numerical simulations in one dimension
These heating rates are extracted from a linear fit of the temperature, and we express them as the energy absorbed per Floquet cycle φðωÞ, which is related to ΦðωÞ through φðωÞ 1⁄4 ðπgÞ2ΦðωÞ
Summary
The study of out-of-equilibrium dynamics in Floquet systems is an exciting new frontier in quantum physics [1,2,3,4,5]. It has been shown that the timescale for heating can be bounded from below as tth ≳ Oðeħω=Jeff Þ for sufficiently large drive frequency ω, where Jeff represents a typical local energy scale of the system [35,36,37,38,39]. At times t ≪ tth, the system can, in principle, exhibit rich dynamics, featuring symmetries, quasiconserved quantities (including an effective Hamiltonian), etc., [37,40,41]
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