Measuring and quantifying quantum memory effects in cold atom systems

Classical memory effects are observable in many systems which are history-dependent, including magnetization and rechargeable batteries, and also have broad applications. On the other hand, the quantum memory effects are also observable in atomic superfluids. Although memory effects exist in quantum systems, some dynamical variables such as steady state current or particle density do not reveal the quantum memory quantitatively. Here, we present three different examples to elaborate on how to quantify quantum memory effects in cold atom systems. First, we consider non-interacting fermions loaded in a ring shape potential. Applying an artificial gauge drives a current and considering the dissipation from the background, the current versus driving forms a hysteresis loop as the current lags behind due to dissipation. The second example, non-interacting particles are loaded in a tunable optical lattice which transforms from triangular to kagome geometry. Since there is a flat band in kagome lattices, the steady state particle density depends on the rate of lattice transformation. In the final example, we show systems undergo interaction imbalance with different ramping timescales and the steady state current exhibits memory of the ramping time for both fermionic and bosonic systems. The memory effects of dynamical variables in cold atoms provide promising applications in atomtronics.