Tailored particle current in an optical lattice by a weak time-symmetric harmonic potential

TL;DR

This paper demonstrates that long-lasting directed currents can be generated in quantum ratchets with symmetric potentials due to quasienergy degeneracies, controllable by weak fields in optical lattice setups.

Contribution

It reveals that degeneracies in the quasienergy spectrum enable directed currents without breaking time reversal symmetry, challenging previous assumptions.

Findings

Directed currents can be sustained without symmetry breaking.

Weak fields effectively control current time scales.

Model applicable to ultracold atoms in optical lattices.

Abstract

Quantum ratchets exhibit asymptotic currents when driven by a time-periodic potential of zero mean if the proper spatio-temporal symmetries are broken. There has been recent debate on whether directed currents may arise for potentials which do not break these symmetries. We show here that, in the presence of degeneracies in the quasienergy spectrum, long-lasting directed currents can be induced, even if the time reversal symmetry is not broken. Our model can be realized with ultracold atoms in optical lattices in the tight-binding regime, and we show that the time scale of the average current can be controlled by extremely weak fields.