Gravity-Sensitive Quantum Dynamics in Cold Atoms

We subject a falling cloud of cold cesium atoms to periodic kicks from a sinusoidal potential created by a vertical standing wave of off-resonant laser light. By controllably accelerating the potential, we show quantum accelerator mode dynamics to be highly sensitive to the effective gravitational acceleration when this is close to specific, resonant values. This quantum sensitivity to a control parameter is reminiscent of that associated with classical chaos, and promises techniques for precision measurement.