Momentum distributions for the quantum delta-kicked rotor with decoherence

Area of Science:

• Quantum chaos
• Atomic physics
• Quantum dynamics

Background:

• The quantum delta-kicked rotor is a model system for studying quantum chaos.
• Dynamical localization is a key phenomenon observed in this system, preventing momentum diffusion.
• Environmental interactions can disrupt quantum coherence and alter system dynamics.

Purpose of the Study:

• To investigate the effect of environment-induced decoherence on the quantum delta-kicked rotor.
• To analyze the momentum distribution line shapes under decoherent conditions.
• To compare experimental findings with numerical simulations.

Main Methods:

• Experimental realization using ultracold cesium atoms in a pulsed optical lattice.
• Application of a near-resonant standing light wave to drive the system.
• Controlled introduction of spontaneous photon scattering to induce decoherence.
• Numerical simulations to model the quantum dynamics with decoherence.

Main Results:

• Decoherence, induced by spontaneous scattering, was observed to destroy dynamical localization.
• The momentum distribution line shapes were experimentally and numerically found to be essentially exponential.
• The observed exponential shapes are characteristic of classical-like diffusion in momentum.

Conclusions:

• Environment-induced decoherence significantly alters the quantum behavior of the delta-kicked rotor.
• The transition to exponential momentum distributions signifies a move towards classical diffusion.
• The study highlights the fragility of quantum coherence in realistic experimental settings.