Quantum Control of Qubits and Atomic Motion Using Ultrafast Laser Pulses

TL;DR

This paper reviews how ultrafast laser pulses can be used to control qubits and atomic motion, highlighting two regimes of laser intensity for coherent manipulation and entanglement creation.

Contribution

It introduces a comprehensive analysis of ultrafast laser pulse regimes for quantum control, including new methods for fast entangling gates outside the Lamb-Dicke regime.

Findings

Weak pulses enable sideband transitions and atom-atom entanglement similar to CW lasers.

Strong pulses allow impulsive spin-dependent kicks for faster entangling gates.

Fast gates are insensitive to thermal motion and operate outside the Lamb-Dicke regime.

Abstract

Pulsed lasers offer significant advantages over CW lasers in the coherent control of qubits. Here we review the theoretical and experimental aspects of controlling the internal and external states of individual trapped atoms with pulse trains. Two distinct regimes of laser intensity are identified. When the pulses are sufficiently weak that the Rabi frequency $\Omega$ is much smaller than the trap frequency $\otrap$, sideband transitions can be addressed and atom-atom entanglement can be accomplished in much the same way as with CW lasers. By contrast, if the pulses are very strong ($\Omega \gg \otrap$), impulsive spin-dependent kicks can be combined to create entangling gates which are much faster than a trap period. These fast entangling gates should work outside of the Lamb-Dicke regime and be insensitive to thermal atomic motion.