Photon storage in Lambda-type optically dense atomic media. IV. Optimal control using gradient ascent

TL;DR

This paper applies gradient ascent optimal control to Lambda-type atomic media to significantly improve photon storage efficiency and bandwidth, especially in non-adiabatic regimes, by shaping control pulses.

Contribution

It introduces a gradient ascent method for optimizing control pulses in photon storage, enabling high efficiency in previously inaccessible regimes and expanding bandwidth.

Findings

Order-of-magnitude increase in memory bandwidth.

Efficient photon storage in non-adiabatic limit achieved.

Demonstrates natural connection between time reversal and optimality.

Abstract

We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in Lambda-type media to previously inaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical control pulses used to mediate photon storage, we open up the possibility of high efficiency photon storage in the non-adiabatic limit, in which analytical solutions to the equations of motion do not exist. This control shaping technique enables an order-of-magnitude increase in the bandwidth of the memory. We also demonstrate that the often discussed connection between time reversal and optimality in photon storage follows naturally from gradient ascent. Finally, we discuss the optimization of controlled reversible inhomogeneous broadening.