# Optimal control for perfect state transfer in linear quantum memory

## TL;DR

This paper presents an optimal control method to simplify the input pulse shape for perfect quantum state transfer in linear quantum memories, enhancing practical implementation.

## Contribution

It introduces a novel optimal control approach that reduces pulse complexity while ensuring perfect state transfer in linear quantum memory systems.

## Key findings

- Effective pulse shape simplification demonstrated in simulations
- Maintains perfect state transfer with less complex input pulses
- Applicable to atomic media and networked atomic ensembles

## Abstract

A quantum memory is a system that enables transfer, storage, and retrieval of optical quantum states by ON/OFF switching of the control signal in each stages of the memory. In particular, it is known that, for perfect transfer of a single-photon state, appropriate shaping of the input pulse is required. However, in general, such a desirable pulse shape has a complicated form, which would be hard to generate in practice. In this paper, for a wide class of linear quantum memory systems, we develop a method that reduces the complexity of the input pulse shape of a single-photon while maintaining the perfect state transfer. The key idea is twofold; (i) the control signal is allowed to vary continuously in time to introduce an additional degree of freedom, and then (ii) an optimal control problem is formulated to design a simple-formed input pulse and the corresponding control signal. Numerical simulations are conducted for Lambda-type atomic media and a networked atomic ensembles, to show the effectiveness of the proposed method.