Modematching an optical quantum memory

TL;DR

This paper analyzes the off-resonant Raman interaction in atomic ensembles, demonstrating how quantum state transfer can be achieved through mode-matching control pulses, with implications for optical quantum memories.

Contribution

It provides a mode decomposition framework for understanding and optimizing quantum state transfer in optical quantum memories using Raman interactions.

Findings

Complete quantum state transfer is possible with proper mode matching.

The interaction can be modeled as a beamsplitter transformation.

Spatial mode structure is characterized by the same mode decomposition.

Abstract

We analyse the off-resonant Raman interaction of a single broadband photon, copropagating with a classical `control' pulse, with an atomic ensemble. It is shown that the classical electrodynamical structure of the interaction guarantees canonical evolution of the quantum mechanical field operators. This allows the interaction to be decomposed as a beamsplitter transformation between optical and material excitations on a mode-by-mode basis. A single, dominant modefunction describes the dynamics for arbitrary control pulse shapes. Complete transfer of the quantum state of the incident photon to a collective dark state within the ensemble can be achieved by shaping the control pulse so as to match the dominant mode to the temporal mode of the photon. Readout of the material excitation, back to the optical field, is considered in the context of the symmetry connecting the input and output modes. Finally, we show that the transverse spatial structure of the interaction is characterised by the same mode decomposition.