# Quantum Memory and Quantum Cloning in Atomic Frequency Comb

## TL;DR

This paper investigates the quantum cloning capabilities of atomic frequency combs (AFCs) used as quantum memories, analyzing their efficiency, fidelity, and noise characteristics for single-photon inputs, and identifying conditions for effective quantum cloning.

## Contribution

It provides a theoretical analysis of AFCs' quantum cloning capacity, deriving expressions for efficiency, fidelity, and noise, and explores conditions for surpassing classical limits.

## Key findings

- AFCs can achieve greater than unit recall efficiency through amplification.
- Fidelity can be maintained above the classical limit in certain AFC configurations.
- Spectral distribution influences the quantum cloning performance of AFCs.

## Abstract

Atomic frequency comb (AFC) made of an ensemble of atoms with a periodic optical resonance was originally proposed as a viable approach for quantum memory for photons. In this paper, we examine the quantum cloning capacity of an AFC in terms of the spectral distribution of the atomic populations in the energy levels associated by the optical transition. Expressions are derived for the memory readout efficiency, signal to noise ratio, and fidelity for an input at the single photon level. When applied to a square toothed AFC, our analysis shows that there is a region where amplification from the excited state results in greater than unit recall efficiency, while maintaining a fidelity greater than the classical limit.

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Source: https://tomesphere.com/paper/1902.01910