Echo-Based Quantum Memory

This chapter focuses on memories that are based on photon echoes. To overcome the problems of population inversion and reabsorption, a number of photon echo schemes have been developed. The chapter also focuses on some of them that have been successfully used to perform storage and on-demand recall of light beyond the classical limit. It considers gradient echo memory (GEM), which is one implementation of a set of protocols based on controlled reversible inhomogeneous broadening (CRIB). The chapter also considers rephased amplified spontaneous emission (RASE), which uses a population inversion to create a pair of photons, one of which is stored in the ensemble. It discusses the methods that must be employed to implement echo-based quantum memory techniques in two common platforms, namely: rare-earth ion systems and vapors of alkali atoms. A widely used platform for echo-based quantum memory demonstrations is rare-earth ions in either crystalline or amorphous materials.