title: Gradient echo quantum memory in warm atomic vapor.
abstract: Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.
authors.affiliation: ARC Centre for Quantum Computation and Communication Technology, Department of Quantum Science, The Australian National University.
authors.forename: Olivier
authors.initials: O
authors.lastname: Pinel
authors.forename: Mahdi
authors.initials: M
authors.lastname: Hosseini
authors.forename: Ben M
authors.initials: BM
authors.lastname: Sparkes
authors.forename: Jesse L
authors.initials: JL
authors.lastname: Everett
authors.forename: Daniel
authors.initials: D
authors.lastname: Higginbottom
authors.forename: Geoff T
authors.initials: GT
authors.lastname: Campbell
authors.forename: Ping Koy
authors.initials: PK
authors.lastname: Lam
authors.forename: Ben C
authors.initials: BC
authors.lastname: Buchler
mesh_terms: D016248:Computer Storage Devices; D005740:Gases / Q000737:chemistry; D055095:Optics and Photonics / Q000379:methods*; D011789:Quantum Theory; D012413:Rubidium / Q000737:chemistry*
chemical_list: D005740:Gases; D012413:Rubidium