title: Dual-rail optical gradient echo memory.
abstract: We introduce a scheme for the parallel storage of frequency separated signals in an optical memory and demonstrate that this dual-rail storage is a suitable memory for high fidelity frequency qubits. The two signals are stored simultaneously in the Zeeman-split Raman absorption lines of a cold atom ensemble using gradient echo memory techniques. Analysis of the split-Zeeman storage shows that the memory can be configured to preserve the relative amplitude and phase of the frequency separated signals. In an experimental demonstration dual-frequency pulses are recalled with 35% efficiency, 82% interference fringe visibility, and 6° phase stability. The fidelity of the frequency-qubit memory is limited by frequency-dependent polarisation rotation and ambient magnetic field fluctuations, our analysis describes how these can be addressed in an alternative configuration.
authors.forename: D B
authors.initials: DB
authors.lastname: Higginbottom
authors.forename: J
authors.initials: J
authors.lastname: Geng
authors.forename: G T
authors.initials: GT
authors.lastname: Campbell
authors.forename: M
authors.initials: M
authors.lastname: Hosseini
authors.forename: M T
authors.initials: MT
authors.lastname: Cao
authors.forename: B M
authors.initials: BM
authors.lastname: Sparkes
authors.forename: J
authors.initials: J
authors.lastname: Bernu
authors.forename: N P
authors.initials: NP
authors.lastname: Robins
authors.forename: P K
authors.initials: PK
authors.lastname: Lam
authors.forename: B C
authors.initials: BC
authors.lastname: Buchler