We report on the delay of optical pulses using electromagnetically induced transparency in an ensemble of cold atoms with an optical depth exceeding 500. To identify the regimes in which four-wave mixing impacts on EIT behaviour, we conduct the exper
iment in both rubidium 85 and rubidium 87. Comparison with theory shows excellent agreement in both isotopes. In rubidium 87, negligible four-wave mixing was observed and we obtained one pulse-width of delay with 50% efficiency. In rubidium 85, four-wave-mixing contributes to the output. In this regime we achieve a delay-bandwidth product of 3.7 at 50% efficiency, allowing temporally multimode delay, which we demonstrate by compressing two pulses into the memory medium.
We show that a set of optical memories can act as a configurable linear optical network operating on frequency-multiplexed optical states. Our protocol is applicable to any quantum memories that employ off-resonant Raman transitions to store optical
information in atomic spins. In addition to the configurability, the protocol also offers favourable scaling with an increasing number of modes where N memories can be configured to implement an arbitrary N-mode unitary operations during storage and readout. We demonstrate the versatility of this protocol by showing an example where cascaded memories are used to implement a conditional CZ gate.
We present experimental observations of interference between an atomic spin coherence and an optical field in a {Lambda}-type gradient echo memory. The interference is mediated by a strong classical field that couples a weak probe field to the atomic
coherence through a resonant Raman transition. Interference can be observed between a prepared spin coherence and another propagating optical field, or between multiple {Lambda} transitions driving a single spin coherence. In principle, the interference in each scheme can yield a near unity visibility.
