Bandwidth and Noise Budget for an Off-Resonant Raman Single-Photon Memory

An off-resonant Raman memory trades optical depth and control energy for bandwidth: it can accept short photons that a narrowband memory cannot, at the price of a noise floor set by spontaneous scattering from the control field. This study computes the quantities that follow from stated assumptions for a warm caesium vapour Raman memory, photon duration 1 ns, detuning 1 to 5 GHz, control energies spanning an order of magnitude, using the relations set out in the Methods. The headline results are efficiency E4 D2 = 0.8347, noise E4 D2 = 0.08, efficiency E10 D5 = 0.5132, noise E10 D5 = 5.120e-03, bandwidth E4 D2 GHz = 1.5. Further computed values are operating points meeting both = 1. The central question is stated as follows: For stated control pulse energies and detunings, what acceptance bandwidth, storage efficiency and noise photons per pulse follow, and is there an operating point with efficiency above one half and noise below one hundredth of a photon? The answer obtained here is conditional on the assumptions listed in the paper and in the deposited calculation; changing an assumption changes the numbers in the way the sensitivity discussion describes. Raman memories have demonstrated gigahertz bandwidths with efficiencies of tens of percent and noise levels that remain the main obstacle to single-photon operation. The work is a computation, not a laboratory measurement, and it is labelled accordingly. Where the computed result is unfavourable to the device or effect under study, that outcome is reported in the same terms as a favourable one, because a bound that only appears when it is welcome is not a bound at all. All numerical statements in this abstract are reproduced by the deposited script from the stated inputs.