Precision spectral manipulation: a demonstration using a coherent   optical memory
  The ability to coherently spectrally manipulate quantum information has the potential to improve qubit rates across quantum channels and find applications in optical quantum computing. In this paper we present experiments that use a multi-element solenoid combined with the three-level gradient echo memory scheme to perform precision spectral manipulation of optical pulses. These operations include bandwidth and frequency manipulation, spectral filtering of separate frequency components, as well as time-delayed interference between pulses with both the same, and different, frequencies. These operations have potential uses in quantum information applications. 
B. M. Sparkes, C. Cairns, M. Hosseini, D. Higginbottom, G. Campbell,   P. K. Lam, and B. C. Buchler
quant-ph