Applied Physics Seminar

One of the key components needed for optical quantum computation and communication technologies is a high efficiency, triggerable single photon source. Here we show correlations between two photons generated using cavity-enhanced rephased amplified spontaneous emission (RASE) in a Pr³⁺:Y₂SiO₅ crystal. This is the first step in demonstrating a triggerable single photon source in an ensemble of rare-earth ions.

The RASE protocol uses photon echo techniques to rephase the coherence generated during a spontaneous emission event, causing an ensemble of ions to emit a second photon identical to the initial spontaneously emitted photon. The release time of the second photon can be controlled by choosing when the coherence is rephased. Therefore RASE constitutes a triggerable single photon source. The novel part of this source is that four levels are utilised during the rephasing process so the coherence is stored on the spin states of the ensemble allowing storage times greater than a second. RASE therefore has an inbuilt quantum memory.

We have demonstrated four-level RASE in the continuous variable regime, showing that the ASE and RASE fields cannot be represented as a separable state.

To enhance the quantum efficiency of our source and improve the fidelity, we have placed the crystal inside an optical cavity. The cavity in conjunction with the four level rephasing process also allows us to improve the recall efficiency, theoretically approaching 100%. Here we show preliminary correlations between the initial and rephased photons.