PhD defense: Karsten Dideriksen

Online at

A room-temperature single-photon source with built-in memory


Coherent light-matter interfaces in atomic ensembles at room-temperature have been studied for decades and have been found to be suitable systems for applications such as magnetometry and frequency references. In particular, warm atomic ensembles are favoured due to their experimental simplicity over cold quantum platforms. At the onset of the second quantum revolution these systems are also receiving much attention as a platform for non-classical light generation and quantum memory for light. Studies are often focused on either probabilistic single-photon generation or fast, high-bandwidth memories with short memory time for external photon sources.

This thesis presents an investigation of on-demand single-photon generation following the DLCZ scheme in a warm caesium vapour. As a novel approach we employ the long-lived collective spin mode in an anti-relaxation-coated cell to extend the memory time by orders of magnitude beyond previous demonstrations.

Initially attempting on the D2 spectral line we show that single-photon readout in this configuration is prohibited by four-wave mixing. When changing to the D1 line, the interaction is performed at the magic detuning where four-wave mixing is strongly suppressed. In this configuration we are able to achieve single-photon generation and retrieval with a conditional anti-bunching of 0.20 ± 0.07 for the readout field. The cross correlation between heralding and readout fields reaches 10 ± 1 which is highly non-classical and sufficient for quantum entanglement generation. The correlation remains non-classical for a memory storage time up to 0.68 ± 0.08 ms. The performance of the source-memory system is limited by a combination of imperfect initial state preparation and readout noise induced by atomic decay.

This work shows that the long-lived collective spin mode of room-temperature atomic vapours can be utilized as a narrowband single-photon source with built-in memory. Such devices could find application in quantum information and communication based on single photon interference where the memory capability can enhance photon coincidence rates or long-distance entanglement generation probability.