We report on a single photon source with highly tunable photon shape based ona cold ensemble of Rubidium atoms. We follow the DLCZ scheme to implement anemissive quantum memory, which can be operated as a photon pair source withcontrollable delay. We find that the temporal wave shape of the emitted readphoton can be precisely controlled by changing the shape of the driving readpulse. We generate photons with temporal durations varying over three orders ofmagnitude up to 10 {\mu}s without a significant change of the read-outefficiency. We prove the non-classicality of the emitted photons by measuringtheir antibunching, showing near single photon behavior at low excitationprobabilities. We also show that the photons are emitted in a pure state bymeasuring unconditional autocorrelation functions. Finally, to demonstrate theusability of the source for realistic applications, we create ultra-long singlephotons with a rising exponential or doubly peaked wave shape which areimportant for several quantum information tasks.
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