Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion

The preparation and storage of photonic entanglement are central to the achievement of scalable linear optical quantum computation 1 , 2 , 3 (LOQC). The most widely used photonic entanglement source (a spontaneous parametric downconversion (SPDC) source) 4 , 5 is not directly suitable for storage, because its working frequency bandwidth is significantly larger than any available quantum memory. To remedy this problem, cavity-enhanced narrow-band SPDC sources 6 , 7 , 8 , 9 , 10 , 11 , 12 have been developed. However, the storage of cavity-enhanced narrow-band entangled photons has not yet been achieved. Also, the spectral correlations between the entangled photons can make them practically useless for scalable LOQC 5 , 13 , 14 . Here, we report the preparation and storage of frequency-uncorrelated narrowband (5 MHz) entangled photons from a cavity-enhanced SPDC source. The frequency correlation between the entangled photons is eliminated by changing the continuous UV pumping beam to short pulses. The storage of the polarization state of a single photon, and of a photon entangled with another flying in the fibre, is demonstrated. Our work demonstrates a quantum interface between narrow-band entangled photons from cavity SPDC and atomic quantum memory, and thus provides an important tool towards the achievement of all-optical quantum information processing. Researchers report the preparation and storage of frequency-uncorrelated narrowband (5 MHz) entangled photons from a cavity-enhanced spontaneous parametric downconversion source. Electromagnetically induced transparency was implemented using ultraviolet pump pulses, and the violation of Bell's inequality was clearly observed for storage times of up to 200 ns.