Generation of Narrow-Bandwidth Single Photons Using Electromagnetically Induced Transparency in Atomic Ensembles

Abstract

We review recent experiments [M. D. Eisaman et al., Nature 438 (2005) 837] demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of 87 Rb atoms. Our method involves creation of an atomic coherence via Raman scattering and projective measurement, followed by the coherent transfer of this atomic coherence onto a single photon using electromagnetically induced transparency (EIT). The single photons generated using this method are shown to have many properties necessary for quantum information protocols, such as narrow bandwidths, directional emission, and controllable pulse shapes. The narrow bandwidths of these single photons (∼MHz), resulting from their matching to the EIT resonance (∼MHz), allow them to be stored in narrow-bandwidth quantum memories. We demonstrate this by using dynamic EIT to store and retrieve the single photons in a second ensemble for storage times up to a few microseconds. We also describe recent improvements to the single-photon fidelity compared to the work by M. D. Eisaman in Nature 438 (2005) 837. These techniques may prove useful in quantum information applications such as quantum repeaters, linear-optics quantum computation, and daytime free-space quantum communication.

Quantum repeaters based on atomic ensembles and linear optics

“…For hot gases, the filtering is more challenging and the two photon components of the heralded anti-Stokes field reported so far are sensibly higher that with cold ensembles, with the lowest value being α = 0.1 ± 0.1 (Eisaman et al, 2005;Walther et al, 2007).…”

“…For these reasons, the filtering of the write and read pulses is more challenging in hot vapors than in cold gases. Strong non classical correlations have nevertheless been observed by using a counterpropagating configuration for the write and read beams (Eisaman et al, 2005;Walther et al, 2007).…”

Quantum memory in warm rubidium vapor with buffer gas

“…However, previous reports employ widely different experimental conditions and geometries and occasionally suffer from ambiguous results. Some of the work is focused on the storage of single photons produced elsewhere rather than on the generation of correlation in a single cell [4][5][6][7][8].The divergence of experimental conditions in the reports claiming quantum memory can be illustrated as follows [4,5,[9][10][11]. In one work, a 4-mm diameter write (read) beam with an intensity of I  10 -4 (10 -3 ) W/m 2 was utilized in a room-temperature 87 Rb vapor cell (atomic density N = 1.3×10 10 cm -3 ) with 30 Torr Ne buffer gas [9].…”

“…In that work, with 87 Rb vapor at 60°C (N = 3.3×10 11 cm -3 ), 7 Torr Ne buffer gas, and write (read) beam I = 1.4(7)×10 4 W/m 2 , the fluorescence was noted to limit the fidelity of QM severely. The maximum observed cross-correlation between Stokes and anti-Stokes photons was 1.3 (still classical and no specified time delay), which implies that the noise was too high for the implementation of the DLCZ protocol.Whereas the two studies discussed above [9,10] employed co-propagating write and read beams, the counter-propagating geometry has also been reported in the literature [4,5] and in fact claimed to be optimal for the observation of correlations [12]. In that work, Stokes and anti-Stokes photons were generated in the source cell without any reported time delay, and the latter were stored and regenerated at a later time in a second (target) cell using electromagnetically induced transparency.…”

“…The divergence of experimental conditions in the reports claiming quantum memory can be illustrated as follows [4,5,[9][10][11]. In one work, a 4-mm diameter write (read) beam with an intensity of I  10 -4 (10 -3 ) W/m 2 was utilized in a room-temperature 87 Rb vapor cell (atomic density N = 1.3×10 10 cm -3 ) with 30 Torr Ne buffer gas [9].…”