Quantum memory in warm rubidium vapor with buffer gas

Abstract

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXXThe realization of quantum memory using warm atomic vapor cells is appealing because of their commercial availability and the perceived reduction in experimental complexity. In spite of the ambiguous results reported in the literature, we demonstrate that quantum memory can be implemented in a single cell with buffer gas using the geometry where the write and read beams are nearly co-propagating. The emitted Stokes and anti-Stokes photons display cross-correlation values greater than 2, characteristic of quantum states, for delay times up to 4 s. © 2011 Optical Society of America OCIS Codes: 020.0020, 270.0270, 300.6210 The implementation of quantum memory (QM) via the interaction between atomic ensembles and optical fields attracted considerable attention ever since the DLCZ (Duan, Lukin, Cirac, and Zoller) protocol was proposed in 2001 [1]. The original DLCZ scheme is based on the correlation between the emission of a Stokes photon and the collective excitation in an atomic ensemble produced by a spontaneous Raman scattering event. Since the original DLCZ proposal, QM in atomic ensembles has been demonstrated in both cold and warm vapors [2,3], the latter being particularly appealing because of commercial availability and the perceived reduction in experimental complexity. 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]. Although quantum correlations between Stokes and antiStokes photons were originally reported, a later Erratum withdrew this claim [9]. A study by a different group [10] employed 87 Rb vapor at 75°C (N = 1.1×10 12 cm -3 ) with 3 Torr Ne buffer gas and a 100 m-wide write beam with intensities in the range of I = 3×10 3 -1.3×10 4 W/m 2 , a two-order of magnitude difference in the number density and a six-order of magnitude difference in the write-beam intensity by comparison with [9]. As discussed in [10], the experiment was not performed in the single-photon regime required for the DLCZ protocol. While the presence of a buffer gas is necessary to reduce atomic diffusion and enable a sufficiently long-lasting QM, another study [11] pointed out the presence of collisionally redistributed fluorescence (CRF) caused by buffer-gas collisions. 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...

Atom-light hybrid interferometer

“…Δ is the detuning from the excited state for both the Stokes and Raman write fields, which satisfy the two-photon resonance condition: ω W − ω S ¼ ω mg . When the write field A W is relatively weak, the collective Raman scattering is in spontaneous mode and can generate correlated atomic excitations and single photons, which has been widely used in quantum memory [24][25][26][27][28]. When the write field A W is relatively strong, the collective Raman scattering is in the stimulated mode and can amplify the input field to produce intensity and phase correlated atom-light fields [29,30].…”

Stokes–anti-Stokes correlations in diamond

“…We show that the intensity cross-correlation g 2 S;aS 0, which describes the simultaneous detection of Stokes and anti-Stokes photons, increases steadily with decreasing laser power and saturates at very low pump powers, implying that the number of Stokes-induced aS photons is comparable to the number of spontaneously generated aS photons. Furthermore, the coincidence rate shows a quadratic plus cubic power dependence, indicating the generation of multiple S photons per pulse at high powers.Raman scattering, typically used to probe the vibrational modes of a system, can also create correlated Stokesanti-Stokes photon pairs in bulk solids such as diamond [1][2][3] or in gases such as Cesium [4,5] or Rubidium vapor [6][7][8]. In the uncorrelated regime, both Stokes (S) and anti-Stokes (aS) intensities are linear with excitation laser power, i.e., a single laser photon spontaneously scatters into a single S or aS photon [see Fig.…”

“…Raman scattering, typically used to probe the vibrational modes of a system, can also create correlated Stokesanti-Stokes photon pairs in bulk solids such as diamond [1][2][3] or in gases such as Cesium [4,5] or Rubidium vapor [6][7][8]. In the uncorrelated regime, both Stokes (S) and anti-Stokes (aS) intensities are linear with excitation laser power, i.e., a single laser photon spontaneously scatters into a single S or aS photon [see Fig.…”

“…In this case, we expect that the aS intensity depends on the squared excitation laser power, since one laser photon creates the phonon in the S process, and another laser photon scatters from the phonon in the aS process [9,10]. Recent work has shown theoretically and experimentally that the Stokes-generated phonon (or spin wave, for Cesium [4,5] and Rubidium vapors [6][7][8]) acts as a quantum memory, where the S and aS signals act as write and read commands [1][2][3]9]. In parallel, research in photon pairs produced through four-wave mixing (FWM) in optical fibers has shown highly nonclassical correlations [11,12], analogous to studies in spontaneous parametric down-conversion (SPDC) [13,14].…”

Nonclassical correlations between terahertz-bandwidth photons mediated by rotational quanta in hydrogen molecules

“…The DLCZ emissive memory protocol [22] has been demonstrated in a variety of systems, including atomic ensembles [23][24][25][26][27] and bulk diamond [28]. We use hydrogen molecules with the relevant level structure shown in Figs.…”