Narrowband biphoton generation near atomic resonance

Abstract

Generating nonclassical light offers a benchmark tool for fundamental research and potential applications in quantum optics. Conventionally, it has become a standard technique to produce nonclassical light through the nonlinear optical processes occurring in nonlinear crystals. We describe this process using cold atomic-gas media to generate such nonclassical light, especially focusing on narrowband biphoton generation. Compared with the standard procedure the new biphoton source has such properties as long coherence time, long coherence length, high spectral brightness, and high conversion efficiency. Although there exist two methodologies describing the physical process, we concentrate on the theoretical aspect of the entangled two-photon state produced from the four-wave mixing in a multilevel atomic ensemble using perturbation theory. We show that both linear and nonlinear optical responses to the generated fields play an important role in determining the biphoton waveform and, consequently, on the two-photon temporal correlation. There are two characteristic regimes determined by whether the linear or nonlinear coherence time is dominant. In addition, our model provides a clear physical picture that brings insight into understanding biphoton optics with this new source. We apply our model to recent work on generating narrowband (and even subnatural linewidth) paired photons using the technique of electromagnetically induced transparency and slow-light effect in cold atoms and find good agreement with experimental results.

Engineering biphoton wave packets with an electromagnetically induced grating

“…Different from previous findings [14][15][16][17][18]20,21,30], Eq. (12) clearly shows that the profile of the biphoton wave form is further manipulated by the periodic modulation of the control fields.…”

“…The paired Stokes and anti-Stokes photon states can be obtained from first-order perturbation theory [16,17,29]. For simplicity, we take the input probe and control beams as classical cw lasers and focus on the two-photon temporal 043814-2 correlation.…”

“…A recent demonstration of the generation of narrow-band biphotons in cold atomic ensembles via spontaneous four-wave mixing (SFWM) [14][15][16][17][18] has attracted considerable attention because of their long coherence time and controllable quantum wave packets. Nonlocal modulation of temporal correlation has been observed with such narrow-band biphotons [19].…”

Narrowband Biphotons: Generation, Manipulation, and Applications

“…For SPDC with χ (2) nonlinearity, this geometry can be achieved by quasiphase matching [29] to submicron periodicity and driven by a single pump laser beam [30,31,32]. For SFWM driven by χ (3) nonlinearity, the phase matching condition can be satisfied by aligning two coherent driving laser beams [33,26]. As compared to conventional forward-wave schemes, the backward-wave geometry allows a much tighter constraint of phase matching that leads to substantially narrow linewidth.…”

“…where |Ψ s,as is the two-photon time-frequency entangled state [26], and m(τ) is the modulation. It is clear that the heralded single-photon waveform is directly modulated by the EOM.…”