Photon bunching in parametric down-conversion with continuous-wave excitation

Abstract

The first direct measurement of photon bunching (g (2) correlation function) in one output arm of a spontaneous-parametric-down-conversion source operated with a continuous pump laser in the single-photon regime is demonstrated. The result is in agreement with the statistics of a thermal field of the same coherence length, and shows the feasibility of investigating photon statistics with compact cw-pumped sources. Implications for entanglement-based quantum cryptography are discussed.

Direct measurement of heralded single-photon statistics from a parametric down-conversion source

“…There have been several theoretical and experimental investigations concerning the issue of simultaneous excitation of photon pairs in SPDC under cw excitations [18][19][20][21]. For example, due to their bosonic nature, correlations (thermal bunching) between the polarization of the photons in the same arm exist, which may pose a threat for the security in application of SPDC in quantum * david.hoeckel@physik.hu-berlin.de key distribution [21,22]. The degree of one-arm correlations in SPDC under cw excitation is thus an important quantity to consider when determining the applicability of photon-pair sources for QIP tasks.…”

“…The measurement therefore represents true second-order correlation measurements on a cw SPDC source. Instead of scrutinizing tiny deviations from thermal statistics in standard SPDC sources [21], our approach relies on increasing the coherence time (or reducing the linewidth) dramatically via SPDC in an optical cavity [26,27]. A configuration resembling an optical parametric oscillator (OPO) far below threshold allows us to channel the emission of signal and idler photons into narrow-band resonances of the cavity lying within the phase-matching envelope.…”

Cancellation of dispersion and temporal modulation with nonentangled frequency-correlated photons

“…This function provides the probability of detecting a signal photon in coincidence with another signal photon at t + τ . Recent experiments suggest [19] that intrabeam correlations in SPDC can be measured when high-power cw beams are used to pump the nonlinear crystal. Then the intrabeam higher-order correlations show classical-like features similar to thermal light [20].…”

Generation of ideal thermal light in warm atomic vapor

“…A number of experimental teams have recently attempted to realize a thermal light source with large spectral bandwidth either as a principal resource or as a side result of attempts to engineer a nonlinear interaction with a high degree of mode purity [12,[25][26][27][28][29][30][31]. Out of these, the sources utilizing the process of amplified spontaneous emission [12,[29][30][31] seem to offer technically feasible spectral bandwidth in a few nanometer regime.…”

“…However, similarly to several characterizations of light statistics coming from blackbody light sources [32,33], the extreme spectral width practically hinders a direct confirmation of ideal thermal statistics with currently available singlephoton detectors. Typical examples of the limit imposed by the detection jitter being much larger than the coherence time of the detected light include attempts with sources of spontaneous parametric down-conversion with generated photon bandwidth at the order of many GHz [26]. Several promising techniques have been developed to circumvent the limited detection bandwidths for observation of the photon bunching on short time scales, including the schemes based on the two-photon absorption [29], or nonlinear sum frequency generation [11,34,35].…”