Ultrabright backward-wave biphoton source

We calculate the properties of a biphoton source based on resonant backward-wave spontaneous parametric down conversion. We show that the biphotons are generated in a single longitudinal mode having a subnatural linewidth and a Glauber correlation time exceeding 65 ns.

Figure 1

(a) Schematic of backward-wave spontaneous parametric down conversion (SPDC). The operators $a_s$ and $a_i$ denote the signal and idler fields. (b) Schematic of backward-wave SPDC within a resonant cavity. The operators $a_{s,i}^{\mathrm{in}}$ and $a_{s,i}^{\mathrm{out}}$ denote the incident fields and output fields, respectively.

Figure 2

The solid (dashed) curve represents the spectral power density of the backward- (forward-) wave spontaneous parametric down conversion at the signal frequency. The vertical (red) lines denote the signal frequencies of adjacent mode pairs of a resonant cavity that are separated by the cluster spacing $\Delta {\Omega }_{\mathrm{Cl}}$. The central vertical line is taken at the degenerate frequency.

Figure 3

(a) Time domain biphoton wave packet of the backward-wave spontaneous down conversion within a resonant cavity. Although difficult to see, this curve is slightly asymmetric [see Eq. (12)]. (b) Spectral power density at the signal frequency.