Shaping Biphoton Temporal Waveforms with Modulated Classical Fields

We experimentally demonstrate a technique for shaping the temporal quantum waveform of narrow-band biphotons generated in a cold atomic ensemble via four-wave mixing by periodically modulating the two input classical lasers. We show that it is possible to generate nonclassical paired photons with a predesigned shape of the correlation function.

Figure 1

Schematic of biphoton generation with modulated driving-laser fields. (a) Experimental configuration. (b) ${}^{85}\mathrm{Rb}$ double-$\Lambda$ energy level diagram for multichannel biphoton generation.

Figure 2

Two-photon coincidence counts per 1 ns bin for 120 s as a function of the relative time delay $\tau$. In (1), The pump and coupling lasers are in the cw mode. In (2) and (3), both pump and coupling lasers are periodically modulated with the same square wave at a frequency of 5 and 10 MHz, respectively.

Figure 3

(a) The 2D two-photon correlation function $R(t_s,t_{\mathrm{as}})$ with 10 MHz square amplitude modulation on both pump and coupling lasers. (b), (c), and (d) are cross-section views (averaged over 5 bins) along the yellow dashed straight lines (1), (2), and (3) in (a), respectively. The red dashed lines in (b) and (c) are the correlation envelope $R_0(t_{\mathrm{as}}-t_s)$ without modulation. The data were collected over 20 min with 1 ns bin width.

Figure 4

Two-photon coincidence counts per 1 ns bin for 120 s as a function of the relative time delay $\tau$. In (1), The pump and coupling lasers are in the cw mode. In (2) both pump and coupling lasers are modulated with the same sine wave at a frequency of 5 MHz.

Figure 5

The proof-of-principle demonstration for generating arbitrary two-photon correlation function with nonidentical modulations on the pump and coupling lasers. The solid line is the targeted waveform. The data (circular points) was collected over 10 min with 2 ns bin width.