Dressing control of biphoton waveform transitions

We experimentally realize and theoretically analyze narrow-band biphotons generated in a hot rubidium vapor cell by four-wave-mixing processing. A dressing laser beam is used to alternate both linear and nonlinear susceptibilities of the vapor, thereby modifying the biphoton's temporal correlation function. Most notably, the correlation time is increased from 6 to 165 ns. The biphoton shape is also shown to change as a result of the coupled-states dressing. We observed Rabi oscillations and optical precursors in hot atomic vapor cells. We also theoretically simulated biphoton correlation times as influenced by dressing-laser detuning and power, the results of which are consistent with our experiments.

Figure 1

(a) Alignment of spatial beams for biphoton-generation process. LD: external cavity diode lasers; PBS: polarization beam splitter, SPCM: single-photon counting module, SMF: single-mode fibers, FP: Fabry–Perot cavity. (b) Energy-level diagram for four-level configuration in ${}^{85}\mathrm{Rb}$ vapor.

Figure 2

Two-photon coincidence counts as a function of relative time delay $\tau$ between paired Stokes and anti-Stokes photons. The bin width is 0.0244 ns. (a) Biphoton generation at $\mathrm{OD}=0.7, P_{\mathrm{c}}=38\mathrm{mW}, P_{\mathrm{p}}=6\mathrm{mW}, {\mathrm{\Delta }}_{\mathrm{c}}=1\mathrm{GHz}$. (b) Biphoton generation at $\mathrm{OD}=0.7, P_{\mathrm{c}}=20\mathrm{mW}, P_{\mathrm{p}}=6\mathrm{mW}, {\mathrm{\Delta }}_{\mathrm{c}}=1\mathrm{GHz}$.

Figure 3

(a)–(c) Changes of biphoton waveform with dressing-field detuning ${\mathrm{\Delta }}_3$. Two-photon coincidence counts, collected over 400 s with 0.0244 ns bin width as a function of the relative time delay $\tau$ between paired Stokes and anti-Stokes photons. The dressing frequency detuning for panels (a)–(c) are 1.0, 0.5, and 0 GHz, respectively. The solid line is the theoretical curve. (d) Theoretically simulation of difference between ${\tau }_{\mathrm{g}}$ and ${\tau }_{\mathrm{e}}$ as a function of dressing detuning ${\mathrm{\Delta }}_3$.

Figure 4

(a) Two-photon coincidence counts as a function of relative time delay $\tau$ between paired Stokes and anti-Stokes photons collected over 1000 s with 0.0244 ns bin width. The dressing-field power is 4 mW, and the Rb temperature is $110{}^{\circ }\mathrm{C}$. The red line is the theoretical curve. (b1)–(b3) Theoretically simulated difference between ${\tau }_{\mathrm{g}}$ and ${\tau }_{\mathrm{e}}$ as a function of dressing Rabi frequency ${\mathrm{\Omega }}_3$.