Generation of Narrow-Bandwidth Paired Photons: Use of a Single Driving Laser

We describe a generator of narrow-band paired photons. A single retroreflected Ti:sapphire laser is used to cool, render transparent, and parametrically pump a cloud of ${}^{87}\mathrm{Rb}$ atoms. We attain a paired-photon generation rate into opposing fibers of $600\mathrm{\text{counts}}/\mathrm{s}$ with an intensity correlation function that has a width of 5 ns, and violates the Cauchy-Schwartz criteria by a factor of 2000.

Figure 1

(a) Energy level diagram. (b) Schematic for paired-photon generation. In the presence of a strong, linear polarized, retroreflected pump beam, Stokes and anti-Stokes photons are generated into opposing single mode fibers. The fibers are aligned at right angles to the direction of the pump beam. (c) The photon generation window of $500\mu \mathrm{s}$ is followed by a trapping and cooling period of 4.5 ms. (d) The Ti:sapphire laser is up-shifted to trap and cool atoms and down-shifted to serve as a pump for the paired-photon generation process.

Figure 2

(a) Anti-Stokes transmission vs the detuning from the $|1⟩\to |3⟩$ transition in the presence of the pump (coupling) laser, (b) non-normalized intensity correlation function $G^{(2)}(t_1-t_2)$. The transmission and $G^{(2)}(t_1-t_2)$ are calculated for two cases: (1) there is no interference; ${\Omega }_c=80{\gamma }_{13}$ and ${\Omega }_p=140{\gamma }_{13}$ (dashed curves). (2) There is interference; ${\Omega }_{c0}=80{\gamma }_{13}$ and ${\Omega }_{p0}=140{\gamma }_{13}$ (solid curves).

Figure 3

Coincidence count rate as a function of the delay between detected photons. (a) Pump $\mathrm{\text{power}}=160\mathrm{mW}$; ${\Omega }_{c0}=80{\gamma }_{13}$ and ${\Omega }_{p0}=140{\gamma }_{13}$. (b) Pump $\mathrm{\text{power}}=40\mathrm{mW}$; ${\Omega }_{c0}=40{\gamma }_{13}$ and ${\Omega }_{p0}=70{\gamma }_{13}$. The pump is tuned to resonance with the $|2⟩\to |3⟩$ transition. Data (⋄) were collected over 200 s. Theoretical curves (solid lines) are scaled vertically by a common factor and are averaged over a 1 ns bin.

Figure 4

Coincidence count rate as a function of the delay between detected photons. (a) Pump $\mathrm{\text{power}}=80\mathrm{mW}$; ${\Omega }_{c0}=56{\gamma }_{13}$ and ${\Omega }_{p0}=100{\gamma }_{13}$. (b) Pump $\mathrm{\text{power}}=20\mathrm{mW}$; ${\Omega }_{c0}=28{\gamma }_{13}$ and ${\Omega }_{p0}=50{\gamma }_{13}$. The pump is tuned 73 MHz above the $|2⟩\to |3⟩$ transition. Data (⋄) were collected over 400 s. Theoretical curves (solid lines) are scaled vertically and are averaged over a 1 ns bin.

Figure 5

(a) Energy level diagram and (b) schematic of the experiment for paired-photon generation in a two-state system. Paired photons are collected at 2° from the direction of the pump beam.

Figure 6

Coincidence count rate as a function of the delay between detected photons for paired-photon generation in a two-state system. The experimental data points (⋄) are connected by straight lines. The data are taken with a pump power of $770\mu \mathrm{W}$, a detuning of 83 MHz, and a run time of 200 s.