Ultraviolet single-photons on demand and entanglement of photons with a large frequency difference

We investigate an efficient scheme for generating ultraviolet single-photons $(\sim 300\mathrm{nm})$. The scheme combines the highly efficient single-photon four-wave mixing scheme and fast developing quantum dot single-photons on demand source technology. We show that near maximum, entanglement between two well matched ultraslowly propagating single-photon wave packets can be achieved. This study may lead to research and development opportunities in highly efficient entanglement schemes using photons of very large frequency difference, quantum information processing, and single-photon metrology and single-photon counting sensors in the uv spectra region.

Figure 1

A lifetime broadened four-level atomic system that interacts with two continuous wave (cw) classical laser fields (frequencies ${\omega }_B$ and ${\omega }_C$, and Rabi frequencies $2{\Omega }_B$ and $2{\Omega }_C$) and a quantized pump field of frequency ${\omega }_{QD}$ to generate a quantized four-wave-mixing field of frequency ${\omega }_F$.

Figure 2

The absorption coefficients $-\mathrm{Re}\left[{\beta }_{\pm }\right]$ versus the dimensionless control field ${\Omega }_B∕{\gamma }_2$. Parameters used are ${\gamma }_1\tau \simeq 2\pi \times 5.9\times {10}^6∕\mathrm{s}$, ${\gamma }_2\tau \simeq 2\pi \times 0.8\times {10}^6∕\mathrm{s}$, ${\gamma }_3\tau \simeq 2\pi \times 0.09\times {10}^6∕\mathrm{s}$, ${\Delta }_1={\Delta }_2=0$, ${\Delta }_3=2\pi \times 0.02\times {10}^6∕\mathrm{s}$, ${\kappa }_{01}=2\times {10}^9∕\left(\mathrm{s}\mathrm{cm}\right)$, ${\kappa }_{03}=2\times {10}^7∕\left(\mathrm{s}\mathrm{cm}\right)$, and ${\Omega }_C$ relates to ${\Omega }_B$ by the expression ${\kappa }_{01}\mid D_{03}{\Omega }_B\mid ={\kappa }_{03}\mid D_{01}{\Omega }_C\mid$ (for maximum entanglement, we assume $3{\omega }_{QD}\sim {\omega }_F$).