Visible-to-telecom quantum frequency conversion of light from a single quantum emitter.

We demonstrate efficient (>30%) quantum frequency conversion of visible single photons (711 nm) emitted by a quantum dot to a telecom wavelength (1313 nm). Analysis of the first- and second-order coherence before and after wavelength conversion clearly proves that pivotal properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with quantum frequency conversion as a promising technique that may pave the way for a number of new applications in quantum technology.

Lock-in detection of single photons after two-step frequency conversion.

We report on cascaded frequency conversion at the single-photon level, consisting of a downconversion from the red (738 nm) to a telecom band (1403 nm) and the reverse upconversion process in the same nonlinear crystal. Detecting the converted single photons suffers from a large noise floor. We were able to recover the signal by implementing a lock-in analyzer technique in the data postprocessing.

Efficient frequency downconversion at the single photon level from the red spectral range to the telecommunications C-band.

We report on single photon frequency downconversion from the red part of the spectrum (738 nm) to the telecommunications C-band. By mixing attenuated laser pulses with an average photon number per pulse < 1 with a strong continuous light field at 1403 nm in a periodically poled Zn:LiNbO3 ridge waveguide an internal conversion efficiency of ∼ 73% is achieved. We further investigate the noise properties of the process by measuring the output spectrum.