Single-Photon Frequency Up-Conversion Detection And Its Quantum Feature

Efficient infrared photon counting probe is of great importance in variable practical applications, such as optical communications, optical time domain reflectometer, laser ranging, laser-guided techniques, quantum information, and so forth. Compared with the visible single-photon detectors based on Si-avalanch photodiodes (APDs), however, the current infrared photon counters based on InGaAs APDs are just passable, especially in quantum efficiency, working repetition rate and background noise. Single-photon frequency up-conversion technology provides an another solution to detect the infrared single-photons, which is the use of nonlinear optical method to convert the infrared signal photons into visible "mirror" photons. The original photon and the "mirror" photon would share the identical quantum feature. Thereby, Si-APDs with better performance can replace the InGaAs-APDs for the enhanced infrared single-photon counting. We focused on a series of key issues in frequency up-conversion detection, such as how to realize long-term stable conversion process, how to achieve unitary conversion efficiency, how to achieve precise frequency tuning, how to reduce the background noise, and so forth. A number of new methods were developed for upgrading the performance of the single-photon frequency converter, and some new quantum properties and mechanisms were investigated.Taking the advantage of the high-intensity and high-stability intracavity laser beam as the pump field, the efficient frequency up-conversion of the c-band single photon was achieved in bulk periodically poled lithium niobate (PPLN). The advanced method could give full play to the merits of solid-state lasers as stable and robust in single-photon frequency up-conversion system, so that the complex servo system was not necessary for sustaining the high pump intensity. In our experiments, the intensity of the SFG signal remained very stable in a few hours, where the standard deviation of the intensity fluctuation was measured to be only 2.2%.The mature technologies on the laser mode control could optimize the spatial mode and spectral line-width to improve the beam quality and the efficiency of the pump field. A unidirectional ring laser was built to improve the performance of the intracavity frequency up-conversion of 1.55μm single photons. So far the highest conversion efficiency of 96% was reported, which could maintain within a few hours. Because the mode hopping and the photorefractive effects were suppressed by the uniform-intensity pump field, the stability of the SFG signal was further improved.On the other hand, the flexible solid-state laser wavelength tuning technique allowed a high-precision real-time frequency control of pump field. Using an intracavity etalon, we demonstrated the wavelength-tunable single-photon frequency conversion process within the spectral bandwidth of the quasi-phase-matching interaction. The working condition and the tolerant parameter values were experimentally investigated in our frequency-tunable single-photon upconversion system.The efficient frequency up-conversion of the 1.06μm single photon with ultra-low background noise was successfully operated by using the Er-doped mode-locking fiber laser and amplifier as the pump source. The single-photon conversion efficiency was 93%, and the corresponding background noise was only 150 /s. We achieved so far the lowest noise equivalent power among the reported up-conversion detectors. Since the background noise was one of the most important factors which restricted the performance of the up-conversion detector, our research is of great significance to upgrade the up-conversion detection technology.In the end, the efficient single-photon frequency upconversion was demonstrated under strong multi-longitudinal-mode pump, where the incident single-photon state was converted to a superposition state according to the intensity distribution of the multi-mode pump field. This new phenomenon allowed us to manipulate the quantum state by having control on the classical laser beam, based on which we developed a simple non-destructive quantum state router model.