Fast time-domain measurements on telecom single photons

Abstract

Abstract. Direct measurements on the temporal envelope of quantum light are a challenging task and not many examples are known since most classical pulse characterisation methods do not work on the single photon level. Knowledge of both spectrum and timing can however give insights on properties that cannot be determined by the spectrum alone. While temporal measurements on single photons on timescales of tens of picoseconds are possible with superconducting photon detectors and picosecond measurements have been performed using streak cameras, there are no commercial single photon sensitive devices with femtosecond resolution available. While time-domain sampling using sumfrequency generation has been already exploited for such measurement, inefficient conversion has necessitated long integration times to build the temporal profile. We demonstrate a highly efficient waveguided sum-frequency generation process in Lithium Niobate to measure the temporal envelope of single photons with femtosecond resolution with short enough acquisition time to provide a live-view of the measurement. We demonstrate the measurement technique and combine it with spectral measurements using a dispersive fiber time-of-flight spectrometer to determine upper and lower bounds for the spectral purity of heralded single photons. The approach complements the joint spectral intensity measurements as a measure on the purity can be given without knowledge of the spectral phase.arXiv:1702.03240v1 [quant-ph]

Direct Characterization of Ultrafast Energy-Time Entangled Photon Pairs

“…The gating is achieved by combining the signal with a short gate pulse in a nonlinear medium and measuring the upconversion signal on the detector. With fast gates and slow detectors, an effective fast de- tector can be engineered to temporally resolve single photons [31,32] and photon pairs [20]. In this work, we develop fast optical gating to achieve subpicosecond timing resolution for spatially separated pairs of single photons.…”

Ultrafast quantum interferometry with energy-time entangled photons

“…In this work, we temporally resolve two-photon interference with subpicosecond timing resolution. The detectors are implemented by optically gating the photons in a nonlinear medium via noncollinear sum-frequency generation (SFG) with a short gate pulse [16,[18][19][20]. Using this technique and single-photon spectrometers, we measure both the joint temporal and joint spectral features of a spatially separated two-photon state at the output of a Franson interferometer.…”

“…However, quantum interferometry with these states is challenging as the interference time scales are below the resolution of standard photon detectors [14,15]. To overcome detector limitations, optical techniques have been developed to directly observe energy-time entangled quantum states on ultrafast time scales [16,17] by building effective fast photon counters using ultrafast optical gating in conjunction with standard photon counters [18][19][20]. Extending the measurement of quantum interference to subpicosecond time scales will be essential for developing new applications with ultrafast energy-time states of light.…”

Universal compressive tomography in the time-frequency domain

“…States with temporal features much faster than the resolution of the single-photon detector are reconstructed, by modulating the input signal with random temporal masks. In addition, the use of compressed sensing facilitates signal reconstruction with fewer measurements than a direct sampling approach [58]. This is especially beneficial in situations in which a signal must be reconstructed from a limited number of photons.…”