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Optics Letters

Time-resolved single-photon detection by femtosecond upconversion

Onur Kuzucu, Franco N. C. Wong, Sunao Kurimura, S. V. Tovstonog

Published Sep 26, 2008• 78 citations
Publisher

Abstract

We demonstrate a time-resolved single-photon detection technique based on ultrafast sum-frequency generation, providing femtosecond measurement capability for single photons in photonic quantum information processing. Noncollinear broadband upconversion in periodically poled MgO-doped stoichiometric lithium tantalate with an ultrafast pump and detection with a Si single-photon counter enable efficient detection of IR photons and temporal resolution of ~150 fs. We utilize the timing resolution to map the generation efficiency profile along the propagation axis of a periodically poled KTiOPO(4) crystal, revealing its local grating quality with millimeter resolution. We also apply the technique to two-photon coincidence measurements and directly demonstrate time anticorrelation between coincident-frequency entangled photons that are parametrically generated under extended phase-matching conditions.

DOI
10.1364/ol.33.002257

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We demonstrate a time-resolved single-photon detection technique based on ultrafast sum-frequency generation, providing femtosecond measurement capability for single photons in photonic quantum information processing. Noncollinear broadband upconversion in periodically poled MgO-doped stoichiometric lithium tantalate with an ultrafast pump and detection with a Si single-photon counter enable efficient detection of IR photons and temporal resolution of ~150 fs. We utilize the timing resolution to map the generation efficiency profile along the propagation axis of a periodically poled KTiOPO(4) crystal, revealing its local grating quality with millimeter resolution. We also apply the technique to two-photon coincidence measurements and directly demonstrate time anticorrelation between coincident-frequency entangled photons that are parametrically generated under extended phase-matching conditions.
In advancing ultrafast quantum communication and computing, it is crucial to develop precise time-resolved measurement techniques for single-photon pulses. However, the measurement of photonic qubits, especially time-bin qubits, is limited by the temporal resolution of single-photon detectors, typically around tens of picoseconds. In this study, we developed a pulse-pumped up-conversion single-photon detector (UCSPD) using periodically poled Mg-doped stoichiometric lithium tantalate (PPMg:SLT) crystals of varying lengths to optimize femtosecond up-conversion. We evaluated the UCSPD’s efficiency and temporal resolution using a convolution model that accounts for group delay in nonlinear crystals. Our results demonstrate that the model calculations enable the accurate prediction of the crystal length dependence of temporal resolution and up-conversion efficiency without fitting parameters. The UCSPD achieved 415 fs resolution and 10.1 \% efficiency with a 2 mm crystal, enabling successful characterization of time-bin qubits with 800 fs pulse intervals.
Ultrafast quantum optics with time-frequency entangled photons is at the forefront of progress towards future quantum technologies. However, to unravel the time domain structure of entangled photons and exploit fully their rich dimensionality, a single-photon detector with sub-picosecond temporal resolution is required. Here, we present ultrafast single-photon detection using an optical Kerr gate composed of a photonic crystal fiber (PCF) placed inside a Sagnac interferometer. A near-rectangle temporal waveform of a heralded single-photon generated via spontaneous parametric down-conversion is measured with temporal resolution as high as 224 ± 9 fs. The large nonlinearity and long effective interaction length of the PCF enables maximum detection efficiency to be achieved with only 30.5 mW gating pulse average power, demonstrating an order-of-magnitude improvement compared to optical gating with sum-frequency generation. Also, we discuss the trade-off relationship between detection efficiency and temporal resolution.
We demonstrate a technique for characterizing two-photon quantum states based on joint temporal correlation measurements using time-resolved single-photon detection by femtosecond up-conversion. We measure for the first time the joint temporal density of a two-photon entangled state, showing clearly the time anticorrelation of the coincident-frequency entangled photon pair generated by ultrafast spontaneous parametric down-conversion under extended phase-matching conditions. The new technique enables us to manipulate the frequency entanglement by varying the down-conversion pump bandwidth to produce a nearly unentangled two-photon state that is expected to yield a heralded single-photon state with a purity of 0.88. The time-domain correlation technique complements existing frequency-domain measurement methods for a more complete characterization of photonic entanglement.
Single-photon signals at 1.56 ¿m were converted into the visible region by sum-frequency generation, with synchronous pump pulses at 1.03 ¿m in a periodically poled lithium niobate crystal. The signal and pump sources were provided by two synchronized mode-locked fiber lasers at the operation rate of 7.88 MHz. Such a high-speed single-photon upconversion system has shown an overall detection efficiency of 10.4%. The corresponding background noise was measured to be 3.3 × 103s-1. The noise-equivalent power in this scheme was 9.93 × 10-17W/Hz1/2, which was the lowest compared to the other upconversion systems with similar pump and signal wavelengths.