Kenji Tsujino

Multipixel silicon avalanche photodiode with ultralow dark count rate at liquid nitrogen temperature

Multipixel silicon avalanche photodiodes (Si APDs) are novel photodetectors used as silicon photomultipliers (SiPMs), or multipixel photon counter (MPPC), because they have fast response, photon-number resolution, and a high count rate; one drawback, however, is the high dark count rate. We developed a system for cooling an MPPC to liquid nitrogen temperature and thus reduce the dark count rate. Our system achieved dark count rates of <0.2 cps. Here we present the afterpulse probability, counting capability, timing jitter, and photon-number resolution of our system at 78.5 K and 295 K.

Sub-shot-noise-limit discrimination of on-off keyed coherent signals via a quantum receiver with a superconducting transition edge sensor.

We demonstrate a sub-shot-noise-limit discrimination of on-off keyed coherent signals by an optimal displacement quantum receiver in which a superconducting transition edge sensor is installed. Use of a transition edge sensor and a fiber beam splitter realizes high total detection efficiency and high interference visibility of the receiver and the observed average error surpasses the shot-noise-limit in a wider range of the signal power. Our technique opens up a new technology for the sub-shot-noise-limit detection of coherent signals in optical communication channels.

Ultrahigh-sensitivity single-photon detection with linear-mode silicon avalanche photodiode

We developed an ultrahigh-sensitivity single-photon detector using a linear-mode avalanche photodiode (APD) with a cryogenic low-noise readout circuit; the APD is operated at 78K. The noise-equivalent power of the detector is as low as 2.2x10(-20)W/Hz(1/2) at a wavelength of 450nm. The photon-detection efficiency and dark-count rate (DCR) are 0.72 and 0.0008counts/s, respectively. A low DCR is achieved by thermal treatment for reducing the trapped carriers when the thermal treatment temperature is above 100K.

Ultralow-noise readout circuit with an avalanche photodiode: toward a photon-number-resolving detector

The charge-integration readout circuit was fabricated to achieve an ultralow-noise preamplifier for photoelectrons generated in an avalanche photodiode with linear mode operation at 77 K. To reduce the various kinds of noise, the capacitive transimpedance amplifier was used and consisted of low-capacitance circuit elements that were cooled with liquid nitrogen. As a result, the readout noise is equal to 3.0 electrons averaged for a period of 40 ms. We discuss the requirements for avalanche photodiodes to achieve photon-number-resolving detectors below this noise level.

Experimental Determination of the Gain Distribution of an Avalanche Photodiode at Low Gains

A measurement system for determining the gain distributions of avalanche photodiodes (APDs) in a low gain range is presented. The system is based on an ultralow-noise charge-sensitive amplifier and detects the output carriers from an APD. The noise of the charge-sensitive amplifier is as low as 4.2 electrons at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with low average gains is presented, demonstrating the McIntyre theory in the low gain range.

Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode

We report on visible light single photon detection using a sinusoidally-gated silicon avalanche photodiode. Detection efficiency of 70.6% was achieved at a wavelength of 520 nm when an electrically cooled silicon avalanche photodiode with a quantum efficiency of 72.4% was used, which implies that a photo-excited single charge carrier in a silicon avalanche photodiode can trigger a detectable avalanche (charge) signal with a probability of 97.6%.

A charge-integration readout circuit with a linear-mode silicon avalanche photodiode for a photon-number resolving detector

A charge-integration readout circuit for a photon-number resolving detector for visible or near-infrared wavelength is presented. In the scheme, photons are converted into electric carriers by a Si APD operating in the linear mode. To read the small number of photo-carriers generated by the Si APD, a charge-integration readout circuit is used. The entire circuit operates at 77 K. The main noise of the readout circuit is attributed to dielectric polarization noise, which is dominant at the operating temperature. The noise of the readout circuit was reduced to 3.0 electrons averaged by a period of 40 ms.

Measurement system for acquiring gain distribution of avalanche photodiodes at low gains

A measurement system is described for acquiring the gain distributions of avalanche photodiodes (APDs) in a range of low average gain. The system is based on an ultralow-noise capacitive transimpedance amplifier to readout the charges generated in an APD. The low noise level of the readout circuit about 7 electrons at the sampling rate of 200 Hz enables us to characterize the gain distributions. The gain distribution of a commercial silicon (Si) APD measured at gain of 3.29 using this system is presented.

Cut-off rate analysis of practical quantum receivers

Quantum communication with binary nonorthogonal pure states and single-shot measurements are discussed in terms of reliability function and cut-off rate. It is shown that some of different measurement strategies simultaneously attain the maximum single-shot cut-off rate. We also apply these measurements to the BPSK optical coherent states and compare them with the homodyne detection. Numerical results show that even including realistic imperfections, it is possible to exceed the homodyne limited cut-off rate.

Near‐optimal quantum receivers for the coherent state discrimination

We propose practical near‐optimal quantum receivers for the binary phase shift keyed coherent signals to overcome the homodyne limit in all areas of the signal power. Our schemes consist of Gaussian operations and photon detection and do not require realtime electrical feedback. We numerically show that the scheme is feasible with the current technology.