Efficient Photon Number Detection

Edo Waks A, Kyo Inoue, William D. Oliver +2 more

The visible light photon counter (VLPC) features high quantum efficiency (QE) and low pulse height dispersion. These properties make it ideal for efficient photon-number state detection. The ability to perform efficient photon-number state detection is important in many quantum information processing applications, including recent proposals for performing quantum computation with linear optical elements. In this paper, we investigate the unique capabilities of the VLPC. The efficiency of the detector and cryogenic system is measured at 543 nm wavelengths to be 85%. A picosecond pulsed laser is then used to excite the detector with pulses having average photon numbers ranging from 3-5. The output of the VLPC is used to discriminate photon numbers in a pulse. The error probability for number state discrimination is an increasing function of the number of photons, due to buildup of multiplication noise. This puts an ultimate limit on the ability of the VLPC to do number state detection. For many applications, it is sufficient to discriminate between 1 and more than one detected photon. The VLPC can do this with 99% accuracy.

HERBERT WALTHER

Neil J. Savage

M. J. Applegate, O. Thomas, J. F. Dynes +3 more

We present an efficient and robust quantum random number generator based upon high-rate room temperature photon number detection. We employ an electric field-modulated silicon avalanche photodiode, a type of device particularly suited to high-rate photon number detection with excellent photon number resolution to detect, without an applied dead-time, up to 4 photons from the optical pulses emitted by a laser. By both measuring and modeling the response of the detector to the incident photons, we are able to determine the illumination conditions that achieve an optimal bit rate that we show is robust against variation in the photon flux. We extract random bits from the detected photon numbers with an efficiency of 99% corresponding to 1.97 bits per detected photon number yielding a bit rate of 143 Mbit/s, and verify that the extracted bits pass stringent statistical tests for randomness. Our scheme is highly scalable and has the potential of multi-Gbit/s bit rates.

Kae Nemoto, S. Braunstein

A simulated photon-number detection via homodyne detectors is considered as a way to improve the efficiency near the single-photon level of communication. Current photon-number detectors at infrared wavelengths are typically characterized by their low detection efficiencies, which significantly reduce the mutual information of a bosonic communication channel. In order to avoid the inefficiency inherent in such direct photon-number detection, we evaluate an alternative set-up based on efficient dual homodyne detection. We show that replacing inefficient direct detectors with homodyne-based simulated direct detectors can yield significant improvements, even near the single-photon level of operation. However we argue that there is a fundamental limit on the ability of homodyne detection to simulate ideal photon number detection, considering the exponential gap between quantum and classical computers. This applies to arbitrarily complicated simulation strategies based on homodyne detection.

Yan Liang, Heping Zeng