arXiv subjects

Mikio Fujiwara

Publications and source records attributed to Mikio Fujiwara.

63 records · Page 4Linked to original sources

arXiv2010

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.

quant-ph↗

arXiv2009

Updating Quantum Cryptography Report ver. 1

Quantum cryptographic technology (QCT) is expected to be a fundamental technology for realizing long-term information security even against as-yet-unknown future technologies. More advanced security could be achieved using QCT together with contemporary cryptographic technologies. To develop and spread the use of QCT, it is necessary to standardize devices, protocols, and security requirements and thus enable interoperability in a multi-vendor, multi-network, and multi-service environment. This report is a technical summary of QCT and related topics from the viewpoints of 1) consensual establishment of specifications and requirements of QCT for standardization and commercialization and 2) the promotion of research and design to realize New-Generation Quantum Cryptography.

quant-ph↗

arXiv2008

Ultra fast quantum key distribution over a 97 km installed telecom fiber with wavelength-division multiplexing clock synchronization

We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78-0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.

quant-ph↗

arXiv2007

The Far-Infrared Surveyor (FIS) for AKARI

The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcmin, and the pixel pitch is matches the diffraction limit of the telescope. Derived point spread functions (PSFs) from observations of asteroids are similar to the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and its performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.

astro-ph↗

arXiv2005

Photon number resolving detection at telecom wavelength with a charge integration photon detector

We demonstrate multiphoton discrimination at telecom wavelength with the readout frequency of 40 Hz by charge integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a pre-amplifier in a charge integration circuit, which is cooled to 4.2 K to reduce thermal noise. The quantum efficiency of the CIPD (detector itself) is 80% for 1530 nm light, and the readout noise is measured as 0.26 electrons at 40 Hz. We can construct Poisson distributions of photo-carriers with distinguished peaks at each photo-carrier number corresponding to the signal to noise ratio of about 3.

quant-ph↗

arXiv2005

Multiphoton discrimination at telecom wavelength with charge integration photon detector

We present a charge integration photon detector (CIPD) that enables the efficient measurement of photon number states at the telecom-fiber wavelengths with a quantum efficiency of 80% and a resolution less than 0.5 electrons at 1 Hz sampling. The CIPD consists of an InGaAs PIN photodiode and a GaAs JFET in a charge integration amplifier, which is cooled to 4.2 K to reduce thermal noise and leakage current. The charge integration amplifier exhibits a low noise level of 470 nV/Hz1/2. The dark count is as low as 500 electrons/hour.

quant-ph↗

arXiv2005

Ultrahigh-sensitivity high-linearity photodetection system using a low-gain avalanche photodiode with an ultralow-noise readout circuit

A highly sensitive photodetection system with a detection limit of 1 photon/s was developed. This system uses a commercially available 200-mm-diameter silicon avalanche photodiode (APD) and an in-house-developed ultralow-noise readout circuit, which are both cooled to 77 K. When the APD operates at a low gain of about 10, it has a high-linearity response to the number of incident photons and a low excess noise factor. The APD also has high quantum efficiency and a dark current of less than 1 e/s at 77 K. This photodetection system will shorten the measurement time and enable higher spatial and wavelength resolution for near-field scanning optical microscopes.

quant-ph↗

arXiv2003

Exceeding classical capacity limit in quantum optical channel

The amount of information transmissible through a communications channel is determined by the noise characteristics of the channel and by the quantities of available transmission resources. In classical information theory, the amount of transmissible information can be increased twice at most when the transmission resource (e.g. the code length, the bandwidth, the signal power) is doubled for fixed noise characteristics. In quantum information theory, however, the amount of information transmitted can increase even more than twice. We present a proof-of-principle demonstration of this super-additivity of classical capacity of a quantum channel by using the ternary symmetric states of a single photon, and by event selection from a weak coherent light source. We also show how the super-additive coding gain, even in a small code length, can boost the communication performance of conventional coding technique.

quant-ph↗

arXiv2001

Optimum detection for extracting maximum information from symmetric qubit sets

We demonstrate a class of optimum detection strategies for extracting the maximum information from sets of equiprobable real symmetric qubit states of a single photon. These optimum strategies have been predicted by Sasaki et al. [Phys. Rev. A{\bf 59}, 3325 (1999)]. The peculiar aspect is that the detections with at least three outputs suffice for optimum extraction of information regardless of the number of signal elements. The cases of ternary (or trine), quinary, and septenary polarization signals are studied where a standard von Neumann detection (a projection onto a binary orthogonal basis) fails to access the maximum information. Our experiments demonstrate that it is possible with present technologies to attain about 96% of the theoretical limit.

quant-ph↗