A. Tomita - Academia.edu (original) (raw)

Papers by A. Tomita

Advanced Photon Counting Techniques VI, 2012

ABSTRACT We present the latest results on two kinds of photon detectors: single photon detectors ... more ABSTRACT We present the latest results on two kinds of photon detectors: single photon detectors (SPDs) and photon number resolving detector (PNRD). We developed high speed and low noise SPDs using superconducting nano-wire (abbreviated by SNSPD) and semiconductor (InGaAs) avalanche photodiode (APD). The SNSPD system has totally four channels all of which have the detection eciency higher than 16% at 100Hz dark count rate. The InGaAs APD system also has four channels and the best performance is represented by the after-pulse probability of 0.61%, the dark count probability of 0.71×10-6 (~1kHz), and the detection eciency of 10.9%. Both systems were applied to wavelength division multiplexing quantum key distribution (WDM-QKD) operated at 1.2GHz repetition rate in a eld environment. The PNRD is made of superconducting transition edge sensor. It was applied to the implementation of quantum receiver which could beat the homodyne limit of the bit error rate of binary coherent states. We discuss future perspective of quantum communications with those photon detection technologies, including multi-user QKD networks and low-power high capacity communications.

OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference, 2008

The world's fastest BB84 QKD through a 97-km installed fiber was demonstrated using P... more The world's fastest BB84 QKD through a 97-km installed fiber was demonstrated using PLC-based interferometers, SSPDs and WDM synchronization. By suppressing nonlinear crosstalk induced by the multiplexed clock, QBER of 2.8% was obtained after 97-km transmission.

Optical and Quantum Electronics, 1987

Applied Physics Letters, 2009

37th European Conference and Exposition on Optical Communications, 2011

ABSTRACT A scalable full QKD system using WDM and key distillation HW engine was developed. The t... more ABSTRACT A scalable full QKD system using WDM and key distillation HW engine was developed. The three-channel multiplexed system achieved the world summit level key generation rate of higher than 200 kbps with 14.5-dB transmission loss.

Quantum Optics in Computing and Communications, 2002

WDM signals can be transmitted through a spatial mode division system with a multi-mode fiber and... more WDM signals can be transmitted through a spatial mode division system with a multi-mode fiber and a volume holographic demultiplexer. Separation-angle for 100 channels of WDM signal can be suppressed two degrees on the demultiplexer.

Optics Letters, 2012

A high-speed quantum key distribution system was developed with the wavelength-division multiplex... more A high-speed quantum key distribution system was developed with the wavelength-division multiplexing (WDM) technique and dedicated key distillation hardware engines. Two interferometers for encoding and decoding are shared over eight wavelengths to reduce the system's size, cost, and control complexity. The key distillation engines can process a huge amount of data from the WDM channels by using a 1 Mbit block in real time. We demonstrated a three-channel WDM system that simultaneously uses avalanche photodiodes and superconducting single-photon detectors. We achieved 12 h continuous key generation with a secure key rate of 208 kilobits per second through a 45 km field fiber with 14.5 dB loss.

Optics and Spectroscopy, 2005

Among a number of candidates, photons have advantages for implementing qubits: very weak coupling... more Among a number of candidates, photons have advantages for implementing qubits: very weak coupling to the environment, the existing single photon measurement technique, and so on. Moreover, commercially available fiber-optic devices enable us to construct quantum circuits that consist of one-qubit operations (including classically controlled gates). Fiber optics resolves the mode matching problems in conventional optics and provides mechanically stable optical circuits. A quantum Fourier transform (QFT) followed by measurement was demonstrated with a simple circuit based on fiber optics. The circuit was shown to be robust against imperfections in the rotation gate. The error probability was estimated to be 0.01 per qubit, which corresponded to error-free operation for 100 qubits. The error probability can be further reduced to achieve successful QFT of 1024 qubits by taking the majority of the accumulated results. As is well known, QFT is a key function in quantum computations such as the final part of Shor’s factorization algorithm. The present QFT circuit, in combination with controlled unitary gates, would make possible practical quantum computers. Possible schemes of realizing quantum computers in this line are explored.

Journal of Modern Optics, 2006

ABSTRACT It was shown by Riedmatten et al. [J. Mod. Opt. 51 1637 (2004)] that two different four-... more ABSTRACT It was shown by Riedmatten et al. [J. Mod. Opt. 51 1637 (2004)] that two different four-photon states could be generated according to the relation between the duration time of the pump laser T and the coherence time t of the single photon from spontaneous parametric down-conversion (SPDC). In this paper, using four photons generated by the SPDC in a Periodically Poled Potassium Titanyl Phosphate (PPKTP), we experimentally observe the four-photon interference in a Michelson interferometer. All experimental results can be explained by the product of two independent two-photon interferences. Our experimental condition corresponds to the case of T t. This experiment clearly confirms the theory given by Riedmatten et al.

Journal of Applied Physics, 1986

ABSTRACT

Journal of Applied Physics, 1995

A simple model has shown that the ratio of carrier transit time to carrier capture time determine... more A simple model has shown that the ratio of carrier transit time to carrier capture time determines the transport properties in multiple quantum well structures. An analysis of carrier transport in the wave picture shows that the transit time is increased by the carrier reflection at the quantum well interface. The carrier reflection thus enhances the hole localization in multiple quantum well structures. Step barrier structures are proposed as antireflection layers to the quantum well interfaces. An optimally designed step barrier structure increases the hole transmittance from 57% to 92% in the lattice-matched InGaAs/InP interface. The transit time per well is also reduced from 0.88 to 0.28 ps, which correspond to the threshold current density of 650 and 430 A/cm2 for a four quantum well laser active layer.

International Journal of Quantum Information, 2004

Quantum Fourier transform (QFT) is a key function to realize quantum computers. A QFT followed by... more Quantum Fourier transform (QFT) is a key function to realize quantum computers. A QFT followed by measurement was demonstrated on a simple circuit based on fiber-optics. The QFT was shown to be robust against imperfections in the rotation gate. Error probability was estimated to be 0.01 per qubit, which corresponded to error-free operation on 100 qubits. The error probability can be further reduced by taking the majority of the accumulated results. The reduction of error probability resulted in a successful QFT demonstration on 1024 qubits.

Advanced Photon Counting Techniques VI, 2012

ABSTRACT We present the latest results on two kinds of photon detectors: single photon detectors ... more ABSTRACT We present the latest results on two kinds of photon detectors: single photon detectors (SPDs) and photon number resolving detector (PNRD). We developed high speed and low noise SPDs using superconducting nano-wire (abbreviated by SNSPD) and semiconductor (InGaAs) avalanche photodiode (APD). The SNSPD system has totally four channels all of which have the detection eciency higher than 16% at 100Hz dark count rate. The InGaAs APD system also has four channels and the best performance is represented by the after-pulse probability of 0.61%, the dark count probability of 0.71×10-6 (~1kHz), and the detection eciency of 10.9%. Both systems were applied to wavelength division multiplexing quantum key distribution (WDM-QKD) operated at 1.2GHz repetition rate in a eld environment. The PNRD is made of superconducting transition edge sensor. It was applied to the implementation of quantum receiver which could beat the homodyne limit of the bit error rate of binary coherent states. We discuss future perspective of quantum communications with those photon detection technologies, including multi-user QKD networks and low-power high capacity communications.

OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference, 2008

The world's fastest BB84 QKD through a 97-km installed fiber was demonstrated using P... more The world's fastest BB84 QKD through a 97-km installed fiber was demonstrated using PLC-based interferometers, SSPDs and WDM synchronization. By suppressing nonlinear crosstalk induced by the multiplexed clock, QBER of 2.8% was obtained after 97-km transmission.

Optical and Quantum Electronics, 1987

Applied Physics Letters, 2009

37th European Conference and Exposition on Optical Communications, 2011

ABSTRACT A scalable full QKD system using WDM and key distillation HW engine was developed. The t... more ABSTRACT A scalable full QKD system using WDM and key distillation HW engine was developed. The three-channel multiplexed system achieved the world summit level key generation rate of higher than 200 kbps with 14.5-dB transmission loss.

Quantum Optics in Computing and Communications, 2002

WDM signals can be transmitted through a spatial mode division system with a multi-mode fiber and... more WDM signals can be transmitted through a spatial mode division system with a multi-mode fiber and a volume holographic demultiplexer. Separation-angle for 100 channels of WDM signal can be suppressed two degrees on the demultiplexer.

Optics Letters, 2012

A high-speed quantum key distribution system was developed with the wavelength-division multiplex... more A high-speed quantum key distribution system was developed with the wavelength-division multiplexing (WDM) technique and dedicated key distillation hardware engines. Two interferometers for encoding and decoding are shared over eight wavelengths to reduce the system's size, cost, and control complexity. The key distillation engines can process a huge amount of data from the WDM channels by using a 1 Mbit block in real time. We demonstrated a three-channel WDM system that simultaneously uses avalanche photodiodes and superconducting single-photon detectors. We achieved 12 h continuous key generation with a secure key rate of 208 kilobits per second through a 45 km field fiber with 14.5 dB loss.

Optics and Spectroscopy, 2005

Among a number of candidates, photons have advantages for implementing qubits: very weak coupling... more Among a number of candidates, photons have advantages for implementing qubits: very weak coupling to the environment, the existing single photon measurement technique, and so on. Moreover, commercially available fiber-optic devices enable us to construct quantum circuits that consist of one-qubit operations (including classically controlled gates). Fiber optics resolves the mode matching problems in conventional optics and provides mechanically stable optical circuits. A quantum Fourier transform (QFT) followed by measurement was demonstrated with a simple circuit based on fiber optics. The circuit was shown to be robust against imperfections in the rotation gate. The error probability was estimated to be 0.01 per qubit, which corresponded to error-free operation for 100 qubits. The error probability can be further reduced to achieve successful QFT of 1024 qubits by taking the majority of the accumulated results. As is well known, QFT is a key function in quantum computations such as the final part of Shor’s factorization algorithm. The present QFT circuit, in combination with controlled unitary gates, would make possible practical quantum computers. Possible schemes of realizing quantum computers in this line are explored.

Journal of Modern Optics, 2006

ABSTRACT It was shown by Riedmatten et al. [J. Mod. Opt. 51 1637 (2004)] that two different four-... more ABSTRACT It was shown by Riedmatten et al. [J. Mod. Opt. 51 1637 (2004)] that two different four-photon states could be generated according to the relation between the duration time of the pump laser T and the coherence time t of the single photon from spontaneous parametric down-conversion (SPDC). In this paper, using four photons generated by the SPDC in a Periodically Poled Potassium Titanyl Phosphate (PPKTP), we experimentally observe the four-photon interference in a Michelson interferometer. All experimental results can be explained by the product of two independent two-photon interferences. Our experimental condition corresponds to the case of T t. This experiment clearly confirms the theory given by Riedmatten et al.

Journal of Applied Physics, 1986

ABSTRACT

Journal of Applied Physics, 1995

A simple model has shown that the ratio of carrier transit time to carrier capture time determine... more A simple model has shown that the ratio of carrier transit time to carrier capture time determines the transport properties in multiple quantum well structures. An analysis of carrier transport in the wave picture shows that the transit time is increased by the carrier reflection at the quantum well interface. The carrier reflection thus enhances the hole localization in multiple quantum well structures. Step barrier structures are proposed as antireflection layers to the quantum well interfaces. An optimally designed step barrier structure increases the hole transmittance from 57% to 92% in the lattice-matched InGaAs/InP interface. The transit time per well is also reduced from 0.88 to 0.28 ps, which correspond to the threshold current density of 650 and 430 A/cm2 for a four quantum well laser active layer.

International Journal of Quantum Information, 2004

Quantum Fourier transform (QFT) is a key function to realize quantum computers. A QFT followed by... more Quantum Fourier transform (QFT) is a key function to realize quantum computers. A QFT followed by measurement was demonstrated on a simple circuit based on fiber-optics. The QFT was shown to be robust against imperfections in the rotation gate. Error probability was estimated to be 0.01 per qubit, which corresponded to error-free operation on 100 qubits. The error probability can be further reduced by taking the majority of the accumulated results. The reduction of error probability resulted in a successful QFT demonstration on 1024 qubits.