A5017444546- Quantum Information and Cryptography
- Quantum Computing Algorithms and Architecture
- Quantum Mechanics and Applications
- Quantum optics and atomic interactions
- Optical Network Technologies
- Advanced Fiber Laser Technologies
- Laser-Matter Interactions and Applications
- Photonic and Optical Devices
- Mechanical and Optical Resonators
- Neural Networks and Reservoir Computing
- Orbital Angular Momentum in Optics
- Cold Atom Physics and Bose-Einstein Condensates
- Photonic Crystal and Fiber Optics
- Advanced Photonic Communication Systems
- Semiconductor Lasers and Optical Devices
- Atomic and Subatomic Physics Research
- Optical Wireless Communication Technologies
- Advanced Optical Sensing Technologies
- Quantum and electron transport phenomena
- Photorefractive and Nonlinear Optics
- Wireless Communication Security Techniques
- Chaos-based Image/Signal Encryption
- Nonlinear Dynamics and Pattern Formation
- Laser Design and Applications
- Diamond and Carbon-based Materials Research
Keio University
2001-2025
National Institute of Information and Communications Technology
2016-2025
National Institute on Consumer Education
2005-2015
RTX (United States)
2013-2014
University of Sussex
2011
Japan Science and Technology Agency
2002-2008
Shibuya (Japan)
2002-2005
Nippon Koei (Japan)
2003
Communications Technology Laboratory
2002-2003
Hearst (United States)
1917
A secure communication network with quantum key distribution in a metropolitan area is reported. Six different QKD systems are integrated into mesh-type network. GHz-clocked links enable us to demonstrate the world-first TV conferencing over distance of 45km. The includes commercial product for long-term stable operation, and application interface mobile phones. Detection an eavesdropper, rerouting path, relay via trusted nodes demonstrated this
Abstract Quantum key distribution (QKD) can offer communication with unconditional security and is a promising technology to protect next generation systems. For QKD see commercial success, several challenges have be solved, such as integrating signals into existing fiber optical networks. In this paper, we present experimental verification of co-propagating large number wavelength division multiplexing (WDM) coherent data channels. We show successful secret over 24 h for continuous-variable...
We propose and demonstrate a novel method to generate large-amplitude coherent-state superposition (CSS) via ancilla-assisted photon subtraction. The ancillary mode induces quantum interference of indistinguishable processes in an extended space, widening the controllability at conditional output. this by simple time-separated two-photon subtraction from continuous wave squeezed light. observe largest CSS traveling light ever reported without correcting any imperfections, which will enable...
We consider the problem of evaluating entanglement non-Gaussian mixed states generated by photon subtraction from entangled squeezed states. The measures we use are negativity and logarithmic negativity. These possess unusual property being computable with linear algebra packages even for high-dimensional quantum systems. numerically evaluate these which on/off detectors. results compared behavior certain operational measures, namely teleportation fidelity mutual information in dense coding...
We address the limit of Gaussian operations and classical communication in problem quantum state discrimination. show that optimal strategy for discrimination binary phase shift keyed (BPSK) coherent signal is a simple homodyne detection. also propose practical near-optimal receivers beat BPSK all areas power. Our scheme does not require realtime electrical feedback.
The optimal discrimination of nonorthogonal quantum states with minimum error probability is a fundamental task in measurement theory as well an important primitive optical communication. In this work, we propose and experimentally realize new simple strategy capable discriminating two coherent smaller probabilities than can be obtained using the standard devices: Kennedy receiver homodyne receiver.
The most efficient modern optical communication is known as coherent and its standard quantum limit (SQL) almost reachable with current technology. Though it has been predicted for a long time that this SQL could be overcome via mechanically optimized receivers, such performance not experimentally realized so far. Here we demonstrate the first unconditional evidence surpassing of communication. We implement receiver simple linear optics configuration achieve more than 90% total detection...
In a new branch of quantum computing, information is encoded into coherent states, the primary carriers optical communication. To exploit it, bits these states are needed, but it notoriously hard to make superpositions such continuous-variable states. We have realized complete engineering and characterization qubit two Using squeezed vacuum as resource special photon-subtraction technique, we could with high precision prepare an arbitrary superposition single photon. This lead way...
We experimentally demonstrate a new measurement scheme for the discrimination of two coherent states. The is based on displacement operation followed by photon-number-resolving detector, and we show that it outperforms standard homodyne detector which we, in addition, prove to be optimal within all Gaussian operations including conditional dynamics. also non-Gaussian superior continuous variable quantum key distribution scheme.
Abstract Entanglement swapping at telecom wavelengths is the heart of quantum networking in optical fiber infrastructures. Although entanglement has been demonstrated experimentally so far using various types entangled photon sources both near-infrared and wavelength regions, rate operation too low to be applied practical protocols, due limited efficiency detectors. Here we demonstrate drastic improvement by two ultra-bright four highly efficient superconducting nanowire single We have...
Abstract Quantum key distribution (QKD) allows two distant parties to share secret keys with the proven security even in presence of an eavesdropper unbounded computational power. Recently, GHz-clock decoy QKD systems have been realized by employing ultrafast optical communication devices. However, loopholes high-speed not fully explored yet. Here we point out a loophole at transmitter QKD, which is common problem using practical band-width limited We experimentally observe inter-pulse...
In spontaneous parametric down conversion (SPDC) based quantum information processing (QIP) experiments, there is a tradeoff between the coincide count rates (i.e. pumping power of SPDC), which limits rate protocol, and visibility interference, quality protocol. This mainly caused by multi-photon pair emissions from SPDCs. theory, problem how to model experiments without truncating these while including practical imperfections. this paper, we establish method theoretically simulate SPDC QIPs...
This paper defines the squashed entanglement of a quantum channel as maximum that can be registered by sender and receiver at input output channel, respectively. A new subadditivity inequality for original measure Christandl Winter leads to conclusion is an additive function tensor product any two channels. More importantly, this inequality, along with prior results Christandl, Winter, et al., establishes upper bound on communication capacity assisted unlimited forward backward classical...
In the lore of quantum metrology, one often hears (or reads) following no-go theorem: If you put a vacuum into input port balanced Mach-Zehnder interferometer, then no matter what other port, and your detection scheme, sensitivity can never be better than shot-noise limit (SNL). Often proof this theorem is cited to in C. Caves, Phys. Rev. D 23, 1693 (1981), but upon further inspection, such claim made there. Quantum-Fisher-information-based arguments suggestive appear elsewhere literature,...
The amount of information transmissible through a communications channel is determined by the noise characteristics and quantities available transmission resources. In classical theory, can be increased twice at most when resource doubled for fixed characteristics. quantum however, transmitted increase even more than twice. We present proof-of-principle demonstration this superadditivity capacity using ternary symmetric states single photon, event selection from weak coherent light source....
Quantum teleportation of a squeezed state is demonstrated experimentally. Due to some inevitable losses in experiments, vacuum necessarily becomes mixed which no longer minimum uncertainty state. We establish an operational method evaluation for quantum such using fidelity and discuss the classical limit The measured input $0.85\ifmmode\pm\else\textpm\fi{}0.05$, higher than case $0.73\ifmmode\pm\else\textpm\fi{}0.04$. also verify that process operates properly nonclassical its variance...
We investigate quantum measurement strategies capable of discriminating two coherent states probabilistically with significantly smaller error probabilities than can be obtained using nonprobabilistic state discrimination. apply a postselection strategy to the data homodyne detector as well photon number resolving in order lower probability. compare different receivers an optimal intermediate scheme where rate is minimized for fixed inconclusive results. The (PNR) receiver experimentally...
The quantum receiver is an important tool for overcoming the standard limit (SQL) of discrimination errors in optical communication. We theoretically study receivers discriminating ternary and quaternary phase-shift-keying coherent states terms average error rate mutual information. Our consists on-off--type photon detectors displacement operations without electrical feedforward operations. show that signals, shows a reasonable gain from SQL even feedforward. This scheme realizable with...
We propose and experimentally demonstrate a near-optimal discrimination scheme for the quadrature phase shift keying protocol (QPSK). show in theory that performance of our hybrid is superior to standard - heterodyne detection all signal amplitudes underpin predictions with experimental results. Furthermore, provides hitherto best domain highly attenuated signals. The composed measurement, conditional displacement threshold detector.
Hong-Ou-Mandel (HOM) interference between independent photon sources (HOMI-IPS) is the fundamental block for quantum information processing. All previous HOMI-IPS experiments were carried out in time-domain, however, spectral during was omitted. Here, we investigate domain using recently developed fast fiber spectrometer, and demonstrate distribution HOM two heralded single-photon sources, thermal sources. This experiment not only can deepen our understanding of from viewpoint domain, but...
We demonstrate a novel scheme to generate frequency-entangled qudits with dimension number higher than 10 and distribute them over optical fibers of 15 km in total length. This combines the technique spectral engineering biphotons generated by spontaneous parametric down-conversion spectrally resolved Hong-Ou-Mandel interference. characterized comb-like correlation structures time arrival measurement correlated intensity measurement. The generation distribution distinct entangled frequency...
We establish several upper bounds on the energy-constrained quantum and private capacities of all single-mode phase-insensitive bosonic Gaussian channels. The first bound, which we call "data-processing bound," is simplest obtained by decomposing a channel as pure-loss followed quantum-limited amplifier channel. prove that data-processing bound can be at most 1.45 bits larger than known lower these discuss another well. Two other bounds, "$\varepsilon$-degradable bound"...