arXiv subjects
Publications and source records attributed to K. Wakui.
A novel secure communication network with quantum key distribution in a metropolitan area is reported. Different QKD schemes are integrated to demonstrate secure TV conferencing over a distance of 45km, stable long-term operation, and application to secure mobile phones.
We report a $^{71}$Ga nuclear-quadrupole-resonance (NQR) study on the characteristics of superconductivity in noncentrosymmetric Ir$_2$Ga$_9$ at zero field (H=0). The $^{71}$Ga-NQR measurements have revealed that $1/T_1$ has the clear coherence peak just below $T_{\rm c}$, and decreases exponentially upon further cooling in Ir$_2$Ga$_9$. From these results, Ir$_2$Ga$_9$ is concluded to be the conventional s-wave superconductor. Despite the lack of spatial centrosymmetry, there are no evidence for unconventional superconducting state ascribed to ASOC in Ir$_2$Ga$_9$.
We present controllable generation of various kinds of highly nonclassical states of light, including the single photon state and superposition states of mesoscopically distinct components. The high nonclassicality of the generated states is measured by the negativity of the Wigner function, which is largest ever observed to our knowledge. Our scheme is based on photon subtraction from a nearly pure squeezed vacuum, generated from an optical parametric oscillator with a periodically-poled KTiOPO$_4$ crystal as a nonlinear medium. This is an important step to realize basic elements of universal quantum gates, and to serve as a highly nonclassical input probe for spectroscopy and the study of quantum memory.
We present the two kinds of experimental results. One is a continuous variable dense coding experiment, and the other is a photon number detector with high linearity response, the so called charge integration photon detector (CIPD). They can be combined together to be a potential tool for implementing the cubic phase gate which is an important gate element to synthesize the measurement induced nonlinearity for photonic quantum information processing.