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Volume 36, Issue 7
Displaying 1-8 of 8 articles from this issue
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Akira FURUSAWA2008 Volume 36 Issue 7 Pages 397-398
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSCoherent quantum communication, which can be regarded as a ‘quantized’ version of coherent optical communication, is reviewed.View full abstractDownload PDF (306K) -
Shigenari SUZUKI2008 Volume 36 Issue 7 Pages 399-403
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSQuadrature squeezed states of light are important resources for continuous-variable quantum inforamtion protocols. Squeezing level or purity of the states often dominate the performances of such protocols. In this article, I review our experiment which generates the quadrature squeezed state of light at 860nm with high squeezing level and purity. The generated state has been improved in its squeezing level and purity by using a periodically-poled KTiOPO4 (PPKTP) crystal as a nonlinear optical medium in a sub-threshold cw pumped optical parametric oscillator.View full abstractDownload PDF (928K) -
Hidehiro YONEZAWA2008 Volume 36 Issue 7 Pages 404-409
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSQuantum teleportation is one of the most fundamental subjects in quantum information technology. This is because quantum teleportation can be used as not only a communication network but also a building block for universal quantum information processing. It is well known that there are two approaches (i. e. discrete and continuous variable approaches) in quantum information processing. In particular, continuous variable one has some advantages, that is, capability for deterministic and efficient quantum operations. In the case of continuous variable quantum teleportation, however, we cannot teleport quantum states perfectly due to finite level of quadrature squeezed states. Hence it is important to improve the fidelity of teleportation to realize more advanced quantum network and circuits. Thanks to the recent improvement of squeezing level, fidelity up to F=0.83 has been achieved. In this article, we review the experiment of high fidelity quantum teleportation for continuous variables, and its applications.View full abstractDownload PDF (4292K) -
Mikio FUJIWARA, Masahide SASAKI, Shigehito MIKI, Zhen WANG2008 Volume 36 Issue 7 Pages 410-414
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSPhoton number detectors are most fundamental and essential devices for quantum information processing and quantum communications. In this article, we introduce the activity of developing of photon number detectors.View full abstractDownload PDF (4743K) -
Kentaro WAKUI2008 Volume 36 Issue 7 Pages 415-420
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSWe present generation of photon-subtracted squeezed state at 860nm, from continuous-wave squeezed vacua generated with a periodically-poled KTiOPO4 crystal as a nonlinear medium of a subthreshold optical parametric oscillator. We observe various kinds of photon-subtracted squeezed states, including “non-Gaussian” states similar to the single-photon state and superposition states of coherent states, simply by changing the pump power. Nonclassicality of the generated states clearly emerges as its negative region around the origin of the phase-space distributions, i. e., the Wigner functions. We obtain the value,-0.083 at the origin of the Wigner function, which is largest ever observed without any correction for experimental imperfections.View full abstractDownload PDF (1829K) -
Mikio KOZUMA2008 Volume 36 Issue 7 Pages 421-427
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSQuantum entanglement plays a central role for implementing quantum information processing. Deterministic control of quantum entanglement has been realized using a squeezed vacuum state. However, since photons are hard to localize, coherent transfer of quantum squeezing between information carrying photons and spatially localized atoms has long been desired. This coherent transfer is equivalent to the storage and retrieval of quantum entanglement and is one of the most important building blocks for implementing the intricate tasks of quantum information processing. Here, for the first time, we successfully demonstrate the storage and retrieval of a squeezed vacuum state with electromagnetically induced transparency using a cold ensemble of Rb atoms as a memory medium.View full abstractDownload PDF (1341K) -
Osamu HIROTA, Tetsuya SHIMIZU, Masaki SOHMA, Kentaro KATO2008 Volume 36 Issue 7 Pages 428-432
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSSince quantum key distribution protocol was invented in 1984, huge number of papers on quantum cryptography have been published. However, they have so many serious technical problems which should overcome difficulties. On the other hand, it is reasonable to develop a quantum version of the conventional mathematical symmetric key cipher. In 2000, Yuen protocol was invented to realize a quantum version of stream cipher. In this paper, we introduce the principle and recent progress on quantum stream cipher by Yuen 2000 protocol.View full abstractDownload PDF (859K) -
Shin-ichi ZAITSU, Totaro IMASAKA2008 Volume 36 Issue 7 Pages 433-439
Published: July 15, 2008
Released on J-STAGE: March 26, 2014
JOURNAL FREE ACCESSWe propose a novel approach to generate a continuous-wave pulse train with an ultrahigh repetition rate. The method utilizes a unique mechanism of lightwave modulation and amplification based on a continuous-wave Raman interaction in a high-finesse optical cavity. We experimentally demonstrated the generation of multifrequency emissions from a hydrogen-filled cavity and measured the intensity-modulated waveform at the frequency of 17.6THz. We found that the intracavity dispersion caused phase mismatch between the related longitudinal modes; thus preventing the phase-locked generation of a continuous-wave-based THz pulse train. This undesirable behavior can be overcome by using a dispersion-managed and bandwidth-extended cavity; this will then lead to a new-type of mode-locked laser operating at a frequency of more than 10THz.View full abstractDownload PDF (1873K)
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