Updated on 2022/12/08

写真a

 
AOKI, Takao
 
Scopus Paper Info  
Paper Count: 0  Citation Count: 0  h-index: 13

Citation count denotes the number of citations in papers published for a particular year.

Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Professor

Concurrent Post

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Degree

  • 東京大学   博士(工学)

 

Research Areas

  • Semiconductors, optical properties of condensed matter and atomic physics

Papers

  • Single-frequency fiber Fabry–Perot Brillouin laser

    Shinya Kato, Takao Aoki

    Optics Letters   47 ( 19 ) 5000 - 5000  2022.10

     View Summary

    We demonstrate single-frequency stimulated Brillouin lasing in short fiber Fabry–Perot resonators. A sub-milliwatt threshold for lasing is observed in resonators with high quality factors of ∼1.5 × 108 and effective resonator lengths as short as ∼5 mm. The strong dispersion of fiber Bragg gratings results in unequal frequency separations for neighboring pairs of longitudinal modes with separation differences larger than the Brillouin gain bandwidth, thereby avoiding cascaded lasing. Our achievement will enable compact, robust, efficient narrow-linewidth light sources.

    DOI

  • Gaussian-wave-packet model for single-photon generation based on cavity quantum electrodynamics under adiabatic and nonadiabatic conditions

    Takeru Utsugi, Akihisa Goban, Yuuki Tokunaga, Hayato Goto, Takao Aoki

    Physical Review A   106 ( 2 )  2022.08

    DOI

  • Photon transport enhancement through a coupled-cavity QED system with dynamic modulation

    Shinya Kato, Takao Aoki

    Optics Express   30 ( 5 ) 6798 - 6798  2022.02

    DOI

  • Requirements for fault-tolerant quantum computation with cavity-QED-based atom-atom gates mediated by a photon with a finite pulse length

    Rui Asaoka, Yuuki Tokunaga, Rina Kanamoto, Hayato Goto, Takao Aoki

    Physical Review A   104 ( 4 )  2021.10

    DOI

  • On-chip photon-pair generation in a silica microtoroidal cavity

    Yosuke Hashimoto, Akihisa Goban, Yuki Hirabayashi, Yuta Kobayashi, Tomohiro Araki, Takao Aoki

    Optics Express   29 ( 3 ) 3533 - 3533  2021.02

    DOI

  • Ultra-low-loss nanofiber Fabry–Perot cavities optimized for cavity quantum electrodynamics

    S. K. Ruddell, K. E. Webb, M. Takahata, S. Kato, T. Aoki

    Optics Letters   45 ( 17 ) 4875 - 4875  2020.09

    DOI

  • Transfer-Matrix Approach to Determining the Linear Response of All-Fiber Networks of Cavity-QED Systems

    Nikolett Német, Donald White, Shinya Kato, Scott Parkins, Takao Aoki

    Physical Review Applied   13 ( 6 )  2020.06

    DOI

  • Observation of dressed states of distant atoms with delocalized photons in coupled-cavities quantum electrodynamics

    Shinya Kato, Nikolett Német, Kohei Senga, Shota Mizukami, Xinhe Huang, Scott Parkins, Takao Aoki

    Nature Communications   10 ( 1 )  2019.12

    DOI

    Scopus

    35
    Citation
    (Scopus)
  • Evaluation of graphene optical nonlinearity with photon-pair generation in graphene-on-silicon waveguides

    Yuya Yonezu, Rai Kou, Hidetaka Nishi, Tai Tsuchizawa, Koji Yamada, Takao Aoki, Atsushi Ishizawa, Nobuyuki Matsuda

    Optics Express   27 ( 21 ) 30262 - 30262  2019.10

    DOI

  • Cavity Dark Mode of Distant Coupled Atom-Cavity Systems

    Donald H. White, Shinya Kato, Nikolett Német, Scott Parkins, Takao Aoki

    Physical Review Letters   122 ( 25 )  2019.06

    DOI

  • Figure of merit for single-photon generation based on cavity quantum electrodynamics

    Hayato Goto, Shota Mizukami, Yuuki Tokunaga, Takao Aoki

    Physical Review A   99 ( 5 )  2019.05

    DOI

  • Inversion of Qubit Energy Levels in Qubit-Oscillator Circuits in the Deep-Strong-Coupling Regime

    F. Yoshihara, T. Fuse, Z. Ao, S. Ashhab, K. Kakuyanagi, S. Saito, T. Aoki, K. Koshino, K. Semba

    Physical Review Letters   120 ( 18 )  2018.05

    DOI

  • Efficient Single-Photon Coupling from a Nitrogen-Vacancy Center Embedded in a Diamond Nanowire Utilizing an Optical Nanofiber

    Yuya Yonezu, Kentaro Wakui, Kentaro Furusawa, Masahiro Takeoka, Kouichi Semba, Takao Aoki

    SCIENTIFIC REPORTS   7 ( 1 )  2017.10  [Refereed]

     View Summary

    Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.

    DOI

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    10
    Citation
    (Scopus)
  • Simple method for fabrication of diamond nanowires by inductively coupled plasma reactive ion etching

    Kentaro Wakui, Yuya Yonezu, Takao Aoki, Masahiro Takeoka, Kouichi Semba

    JAPANESE JOURNAL OF APPLIED PHYSICS   56 ( 5 )  2017.05  [Refereed]

     View Summary

    Diamond nanowires are fabricated on a bulk, single crystalline diamond near an edge of aluminum coating using inductively coupled plasma reactive ion etching. Two different density areas are simultaneously appeared where the dense area has 9 times higher density than that of the sparse area while keeping the size of nanowires almost uniform in these areas. The nanowire sizes realized in the dense (sparse) area are 858 +/- 22nm (876 +/- 25nm) in height and 126 +/- 6 nm (124 +/- 7 nm) in diameter, which is suitable for applications in optical quantum information processing. (C) 2017 The Japan Society of Applied Physics

    DOI

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    3
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  • Free-space optical channel estimation for physical layer security

    Hiroyuki Endo, Mikio Fujiwara, Mitsuo Kitamura, Toshiyuki Ito, Morio Toyoshima, Yoshihisa Takayama, Hideki Takenaka, Ryosuke Shimizu, Nicola Laurenti, Giuseppe Vallone, Paolo Villoresi, Takao Aoki, Masahide Sasaki

    OPTICS EXPRESS   24 ( 8 ) 8940 - 8955  2016.04  [Refereed]

     View Summary

    We present experimental data on message transmission in a free-space optical (FSO) link at an eye-safe wavelength, using a testbed consisting of one sender and two receiver terminals, where the latter two are a legitimate receiver and an eavesdropper. The testbed allows us to emulate a typical scenario of physical-layer (PHY) security such as satellite-to-ground laser communications. We estimate information-theoretic metrics including secrecy rate, secrecy outage probability, and expected code lengths for given secrecy criteria based on observed channel statistics. We then discuss operation principles of secure message transmission under realistic fading conditions, and provide a guideline on a multi-layer security architecture by combining PHY security and upper-layer (algorithmic) security. (C) 2016 Optical Society of America

    DOI

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    38
    Citation
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  • 19pBJ-11 Nonlinear optical response of cold atoms via ultra-low-loss optical nanofiber

    Senga K, Matsuhashi Y, Kato S, Aoki T

    Meeting Abstracts of the Physical Society of Japan   71 ( 0 ) 653 - 653  2016

    DOI CiNii

  • 19pBJ-11 Nonlinear optical response of cold atoms via ultra-low-loss optical nanofiber

    Senga K, Matsuhashi Y, Kato S, Aoki T

    Meeting Abstracts of the Physical Society of Japan   71 ( 0 ) 653 - 653  2016

    DOI CiNii

  • Time-resolved observation of coherent excitonic nonlinear response with a table-top narrowband THz pulse wave

    K. Uchida, H. Hirori, T. Aoki, C. Wolpert, T. Tamaya, K. Tanaka, T. Mochizuki, C. Kim, M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West

    APPLIED PHYSICS LETTERS   107 ( 22 )  2015.11  [Refereed]

     View Summary

    By combining a tilted-pulse-intensity-front scheme using a LiNbO3 crystal and a chirped-pulsebeating method, we generated a narrowband intense terahertz (THz) pulse, which had a maximum electric field of more than 10 kV/cm at around 2 THz, a bandwidth of similar to 50 GHz, and frequency tunability from 0.5 to 2 THz. By performing THz-pump and near-infrared-probe experiments on GaAs quantum wells, we observed that the resonant excitation of the intraexcitonic 1s-2p transition induces a clear and large Autler-Townes splitting. Our time-resolved measurements show that the splitting energy observed in the rising edge region of electric field is larger than in the constant region. This result implies that the splitting energy depends on the time-averaged THz field over the excitonic dephasing time rather than that at the instant of the exciton creation by a probe pulse. (C) 2015 AIP Publishing LLC.

    DOI

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    18
    Citation
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  • Numerical Study on Secrecy Capacity and Code Length Dependence of the Performances in Optical Wiretap Channels

    H. Endo, T. S. Han, T. Aoki, M. Sasaki

    IEEE PHOTONICS JOURNAL   7 ( 5 )  2015.10  [Refereed]

     View Summary

    Secrecy issues of free-space optical links realizing information theoretically secure communications and high transmission rates are discussed. We numerically study secrecy communication rates of optical wiretap channel based on on-off keying (OOK) modulation under typical conditions met in satellite-ground links. It is shown that, under reasonable degraded conditions on a wiretapper, information theoretically secure communications should be possible in a much wider distance range than a range limit of quantum key distribution, enabling secure optical links between geostationary Earth orbit satellites and ground stations with currently available technologies. We also provide the upper bounds on the decoding error probability and the leaked information to estimate a necessary code length for given required levels of performances. This result ensures that a reasonable length of wiretap channel code for our proposed scheme must exist.

    DOI

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    30
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  • Numerical Study on Secrecy Capacity and Code Length Dependence of the Performances in Optical Wiretap Channels

    H. Endo, T. S. Han, T. Aoki, M. Sasaki

    IEEE PHOTONICS JOURNAL   7 ( 5 )  2015.10

     View Summary

    Secrecy issues of free-space optical links realizing information theoretically secure communications and high transmission rates are discussed. We numerically study secrecy communication rates of optical wiretap channel based on on-off keying (OOK) modulation under typical conditions met in satellite-ground links. It is shown that, under reasonable degraded conditions on a wiretapper, information theoretically secure communications should be possible in a much wider distance range than a range limit of quantum key distribution, enabling secure optical links between geostationary Earth orbit satellites and ground stations with currently available technologies. We also provide the upper bounds on the decoding error probability and the leaked information to estimate a necessary code length for given required levels of performances. This result ensures that a reasonable length of wiretap channel code for our proposed scheme must exist.

    DOI

    Scopus

    30
    Citation
    (Scopus)
  • 18pBA-5 Wavelength meter with a sub-pixel resolution using a grating spectrograph II

    Kususaki K, Aoki T

    Meeting Abstracts of the Physical Society of Japan   70 ( 2 ) 556 - 556  2015.09

    DOI CiNii

  • 17aAC-9 Observation of strong coupling between a trapped single Cs atom and a nanofiber-based cavity

    Kato Shinya, Aoki Takao

    Meeting Abstracts of the Physical Society of Japan   70 ( 2 ) 501 - 501  2015.09

    DOI CiNii

  • Strong Coupling between a Trapped Single Atom and an All-Fiber Cavity.

    Shinya Kato, Takao Aoki

    Physical review letters   115 ( 9 ) 093603 - 093603  2015.08  [International journal]

     View Summary

    We demonstrate an all-fiber cavity quantum electrodynamics system with a trapped single atom in the strong coupling regime. We use a nanofiber Fabry-Perot cavity, that is, an optical nanofiber sandwiched by two fiber-Bragg-grating mirrors. Measurements of the cavity transmission spectrum with a single atom in a state-insensitive nanofiber trap clearly reveal the vacuum Rabi splitting.

    DOI PubMed

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    89
    Citation
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  • Time-bin entangled photon pair generation from Si micro-ring resonator

    Ryota Wakabayashi, Mikio Fujiwara, Ken-ichiro Yoshino, Yoshihiro Nambu, Masahide Sasaki, Takao Aoki

    OPTICS EXPRESS   23 ( 2 ) 1103 - 1113  2015.01  [Refereed]

     View Summary

    We demonstrate time-bin entanglement generation in telecom wavelength using a 7 mu m radius Si micro-ring resonator pumped by a continuous wave laser. The resonator structure can enhance spontaneous four wave mixing, leading to a photon pair generation rate of about 90-100 Hz with a laser pump power of as low as -3.92 dBm (0.41 mW). We succeed in observing time-bin entanglement with the visibility over 92%. Moreover, wavelength-tunability of the entangled photon pair is demonstrated by changing the operation temperature. (C) 2015 Optical Society of America

    DOI

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    77
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  • Microtoroidal cavity QED with fiber overcoupling and strong atom-field coupling: A single-atom quantum switch for coherent light fields

    Scott Parkins, Takao Aoki

    PHYSICAL REVIEW A   90 ( 5 )  2014.11  [Refereed]

     View Summary

    We propose a scheme for single-atom, quantum control of the direction of propagation of a coherent field incident, via a tapered fiber, upon a microtoroidal whispering-gallery-mode (WGM) resonator. The scheme involves overcoupling of the fiber taper to the resonator and strong coupling of an atom to the evanescent field of the WGM, i.e., an atom-field coupling that exceeds the total WGM linewidth. In contrast to previous, related schemes that operate in the bad-cavity regime, the proposed scheme can operate effectively with much stronger incident fields, while also preserving their coherent nature. It can also serve to prepare an entangled state of the atom and coherent optical pulses propagating in opposite directions along the fiber. We evaluate the fidelity of preparation of such a state taking into account absorption and atomic spontaneous emission and demonstrate that high fidelities should be possible with realistic parameters.

    DOI

    Scopus

    15
    Citation
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  • Ultra-low-loss tapered optical fibers with minimal lengths

    Ryutaro Nagai, Takao Aoki

    OPTICS EXPRESS   22 ( 23 ) 28427 - 28436  2014.11  [Refereed]

     View Summary

    We design and fabricate ultra-low-loss tapered optical fibers (TOFs) with minimal lengths. We first optimize variations of the torch scan length using the flame-brush method for fabricating TOFs with taper angles that satisfy the adiabaticity criteria. We accordingly fabricate TOFs with optimal shapes and compare their transmission to TOFs with a constant taper angle and TOFs with an exponential shape. The highest transmission measured for TOFs with an optimal shape is in excess of 99.7% with a total TOF length of only 23 mm, whereas TOFs with a constant taper angle of 2 mrad reach 99.6% transmission for a 63 mm TOF length. (C) 2014 Optical Society of America

    DOI

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    43
    Citation
    (Scopus)
  • Elimination of the chirp of narrowband terahertz pulses generated by chirped pulse beating using a tandem grating pair laser pulse stretcher

    Tetsuya Yoshida, Shohei Kamada, Takao Aoki

    OPTICS EXPRESS   22 ( 19 ) 23679 - 23685  2014.09  [Refereed]

     View Summary

    We study the elimination of the chirp of narrowband terahertz pulses generated by chirped laser pulse beating using a laser pulse stretcher with two grating pairs that cancel out the third-order spectral phase. First, we show that positively chirped terahertz pulses can be generated using a pulse stretcher with a grating pair and internal lenses. We then combine this with a second grating pair, the spectral phase of which has the opposite sign to that of the first one. By varying the separation of the second grating pair, we experimentally verify that the chirp of the generated terahertz pulses can be eliminated. (C) 2014 Optical Society of America

    DOI

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    2
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  • Efficient Single-Mode Photon-Coupling Device Utilizing a Nanofiber Tip

    Sho Chonan, Shinya Kato, Takao Aoki

    SCIENTIFIC REPORTS   4  2014.04  [Refereed]

     View Summary

    Single-photon sources are important elements in quantum optics and quantum information science. It is crucial that such sources be able to couple photons emitted from a single quantum emitter to a single propagating mode, preferably to the guided mode of a single-mode optical fiber, with high efficiency. Various photonic devices have been successfully demonstrated to efficiently couple photons from an emitter to a single mode of a cavity or a waveguide. However, efficient coupling of these devices to optical fibers is sometimes challenging. Here we show that up to 38% of photons from an emitter can be directly coupled to a single-mode optical fiber by utilizing the flat tip of a silica nanofiber. With the aid of a metallic mirror, the efficiency can be increased to 76%. The use of a silicon waveguide further increases the efficiency to 87%. This simple device can be applied to various quantum emitters.

    DOI

    Scopus

    21
    Citation
    (Scopus)
  • Efficient Single-Mode Photon-Coupling Device Utilizing a Nanofiber Tip

    Sho Chonan, Shinya Kato, Takao Aoki

    SCIENTIFIC REPORTS   4  2014.04  [Refereed]

     View Summary

    Single-photon sources are important elements in quantum optics and quantum information science. It is crucial that such sources be able to couple photons emitted from a single quantum emitter to a single propagating mode, preferably to the guided mode of a single-mode optical fiber, with high efficiency. Various photonic devices have been successfully demonstrated to efficiently couple photons from an emitter to a single mode of a cavity or a waveguide. However, efficient coupling of these devices to optical fibers is sometimes challenging. Here we show that up to 38% of photons from an emitter can be directly coupled to a single-mode optical fiber by utilizing the flat tip of a silica nanofiber. With the aid of a metallic mirror, the efficiency can be increased to 76%. The use of a silicon waveguide further increases the efficiency to 87%. This simple device can be applied to various quantum emitters.

    DOI

    Scopus

    21
    Citation
    (Scopus)
  • The chirp-control of frequency-tunable narrowband terahertz pulses by nonlinearly chirped laser pulse beating

    Shohei Kamada, Tetsuya Yoshida, Takao Aoki

    APPLIED PHYSICS LETTERS   104 ( 10 )  2014.03  [Refereed]

     View Summary

    We demonstrate a method for controlling the chirp of the frequency-tunable narrowband terahertz pulses that are generated by photomixing with nonlinearly chirped laser pulse pairs. We find that in a grating-based laser-pulse stretcher, the frequency sweep rates of the generated terahertz pulses can be controlled by simply changing the incident angle. This method is also applicable to other mechanisms of terahertz pulse generation. (C) 2014 AIP Publishing LLC.

    DOI

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    7
    Citation
    (Scopus)
  • Guided resonance fluorescence of a single emitter after pulsed excitation

    Kazuki Koshino, Takao Aoki

    PHYSICAL REVIEW A   89 ( 2 )  2014.02  [Refereed]

     View Summary

    We theoretically investigated a microtoroidal cavity quantum electrodynamics system in which radiation from the emitter is nearly perfectly guided into a fiber mode, and analyzed the resonance fluorescence from the emitter after pulsed excitation. We derived analytic formulas to rigorously evaluate the photon statistics of the pulse emitted into the fiber, and clarified the conditions needed for the excitation pulse to generate single- and two-photon pulses.

    DOI

    Scopus

    1
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    (Scopus)
  • High-numerical-aperture microlensed tip on an air-clad optical fiber

    Shinya Kato, Sho Chonan, Takao Aoki

    OPTICS LETTERS   39 ( 4 ) 773 - 776  2014.02  [Refereed]

     View Summary

    We show that a hemispherically shaped tip on an air-clad optical fiber simultaneously works as a high-numerical-aperture lens and efficiently collects photons from an emitter placed near the beam waist into the fundamental guided mode. Numerical simulations show that the coupling efficiency reaches about 25%. We have constructed a confocal microscope with such a lensed fiber. The measurements are in good agreement with the numerical simulation. The monolithic structure with a high-photon-collection efficiency will provide a flexible substitute for a conventional lens system in various experiments such as single-atom trapping with a tightly focused optical trap. (C) 2014 Optical Society of America

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    32
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  • On the Chirp of Narrowband Terahertz Pulses Generated by Photomixing with Nonlinearly Chirped Laser Pulse Pairs (vol 6, 032701, 2013)

    Shohei Kamada, Shuhei Murata, Takao Aoki

    APPLIED PHYSICS EXPRESS   7 ( 2 )  2014.02  [Refereed]

    DOI

    Scopus

  • Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method

    Tetsuya Yoshida, Shohei Kamada, Shuhei Murata, Takao Aoki

    Applied Physics Letters   103 ( 15 )  2013.10

     View Summary

    We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory. © 2013 AIP Publishing LLC.

    DOI

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    2
    Citation
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  • Cavity QED with Whispering-Gallery Mode Microresonators

    AOKI Takao

      41 ( 7 ) 497 - 501  2013.07

    CiNii

  • Highly efficient coupling photons from single photon source utilizing a nanofiber tip

    CHONAN Sho, KATOI Shinya, AOKI Takao

    Technical report of IEICE. LQE   113 ( 49 ) 31 - 34  2013.05

     View Summary

    Efficient coupling of photons from single-photon source to the single-mode fiber is requied for quantum information and cryptography technology. We have performed simulations of photon-collecting devices utilizing a nanofiber tip. Up to 38% of light from point dipole source is coupled to the fundamental guided mode of the nanofiber. These devices utilizing a nanofiber tip are promising to achive efficient single-photon sources.

    CiNii

  • On the Chirp of Narrowband Terahertz Pulses Generated by Photomixing with Nonlinearly Chirped Laser Pulse Pairs

    Shohei Kamada, Shuhei Murata, Takao Aoki

    APPLIED PHYSICS EXPRESS   6 ( 3 )  2013.03  [Refereed]

     View Summary

    The spectral linewidth and intensity of narrowband terahertz pulses generated by photomixing with beating of nonlinearly chirped laser pulse pairs are studied. The direct relationship between the dispersion of the pump pulse stretcher and the chirp of the terahertz pulse is shown. Simple analytical expressions for the linewidth and intensity of the terahertz spectrum are obtained and their validity is confirmed by numerical simulations. Generation of narrowband terahertz pulses with minimal chirp is demonstrated. (C) 2013 The Japan Society of Applied Physics

    DOI

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    10
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  • Properties of a Single Photon Generated by a Solid-State Emitter: Effects of Pure Dephasing

    Eiki Iyoda, Takeo Kato, Takao Aoki, Keiichi Edamatsu, Kazuki Koshino

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 1 )  2013.01  [Refereed]

     View Summary

    We investigate the properties of a single photon generated by a solid-state emitter subject to strong pure dephasing. We employ a model in which all the elements of the system, including the propagating fields, are treated quantum mechanically. We analytically derive the density matrix of the emitted photon, which contains full information about the photon, such as its pulse profile, power spectrum, and purity. We visualize these analytical results using realistic parameters and reveal the conditions for maximizing the purity of generated photons.

    DOI

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    1
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  • Strong interactions of single atoms and photons near a dielectric boundary

    D. J. Alton, N. P. Stern, Takao Aoki, H. Lee, E. Ostby, K. J. Vahala, H. J. Kimble

    NATURE PHYSICS   7 ( 2 ) 159 - 165  2011.02  [Refereed]

     View Summary

    Cavity quantum electrodynamics provides the setting for quantum control of strong interactions between a single atom and one photon. Many such atom-cavity systems interacting by coherent exchanges of single photons could be the basis for scalable quantum networks. However, moving beyond current proof-of-principle experiments involving just one or two conventional optical cavities requires the localization of individual atoms at distances less than or similar to 100 nm from a resonator's surface. In this regime an atom can be strongly coupled to a single intracavity photon while at the same time experiencing significant radiative interactions with the dielectric boundaries of the resonator. Here, we report using real-time detection and high-bandwidth feedback to select and monitor single caesium atoms located similar to 100 nm from the surface of a microtoroidal optical resonator. Strong radiative interactions of atom and cavity field probe atomic motion through the evanescent field of the resonator and reveal both the significant role of Casimir-Polder attraction and the manifestly quantum nature of the atom-cavity dynamics.

    DOI

  • Fabrication of Ultralow-Loss Tapered Optical Fibers and Microtoroidal Resonators

    Takao Aoki

    JAPANESE JOURNAL OF APPLIED PHYSICS   49 ( 11 ) 118001  2010.11  [Refereed]

     View Summary

    We report simple, reproducible methods of fabricating tapered optical fibers with subwavelength diameter and silica microtoroidal resonators, both operating at a wavelength of 850 nm. The transmission loss of tapered fibers was reduced to 0.03 dB by controlling the adiabaticity of the tapered region. The Q factor of 3 x 10(8) was obtained for a toroidal microresonator with 40 mu m diameter. (C) 2010 The Japan Society of Applied Physics

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    11
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  • Quantum error correction beyond qubits

    Takao Aoki, Go Takahashi, Tadashi Kajiya, Jun-ichi Yoshikawa, Samuel L. Braunstein, Peter van Loock, Akira Furusawa

    NATURE PHYSICS   5 ( 8 ) 541 - 546  2009.08  [Refereed]

     View Summary

    Quantum computation and communication rely on the ability to manipulate quantum states robustly and with high fidelity. To protect fragile quantum-superposition states from corruption through so-called decoherence noise, some form of error correction is needed. Therefore, the discovery of quantum error correction(1,2) (QEC) was a key step to turn the field of quantum information from an academic curiosity into a developing technology. Here, we present an experimental implementation of a QEC code for quantum information encoded in continuous variables, based on entanglement among nine optical beams(3). This nine-wave-packet adaptation of Shor's original nine-qubit scheme(1) enables, at least in principle, full quantum error correction against an arbitrary single-beam error.

    DOI

  • Efficient Routing of Single Photons by One Atom and a Microtoroidal Cavity

    Takao Aoki, A. S. Parkins, D. J. Alton, C. A. Regal, Barak Dayan, E. Ostby, K. J. Vahala, H. J. Kimble

    PHYSICAL REVIEW LETTERS   102 ( 8 ) 083601  2009.02  [Refereed]

     View Summary

    Single photons from a coherent input are efficiently redirected to a separate output by way of a fiber-coupled microtoroidal cavity interacting with individual cesium atoms. By operating in an overcoupled regime for the input-output to a tapered fiber, our system functions as a quantum router with high efficiency for photon sorting. Single photons are reflected and excess photons transmitted, as confirmed by observations of photon antibunching (bunching) for the reflected (transmitted) light. Our photon router is robust against large variations of atomic position and input power, with the observed photon antibunching persisting for intracavity photon number 0.03 less than or similar to(n)over bar less than or similar to 0.7.

    DOI

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    205
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  • A photon turnstile dynamically regulated by one atom

    Barak Dayan, A. S. Parkins, Takao Aoki, E. P. Ostby, K. J. Vahala, H. J. Kimble

    SCIENCE   319 ( 5866 ) 1062 - 1065  2008.02  [Refereed]

     View Summary

    Beyond traditional nonlinear optics with large numbers of atoms and photons, qualitatively new phenomena arise in a quantum regime of strong interactions between single atoms and photons. By using a microscopic optical resonator, we achieved such interactions and demonstrated a robust, efficient mechanism for the regulated transport of photons one by one. With critical coupling of the input light, a single atom within the resonator dynamically controls the cavity output conditioned on the photon number at the input, thereby functioning as a photon turnstile. We verified the transformation from a Poissonian to a sub- Poissonian photon stream by photon counting measurements of the input and output fields. The results have applications in quantum information science, including for controlled interactions of single light quanta and for scalable quantum processing on atom chips.

    DOI

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    510
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  • Generation of continuous-wave broadband entangled beams using periodically poled lithium niobate waveguides

    Ken-ichiro Yoshino, Takao Aoki, Akira Furusawa

    APPLIED PHYSICS LETTERS   90 ( 4 ) 041111  2007.01  [Refereed]

     View Summary

    Continuous-wave light beams with broadband quantum entanglement are created with two independent squeezed light beams generated by two periodically poled lithium niobate waveguides and a symmentric beam splitter. The quantum entanglement is confirmed with a sufficient criterion Delta(2)(A,B)=<[Delta(x(A)-x(B))](2)>+<[Delta(p(A)+p(B))](2)>< 1 and the observed Delta(2)(A,B) is 0.75 over the bandwidth of 30 MHz. Although the bandwidth is limited by that of the detector so far, it would be broadened up to 10 THz which would be only limited by the bandwidth of phase matching for the second-order nonlinear process. (c) 2007 American Institute of Physics.

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    51
    Citation
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  • Observation of strong coupling between one atom and a monolithic microresonator

    Takao Aoki, Barak Dayan, E. Wilcut, W. P. Bowen, A. S. Parkins, T. J. Kippenberg, K. J. Vahala, H. J. Kimble

    NATURE   443 ( 7112 ) 671 - 674  2006.10  [Refereed]

     View Summary

    Over the past decade, strong interactions of light and matter at the single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science. This work has been performed principally within the setting of cavity quantum electrodynamics(1-4) with diverse physical systems(5), including single atoms in Fabry-Perot resonators(1,6), quantum dots coupled to micropillars and photonic bandgap cavities(7,8) and Cooper pairs interacting with superconducting resonators(9,10). Experiments with single, localized atoms have been at the forefront of these advances(11-15) with the use of optical resonators in high-finesse Fabry-Perot configurations(16). As a result of the extreme technical challenges involved in further improving the multilayer dielectric mirror coatings(17) of these resonators and in scaling to large numbers of devices, there has been increased interest in the development of alternative microcavity systems(5). Here we show strong coupling between individual caesium atoms and the fields of a high-quality toroidal microresonator. From observations of transit events for single atoms falling through the resonator's evanescent field, we determine the coherent coupling rate for interactions near the surface of the resonator. We develop a theoretical model to quantify our observations, demonstrating that strong coupling is achieved, with the rate of coherent coupling exceeding the dissipative rates of the atom and the cavity. Our work opens the way for investigations of optical processes with single atoms and photons in lithographically fabricated microresonators. Applications include the implementation of quantum networks(18,19), scalable quantum logic with photons(20), and quantum information processing on atom chips(21).

    DOI

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    652
    Citation
    (Scopus)
  • Squeezing at 946nm with periodically poled KTiOPO4

    Takao Aoki, Go Takahashi, Akira Furusawa

    OPTICS EXPRESS   14 ( 15 ) 6930 - 6935  2006.07  [Refereed]

     View Summary

    We report generation of squeezed vacuum in sideband modes of continuous-wave light at 946nm using a periodically poled KTiOPO4 crystal in an optical parametric oscillator. At the pump power of 250mW, we observe the squeezing level of -5.6 +/- 0.1dB and the anti- squeezing level of + 12.7 +/- 0.1dB. The pump power dependence of the observed squeezing/anti- squeezing levels agrees with theoretically calculated values when phase fluctuation of locking is taken into account. (c) 2006 Optical Society of America.

  • Demonstration of quantum telecloning of optical coherent states

    S Koike, H Takahashi, H Yonezawa, N Takei, SL Braunstein, T Aoki, A Furusawa

    PHYSICAL REVIEW LETTERS   96 ( 6 ) 060504  2006.02  [Refereed]

     View Summary

    We demonstrate unconditional telecloning for the first time. In particular, we symmetrically and unconditionally teleclone coherent states of light from one sender to two receivers, achieving a fidelity for each clone of F=0.58 +/- 0.01, which surpasses the classical limit. This is a manipulation of a new type of multipartite entanglement whose nature is neither purely bipartite nor purely tripartite.

    DOI

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    77
    Citation
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  • Experimental demonstration of quantum teleportation of a squeezed state

    N Takei, T Aoki, S Koike, K Yoshino, K Wakui, H Yonezawa, T Hiraoka, J Mizuno, M Takeoka, M Ban, A Furusawa

    PHYSICAL REVIEW A   72 ( 4 ) 042304  2005.10  [Refereed]

     View Summary

    Quantum teleportation of a squeezed state is demonstrated experimentally. Due to some inevitable losses in experiments, a squeezed vacuum necessarily becomes a mixed state which is no longer a minimum uncertainty state. We establish an operational method of evaluation for quantum teleportation of such a state using fidelity and discuss the classical limit for the state. The measured fidelity for the input state is 0.85 +/- 0.05, which is higher than the classical case of 0.73 +/- 0.04. We also verify that the teleportation process operates properly for the nonclassical state input and its squeezed variance is certainly transferred through the process. We observe the smaller variance of the teleported squeezed state than that for the vacuum state input.

    DOI

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    87
    Citation
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  • High-fidelity teleportation beyond the no-cloning limit and entanglement swapping for continuous variables

    N Takei, H Yonezawa, T Aoki, A Furusawa

    PHYSICAL REVIEW LETTERS   94 ( 22 ) 220502  2005.06  [Refereed]

     View Summary

    We experimentally demonstrate continuous-variable quantum teleportation beyond the no-cloning limit. We teleport a coherent state and achieve the fidelity of 0.70 +/- 0.02 that surpasses the no-cloning limit of 2/3. Surpassing the limit is necessary to transfer the nonclassicality of an input quantum state. By using our high-fidelity teleporter, we demonstrate entanglement swapping, namely, teleportation of quantum entanglement, as an example of transfer of nonclassicality.

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    209
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    (Scopus)
  • Demonstration of a quantum teleportation network for continuous variables

    H Yonezawa, T Aoki, A Furusawa

    NATURE   431 ( 7007 ) 430 - 433  2004.09  [Refereed]

     View Summary

    Quantum teleportation(1-8) involves the transportation of an unknown quantum state from one location to another, without physical transfer of the information carrier. Although quantum teleportation is a naturally bipartite process, it can be extended to a multipartite protocol known as a quantum teleportation network(9). In such a network, entanglement is shared between three or more parties. For the case of three parties ( a tripartite network), teleportation of a quantum state can occur between any pair, but only with the assistance of the third party. Multipartite quantum protocols are expected to form fundamental components for larger-scale quantum communication and computation(10,11). Here we report the experimental realization of a tripartite quantum teleportation network for quantum states of continuous variables ( electromagnetic field modes). We demonstrate teleportation of a coherent state between three different pairs in the network, unambiguously demonstrating its tripartite character.

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    277
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  • Experimental creation of a fully inseparable tripartite continuous-variable state

    T Aoki, N Takei, H Yonezawa, K Wakui, T Hiraoka, A Furusawa, P van Loock

    PHYSICAL REVIEW LETTERS   91 ( 8 ) 080404  2003.08  [Refereed]

     View Summary

    A continuous-variable tripartite entangled state is experimentally generated by combining three independent squeezed vacuum states, and the variances of its relative positions and total momentum are measured. We show that the measured values violate the separability criteria based on the sum of these quantities and prove the full inseparability of the generated state.

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    238
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  • Biexcitonic effects in the time integrated four-wave mixing with picosecond pulses

    T Aoki, YP Svirko, M Kuwata-Gonokami

    SOLID STATE COMMUNICATIONS   127 ( 3 ) 197 - 201  2003.07  [Refereed]

     View Summary

    We propose a simple method to estimate the biexcitonic contribution to the excitonic non-linearity. The method is based on the time integrated four-wave mixing (TI FWM) with picosecond pulses. The TI FWM signal, which is measured as a function of the delay between pump and test pulses, shows shift towards positive and negative time delay when the laser is tuned at the exciton and biexciton resonance, respectively. We show theoretically that the magnitude of the shift allows us to estimate the biexcitonic contribution to the third-order non-linearity at the fundamental band edge. (C) 2003 Elsevier Science Ltd. All rights reserved.

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  • Coherent exciton-biexciton dynamics in GaN

    K Kyhm, RA Taylor, JF Ryan, T Aoki, M Kuwata-Gonokami, B Beaumont, P Gibart

    PHYSICAL REVIEW B   65 ( 19 ) 193102  2002.05  [Refereed]

     View Summary

    Spectrally resolved and time-integrated four-wave mixing are used to measure the polarization dependence of biexcitonic signals and quantum beats between two-A-exciton (XAXA*) and A-biexciton (XAXA) states in a high-quality GaN epilayer. Mixed beats with two periods are observed: the first beating period corresponds to the energy splitting between XAXA* and XAXA; the second period corresponds to beating between A excitons (X-A) and donor bound excitons ((DX)-X-0). We also measure the polarization-dependent B-biexciton (XBXB) signal. The effective masses for the A and B holes are deduced from the binding energy.

    DOI

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    1
    Citation
    (Scopus)
  • Comparison of exciton-biexciton with bound exciton-biexciton dynamics in GaN: Quantum beats and temperature dependence of the acoustic-phonon interaction

    K Kyhm, RA Taylor, JF Ryan, T Aoki, M Kuwata-Gonokami, B Beaumont, P Gibart

    PHYSICA STATUS SOLIDI B-BASIC RESEARCH   228 ( 2 ) 475 - 479  2001.11  [Refereed]

     View Summary

    The polarization dependence of biexcitonic signals and quantum beats between A-excitons (X-A) and A-biexcitons (XAXA) in a high-quality GaN epilayer is measured by spectrally-resolved and time-integrated four-wave mixing. With cross-linear polarised light, mixed beats with two periods are observed: the first beating period corresponds to the energy splitting between X-A and XAXA, and agrees well with the calculated XAXA binding energy, while the second beating period corresponds to that between X-A and donor bound excitons ((DX)-X-0). The temperature-dependent homogeneous linewidth shows that the (DX)-X-0 has a larger acoustic phonon coupling coefficient than the XAXA. We also measured the polarization dependent B-biexciton (XBXB) signal. The effective masses for the A- and B-hole were deduced from the binding energy.

  • Quantum beats of free and bound excitons in GaN

    K Kyhm, RA Taylor, JF Ryan, T Aoki, M Kuwata-Gonokami, B Beaumont, P Gibart

    APPLIED PHYSICS LETTERS   79 ( 8 ) 1097 - 1099  2001.08  [Refereed]

     View Summary

    We present spectrally resolved and time-integrated four-wave mixing measurements at coherent dynamics of bound excitons in a high-quality GaN epilayer. Coherent excitation, with co-circular polarized light, of the neutral donor-bound excitons (D X-0) and A excitons (X-A) results in quantum beats, corresponding to the energy splitting between D X-0 and X-A. The temperature-dependent dephasing rate is used to deduce the strength of the D X-0-acoustic-phonon interaction via the homogeneous linewidth. (C) 2001 American Institute of Physics.

  • Time-integrated four-wave mixing in GaN and ZnSe: Polarization-sensitive phase shift of the excitonic quantum beats

    T Aoki, G Mohs, YP Svirko, M Kuwata-Gonokami

    PHYSICAL REVIEW B   64 ( 4 ) 045212  2001.07  [Refereed]

     View Summary

    We report on the study of quantum beats in the time-integrated four-wave mixing signal in reflection geometry from a pair of excitons with different valence orbitals in GaN and ZnSe. We observe a pi -phase shift between quantum beats in the co- and cross-linear polarization configuration, and nearly 100% modulation of the signal for both materials. In the co-circular polarization configuration, the observed phases of the quantum beats at the frequency of the A exciton in GaN and heavy-hole exciton in ZnSe are 0.2 pi and 0.1 pi, respectively. The phases of the quantum beats change sign for co- and counter-circular polarization configurations and also for A- (heavy-hole) and B-(light-hole) excitons in GaN(ZnSe). We describe the third-order coherent optical response of the exciton pair with different valence orbitals by taking into account the finite memory depth of the four-particle correlation. In particular, our experimental findings indicate that excitons with different valence orbitals and equal angular momentum attract each other similar to excitons with the same valence orbitals but opposite angular momentum. Excitons with different orbitals and opposite angular momenta repel one another. The comparison between experimental and theoretical results allows us to develop a quantitative analysis of the four-particle correlation in the presence of an exciton pair with different valence orbitals. We show that the observed pi -phase shift and nearly 100% modulation of the signal in the co- and cross-linear polarization configuration impose restraints on the memory functions. which describe the exciton-exciton interaction. These restraints imply, in particular, that electron spins play a more important role in the exciton-exciton interaction in comparison to hole spins. We show that a striking similarity, which we observe in the quantum beat signal from GaN and ZnSe, originates from the strong four-particle correlation contribution to the third-order excitonic nonlinearity.

  • Room-temperature random telegraph noise in luminescence from macroscopic InGaN clusters

    T Aoki, Y Nishikawa, M Kuwata-Gonokami

    APPLIED PHYSICS LETTERS   78 ( 8 ) 1065 - 1067  2001.02  [Refereed]

     View Summary

    We report on photoluminescence properties of individual macroscopically sized InGaN clusters that were formed in InGaN multiple quantum wells. Phase separation in InGaN results in the formation of clusters with a size of 1-2 mum with three different indium compositions. A small fraction (one in 100-1000) of the clusters shows random telegraph noise in luminescence at room temperature. Superlinear dependence of the luminescence switching rate on excitation intensity indicates that the switching is induced by the cooperation of multiple carriers. (C) 2001 American Institute of Physics.

  • Quantitative study of exciton-exciton interaction in a GaAs microcavity

    C Ramkumar, T Aoki, R Shimano, YP Svirko, T Kise, T Someya, H Sakaki, M Kuwata-Gonokami

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   69 ( 8 ) 2439 - 2442  2000.08  [Refereed]

     View Summary

    We employ a pump-induced polarization rotation scheme for the quantitative study of four-particle (exciton-exciton) correlations in a strongly coupled semiconductor microcavity. From the measured rotation angle in the chi((3))-regime, in which the nonlinear response is linearly proportional to pump intensity (I-pump), we evaluate the absolute value of anharmonicity of two-dimensional excitons. Deviation from the chi((3))-regime is observed beyond I-pump = 0.2 kW/cm(2).

  • Role of exciton-exciton interaction on resonant third-order nonlinear optical responses

    M Kuwata-Gonokami, T Aoki, C Ramkumar, R Shimano, YP Svirko

    JOURNAL OF LUMINESCENCE   87-9   162 - 167  2000.05  [Refereed]

     View Summary

    Weakly interacting boson model with the account for the bound biexciton is employed to obtain the evolution equations for the macroscopic exciton polarization. The polarization-sensitive degenerate four-wave mixing measurements in frequency domain enable us to estimate the relative contribution of the bound biexciton stale on the nonlinear optical response. In the time-domain measurements, we study the amplitude and phase of the beating in the time-integrated four-wave mixing signal. On the basis of the developed evolution equations, we show that the phase shift of the beating signal is polarization sensitive and is determined by the interplay between excitation-induced dephasing, exciton-exciton interaction and other mechanisms of the nonlinearity, (C) 2000 Published by Elsevier Science B.V. All rights reserved.

  • Influence of exciton-exciton interaction on quantum beats

    T Aoki, G Mohs, M Kuwata-Gonokami, AA Yamaguchi

    PHYSICAL REVIEW LETTERS   82 ( 15 ) 3108 - 3111  1999.04  [Refereed]

     View Summary

    Spectrally resolved four-wave mixing measurements in wurtzite GaN show a dependence of the quantum beats' phase on incident polarizations. We observe different phases at the A-exciton and the B-exciton resonances when exciting with circular polarized light. The observed phase difference indicates that exciton-exciton interaction plays a major role in the quantum beat process. The developed analysis allows us to conclude that the spins of the electrons rather than the holes give the major contribution to the exciton-exciton interaction in GaN.

  • On the gain mechanism in GaN based laser diodes

    G Mohs, T Aoki, R Shimano, M Kuwata-Gonokami, S Nakamura

    SOLID STATE COMMUNICATIONS   108 ( 2 ) 105 - 109  1998  [Refereed]

     View Summary

    We investigate the gain mechanism in a current GaN based laser diode design using the variable stripe length method and optical nanosecond excitation. The combination of absorption measurements, gain spectra and photoluminescence excitation data allows us to understand the fundamental mechanisms responsible for gain in these devices. We conclude that optical amplification is due to a conventional two-dimensional electron-hole plasma in contrast to the spontaneous emission mechanism in similar light emitting diode structures. (C) 1998 Elsevier Science Ltd. All rights reserved.

  • Polarization dependent quantum beats of homogeneously broadened excitons

    Takao Aoki, Georg Mohs, Takeshi Ogasawara, Ryo Shimano, Makoto Kuwata-Gonokami

    OPTICS EXPRESS   1 ( 12 ) 364 - 369  1997.12  [Refereed]

     View Summary

    The polarization dependence of quantum beats from the A-exciton and the B-exciton in a GaN sample of exceptional quality is studied with four-wave mixing experiments. When changing the incident polarizations from collinear to crossed linear, a pi-phase shift of the beats is observed while the decay rate remains unchanged. This confirms previous theoretical predictions. (C) 1997 Optical Society of America

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  • Failure of the modal gain model in a GaN based laser diode

    G Mohs, T Aoki, M Nagai, R Shimano, M Kuwata-Gonokami, S Nakamura

    SOLID STATE COMMUNICATIONS   104 ( 11 ) 643 - 648  1997.12  [Refereed]

     View Summary

    The optical gain in a Nichia(R) group-III nitride based blue laser diode has been measured at room temperature using the variable stripe length method and nanosecond excitation. Except for stripe lengths less than 50 mu m the device shows considerable deviation from the expected exponential intensity behavior. However, for short stripe lengths large gain values of up to 650 cm(-1) are observed when exciting with 20 MW cm(-2). Plasma recombination from a quantum confined level is suggested as the gain mechanism. (C) 1997 Elsevier Science Ltd.

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Industrial Property Rights

  • 光子生成装置

    青木 隆朗

    Patent

  • 量子計算ユニット、単一光子源、および量子計算装置

    青木 隆朗

    Patent

  • 光子生成装置

    青木 隆朗, 宇津木 健

    Patent

  • 量子もつれ生成装置及び方法

    青木 隆朗

    Patent

  • 量子ゲート装置および量子計算方法

    青木 隆朗

    Patent

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    長南 翔, 青木 隆朗

    Patent

  • チャープ制御方法及びチャープ制御装置

    青木 隆朗, 鎌田 祥平

    Patent

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Research Projects

  • Study on time-domain-multiplexed 2D continuous-variable cluster states and its application to large-scale quantum information processing

    Project Year :

    2018.04
    -
    2023.03
     

  • 多原子と多光子の強結合ハイブリッド量子系の研究

    Project Year :

    2018.04
    -
    2020.03
     

     View Summary

    平成31年度は、多原子強結合共振器QED系を独立に2台構築し、それらを光ファイバーで連結した結合共振器QED系を構築した。前年度と同様、ナノ光ファイバーは、研究代表者が開発したフレームブラシ法に基づく方法により作製した。具体的には、トーチのスキャンプロファイルを最適化し、長さ3mm程度のウェイスト部を持つナノファイバーを作製した。さらに、作製したナノファイバー共振器を新規に設計・作製した金属製真空チャンバーに導入した。真空チャンバー内に生成した磁気光学トラップ中の原子を、ナノファイバー共振器のウェイスト部における2色双極子トラップにロードし、多原子強結合共振器QED系を構築した。このようにして構築した2台の多原子強結合共振器QED系を光ファイバーで連結し、結合共振器QED系を構築した。構築した全ファイバー結合共振器QED系に対して、原子と光子のコヒーレント相互作用により形成される5つの固有モードを全て分光学的に測定・同定することに成功した。これら5つの固有モードは、明モード、ファイバー暗モード、共振器暗モードに分類される。本研究の最も特筆すべき成果は、共振器暗モードを初めて観測したことにある。一般に暗モードは、コヒーレント結合系における複数の励起の破壊的な干渉により特定の励起が抑制されたモードであるが、本研究で観測した共振器暗モードは、原子からの放射とファイバーからの放射の破壊的な干渉により、原子が存在する共振器中の光子の励起が抑制されたモードである。これは、原子は励起されているにもかかわらず、局所的には電磁場にさらされていない、極めて特異なモードである。さらに、励起光強度依存性から、原子の非局所的な励起と飽和を観測した。令和元年度が最終年度であるため、記入しない。令和元年度が最終年度であるため、記入しない

  • 共振器量子電気力学系の非局所コヒーレント結合の研究

    Project Year :

    2016.04
    -
    2018.03
     

     View Summary

    本研究では前年度(平成28年度)に、ナノ光ファイバー共振器とセシウム原子を用いた全ファイバーキャビティQED系を2台独立に構築したが、ナノ光ファイバー共振器は光ファイバーそのものに作り込まれた全ファイバー共振器であるため、光ファイバーを用いて複数の共振器を低損失に接続できる。この特長を活かし、今年度(平成29年度)は、2台の共振器QED系を1本の光ファイバーで融着接続し、全ファイバー結合共振器QED系を構築した。このような結合共振器QED系の構築は、世界で初めての成果である。(1)いずれの共振器にも原子をロードしない場合(2)1台の共振器のみに原子をロードした場合(3)両方の共振器に原子をロードした場合の3通りについて、弱励起領域での透過スペクトルを測定した結果、複数の共振器QED系がコヒーレントに結合した系における、原子と非局在光子のコヒーレント結合モードの観測に成功した。また、原子と非局在光子の相互作用が、共振器QED系を繋ぐファイバーチャンネルの長さに依存しないことから、非局在光子がファイバーチャンネル光子の成分を含まないことが示された。この成果は、多数の共振器QED系がコヒーレントに結合した大規模量子ネットワークの構築につながり、そのような系における光子の量子多体系の実現や、巨視的量子エンタングルメントの生成、光子の結晶化の観測、光子の量子相転移現象の観測、分散型量子計算への応用といった展開が期待される。29年度が最終年度であるため、記入しない。29年度が最終年度であるため、記入しない

  • Waveguide quantum electrodynamics using optical nanofiber

    Project Year :

    2014.04
    -
    2017.03
     

     View Summary

    Toward realization of highly efficient interaction between single quantum emitters and sub-wavelength optical nanofibers adiabatically connected to standard single-mode optical fibers, we developed ultra-low-loss tapered optical fibers and novel nanofiber resonators. Furthermore, we have realized strong coupling between single atoms and nanofiber resonators. Toward “waveguide quantum electrodynamics”, we have numerically studied high-efficiency coupling between NV centers in diamond nanowires and optical nanofibers

  • ファイバー結合スクイーズド光発生と量子エンタングルメント

    Project Year :

    2011.04
    -
    2013.03
     

     View Summary

    量子光学的手法による連続量量子情報への応用を目指し、光ファイバーベースでの新しい直交位相成分スクイーズド光発生法の検討を行った。具体的には、超短パルスを用いた従来の直交位相成分スクイーズド光発生法に対して、現在の連続量量子情報技術の主流である連続光を用いた多モード量子エンタングルメントの生成・制御技術との整合性を重視し、光ファイバーに直接結合したシリコンチップ上モノリシック微小共振器を用いた連続光励起での直交位相成分スクイーズド光の発生に関する理論的検討と、共振器設計の最適化、さらに高Q値微小共振器の作製技術の開発を行った。特に、本手法による直交位相成分スクイーズド光の発生には高いQ値と同時に小さなモード体積を持ち、さらに共振スペクトルの測定結果からモード次数を同定できる共振器の開発が必要である。そのような条件を満たす共振器として微小球共振器に着目し、シリコン基板上にモノリシックに作製することで直径20μm以下の極微小球共振器に対して10^8オーダーのQ値を達成した。WGM型共振器のQ値は放射損失、物質の散乱・吸収による損失、表面の凹凸による散乱や不純物による外因性損失等で決まり、究極的には放射損失によって上限が定められる。本研究で達成したQ値は、直径20μm以下の極微小球共振器としては従来の値を1桁以上改善するものであり、放射損失によって決まる理論限界に肉薄するものである。また、共振器を使わずに光ファイバーで直接、光と物質の強い相互作用を実現できるナノファイバーデバイスを開発した。24年度が最終年度であるため、記入しない。24年度が最終年度であるため、記入しない

  • Experimental study on super-dense coding

     View Summary

    We made experimental studies on manipulation of quantum entanglement and super-dense coding wjth continuous variables.In detail,I.We succeeded in creating multipartite entanglement with 3 squeezed vacuums and making a quantum teleportation network.II.We succeeded in high-fidelity quantum teleportation.III.We succeeded in teleporting a squeezed state.IV.We succeeded in the experiment of super-dense coding with continuous variables

  • 半導体レーザーを用いた多者間量子テレポーテーションの研究

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    前年度において生成に成功した連続量3者間量子エンタングルメントを用いて、3者間の量子テレポーテーション・ネットワークを構築した。連続量3者間量子エンタングルメントをアリス、ボブ、クレアの3者に分配し、この3者の間で任意の送信者・受信者の組み合わせにおいて量子テレポーテーションに成功すれば、3者間の量子テレポーテーション・ネットワークの構築に成功したといえる。ただし、2者間の量子テレポーテーションの場合と異なり、送受信に関わらない残りの1者も3者間量子エンタングルメントを共有しているため、他の2者の間の量子テレポーテーションが成功するためにはこの1者もエンタングルメントの測定を行い、その結果を受信者に伝達する必要がある。例としてアリスが送信者、ボブが受信者の場合、アリスは送信状態であるコヒーレント状態を自分の量子エンタングルメントビームとビームスプリッターを用いて合波し、その出力をそれぞれ直交した位相成分x、pについてホモダイン測定する。クレアは自分の量子エンタングルメントビームのみをp成分についてホモダイン測定する。ボブはこれらの結果をそれぞれ受け取り、自分の量子エンタングルメントビームに変位操作を行うことで、送信状態を再現する。クレアからボブへの情報伝達路のゲインを0から1の間で変化させると、ゲインが約0.1以下では再現された状態のフィデリティは古典限界を下回り、約0.1以上では古典限界を上回った。これは3者間量子エンタングルメントを用いて初めて可能な量子操作である。ゲインが約0.9の時に最大のフィデリティ0.63を得た。このような実験を他の2つの組み合わせについても行い、同様の結果を得た。これにより、初めて3者間の量子テレポーテーションに成功した

  • Quantum non-demolition measurement with measurement and feed-forward

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    We succeeded in creating highly squeezed states of light and our record of squeezing level was 9 dB. By using such highly squeezed states of light, we succeeded in creating high level of quantum entanglement. Moreover, we succeeded in building a universal squeezer with the high level of quantum entanglement and measurement and feed-forward" technique.By combining two universal squeezers with two beam splitters, we succeeded in building a setup for quantum non-demolition interaction. Finally, we succeeded in quantum non-demolition measurement in two conjugate variables and checked the existence of quantum entanglement between outputs

  • 半導体量子ドット-微小共振器結合系のコヒーレント量子分光

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    前年度に引き続き、超低損失なトロイド型微小光共振器およびサブ波長径テーパー・ファイバーを作製した。特にテーパー・ファイバーについては、任意のウエスト径、ウエスト長、テーパー角を持ったファイバーの作製技術を確立した。これにより例えば、共振器へ光を入出力するための外部導波路に適した、短い(数mm程度の)ウエスト長のファイバーから、シリカガラスの非線形性を利用した非線形光学ファイバーに適した、長い(数10mm程度の)ウエスト長のファイバーまで、用途に応じて最適な設計のテーパー・ファイバーを作製することができるようになった。後者のデモンストレーションとして、長いウエスト長のテーパー・ファイバーに受動モード同期チタン・サファイアレーザーを入力し、シリカガラスの非線形性とテーパー・ファイバーの特殊な群速度分散による白色光発生に成功した。これは、現在白色光発生に広く用いられているフォトニック結晶ファイバーと比較して格段に安価に作製できる点、さらに通常の単一モード光ファイバーとシームレスに結合した構造である点において有利である。次に、単一半導体量子ドットのコヒーレント量子分光を行うため、上記の技術で作製したテーパー・ファイバーの表面上にコロイド型半導体量子ドットを配置し、テーパー・ファイバーの伝搬モードのエヴァネッセント波と半導体量子ドットの蛍光とを結合させた。この系を用いることで、単一のコロイド型半導体量子ドットの共鳴蛍光を世界で初めて観測した

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Specific Research

  • ナノ光ファイバー共振器量子電気力学系の研究

    2022  

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    共振器量子電気力学系は、光共振器に閉じ込められた光子と、それと相互作用する単一原子からなる系であり、特に強結合領域の共振器量子電気力学系では、光と原子のコヒーレントな相互作用による様々な量子現象が観測できる。従来の共振器量子電気力学系に用いられてきた自由空間共振器は、ファイバー光学との整合性が悪く、スケーラビリティが低いという課題があった。本研究では、独自に開発したナノ光ファイバー共振器を用いた共振器量子電気力学の研究を実施した。

  • トロイド型微小光共振器を用いた微弱光の相互位相変調の研究

    2021  

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    我々は、Q値が極めて高く(=損失が低く)、モード体積Vが極めて小さな(=光のエネルギー密度が大きな)トロイド型微小光共振器を継続して開発している。共振器の光カー効果はQ値とモード体積の比(Q/V値)に比例するが、我々の開発したトロイド型微小光共振器はQ/V値が極めて高いため、この共振器を用いることで、微弱光による相互位相変調が発現する。本研究では、昨年度に引き続き、新規作製方法による共振器開発を実施した。

  • トロイド型微小光共振器を用いた微弱光の相互位相変調の研究

    2020  

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    我々は、Q値が極めて高く(=損失が低く)、モード体積Vが極めて小さな(=光のエネルギー密度が大きな)トロイド型微小光共振器を継続して開発している。共振器の光カー効果はQ値とモード体積の比(Q/V値)に比例するが、我々の開発したトロイド型微小光共振器はQ/V値が極めて高いため、この共振器を用いることで、微弱光による相互位相変調が発現する。本研究では、より大きな相互位相変調を実現するため、新たな共振器作製方法を開発した。

  • 微小光共振器の光カー効果による光子の量子非破壊測定

    2020  

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    我々は、光ファイバーに直接結合した微小共振器を用いて、光子の量子非破壊測定の実現を目指し、その基盤技術を継続的に開発している。すなわち、高Q/V値の微小光共振器が持つ極めて強い光閉じ込めを利用して単一光子レベルでの巨大非線形光学効果(光カー効果)を発現させ、信号光の光子数に比例したプローブ光の位相変化を誘起させることで、信号光の光子数とプローブ光の位相の間に量子相関を生じさせ、量子非破壊測定条件の検証を実施するために必要な技術である。本研究では、高Q/V値ナノ光ファイバー共振器の開発に取り組んだ。

  • トロイド型微小光共振器を用いた微弱光の相互位相変調の研究

    2019  

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    我々は、Q値が極めて高く(=損失が低く)、モード体積Vが極めて小さな(=光のエネルギー密度が大きな)トロイド型微小光共振器を継続して開発している。共振器の光カー効果はQ値とモード体積の比(Q/V値)に比例するが、我々の開発したトロイド型微小光共振器はQ/V値が極めて高いため、この共振器を用いることで、微弱光による相互位相変調が発現する。本研究では、より大きな相互位相変調を実現するため、新たな共振器作製方法を開発した。

  • トロイド型微小光共振器を用いた微弱光の相互位相変調の研究

    2018  

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    我々は、Q値が極めて高く(=損失が低く)、モード体積Vが極めて小さな(=光のエネルギー密度が大きな)トロイド型微小光共振器を継続して開発している。共振器の光カー効果はQ値とモード体積の比(Q/V値)に比例するが、我々の開発したトロイド型微小光共振器はQ/V値が極めて高いため、この共振器を用いることで、微弱光による相互位相変調が発現する。本研究では、より大きな相互位相変調を実現するため、共振器の作製方法を改良した。

  • 微小光共振器を用いた光子の量子非破壊測定の研究

    2018  

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    我々は、光ファイバーに直接結合した微小共振器を用いて、光子の量子非破壊測定の実現を目指し、その基盤技術を継続的に開発している。すなわち、高Q/V値のトロイド型微小光共振器が持つ極めて強い光閉じ込めを利用して単一光子レベルでの巨大非線形光学効果(光カー効果)を発現させ、信号光の光子数に比例したプローブ光の位相変化を誘起させることで、信号光の光子数とプローブ光の位相の間に量子相関を生じさせ、量子非破壊測定条件の検証を実施するために必要な技術である。本研究では、プローブ光の位相測定におけるノイズの低減に取り組んだ。

  • 微小光共振器を用いた光子の量子非破壊測定の研究

    2017  

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    本研究では、光ファイバーに直接結合した微小共振器を用いて、光子の量子非破壊測定の実現を目指し、その基盤技術開発を実施した。すなわち、高Q/V値のトロイド型微小光共振器が持つ極めて強い光閉じ込めを利用して単一光子レベルでの巨大非線形光学効果(光カー効果)を発現させ、信号光の光子数に比例したプローブ光の位相変化を誘起させることで、信号光の光子数とプローブ光の位相の間に量子相関を生じさせ、量子非破壊測定条件の検証を実施するために必要な技術を開発した。

  • トロイド型微小光共振器を用いた微弱光の相互位相変調の研究

    2017  

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    我々は、Q値が極めて高く(=損失が低く)、モード体積Vが極めて小さな(=光のエネルギー密度が大きな)トロイド型微小光共振器を開発した。共振器の光カー効果はQ値とモード体積の比(Q/V値)に比例するが、我々の開発したトロイド型微小光共振器はQ/V値が極めて高いため、この共振器を用いることで、微弱光による相互位相変調が発現する。本研究では、実際にこの相互位相変調を観測した。

  • 共振器量子電気力学系の非局所コヒーレント結合の研究

    2016  

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    共振器量子電気力学系は、光共振器に閉じ込められた光子と、それと相互作用する単一原子からなる系であり、特に強結合領域の共振器量子電気力学系では、光と原子のコヒーレントな相互作用による様々な量子現象が観測できる。研究代表者らは、ごく最近、ナノ光ファイバーとファイバーブラッグ格子を組み合わせた新奇な全ファイバー共振器を開発し、トラップされた単一原子と全ファイバー共振器の共振器量子電気力学系を実現した。本研究では、これらの成果をもとに、全ファイバー共振器量子電気力学系を複数独立に構築し、それらをファイバーで直接結合した連結共振器量子電気力学系の実現に向けた予備的な研究を実施した。

  • ナノ加工ファイバーを用いた単一原子のトラップと量子測定・操作の研究

    2014   永井隆太郎, 加藤真也

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    ナノ光ファイバーの両端を単一モード光ファイバーと連続的に接続するテーパー部において、基本導波モードと高次導波モードの結合による損失は局所的なファイバー径と各モードの伝搬定数に強く依存する。本研究では、損失を押さえながらも全長を最短にするテーパー形状を設計するとともに、その作製方法を確立した。具体的には、99.7%を超える透過率を持ちながら全長わずか23 mmのナノ光ファイバーの作製に成功した。この結果はOptics Express誌に発表した[R. Nagai and T. Aoki, Opt.Express 22, 28427 (2014)]。今後は、作製した超低損失ナノ光ファイバーを用いた単一原子のレーザー冷却・トラップとその量子測定・操作を目指す。

  • 量子光学に適した超高Q値微小旧型光共振器の研究

    2011  

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    量子光学の実験的研究において、高Q値微小光共振器を用いて光を波長スケールの微小体積中に強く閉じ込めることで、光の量子性が増強され、通常の系では困難な非古典的光学現象の観測が可能となる。我々は過去の研究において107~108程度の高Q値微小トロイド型光共振器を用いてさまざまな非古典的光学現象の観測に成功した。しかし、これらの研究で観測された非古典的光学現象あるいは生成された光の量子状態の量子性は依然として低く、量子通信をはじめとした光学的量子情報への応用には不十分である。そのため、より高いQ値の微小共振器の開発が求められている。上記の研究で用いた微小トロイド型光共振器は、エレクトロニクス用途のシリコン基板上のシリコン酸化膜を材料とするが、低損失光ファイバーを材料とすることでさらにQ値の高い共振器の実現が期待される。そこで本研究では、低損失光ファイバーを材料として微小球型光共振器を作成し、109~1010の超高Q値微小光共振器の実現を目指した。まず、光ファイバーを溶融し、表面張力により真球形状の微小光共振器を作製する技術を開発した。具体的には、被覆を除去しクラッド表面を洗浄した光ファイバーの先端を、CO2レーザーを用いて溶融した。シリカガラスはCO2レーザーの発振波長である中赤外領域に大きな吸収係数を持つため、CO2レーザーの照射によって局所的に加熱することができる。ただしこの方法では、流入熱量は加熱領域の体積に比例するが放射による熱の流出は表面積に比例するため、数μmスケールの微小な体積の高温加熱は困難であることも予想された。しかし、開口数の大きなレンズを用いてレーザーを集光することで、直径数μm程度の極細光ファイバーの先端であっても容易に溶融させることができた。上記の方法で作製した微小球共振器のQ値を周波数領域において測定した。テーパーファイバーを外部導波路として結合した微小球共振器に対して狭線幅の外部共振器型半導体レーザーを入力し、レーザー波長を掃引することで共振スペクトルを測定し、その幅からQ値を得た。結合損失を考慮し、共振器の真性Q値を見積もった結果、1×109を達成した。作製条件の最適化によって、更なるQ値の向上が見込まれる。

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