Details of a Researcher - Ota, Yasutomo

Papers - Ota, Yasutomo

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Spin dynamics of excited trion states in a single InAs quantum dot

Y Igarashi, M Shirane, Y Ota, M Nomura, N Kumagai, S Ohkouchi, ...

Physical Review B 81 (24), 245304 2010

Research paper (scientific journal), Joint Work, Accepted

Phonon-induced asymmetry in vacuum Rabi doublet for coupled quantum dot-cavity system

Y Ota, N Kumagai, S Ohkouchi, M Shirane, M Nomura, S Ishida, ...

Quantum Electronics and Laser Science Conference, QThM2 (IEEE) 2010

Research paper (scientific journal), Joint Work, Accepted

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Observation of unique photon statistics of single artificial atom laser

M Nomura, N Kumagai, S Iwamoto, Y Ota, Y Arakawa

Physica E: Low-dimensional Systems and Nanostructures 42 (10), 2489-2492 (ELSEVIER SCIENCE BV) 42 ( 10 ) 2489 - 2492 2010

Research paper (scientific journal), Joint Work, Accepted, ISSN 1386-9477

We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain and its unique photon statistics. Gain tuning measurements and photon correlation measurements indicated that a single quantum dot plays a substantial role in the laser oscillation. Photon correlation measurements showed a distinct transition from anti-bunching to Poissonian via photon bunching around the threshold with the increase of the excitation power. Numerical simulations, including contributions of other light sources besides a single quantum dot, indicated that the photon bunching feature around the threshold can be enhanced by the interfusion of incoherent photons into the cavity mode. (C) 2009 Elsevier B.V. All rights reserved.

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Neutralization of positively charged excitonic state in single InAs quantum dot by Si delta doping

N Kumagai, S Ohkouchi, M Shirane, Y Igarashi, M Nomura, Y Ota, ...

Journal of Physics: Conference Series 245 (1), 012088 (Institute of Physics Publishing) 244 2010

Research paper (scientific journal), Joint Work, Accepted, ISSN 1742-6596

Positively charged excitonic state in single InAs quantum dot (QD) has been neutralized by Si delta doping and the optical properties of the fabricated samples are characterized by micro-photoluminescence measurements (μ-PL) at low temperature. An InAs QD sample having dominant emissions from positively charged excitonic states is prepared for a reference. By optimizing Si delta doping conditions, positively charged QDs are neutralized successfully and distinctive emissions from neutral exciton and biexciton from single QDs are achieved. For excessive doping condition, μ-PL spectra show optical degradation of lowering of peak intensity and broadening of peak width as doping concentration increases. © 2010 IOP Publishing Ltd.

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Zero-cell photonic crystal nanocavity laser with quantum dot gain

M Nomura, Y Ota, N Kumagai, S Iwamoto, Y Arakawa

Applied Physics Letters 97 (19), 191108 (AMER INST PHYSICS) 97 ( 19 ) 2010

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We demonstrate laser oscillation in a hexagonal-lattice photonic crystal nanocavity using an InGaAs quantum dot gain material by optical pumping at 5 K. The cavity comprises a defect created by shifting several air holes in a two-dimensional photonic crystal slab structure without removing any air holes to achieve both small mode volume and a high cavity quality factor. The measured cavity quality factors and estimated mode volume for the nanocavity are similar to 33 000 and 0.004 mu m(3) [0.23(lambda(0)/n)(3)]. The laser threshold is compared between the zero-cell and L3-type nanocavity lasers, and the zero-cell nanolasers are found to have lower thresholds of about one-third of the L3-type nanolasers. This result suggests that a higher Purcell factor of the zero-cell nanolaser is reflected as a lower laser threshold. (C) 2010 American Institute of Physics. [doi:10.1063/1.3514556]

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Single quantum dot-photonic crystal nanocavity laser

M Nomura, N Kumagai, Y Ota, S Iwamoto, Y Arakawa

IEICE Technical Report; IEICE Tech. Rep. 109 (403), 11-14 (The Institute of Electronics, Information and Communication Engineers) 109 ( 401 ) 11 - 14 2010

Joint Work, ISSN 0913-5685

Strong light-matter interaction in a single semiconductor quantum dot-nanocavity coupled system provides various interesting physics, which can be described by cavity quantum electrodynamics. A single quantum dot-photonic crystal nanocavity system provides excellent test beds for solid cavity quantum electrodynamics because photons can be confined in ultimately small volume on the order of its wavelength. An ultimately small laser can be achievable by using a single quantum dot gain material in this system. Here we demonstrate laser oscillation in both weak- and strong-coupling regimes in this system. In the strong-coupling regime, quanta are coherently going back and forth between the excitonic and phonic states, while irreversible photon emission from an excitonic state occurs in the lasing regime. The onset of lasing in the strong-coupling regime is of great interest and its demonstration in solid state materials is reported for the first time.

Investigation of the Spectral Triplet in Strongly Coupled Quantum Dot-Nanocavity System

Yasutomo Ota, Naoto Kumagai, Shunsuke Ohkouchi, Masayuki Shirane, Masahiro Nomura, Satomi Ishida, Satoshi Iwamoto, Shinichi Yorozu, Yasuhiko Arakawa

APPLIED PHYSICS EXPRESS (JAPAN SOC APPLIED PHYSICS) 2 ( 12 ) 2009.12

Research paper (scientific journal), Joint Work, Accepted, ISSN 1882-0778

We experimentally investigated the excitation power dependence of a strongly coupled quantum dot (QD)-photonic crystal nanocavity system by photoluminescence measurements. At a low excitation power regime, we observed a vacuum Rabi doublet emission at the QD-cavity resonance condition. With increasing excitation power, in addition to the doublet, a third emission peak appeared. This observed spectral change is unexpected from conventional atomic cavity quantum electrodynamics. The observations can be attributed to featured pumping processes in the semiconductor QD-cavity system. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/APEX.2.122301

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Vacuum Rabi splitting with a single quantum dot embedded in a H1 photonic crystal nanocavity

Yasutomo Ota, Masayuki Shirane, Masahiro Nomura, Naoto Kumagai, Satomi Ishida, Satoshi Iwamoto, Shinichi Yorozu, Yasuhiko Arakawa

APPLIED PHYSICS LETTERS (AMER INST PHYSICS) 94 ( 3 ) 2009.01

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We report here the first observation of vacuum Rabi splitting in a single quantum dot (QD) embedded in a H1 photonic crystal nanocavity by photoluminescence measurement. The QD emission was tuned into a cavity mode by controlling the temperature. At the resonance condition, clear anticrossing with a Rabi splitting of similar to 124 mu eV was observed, where the cavity mode possesses the smallest mode volume V similar to 0.43(lambda/n)(3) among strongly coupled QD-cavity systems reported to date.

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Impact of electron-phonon interactions on quantum-dot cavity quantum electrodynamics

Y Ota, S Iwamoto, N Kumagai, Y Arakawa

arXiv preprint arXiv:0908.0788 2009

Research paper (scientific journal), Joint Work, Accepted

Photonic Crystal Nanocavity Laser with Single Quantum Dot Gain

Masahiro Nomura, Naoto Kumagai, Satoshi Iwamoto, Yasutomo Ota, Yasuhiko Arakawa

2009 CONFERENCE ON LASERS AND ELECTRO-OPTICS AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2009), VOLS 1-5 (IEEE) 626 - 627 2009

Research paper (scientific journal), Joint Work, Accepted, ISSN 978-1-4244-5184-5

Photonic crystal nanocavity laser with a single quantum dot gain

M Nomura, N Kumagai, S Iwamoto, Y Ota, Y Arakawa

Optics Express 17 (18), 15975-15982 (OPTICAL SOC AMER) 17 ( 18 ) 15975 - 15982 2009

Research paper (scientific journal), Joint Work, Accepted, ISSN 1094-4087

We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10(8) cm(-2)) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require similar to 145 nW for lasing. This spectral detuning dependence of laser threshold indicates substantial contribution of the single quantum dot to the total gain. Moreover, photon correlation measurements show a distinct transition from anti-bunching to Poissonian via bunching with the increase of the excitation power, which is also an evidence of laser oscillation using the single quantum dot gain. (C) 2009 Optical Society of America

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Photonic band-edge micro lasers with quantum dot gain

M Nomura, S Iwamoto, A Tandaechanurat, Y Ota, N Kumagai, Y Arakawa

Optics express 17 (2), 640-648 (OPTICAL SOC AMER) 17 ( 2 ) 640 - 648 2009

Research paper (scientific journal), Joint Work, Accepted, ISSN 1094-4087

We demonstrate optically pumped continuous-wave photonic band-edge microlasers on a two-dimensional photonic crystal slab. Lasing was observed at a photonic band-edge, where the group velocity was significantly small near the K point of the band structure having a triangular lattice. Lasing was achieved by using a quantum dot gain material, which resulted in a significant decrease in the laser threshold, compared with photonic band-edge lasers using quantum well gain material. Extremely low laser thresholds of similar to 80 nW at 6 K was achieved. Lasing was observed in a defect-free photonic crystal as small as similar to 7 mu m square. (C) 2009 Optical Society of America

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Light-matter interaction in single quantum dot with photonic crystal nanocavity

Y Arakawa, M Nomura, S Iwamoto, Y Ota

Conference on Lasers and Electro-Optics/Pacific Rim, TuH2_2 (Optics InfoBase Conference Papers) 2009

Research paper (scientific journal), Joint Work, Accepted

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Investigation of the spectral triplet in strongly coupled quantum dot–nanocavity system

Y Ota, N Kumagai, S Ohkouchi, M Shirane, M Nomura, S Ishida, ...

Applied physics express 2 (12), 122301 2009

Research paper (scientific journal), Joint Work, Accepted

Vacuum Rabi splitting with a single quantum dot embedded in a photonic crystal nanocavity

Y Ota, M Shirane, M Nomura, N Kumagai, S Ishida, S Iwamoto, S Yorozu, ...

Applied Physics Letters 94 (3), 033102 2009

Research paper (scientific journal), Joint Work, Accepted

Achievement of ultra-low threshold excitation power (8 nW) in a nearly-single quantum dot nanocavity laser

M Nomura, Y Ota, N Kumagai, S Iwamoto, Y Arakawa

Conference on lasers and Electro-Optics, CTuW3 (IEEE) 1714 - + 2008

Research paper (scientific journal), Joint Work, Accepted, ISSN 978-1-55752-859-9

Efficient excitation and emission of single quantum dot by simultaneous coupling to two different photonic crystal nanocavity modes

Y Ota, M Nomura, N Kumagai, K Watanabe, S Ishida, S Iwamoto, ...

Conference on Lasers and Electro-Optics, CTuW2 (IEEE) 1712 - + 2008

Research paper (scientific journal), Joint Work, Accepted, ISSN 978-1-55752-859-9

Enhanced photon emission and absorption of single quantum dot in resonance with two modes in photonic crystal nanocavity

Y Ota, M Nomura, N Kumagai, K Watanabe, S Ishida, S Iwamoto, ...

Applied Physics Letters 93 (18), 183114 (AMER INST PHYSICS) 93 ( 18 ) 2008

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We demonstrate simultaneous enhancement of photon emission and absorption of a single InGaAs self-assembled quantum dot (QD) in resonance with two modes in a photonic crystal nanocavity. The QD, whose ground and excited states are resonant, respectively, with the first and second lowest order cavity modes, is excited by cavity resonant excitation at the wavelength of the second order cavity mode and shows 180 times greater photon emission from the ground state than a bare QD. This large enhancement is attributed to a combination of Purcell effect, efficient photon extraction, and cavity resonant absorption enhancement.

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Refraction and diffraction by a metal-dielectric multilayered structure

S Kameda, Y Ohta, H Kikuta

JOSA A 25 (4), 903-910 (Journal of the Optical Society of America A: Optics and Image Science, and Vision) 25 ( 4 ) 903 - 910 2008

Research paper (scientific journal), Joint Work, Accepted, ISSN 10847529

An optical refraction prism consisting of metal and dielectric, subwavelength, periodic multilayered thin films has been proposed. The multilayered structure of metal and dielectric thin films has a cylindrical dispersion surface for TM polarized light. The light behaviors are very different from those of conventional glass prisms and photonic crystal superprisms. Refraction and diffraction of the light wave for the metal-dielectric multilayered prism has been investigated by numerical simulations and graphical representation based on the dispersion surface. A prism with 0.2 μm period had an angular dispersion of 0.20̊/nm for ̃0.8 μm wavelength light. The finite thick metal-dielectric multilayered structure acted as a slab waveguide. © 2008 Optical Society of America.

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Large vacuum Rabi splitting in single self-assembled quantum dot-nanocavity system

M Nomura, Y Ota, N Kumagai, S Iwamoto, Y Arakawa

Applied physics express 1 (7), 072102 (JAPAN SOCIETY APPLIED PHYSICS) 1 ( 7 ) 2008

Research paper (scientific journal), Joint Work, Accepted, ISSN 1882-0778

We report on the observation of the strong-coupling regime in a single InGaAs self-assembled quantum dot (OD) and photonic crystal nanocavity system. There was a strong interaction between the OD exciton and discretized photon mode and the strong coupling was manifest in photoluminescence data, which displayed a distinct anti-crossing in temperature tuning measurements. A vacuum Rabi splitting of 180 mu eV was observed, which was larger than the values given in previous studies with clear exciton polariton modes. In addition, the exciton-photon coupling strength amounted to about 90 peV. A distinct energy mixing, which resulted from the reversible photon emission process of a OD, was also observed when the system formed a QD exciton polariton state. (C) 2008 The Japan Society of Applied Physics.

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