Papers - Ota, Yasutomo

Time-domain observation of vacuum rabi oscillations in a strongly coupled quantum dot-nanocavity system

Kuruma K., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F43-CLEO_AT 2017 2017

Research paper (international conference proceedings), Joint Work, Accepted

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We report the time-domain observation of vacuum Rabi oscillations in a single quantum dot-photonic crystal nanocavity system under optical carrier injection. A significantlyimproved cavity Q-factor facilitates the direct access to the ultrafast exciton-photon dynamics.

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Position dependent optical coupling between single quantum dots and photonic crystal nanocavities

Kuruma K., Ota Y., Kakuda M., Takamiya D., Iwamoto S., Arakawa Y.

Applied Physics Letters 109 ( 7 )  2016.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate precise and quick detection of the positions of quantum dots (QDs) embedded in two-dimensional photonic crystal nanocavities. We apply this technique to investigate the QD position dependence of the optical coupling between the QD and the nanocavity. We use a scanning electron microscope (SEM) operating at a low acceleration voltage to detect surface bumps induced by the QDs buried underneath. This enables QD detection with a sub-10 nm precision. We then experimentally measure the vacuum Rabi spectra to extract the optical coupling strengths (gs) between single QDs and cavities, and compare them to the values estimated by a combination of the SEM-measured QD positions and electromagnetic cavity field simulations. We found a highly linear relationship between the local cavity field intensities and the QD-cavity gs, suggesting the validity of the point dipole approximation used in the estimation of the gs. The estimation using SEM has a small standard deviation of ±6.2%, which potentially enables the high accuracy prediction of g prior to optical measurements. Our technique will play a key role for deeply understanding the interaction between QDs and photonic nanostructures and for advancing QD-based cavity quantum electrodynamics.

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Effect of metal side claddings on emission decay rates of single quantum dots embedded in a sub-wavelength semiconductor waveguide

Yamamoto T., Ota Y., Ishida S., Kumagai N., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 55 ( 8 )  2016.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We experimentally investigate the emission decay rates of self-assembled single InAs quantum dots (QDs) embedded in sub-wavelength semiconductor waveguides with and without metal side claddings. Compared with as-grown single QDs, we observe a clear suppression (enhancement) in the radiative decay rates of single InAs QDs embedded in the sub-wavelength semiconductor waveguides without (with) metal cladding, respectively. The decay rate for QDs in metal-clad waveguides is >2 times faster than that in waveguides without metal. Numerical calculations using models that include the effects of structural imperfections show good agreement with the experimental results, and reveal that the most important structural imperfection is the gap between the metal and the semiconductor.

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A Nanowire-Based Plasmonic Quantum Dot Laser

Ho J., Tatebayashi J., Sergent S., Fong C.F., Ota Y., Iwamoto S., Arakawa Y.

Nano Letters 16 ( 4 ) 2845 - 2850 2016.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  15306984

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Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm² was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

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P-shell carrier assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field

Fong C.F., Ota Y., Harbord E., Iwamoto S., Arakawa Y.

Physical Review B 93 ( 12 )  2016.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

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Repeated injection of spin-polarized carriers in a quantum dot (QD) leads to the polarization of nuclear spins, a process known as dynamic nuclear spin polarization (DNP). Here, we report the observation of p-shell carrier assisted DNP in single QDs at zero external magnetic field. The nuclear field - measured by using the Overhauser shift of the singly charged exciton state of the QDs - continues to increase, even after the carrier population in the s-shell saturates. This is also accompanied by an abrupt increase in nuclear spin buildup time as p-shell emission overtakes that of the s shell. We attribute the observation to p-shell electrons strongly altering the nuclear spin dynamics in the QD, supported by numerical simulation results based on a rate equation model of coupling between electron and nuclear spin system. Dynamic nuclear spin polarization with p-shell carriers could open up avenues for further control to increase the degree of nuclear spin polarization in QDs.

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Effect of metal side claddings on emission decay rate of single quantum dots embedded in a subwavelength semiconductor waveguide

Yamamoto T., Ota Y., Ishida S., Kumagai N., Iwamoto S., Arakawa Y.

Moc 2015 Technical Digest of 20th Microoptics Conference  2016.02

Research paper (international conference proceedings), Joint Work, Accepted

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We measured the emission decay rates of self-assembled InAs single quantum dots (QDs) embedded in subwavelength-width semiconductor waveguides with and without Au side claddings. The Au claddings increased the decay rate of single QDs by ∼2 times, which is consistent with numerical simulations taking account of fabrication imperfection.

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Influence of the relative positions of quantum dots and nanocavities on the optical coupling strength

Kuruma K., Ota Y., Takamiya D., Kakuda M., Iwamoto S., Arakawa Y.

2015 11th Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2015 3 2016.01

Research paper (international conference proceedings), Joint Work, Accepted

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We use scanning electron microscopy to precisely measure the locations of quantum dots buried in photonic crystal nanocavities. We show that well-positioned dots (at the field maximum) can exhibit vacuum Rabi splittings larger than 180μeV.

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Demonstration of a three-dimensional photonic crystal nanocavity in a 〈110〉-layered diamond structure

Tajiri T., Takahashi S., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Applied Physics Letters 107 ( 7 )  2015.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We experimentally demonstrate a three-dimensional photonic crystal (3D PC) nanocavity in a 〈110a〉-layered diamond structure with a quality factor (Q-factor) of 12800 at a wavelength of 1.1 μm. The observed Q is 1.2 times higher than that of a 3D PC nanocavity in a woodpile structure with the same in-plane size and the same number of stacked layers. This result indicates the potential importance of the 〈110a〉-layered diamond structure for getting high Q 3D PC nanocavities within a limited in-plane space.

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Circularly polarized light emission of quantum dots at the band edge of three-dimensional chiral photonic crystals

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate highly circularly polarized emission from quantum dots in semiconductor chiral photonic crystals. The emission is influenced by the difference in density of states between the orthogonal circular polarizations at the polarization band edge.

Room-temperature lasing in GaAs nanowires embedding multi-stacked InGaAs/GaAs quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

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We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μm/cm².

Single emitter vacuum Rabi splitting measured through direct free space spontaneous emission

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

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We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission.

Room-temperature lasing in a single nanowire with quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

Nature Photonics 9 ( 8 ) 501 - 505 2015.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  17494885

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Semiconductor nanowire lasers are promising as ultrasmall, highly efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of nanowire lasers using homogeneous bulk gain materials or multi-quantum-wells/disks, it is crucial to incorporate lower-dimensional quantum nanostructures into the nanowire to achieve superior device performance in relation to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot is a useful and essential nanostructure that can meet these requirements. However, difficulties in forming stacks of quantum dots in a single nanowire hamper the realization of lasing operation. Here, we demonstrate room-temperature lasing of a single nanowire containing 50 quantum dots by properly designing the nanowire cavity and tailoring the emission energy of each dot to enhance the optical gain. Our demonstration paves the way toward ultrasmall lasers with extremely low power consumption for integrated photonic systems.

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Circularly polarized light emission of quantum dots at the band edge of three-dimensional chiral photonic crystals

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

CLEO QELS Fundamental Science CLEO QELS 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate highly circularly polarized emission from quantum dots in semiconductor chiral photonic crystals. The emission is influenced by the difference in density of states between the orthogonal circular polarizations at the polarization band edge. © OSA 2015.

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Room-temperature lasing in GaAs nanowires embedding multi-stacked InGaAs/GaAs quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

CLEO Science and Innovations CLEO Si 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

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We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μJ/cm². ©2015 Optical Society of America.

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Single emitter vacuum Rabi splitting measured through direct free space spontaneous emission

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

CLEO QELS Fundamental Science CLEO QELS 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

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We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission. © OSA 2015.

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Vacuum Rabi spectra of a single quantum emitter

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

Physical Review Letters 114 ( 14 )  2015.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00319007

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We report the observation of the vacuum Rabi splitting of a single quantum emitter by measuring its direct spontaneous emission into free space. We use a semiconductor quantum dot inside a photonic crystal nanocavity, in conjunction with an appropriate cavity design and filtering with a polarizer and an aperture, enabling the extraction of the inherently weak emitter's signal. The emitter's vacuum Rabi spectra exhibit clear differences from those measured by detecting the cavity photon leakage. Moreover, we observe an asymmetric vacuum Rabi spectrum induced by interference between the emitter and cavity detection channels. Our observations lay the groundwork for accessing various cavity quantum electrodynamics phenomena that manifest themselves only in the emitter's direct spontaneous emission.

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Asymmetric out-of-plane power distribution in a two-dimensional photonic crystal nanocavity

Ota Y., Iwamoto S., Arakawa Y.

Optics Letters 40 ( 14 ) 3372 - 3375 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

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Conventional air-bridge two-dimensional photonic crystal (2D-PhC) nanocavities emit light with an equal power distribution for upward and downward out-of-plane directions. Some applications, however, require concentration of the radiation in a preferred direction. In this Letter, we design a 2D-PhC nanocavity that radiates dominantly into one of the out-of-plane directions with a narrow far-field distribution. Our design is based on a conventional airbridge L3 photonic crystal nanocavity. The asymmetric out-of-plane power distribution is achieved solely by adding periodic shallow holes on the slab surface, which also function as a second-order grating for the directional beaming.

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Cavity QED in quantum dot-photonic crystal nanocavity coupled systems

Arakawa Y., Iwamoto S., Ota Y., Kamide K.

Optics Infobase Conference Papers  2014.10

Research paper (international conference proceedings), Joint Work, Accepted

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Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

Tatebayashi J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Applied Physics Letters 105 ( 10 )  2014.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate a highly uniform, dense stack of In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dotto-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3 meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

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Circular dichroism in a three-dimensional semiconductor chiral photonic crystal

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Applied Physics Letters 105 ( 5 )  2014.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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Circular dichroism covering the telecommunication band is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC). We design a rotationally stacked woodpile PhC structure where neighboring layers are rotated by 60° and three layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. Due to the large contrast of refractive indices between GaAs and air, the experimentally obtained circular dichroism extends over a wide wavelength range, with the transmittance of right-handed circularly polarized incident light being 85% and that of left-handed light being 15% at a wavelength of 1.3 μ m. The obtained results show good agreement with numerical simulations. © 2014 AIP Publishing LLC.

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