Papers - Ota, Yasutomo

Transfer-printed quantum-dot nanolasers on a silicon photonic circuit

Osada A., Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Applied Physics Express 11 ( 7 )  2018.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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Quantum-dot (QD) nanolasers integrated on a silicon photonic circuit are demonstrated for the first time. QD nanolasers based on one-dimensional photonic crystal nanocavities containing InAs/GaAs QDs are integrated on CMOS-processed silicon waveguides with silicon dioxide cladding. We employed transfer printing, whereby the three-dimensional stack of photonic nanostructures is assembled in a pick-and-place manner. The lasing operation and waveguide coupling of an assembled single nanolaser are confirmed through micro-photoluminescence spectroscopy. Furthermore, by repetitive transfer printing, two QD nanolasers integrated onto a single silicon waveguide are demonstrated, opening a path to the development of compact light sources potentially applicable to wavelength division multiplexing.

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Time-resolved vacuum Rabi oscillations in a quantum-dot-nanocavity system

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

Physical Review B 97 ( 23 )  2018.06

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

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We report time domain observation of vacuum Rabi oscillations in a single quantum dot strongly coupled to a nanocavity under incoherent optical carrier injection. We realize a photonic crystal nanocavity with a very high quality factor of >80000 and employ it to clearly resolve the ultrafast vacuum Rabi oscillations by simple photoluminescence-based experiments. We found that the time domain vacuum Rabi oscillations were largely modified when changing the pump wavelength and intensity, even when marginal changes were detected in the corresponding photoluminescence spectra. We analyze the measured time domain oscillations by fitting to simulation curves obtained with a cavity quantum electrodynamics model. The observed modifications of the oscillation curves were mainly induced by the change in the carrier capture and dephasing dynamics in the quantum dot, as well as the change in bare-cavity emission. This result suggests that vacuum Rabi oscillations can be utilized as a highly sensitive probe for the quantum-dot dynamics. Our work points out a powerful alternative to conventional spectral-domain measurements for a deeper understanding of the vacuum Rabi dynamics in quantum-dot-based-cavity quantum electrodynamics systems.

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Transfer-printed single-photon sources coupled to wire waveguides

Katsumi R., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optica 5 ( 6 ) 691 - 694 2018.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  23342536

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Photonic integrated circuits (PICs) are attractive platforms to perform large-scale quantum information processing. While highly functional PICs (e.g., silicon-based photonic circuits) and high-performance single-photon sources [SPSs, e.g., compound-semiconductor quantum dots (QDs)] have been independently demonstrated, their combination for single-photon-based applications has still been limited. This is largely due to the complexities of introducing SPSs into existing PIC platforms, which are generally realized with different materials and using distinct fabrication protocols. Here, we report a novel approach to combine SPSs and PICs prepared independently. We employ transfer printing, by which multiple desired SPSs can be integrated in a simple pick-and-place manner with a theoretical waveguide coupling efficiency >99%, fulfilling the demanding requirements of large-scale quantum applications. Experimentally, we demonstrated QD-based SPSs with high waveguide coupling efficiencies, together with the integration of two SPSs into a waveguide. Our approach will accelerate scalable fusion between modern PICs and cutting-edge quantum technologies.

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Nanowire-quantum-dot lasers on flexible membranes

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

Applied Physics Express 11 ( 6 )  2018.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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We demonstrate lasing in a single nanowire with quantum dots as an active medium embedded on poly(dimethylsiloxane) membranes towards application in nanowire-based flexible nanophotonic devices. Nanowire laser structures with 50 quantum dots are grown on patterned GaAs(111)B substrates and then transferred from the as-grown substrates on poly(dimethylsiloxane) transparent flexible organosilicon membranes, by means of spin-casting and curing processes. We observe lasing oscillation in the transferred single nanowire cavity with quantum dots at 1.425 eV with a threshold pump pulse fluence of ∼876 μJ/cm², which enables the realization of high-performance multifunctional NW-based flexible photonic devices.

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High-Q nanocavities in semiconductor-based three-dimensional photonic crystals

Takahashi S., Tajiri T., Watanabe K., Ota Y., Iwamoto S., Arakawa Y.

Electronics Letters 54 ( 5 ) 305 - 307 2018.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00135194

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The high-quality factors (Q-factors) of nanocavities in three-dimensional photonic crystals were experimentally demonstrated by increasing the in-plane area of the structure. Entire structures made of GaAs were fabricated by a micro-manipulation technique, and the nanocavities contained InAs self-assembled quantum dots that emitted near-infrared light. The obtained Q-factor was improved to 93,000, which is 2.4 times larger than that in a previous report of a three-dimensional photonic crystal nanocavity. Due to this large Q-factor, a lasing oscillation from this cavity mode was successfully observed.

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Large vacuum Rabi splitting between a single quantum dot and an H0 photonic crystal nanocavity

Ota Y., Takamiya D., Ohta R., Takagi H., Kumagai N., Iwamoto S., Arakawa Y.

Applied Physics Letters 112 ( 9 )  2018.02

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

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Strong light matter interactions between semiconductor quantum dots and optical micro/nanocavities are useful resources for developing quantum information processing devices and for exploring diverse quantum optical phenomena. In pursuit of better device performances and novel physics, it is desirable to achieve a larger coupling constant between the quantum dot and the cavity while keeping the high coherence of the coupled system. In this letter, we report the observation of a large vacuum Rabi splitting of ∼328 μeV using a single InAs quantum dot embedded in a GaAs-based H0 photonic crystal nanocavity, which possesses a near-diffraction limited mode volume as well as a high experimental Q factor of ∼52 000. The resulting figure of merit of the strongly coupled systems, defined as a ratio of the coupling constant to the cavity decay rate, reaches 6.4, which is the record high value for semiconductor QD-nanocavity systems reported to date.

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Lasing in a topological photonic crystal nanocavity

Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F94-CLEO_SI 2018 2018

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

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We report lasing oscillation in a zero-dimensional edge state formed at the boundary of two photonic crystal nanobeams with distinct band topologies. The topological origin of the nanocavity mode ensures a single mode operation.

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Quantum dot single photon sources transfer-printed on wire waveguides

Katsumi R., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F93-CLEO_QELS 2018 2018

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

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We report quantum dot single photon sources coupled to glass-clad wire waveguides by transfer printing, which enables the heterogeneous source integration in a simple pick-and-place manner. A high waveguide coupling efficiency > 60% is experimentally demonstrated.

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Topological confinement of light in photonic crystals

Iwamoto S., Ota Y., Arakawa Y.

Optics Infobase Conference Papers Part F125-OPJ 2018 2018

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

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We will discuss a topological locarized state of light realizedin a photonic crystal (PhC) nanbeam platform. By carefuly tunig the unit cell structure, we can design two topologically distinct PhC nanobeams. The bulk-edge correpondence guarantees the existence of single localized mode at the interface between them within their common bandgap. We demonstrate the lasing osscilation using the mode as a nanocavity mode.

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Quantum-dot nanolasers on Si photonic circuits

Osada A., Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F94-CLEO_SI 2018 2018

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

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We report the hybrid integration of quantum dot nanolasers on silicon photonic circuits using transfer printing. The pick-and-place assembly method facilitates the integration of two nanolasers on a single CMOS-processed waveguide that supports two-wavelength output.

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A photonic crystal nanocavity with a quantum dot active region embedded by MBE regrowth

Vo Q.H., Ota Y., Watanabe K., Kageyama T., Iwamoto S., Arakawa Y.

22nd Microoptics Conference Moc 2017 2017-November   90 - 91 2017.11

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

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We fabricated a two dimensional photonic crystal nanocavity embedding a spatially-isolated active region containing InAs quantum dots using crystal regrowth with molecular beam epitaxy. We observed a cavity mode with a quality factor over 10,000, despite the existence of a mound structure on top of the buried active region due to faceting during the regrowth.

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Circularly polarized vacuum field in three-dimensional chiral photonic crystals probed by quantum dot emission

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

Physical Review B 96 ( 19 )  2017.11

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

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The modification of a circularly polarized vacuum field in three-dimensional chiral photonic crystals was measured by spontaneous emission from quantum dots in the structures. Due to the circularly polarized eigenmodes along the helical axis in the GaAs-based mirror-asymmetric structures we studied, we observed highly circularly polarized emission from the quantum dots. Both spectroscopic and time-resolved measurements confirmed that the obtained circularly polarized light was influenced by a large difference in the photonic density of states between the orthogonal components of the circular polarization in the vacuum field.

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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.

2017 Conference on Lasers and Electro Optics CLEO 2017 Proceedings 2017-January   1 - 2 2017.10

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 significantly-improved cavity Q-factor facilitates the direct access to the ultrafast exciton-photon dynamics.

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Demonstration of lasing oscillation in a plasmonic microring resonator containing quantum dots fabricated by transfer printing

Tamada A., Ota Y., Kuruma K., Ho J., Watanabe K., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 56 ( 10 )  2017.10

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

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We demonstrate room-temperature lasing oscillation in a plasmonic microring resonator containing InAs/GaAs self-assembled quantum dots. The resonator is composed of a GaAs microring placed on an atomically flat silver surface. Such a structure was fabricated by transfer printing, through which we can pick the dielectric microring and place it on the silver surface at will, hence maintaining a high-quality metal surface without introducing any complex fabrication process. Our result will be important in the development of nanoscale light sources in future densely integrated plasmonic circuits.

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Method for generating a photonic NOON state with quantum dots in coupled nanocavities

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

Physical Review A 96 ( 1 )  2017.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699926

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We propose a method to generate path-entangled NOON-state photons from quantum dots and coupled nanocavities. In the systems we considered, cavity mode frequencies are tuned close to the biexciton two-photon resonance. Under appropriate conditions, the system can have the target NOON state in the energy eigenstate, as a consequence of destructive quantum interference. The NOON state can be generated by a resonant laser excitation. This method, first introduced for a two-photon NOON state (N=2), can be extended toward a higher NOON state (N>2) based on our recipe, which is applied to the case of N=4 as an example.

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Manipulation of dynamic nuclear spin polarization in single quantum dots by photonic environment engineering

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

Physical Review B 95 ( 24 )  2017.06

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

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Optically induced dynamic nuclear spin polarization (DNP) in a semiconductor quantum dot (QD) requires many cycles of excitation of spin polarized carriers and carrier recombination. As such, the radiative lifetime of the exciton containing the electron becomes one of the limiting factors of DNP. In principle, changing the radiative lifetime of the exciton will affect DNP and thus the nuclear spin polarization. Here, we demonstrate the manipulation of DNP in single QDs through the engineering of the photonic environment using two-dimensional photonic crystals. We find that the achievable degree of nuclear spin polarization can be controlled through the modification of exciton radiative lifetime. Our results show the promise of achieving a higher degree of nuclear spin polarization via photonic environment engineering, with implications on spin-based quantum information processing.

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Growth of InGaAs/GaAs nanowire-quantum dots on AlGaAs/GaAs distributed Bragg reflectors for laser applications

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

Journal of Crystal Growth 468   144 - 148 2017.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00220248

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We report the formation of GaAs nanowires (NWs) containing In<inf>0.2</inf>Ga<inf>0.8</inf>As/GaAs quantum dots (QDs) on patterned Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs distributed Bragg reflectors (DBRs) grown on GaAs(111)B substrates. The growth conditions of both GaAs and Al<inf>0.65</inf>Ga<inf>0.35</inf>As layers on GaAs(111)B are optimized for the growth of high-quality Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs DBRs with (111) orientation in order to obtain high reflectivity at the NW/DBR interface. Moderately high growth temperature and low V/III ratio can mitigate the formation of pyramidal hillocks, resulting in the formation of high-quality DBRs on GaAs(111)B substrates. Optical characterization at 7 K of single GaAs NW cavities containing 75-stacked InGaAs/GaAs NWQDs grown on patterned such Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs DBRs/GaAs(111)B substrates exhibits lasing oscillation at 1.43 eV with a threshold pump pulse fluence of 250 μJ/cm².

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Enhanced optical Stark shifts in a single quantum dot embedded in an H1 photonic crystal nanocavity

Takagi H., Ota Y., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Applied Physics Express 10 ( 6 )  2017.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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We demonstrate large optical Stark shifts in a single quantum dot embedded in a modified H1 photonic crystal nanocavity. We designed the nanocavity to simultaneously possess a high Q factor, a small mode volume, and a high coupling efficiency to the external laser field. This nanocavity enabled the observation of a large Stark shift of 70 μeV even under very weak laser irradiation. The large shift was sustained by only four intracavity photons on average, paving the way for the development of ultralow-power quantum/classical optical devices.

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Optical coupling between atomically thin black phosphorus and a two dimensional photonic crystal nanocavity

Ota Y., Moriya R., Yabuki N., Arai M., Kakuda M., Iwamoto S., Machida T., Arakawa Y.

Applied Physics Letters 110 ( 22 )  2017.05

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

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Atomically thin black phosphorus (BP) is an emerging two dimensional (2D) material exhibiting bright photoluminescence in the near infrared region. Coupling its radiation to photonic nanostructures will be an important step toward the realization of 2D material based nanophotonic devices that operate efficiently in the near infrared region, which includes the technologically important optical telecommunication wavelength bands. In this letter, we demonstrate the optical coupling between atomically thin BP and a 2D photonic crystal nanocavity. We employed a home-build dry transfer apparatus for placing a thin BP flake on the surface of the nanocavity. Their optical coupling was analyzed through measuring cavity mode emission under optical carrier injection at room temperature.

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Thresholdless quantum dot nanolaser

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

Optics Express 25 ( 17 ) 19981 - 19994 2017

Research paper (scientific journal), Joint Work, Accepted

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Thresholdless lasing is an outstanding challenge in laser science and is achievable only in devices having near unity quantum efficiency even when not lasing. Such lasers are expected to exhibit featureless linear light output curves. However, such thresholdless behavior hinders identification of the laser transition, triggering a long-lasting argument on how to identify the lasing. Here, we demonstrate thresholdless lasing in a semiconductor quantum dot nanolaser with a photonic crystal nanocavity. We employ cavity resonant excitation for enabling the thresholdless operation via focused carrier injection into high cavity field regions. Under conventional (above bandgap) excitation, the same nanolaser exhibits a typical thresholded lasing transition, thereby facilitating a systematic comparison between the thresholdless and thresholded laser transitions in the single device. Our approach enables a clear verification of the thresholdless lasing and reveals core elements for its realization using quantum dots, paving the way to the development of ultimately energy-efficient nanolasers.

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