arXiv subjects

Satoshi Iwamoto

Publications and source records attributed to Satoshi Iwamoto.

At least 55 records · Page 3Linked to original sources

arXiv2020

Surface-passivated high-Q GaAs photonic crystal nanocavity with quantum dots

Photonic crystal (PhC) nanocavities with high quality (Q) factors have attracted much attention because of their strong spatial and temporal light confinement capability. The resulting enhanced light-matter interactions are beneficial for diverse photonic applications, ranging from on-chip optical communications to sensing. However, currently achievable Q factors for active PhC nanocavities, which embed active emitters inside, are much lower than those of the passive structures because of large optical loss, presumably originating from light scattering by structural imperfections and/or optical absorptions. Here, we demonstrate a significant improvement of Q factors up to ~160,000 in GaAs active PhC nanocavities using a sulfur-based surface passivation technique. This value is the highest ever reported for any active PhC nanocavities with semiconductor quantum dots. The surface-passivated cavities also exhibit reduced variation in both Q factors and cavity resonant wavelengths. We find that the improvement in the cavity performance presumably arises from suppressed light absorption at the surface of the PhC's host material by performing a set of PL measurements in spectral and time domains. With the surface passivation technique, we also demonstrate a strongly-coupled single quantum dot-cavity system based on a PhC nanocavity with a high Q factor of ~100,000. These results will pave the way for advanced quantum dot-based cavity quantum electrodynamics and for GaAs micro/nanophotonic applications containing active emitters.

physics.app-ph↗

arXiv2020

Reflectivity of Finite 3D GaAs Photonic Band Gap Crystals

We study the optical reflectivity of three-dimensional (3D) photonic band gap crystals with increasing thickness. The crystals consist of GaAs plates with nanorod arrays that are assembled by an advanced stacking method into high-quality 3D woodpile structures. We observe intense and broad reflectivity peak with stop bands that correspond to a broad gap in the photonic band structures. The maximum reflectivity quickly reaches high values even for a few crystal layers. Remarkably, the bandwidth of the stop bands hardly decreases with increasing crystal thickness, in good agreement with FDTD simulations. This behavior differs remarkably from the large changes observed earlier in weakly interacting 3D photonic crystals. The nearly constant bandwidth and high reflectivity are rationalized by multiple Bragg interference that occurs in strongly interacting photonic band gap crystals, whereby the incident light scatters from multiple reciprocal lattice vectors simultaneously, in particular from oblique ones that are parallel to a longer crystal dimension and thus experience hardly any finite size effects. Our new insights have favorable consequences for the application of 3D photonic band gap crystals, notably since even thin structures reveal the full band gap functionality, including devices that shield quantum bits from vacuum fluctuations.

physics.optics↗

arXiv2019

Active topological photonics

Topological photonics has emerged as a novel route to engineer the flow of light. Topologically-protected photonic edge modes, which are supported at the perimeters of topologically-nontrivial insulating bulk structures, have been of particular interest as they may enable low-loss optical waveguides immune to structural disorder. Very recently, there is a sharp rise of interest in introducing gain materials into such topological photonic structures, primarily aiming at revolu-tionizing semiconductor lasers with the aid of physical mechanisms existing in topological physics. Examples of re-markable realizations are topological lasers with unidirectional light output under time-reversal symmetry breaking and topologically-protected polariton and micro/nano-cavity lasers. Moreover, the introduction of gain and loss provides a fascinating playground to explore novel topological phases, which are in close relevance to non-Hermitian and parity-time symmetric quantum physics and are in general difficult to access using fermionic condensed matter systems. Here, we review the cutting-edge research on active topological photonics, in which optical gain plays a pivotal role. We discuss recent realizations of topological lasers of various kinds, together with the underlying physics explaining the emergence of topological edge modes. In such demonstrations, the optical modes of the topological lasers are deter-mined by the dielectric structures and support lasing oscillation with the help of optical gain. We also address recent researches on topological photonic systems in which gain and loss themselves essentially influence on topological prop-erties of the bulk systems. We believe that active topological photonics provides powerful means to advance mi-cro/nanophotonics systems for diverse applications and topological physics itself as well.

physics.optics↗

arXiv2019

In-situ wavelength tuning of quantum-dot single-photon sources integrated on a CMOS silicon chip

Silicon quantum photonics provides a promising pathway to realize large-scale quantum photonic integrated circuits (QPICs) by exploiting the power of complementary-metal-oxide-semiconductor (CMOS) technology. Toward scalable operation of such silicon-based QPICs, a straightforward approach is to integrate deterministic single-photon sources (SPSs). To this end, hybrid integration of deterministic solid-state SPSs, such as those based on InAs/GaAs quantum dots (QDs), is highly promising. However, the spectral and spatial randomness inherent in the QDs pose a serious challenge for scalable implementation of multiple identical SPSs on a silicon CMOS chip. To overcome this challenge, we have been investigating a new hybrid integration technique called transfer printing, which is based on a pick-and-place operation and allows for the integration of desired QD SPSs on any locations on the silicon CMOS chips at will. Nevertheless, even in this scenario, in-situ fine tuning for perfect wavelength matching among the integrated QD SPSs will be required for interfering photons from the dissimilar sources. Here, we demonstrate in-situ wavelength tuning of QD SPSs integrated on a CMOS silicon chip. To thermally tune the emission wavelengths of the integrated QDs, we augmented the QD SPSs with optically driven heating pads. The integration of all the necessary elements was performed using transfer printing, which largely simplified the fabrication of the three-dimensional stack of micro/nanophotonic structures. We further demonstrate in-situ wavelength matching between two dissimilar QD sources integrated on the same silicon chip. Our transfer-printing-based approach will open the possibility for realizing large-scale QPICs that leverage CMOS technology.

physics.app-ph↗

arXiv2019

Valley Anisotropy in Elastic Metamaterials

Valley, as a new degree of freedom, raises the valleytronics in fundamental and applied science. The elastic analogs of valley states have been proposed by mimicking the symmetrical structure of either two-dimensional materials or photonic valley crystals. However, the asymmetrical valley construction remains unfulfilled. Here, we present the valley anisotropy by introducing asymmetrical design into elastic metamaterials. The elastic valley metamaterials are composed of bio-inspired hard spirals and soft materials. The anisotropic topological nature of valley is verified by asymmetrical distribution of the Berry curvature. We show the high tunability of the Berry curvature both in magnitude and sign enabled by our anisotropic valley metamaterials. Finally, we demonstrate the creation of valley topological insulators and show topologically protected propagation of transverse elastic waves relying on operating frequency. The proposed topological properties of elastic valley metamaterials pave the way to better understanding the valley topology and to creating a new type of topological insulators enabled by an additional valley degree of freedom.

physics.app-ph↗

arXiv2019

Single plasmon generation in an InAs/GaAs quantum dot in a transfer-printed plasmonic microring resonator

We report single plasmon generation with a self-assembled InAs/GaAs quantum dot embedded in a plasmonic microring resonator. The plasmonic cavity based on a GaAs microring is defined on an atomically-smooth silver surface. We fabricated this structure with the help of transfer printing, which enables the pick-and-place assembly of the complicated, heterogeneous three dimensional stack. We show that a high-order surface-plasmon-polariton transverse mode mediates efficient coupling between the InAs/GaAs quantum dots and the plasmonic cavity, paving the way for developing plasmonic quantum light sources based on the state-of-the-art solid-state quantum emitters. Experimentally, we observed Purcell-enhanced radiation from the quantum dot coupled to the plasmonic mode. We also observed a strong anti-bunching in the intensity correlation histogram measured for scattered photons from the plasmonic resonator, indicating single plasmon generation in the resonator. Our results will be important in the development of quantum plasmonic circuits integrating high-performance single plasmon generators.

physics.optics↗

arXiv2019

GaAs valley photonic crystal waveguide with light-emitting InAs quantum dots

We report a valley photonic crystal (VPhC) waveguide in a GaAs slab with InAs quantum dots (QDs) as an internal light source exploited for experimental characterization of the waveguide. A topological interface state formed at the interface between two topologically-distinct VPhCs is used as the waveguide mode. We demonstrate robust propagation for near-infrared light emitted from the QDs even under the presence of sharp bends as a consequence of the topological protection of the guided mode. Our work will be of importance for developing robust photonic integrated circuits with small footprints, as well as for exploring active semiconductor topological photonics.

physics.optics↗

arXiv2019

Spin-dependent directional emission from an asymmetry optical waveguide with an embedded quantum dot ensemble

In this study, we examine a photonic wire waveguide embedded with an ensemble of quantum dots that directionally emits into the waveguide depending on the spin state of the ensemble. This is accomplished through the aid of the spin-orbit interaction of light. The waveguide has a two-step stair-like cross section and embeds quantum dots (QDs) only in the upper step, such that the circular polarization of emission from the spin-polarized QDs controls the direction of the radiation. We numerically verify that more than 70% of the radiation from the ensemble emitter is toward a specific direction in the waveguide. We also examine a microdisk resonator with a stair-like edge, that supports selective coupling of the QD ensemble radiation into a whispering galley mode rotating unidirectionally. Our study provides a foundation for spin-dependent optoelectronic devices.

physics.optics↗

arXiv2019

Design of GaAs-based valley phononic crystals with multiple complete phononic bandgaps at ultra-high frequency

We report the design of GaAs-based monolithic valley phononic crystals (VPnCs) with multiple complete phononic bandgaps, which support simultaneous valley-protected edge states with different symmetries in the gigahertz (GHz) range. Rotation of triangular holes in the unit cells breaks the mirror symmetry, and this orientation degree of freedom enables the structures to exhibit different valley vortex chiralities. We numerically demonstrate the transport of multi-band valley-protected edge states with suppressed backscattering at the sharp corners of the interfaces between different VPnCs. Such monolithic semiconductor structures pave the way for ultra-high frequency topological nanophononic applications by using the lithographic technique.

cond-mat.mes-hall↗

arXiv2018

Quantum-dot single-photon source on a CMOS silicon photonic chip integrated using transfer printing

Silicon photonics is a powerful platform for implementing large-scale photonic integrated circuits (PICs), because of its compatibility with mature complementary-metal-oxide-semiconductor (CMOS) technology. Exploiting silicon-based PICs for quantum photonic information processing (or the so-called silicon quantum photonics) provides a promising pathway for large-scale quantum applications. For the development of scalable silicon quantum PICs, a major challenge is integrating on-silicon quantum light sources that deterministically emit single photons. In this regard, the use of epitaxial InAs/GaAs quantum dots (QDs) is a very promising approach, because of their capability of deterministic single-photon emission with high purity and indistinguishability. However, the required hybrid integration is inherently difficult and often lacks the compatibility with CMOS processes. Here, we demonstrate a QD single-photon source (SPS) integrated on a glass-clad silicon photonic waveguide processed by a CMOS foundry. Hybrid integration is performed using transfer printing, which enables us to integrate heterogeneous optical components in a simple pick-and-place manner and thus assemble them after the entire CMOS process is completed. We observe single-photon emission from the integrated QD and its efficient coupling into the silicon waveguide. Our transfer-printing-based approach is fully compatible with CMOS back-end processes, and thus will open the possibility for realizing large-scale quantum PICs that leverage CMOS technology.

physics.app-ph↗

arXiv2018

Photonic crystal nanocavity based on a topological corner state

Topological phonics has emerged as a novel approach to engineer the flow of light and provides unprecedented means for developing diverse photonic elements, including robust optical waveguides immune to structural imperfections. However, the development of nanoscale standing-wave cavities in topological photonics is rather slow, despite its importance when building densely-integrated photonic integrated circuits. In this Letter, we report a photonic crystal nanocavity based on a topological corner state, supported at a 90-degrees-angled rim of a two dimensional photonic crystal. A combination of the bulk-edge and edge-corner correspondences guarantees the presence of the higher-order topological state in a hierarchical manner. We experimentally observed a corner mode that is tightly localized in space while supporting a high Q factor over 2,000, verifying its promise as a nanocavity. These results cast new light on the way to introduce nanocavities in topological photonics platforms.

cond-mat.mes-hall↗

arXiv2018

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

Atomically-thin black phosphorus (BP) is an emerging two dimensional (2D) material exhibiting bright photoluminescence in the near infrared. 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, 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.

cond-mat.mes-hall↗

arXiv2018

Strongly coupled single quantum dot-cavity system integrated on a CMOS-processed silicon photonic chip

Quantum photonic integrated circuit (QPIC) is a promising tool for constructing integrated devices for quantum technology applications. In the optical regime, silicon photonics empowered by complementary-metal-oxide-semiconductor (CMOS) technology provides optical components useful for realizing large-scale QPICs. Optical nonlinearity at the single-photon level is required for QPIC to facilitate photon-photon interaction. However, to date, realization of optical elements with deterministic( i.e., not probabilistic) single-photon nonlinearity by using silicon-based components is challenging, despite the enhancement of the functionality of QPICs based on silicon photonics. In this study, we realize for the first time a strongly coupled InAs/GaAs quantum dot-cavity quantum electrodynamics (QED) system on a CMOS-processed silicon photonic chip. The heterogeneous integration of the GaAs cavity on the silicon chip is performed by transfer printing. The cavity QED system on the CMOS photonic chip realized in this work is a promising candidate for on-chip single-photon nonlinear element, which constitutes the fundamental component for future applications based on QPIC, such as, coherent manipulation and nondestructive measurement of qubit states via a cavity, and efficient single-photon filter and router.

cond-mat.mes-hall↗

arXiv2018

Topological photonic crystal nanocavity laser

Topological edge states exist at the interfaces between two topologically-distinct materials. The presence and number of such modes are deterministically predicted from the bulk-band topologies, known as the bulk-edge correspondence. This principle is highly useful for predictably controlling optical modes in resonators made of photonic crystals (PhCs), leading to the recent demonstrations of micro-scale topological lasers. Meanwhile, zero-dimensional topological trapped states in the nanoscale remained unexplored, despite its importance for enhancing light-matter interactions and for wide applications including single-mode nanolasers. Here, we report a topological PhC nanocavity with a near-diffraction-limited mode volume and its application to single-mode lasing. The topological origin of the nanocavity, formed at the interface between two topologically-distinct PhCs, guarantees the existence of only one mode within its photonic bandgap. The observed lasing accompanies a high spontaneous emission coupling factor stemming from the nanoscale confinement. These results encompass a way to greatly downscale topological photonics.

physics.optics↗

arXiv2018

Scheme for media conversion between electronic spin and photonic orbital angular momentum based on photonic nanocavity

Light with nonzero orbital angular momentum (OAM) or twisted light is promising for quantum communication applications such as OAM-entangled photonic qubits. There exist photonic OAM to photonic spin angular momentum (SAM), as well as photonic SAM to electronic SAM interfaces but not any direct photonic OAM-electronic SAM (flying to stationary) media converter within a single device. Here, we propose a scheme which converts photonic OAM to electronic SAM and vice versa within a single nanophotonic device. We employed a photonic crystal nanocavity with an embedded quantum dot (QD) which confines an electron spin as a stationary qubit. Spin polarized emission from the QD drive the rotation of the nanocavity modes via the strong optical spin-orbit interaction. The rotating modes then radiate light with nonzero OAM, allowing this device to serve as a transmitter. As this can be a unitary process, the time-reversed case enables the device to function as a receiver. This scheme could be generalized to other systems of resonator and quantum emitters such as a microdisk and defects in diamond for example. Our scheme shows the potential for realizing an (ultra)compact electronic SAM-photonic OAM interface to accommodate OAM as an additional degree of freedom for quantum information purposes.

cond-mat.mes-hall↗

arXiv2018

Transfer-printed single photon sources coupled to wire waveguides

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.

physics.app-ph↗

arXiv2017

Topologically protected elastic waves in one-dimensional phononic crystals of continuous media

We report the design of silica-based 1D phononic crystals (PnCs) with topologically distinct complete phononic bandgaps (PnBGs) and the observation of a topologically protected state of elastic waves at their interface. By choosing different structural parameters of unit cells, two PnCs can possess a common PnBG with different topological nature. At the interface between the two PnCs, a topological interface mode with a quality factor of ~5,650 is observed in the PnBG. Spatial confinement of the interface mode is also confirmed by using photoelastic imaging technique. Such topologically protected elastic states are potentially applicable for constructing novel phononic devices.

cond-mat.mes-hall↗

arXiv2017

Generation method of a photonic NOON state with quantum dots in coupled nanocavities

We propose a method to generate path-entangled $N00N$-state photons from quantum dots (QDs) 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 $N00N$ state in the energy eigenstate, as a consequence of destructive quantum interference. The $N00N$ state can be generated by the resonant laser excitation. This method, first introduced for two-photon $N00N$ state ($N=2$), can be extended toward higher $N00N$ state ($N>2$) based on our recipe, which is applied to the case of $N=4$ as an example.

quant-ph↗