Search

Micro-/nanocavities that combine high quality factor (Q) and small mode volume (V) have been used to enhance light–matter interactions for cavity quantum electrodynamics (cQED). Whispering gallery mode (WGM) geometries such as microdisks and microrings support high-Q and are design- and fabrication-friendly, but V is often limited to tens of cubic wavelengths to avoid WGM radiation. The stronger modal confinement provided by either one-dimensional or two-dimensional photonic crystal defect geometries can yield sub-cubic-wavelength V, yet the requirements on precise design and dimensional control are typically much more stringent to ensure high-Q. Given their complementary features, there has been sustained interest in geometries that combine the advantages of WGM and photonic crystal cavities. Recently, a “microgear” photonic crystal ring (MPhCR) has shown promise in enabling additional defect localization ( > $ > $ 10× reduction of V) of a WGM, while maintaining high-Q ( ≈ 1 0 6 ) $(\approx 1{0}^{6})$ and other WGM characteristics in ease of coupling and design. However, the unit cell geometry used is unlike traditional PhC cavities, and etched surfaces may be too close to embedded quantum nodes (quantum dots, atomic defect spins, etc.) for cQED applications. Here, we report two novel PhCR designs with “rod” and “slit” unit cells, whose geometries are more traditional and suitable for solid-state cQED. Both rod and slit PhCRs have high-Q ( > 1 0 6 ) $( > 1{0}^{6})$ with WGM coupling properties preserved. A further ≈10× reduction of V by defect localization is observed in rod PhCRs. Moreover, both fundamental and 2nd-order PhC modes co-exist in slit PhCRs with high Qs and good coupling. Our work showcases that high-Q/V PhCRs are in general straightforward to design and fabricate and are a promising platform to explore for cQED.

Quantum photonic devices are candidates for realizing practical quantum computers and networks. The development of integrated quantum photonic devices can greatly benefit from the ability to incorporate different types of materials with complementary, superior optical or electrical properties on a single chip. Semiconductor quantum dots (QDs) serve as a core element in the emerging modern photonic quantum technologies by allowing on-demand generation of single-photons and entangled photon pairs. During each excitation cycle, there is one and only one emitted photon or photon pair. QD photonic devices are on the verge of unfolding for advanced quantum technology applications. In this review, we focus on the latest significant progress of QD photonic devices. We first discuss advanced technologies in QD growth, with special attention to droplet epitaxy and site-controlled QDs. Then we overview the wavelength engineering of QDs via strain tuning and quantum frequency conversion techniques. We extend our discussion to advanced optical excitation techniques recently developed for achieving the desired emission properties of QDs. Finally, the advances in heterogeneous integration of active quantum light-emitting devices and passive integrated photonic circuits are reviewed, in the context of realizing scalable quantum information processing chips.

Whispering gallery modes (WGMs) in circularly symmetric optical microresonators exhibit integer quantized angular momentum numbers due to the boundary condition imposed by the geometry. Here, we show that incorporating a photonic crystal pattern in an integrated microring can result in WGMs with fractional optical angular momentum. By choosing the photonic crystal periodicity to open a photonic bandgap with a band-edge momentum lying between that of two WGMs of the unperturbed ring, we observe hybridized WGMs with half-integer quantized angular momentum numbers ($m \in \mathbb{Z}$ + 1/2). Moreover, we show that these modes with fractional angular momenta exhibit high optical quality factors with good cavity-waveguide coupling and an order of magnitude reduced group velocity. Additionally, by introducing multiple artificial defects, multiple modes can be localized to small volumes within the ring, while the relative orientation of the de-localized band-edge states can be well-controlled. Our work unveils the renormalization of WGMs by the photonic crystal, demonstrating novel fractional angular momentum states and nontrivial multi-mode orientation control arising from continuous rotational symmetry breaking. The findings are expected to be useful for sensing/metrology, nonlinear optics, and cavity quantum electrodynamics., Accept by Physical Review Letter

The ability to combine different materials enables a combination of complementary properties and device engineering that cannot be found or exploited within a single material system. In the realm of quantum nanophotonics, one might want to increase device functionality by, for instance, combining efficient classical and quantum light emission available in III–V semiconductors, low-loss light propagation accessible in silicon-based materials, fast electro-optical properties of lithium niobate, and broadband reflectors and/or buried metallic contacts for local electric field application or electrical injection of emitters. However, combining different materials on a single wafer is challenging and may result in low reproducibility and/or low yield. For instance, direct epitaxial growth requires crystal lattice matching for producing of defect-free films, and wafer bonding requires considerable and costly process development for high bond strength and yield. We propose a transfer printing technique based on the removal of arrays of free-standing membranes and their deposition onto a host material using a thermal release adhesive tape-assisted process. This approach is versatile, in that it poses limited restrictions on the transferred and host materials. In particular, we transfer 190 nm-thick GaAs membranes that contain InAs quantum dots and which have dimensions up to about 260 μm × 80 μm onto a gold-coated silicon substrate. We show that the presence of a back reflector combined with the etching of micropillars significantly increases the extraction efficiency of quantum light from a single quantum dot line, reaching photon fluxes exceeding 8 × 105 photons per second. This flux is four times higher than the highest count rates measured from emitters outside the pillars on the same chip. Given its versatility and ease of processing, this technique provides a path to realising hybrid quantum nanophotonic devices that combine virtually any material in which free-standing membranes can be made onto any host substrate, without specific compatibility issues and/or requirements.

The anisotropy of hexagonal boron nitride (hBN) gives rise to hyperbolic phonon-polaritons (HPhPs), notable for their volumetric frequency-dependent propagation and strong confinement. For frustum (truncated nanocone) structures, theory predicts five, high-order HPhPs, sets, but only one set was observed previously with far-field reflectance and scattering-type scanning near-field optical microscopy. In contrast, the photothermal induced resonance (PTIR) technique has recently permitted sampling of the full HPhP dispersion and observing such elusive predicted modes; however, the mechanism underlying PTIR sensitivity to these weakly-scattering modes, while critical to their understanding, has not yet been clarified. Here, by comparing conventional contact- and newly developed tapping-mode PTIR, we show that the PTIR sensitivity to those weakly-scattering, high-Q (up to ≈280) modes is, contrary to a previous hypothesis, unrelated to the probe operation (contact or tapping) and is instead linked to PTIR ability to detect tip-launched dark, volumetrically-confined polaritons, rather than nanostructure-launched HPhPs modes observed by other techniques. Furthermore, we show that in contrast with plasmons and surface phonon-polaritons, whose Q-factors and optical cross-sections are typically degraded by the proximity of other nanostructures, the high-Q HPhP resonances are preserved even in high-density hBN frustum arrays, which is useful in sensing and quantum emission applications.

Continuous wave optical parametric oscillation (OPO) provides a flexible approach for accessing mid-infrared wavelengths between 2 $\mu$m to 5 $\mu$m, but has not yet been integrated into silicon nanophotonics. Typically, Kerr OPO uses a single transverse mode family for pump, signal, and idler modes, and relies on a delicate balance to achieve normal (but close-to-zero) dispersion near the pump and the requisite higher-order dispersion needed for phase- and frequency-matching. Within integrated photonics platforms, this approach results in two major problems. First, the dispersion is very sensitive to geometry, so that small fabrication errors can have a large impact. Second, the device is susceptible to competing nonlinear processes near the pump. In this letter, we propose a flexible solution to infrared OPO that addresses these two problems, by using a silicon nitride photonic crystal microring (PhCR). The frequency shifts created by the PhCR bandgap enable OPO that would otherwise be forbidden. We report an intrinsic optical quality factor up to (1.2 $\pm$ 0.1)$\times$10$^6$ in the 2 $\mu$m band, and use a PhCR ring to demonstrate an OPO with threshold power of (90 $\pm$ 20) mW dropped into the cavity, with the pump wavelength at 1998~nm, and the signal and idler wavelengths at 1937 nm and 2063 nm, respectively. We further discuss how to extend OPO spectral coverage in the mid-infrared. These results establish the PhCR OPO as a promising route for integrated laser sources in the infrared., Comment: 4 pages, 3 figures

We use inverse design to develop an optimized nanophotonic geometry for efficient, waveguide-coupled, path-entangled photon pair sources based on single embedded quan-tum dots.

We show that metallic nano-rings, deposited on the surface of a chip, centered around single InAs/GaAs quantum dots, allow increasing the single-photon flux, reaching 7M photons/s, in a device comprising a ring and gold back-reflector.

Integrated photonics will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying optical quantum technologies can only be realized through the integration of these components onto quantum photonic integrated circuits (QPICs) with accompanying electronics. In the last decade, remarkable advances in quantum photonic integration have enabled table-top experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. These advances have enabled integrated quantum photonic technologies combining up to 650 optical and electrical components onto a single chip that are capable of programmable quantum information processing, chip-to-chip networking, hybrid quantum system integration, and high-speed communications. In this roadmap article, we highlight the status, current and future challenges, and emerging technologies in several key research areas in integrated quantum photonics, including photonic platforms, quantum and classical light sources, quantum frequency conversion, integrated detectors, and applications in computing, communications, and sensing. With advances in materials, photonic design architectures, fabrication and integration processes, packaging, and testing and benchmarking, in the next decade we can expect a transition from single- and few-function prototypes to large-scale integration of multi-functional and reconfigurable devices that will have a transformative impact on quantum information science and engineering., JPhys Photonics, 4 (1), ISSN:2515-7647

The deterministic integration of quantum emitters into on-chip photonic elements is crucial for the implementation of scalable on-chip quantum circuits. Here, we report on the deterministic integration of single quantum dots (QD) into tapered multimode interference beam splitters using in-situ electron beam lithography (EBL). We demonstrate the functionality of the deterministic QD-waveguide structures by µPL spectroscopy and by studying the photon cross-correlation between the two MMI output ports. The latter confirms single-photon emission and on-chip splitting associated with g(2)(0) << 0.5. Moreover, the deterministic integration of QDs enables the demonstration and controlled study of chiral light-matter effects and directional emission in QD-WGs, and the realization of low-loss heterogenous QD-WG systems with excellent quantum optical properties.

We demonstrate a deterministic Purcell-enhanced single photon source realized by integrating an atomically thin WSe

Mechanical failure occurs through a hierarchical process, making it necessary to understand deformation at all length scales in order to develop advanced materials with, for example, enhanced toughness. This study addresses this challenge by demonstrating an optical imaging technique that detects damage at the nanoscale. We use single-molecule fluorescence microscopy experiments to simultaneously determine the position and orientation of single fluorophores from in-focus widefield images by fitting orientation-dependent point-spread functions determined by vectorial diffraction calculations. This capability is combined with switchable fluorophores in a single-molecule super-resolution microscopy scheme, enabling reconstruction of fluorophore orientation and alignment information at the nanoscale. We apply this method to polymer films deformed by thermal nanoimprint lithography, using fluorophore orientation mapping to detect areas of deformed material as small as 20 nm and distinguish them from neighboring, unperturbed regions. This technique advances the application of super-resolution microscopy in materials science, and may be applied to further the study of nanomechanical phenomena.

Semiconductor quantum dots are excellent emitters of single photons. Often, the same mode is used to resonantly excite a QD and to collect the emitted single-photons, requiring cross polarization to separate out scattered laser light. This reduces the source brightness to ≤50%, and potentially eliminates their use in some quantum applications. We demonstrate a resonant-excitation approach to creating single photons that is free of any filtering whatsoever. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected cavity-waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode.

We demonstrate a deterministic Purcell-enhanced single-photon source realized by integrating an atomically thin WSe$_{2}$ layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer, and supports single-photon generation with $g^{(2)}(0), 11 pages, 3 figures in the main text, 6 figures in the supplementary material

To implement quantum light sources based on quantum emitters in applications, it is desirable to improve the extraction efficiency of single photons. In particular controlling the directionality and solid angle of the emission are key parameters, for instance, to couple single photons into optical fibers and send the information encoded in quantum light over long distances, for quantum communication applications. In addition, fundamental studies of the radiative behavior of quantum emitters, including studies of coherence and blinking, benefit from such improved photon collection. Quantum dots grown via Stranski-Krastanov technique have shown to be good candidates for bright, coherent, indistinguishable quantum light emission. However, one of the challenges associated with these quantum light sources arises from the fact that the emission wavelengths can vary from one emitter to the other. To this end, broadband light extractors that do not rely on high-quality factor optical cavities would be desirable, so that no tuning between the quantum dot emission wavelength and the resonator used to increase the light extraction is needed. Here, we show that metallic nano-rings combined with gold back reflectors increase the collection efficiency of single photons and we study the statistics of this effect when quantum dots are spatially randomly distributed within the nano-rings. We show an average increase in the brightness of about a factor 7.5, when comparing emitters within and outside the nano-rings in devices with a gold back reflector, we measure count rates exceeding 7 x 10^6 photons per second and single photon purities as high as 85% +/- 1%. These results are important steps towards the realisation of scalable, broadband, easy to fabricate sources of quantum light for quantum communication applications., Comment: 5 pages, 4 figures

We demonstrate hybrid quantum photonic circuits comprising Si3N4 waveguides featuring losses in the dB/m range, with directly integrated quantum dot based single-photon sources.

The anisotropy of hexagonal boron nitride (hBN) gives rise to hyperbolic phonon-polaritons (HPhPs), notable for their volumetric frequency-dependent propagation and strong confinement. For frustum (truncated nanocone) structures, theory predicts five, high-order HPhPs, sets, but only one set was observed previously with far-field reflectance and scattering-type scanning near-field optical microscopy. In contrast, the photothermal induced resonance (PTIR) technique has recently permitted sampling of the full HPhP dispersion and observing such elusive predicted modes; however, the mechanism underlying PTIR sensitivity to these weakly-scattering modes, while critical to their understanding, has not yet been clarified. Here, by comparing conventional contact- and newly developed tapping-mode PTIR, we show that the PTIR sensitivity to those weakly-scattering, high-Q (up to ≈280) modes is, contrary to a previous hypothesis, unrelated to the probe operation (contact or tapping) and is instead linked to PTIR ability to detect tip-launched dark, volumetrically-confined polaritons, rather than nanostructure-launched HPhPs modes observed by other techniques. Furthermore, we show that in contrast with plasmons and surface phonon-polaritons, whose Q-factors and optical cross-sections are typically degraded by the proximity of other nanostructures, the high-Q HPhP resonances are preserved even in high-density hBN frustum arrays, which is useful in sensing and quantum emission applications.

We report progress in bi-directional microwave-to-optical conversion mediated by a resonant mechanical super-mode in a coupled piezo-optomechanical system with theoretically predicted high conversion efficiency and potential in quantum networks.

We demonstrate stable microresonator Kerr solitons in an Alo^Gao.gAs-on-insulator resonator thanks to cryogenic quenching of the thermorefractive effect. Reaching such a phase-stable state is a prerequisite to fully exploit the potential of this platform.

We demonstrate integrated Si3N4 waveguides containing single-photon emitters based on single InAs quantum dots that were deterministically positioned in a GaAs nanowaveguide via a low-temperature in-situ electron-beam lithography.

Integrated quantum nanophotonics aims at combining optical elements on-chip to realize complex circuits with full quantum functionality. Examples are integrated boson sampling circuits and chips that generate 2D photonic cluster states. As such, this modern field of photonics opens up many exciting opportunities in quantum technology with the overarching goal of implementing large quantum networks and photonic quantum computers. This chapter provides an overview of important basics of integrated quantum nanophotonics, represents the state of the art, and provides an outlook on possible future developments. It includes an insight into numerical design and optimization processes and introduces modern manufacturing processes for quantum circuits. Based on this, corresponding circuits relying on homogeneous semiconductor structures are discussed, with a focus on elements with integrated quantum emitters. In addition, advanced concepts are also presented, which are enabled by the heterogeneous combination of different materials in order to develop fully integrated quantum chips. The chapter closes with an outlook on future developments and a summary.

Semiconductor quantum dots embedded in micro-pillar cavities are excellent emitters of single photons when pumped resonantly. Often, the same spatial mode is used to both resonantly excite a quantum dot and to collect the emitted single photons, requiring cross-polarization to reduce the uncoupled scattered laser light. This inherently reduces the source brightness to 50 %. Critically, for some quantum applications the total efficiency from generation to detection must be over 50 %. Here, we demonstrate a resonant-excitation approach to creating single photons that is free of any cross-polarization, and in fact any filtering whatsoever. It potentially increases single-photon rates and collection efficiencies, and simplifies operation. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected waveguides, while the cavity-enhanced single-photon fluorescence is directed vertical (off-chip) in a Gaussian mode. We expect this design to be a prototype for larger chip-scale quantum photonics., 6 pages, 5 figures

Silicon photonics enables scaling of quantum photonic systems by allowing the creation of extensive, low-loss, reconfigurable networks linking various functional on-chip elements. Inclusion of single quantum emitters onto photonic circuits, acting as on-demand sources of indistinguishable photons or single-photon nonlinearities, may enable large-scale chip-based quantum photonic circuits and networks. Towards this, we use low-temperature in situ electron-beam lithography to deterministically produce hybrid GaAs/Si(3)N(4) photonic devices containing single InAs quantum dots precisely located inside nanophotonic structures, which act as efficient, Si(3)N(4) waveguide-coupled on-chip, on-demand single-photon sources. The precise positioning afforded by our scalable fabrication method furthermore allows observation of post-selected indistinguishable photons. This indicates a promising path towards significant scaling of chip-based quantum photonics, enabled by large fluxes of indistinguishable single-photons produced on-demand, directly on-chip.

Silicon photonics enables scaling of quantum photonic systems by allowing the creation of extensive, low-loss, reconfigurable networks linking various functional on-chip elements. Inclusion of single quantum emitters onto photonic circuits, acting as on-demand sources of indistinguishable photons or single-photon nonlinearities, may enable large-scale chip-based quantum photonic circuits and networks. Towards this, we use low-temperature $\textit{in situ}$ electron-beam lithography to deterministically produce hybrid GaAs/Si$_3$N$_4$ photonic devices containing single InAs quantum dots precisely located inside nanophotonic structures, which act as efficient, Si$_3$N$_4$ waveguide-coupled on-chip, on-demand single-photon sources. The precise positioning afforded by our scalable fabrication method furthermore allows observation of post-selected indistinguishable photons. This indicates a promising path towards significant scaling of chip-based quantum photonics, enabled by large fluxes of indistinguishable single-photons produced on-demand, directly on-chip.

Optomechanical cavities have been studied for applications ranging from sensing to quantum information science. Here, we develop a platform for nanoscale cavity optomechanical circuits in which optomechanical cavities supporting co-localized 1550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides. Working in GaAs facilitates manipulation of the localized mechanical mode either with a radio frequency (RF) field through the piezo-electric effect, which produces acoustic waves that are routed and coupled to the optomechanical cavity by phononic crystal waveguides, or optically through the strong photoelastic effect. Along with mechanical state preparation and sensitive readout, we use this to demonstrate an acoustic wave interference effect, similar to atomic coherent population trapping, in which RF-driven coherent mechanical motion is cancelled by optically-driven motion. Manipulating cavity optomechanical systems with equal facility through both photonic and phononic channels enables new architectures for signal transduction between the optical, electrical, and mechanical domains.

We demonstrate stable microresonator Kerr soliton frequency combs in a III-V platform (AlGaAs on SiO$_2$) through quenching of thermorefractive effects by cryogenic cooling to temperatures between 4~K and 20~K. This cooling reduces the resonator's thermorefractive coefficient, whose room-temperature value is an order of magnitude larger than that of other microcomb platforms like Si$_3$N$_4$, SiO$_2$, and AlN, by more than two orders of magnitude, and makes soliton states adiabatically accessible. Realizing such phase-stable soliton operation is critical for applications that fully exploit the ultra-high effective nonlinearity and high optical quality factors exhibited by this platform.

Single self-assembled InAs/GaAs quantum dots are a promising solid-state quantum technology, with which vacuum Rabi splitting, single-photon-level nonlinearities, and bright, pure, and indistinguishable single-photon generation having been demonstrated. For such achievements, nanofabrication is used to create structures in which the quantum dot preferentially interacts with strongly-confined optical modes. An open question is the extent to which such nanofabrication may also have an adverse influence, through the creation of traps and surface states that could induce blinking, spectral diffusion, and dephasing. Here, we use photoluminescence imaging to locate the positions of single InAs/GaAs quantum dots with respect to alignment marks with < 5 nm uncertainty, allowing us to measure their behavior before and after fabrication. We track the quantum dot emission linewidth and photon statistics as a function of distance from an etched surface, and find that the linewidth is significantly broadened (up to several GHz) for etched surfaces within a couple hundred nanometers of the quantum dot. However, we do not observe appreciable reduction of the quantum dot radiative efficiency due to blinking. We also show that atomic layer deposition can stabilize spectral diffusion of the quantum dot emission, and partially recover its linewidth.

The development of ${\text{Si}}_{\text{3}}{\text{N}}_{\text{4}}$ nanobeam optomechanical crystals is reviewed. These structures consist of a 350-nm thick, 700-nm wide doubly-clamped ${\text{Si}}_{\text{3}}{\text{N}}_{\text{4}}$ nanobeam that is periodically patterned with an array of air holes to which a defect region is introduced. The periodic patterning simultaneously creates a photonic bandgap for 980 nm band photons and a phononic bandgap for 4 GHz phonons, with the defect region serving to colocalize optical and mechanical modes within their respective bandgaps. These optical and mechanical modes interact dispersively with a coupling rate $g_{0}/2\pi \approx$ 100 kHz, which describes the shift in cavity mode optical frequency due to the zero-point motion of the mechanical mode. Optical sidebands generated by interaction with the mechanical mode lie outside of the optical cavity linewidth, enabling possible use of this system in applications requiring sideband-resolved operation. Along with a review of the basic device design, fabrication, and measurement procedures, we present new results on improved optical quality factors (up to $4\times 10^5$ ) through optimized lithography, measurements of devices after HF acid surface treatment, and temperature dependent measurements of mechanical damping between 6 and 300 K. A frequency-mechanical quality factor product $\left(f\,{\times }\,Q_m\right)$ as high as $\approx 2.6\times 10^{13}$ Hz is measured.

The inherent crystal anisotropy of hexagonal boron nitride (hBN) sustains naturally hyperbolic phonon polaritons, i.e. polaritons that can propagate with very large wavevectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, previous research has shown that nanometer-scale truncated nanocone hBN cavities, with deep subwavelength dimensions, support three-dimensionally confined optical modes in the mid-infrared. Due to optical selection rules, only a few of many such modes predicted theoretically have been observed experimentally via far-field reflection and scattering-type scanning near-field optical microscopy. The Photothermal induced resonance (PTIR) technique probes optical and vibrational resonances overcoming weak far-field emission by leveraging an atomic force microscope (AFM) probe to transduce local sample expansion due to light absorption. Here we show that PTIR enables the direct observation of previously unobserved, dark hyperbolic modes of hBN nanostructures. Leveraging these optical modes could yield a new degree of control over the electromagnetic near-field concentration, polarization and angular momentum in nanophotonic applications., 14 pages with references, 4 figures

Photonic integration is an enabling technology for photonic quantum science, offering greater scalability, stability, and functionality than traditional bulk optics. Here, we describe a scalable, heterogeneous III-V/silicon integration platform to produce Si3N4 photonic circuits incorporating GaAs-based nanophotonic devices containing self-assembled InAs/GaAs quantum dots. We demonstrate pure single-photon emission from individual quantum dots in GaAs waveguides and cavities - where strong control of spontaneous emission rate is observed - directly launched into Si3N4 waveguides with > 90 % efficiency through evanescent coupling. To date, InAs/GaAs quantum dots constitute the most promising solid state triggered single-photon sources, offering bright, pure and indistinguishable emission that can be electrically and optically controlled. Si3N4 waveguides offer low-loss propagation, tailorable dispersion and high Kerr nonlinearities, desirable for linear and nonlinear optical signal processing down to the quantum level. We combine these two in an integration platform that will enable a new class of scalable, efficient and versatile integrated quantum photonic devices.

Deterministic techniques enabling the implementation and engineering of bright and coherent solid-state quantum light sources are key for the reliable realization of a next generation of quantum devices. Such a technology, at best, should allow one to significantly scale up the number of implemented devices within a given processing time. In this work, we discuss a possible technology platform for such a scaling procedure, relying on the application of nanoscale quantum dot imaging to the pillar microcavity architecture, which promises to combine very high photon extraction efficiency and indistinguishability. We discuss the alignment technology in detail, and present the optical characterization of a selected device which features a strongly Purcell-enhanced emission output. This device, which yields an extraction efficiency of $\eta=(49\pm4)~\%$, facilitates the emission of photons with $(94\pm2.7)~\%$ indistinguishability., Comment: 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:1512.07453

Photonic integration is as an enabling technology for photonic quantum science, providing great experimental scalability, stability, and functionality. Although the increasing complexity of quantum photonic circuits has allowed proof-of-principle demonstrations of quantum computation, simulation, and metrology[1], further development is severely limited by the on-chip photon flux that can be made available from external quantum light sources[2]. Overcoming such limitations would allow a significant scaling of quantum photonic experiments, and enable quantum-level investigation of many physical processes observable on-chip through nanophotonic and nanoplasmonic structures (e.g., Kerr, optomechanical, single-photon nonlinearities). Towards such goals, we have developed a scalable, heterogeneous III-V/Si 3 N 4 integration platform for quantum photonic circuits based on passive Si 3 N 4 waveguides which directly incorporate nanophotonic single-photon sources based on self-assembled InAs quantum dots (QDs)[3]. InAs quantum dots constitute the most promising solid-state triggered single-photon sources to date[4], while SI3N4 waveguides offer low-loss propagation, tailorable dispersion and high Kerr nonlinearities which can be used for linear and nonlinear optical signal processing down to the quantum level. In our platform, the building blocks of which are shown in Fig. 1(a), active GaAs waveguide-based geometries containing InAs QDs are designed to efficiently capture QD-emitted single-photons. Captured photons, confined within the GaAs core, are then transferred with high efficiency into a passive Si 3 N 4 waveguide network via adiabatic mode transformers. Figure 1(b) shows an example device fabricated with our platform: a GaAs microring resonator containing InAs quantum dots, evanescently coupled to a GaAs bus waveguide, which is in turn coupled to an underlying Si 3 N 4 waveguide through adiabatic mode-transformers. The photoluminescence spectrum for this device, in Fig. 1(b), shows that a single QD exciton near 1125 nm, coupled to a microring whispering-gallery mode, acts as a source of single-photons that are launched directly into the Si3N4 waveguide. This geometry also allows us to effectively control the QD spontaneous emission decay lifetime by spectrally detuning the WGM with respect to the QD, as shown in Fig. 1(d).

We develop a scalable heterogeneous integration platform for quantum photonic circuits based on Si3N4 waveguides and on-chip, self-assembled InAs quantum dot-based single-photon sources. Hybrid waveguides, photonic crystals, and microring resonators are demonstrated.

Acoustic wave devices provide a promising chip-scale platform for efficiently coupling radio frequency (RF) and optical fields. Here, we use an integrated piezo-optomechanical circuit platform that exploits both the piezoelectric and photoelastic coupling mechanisms to link 2.4 GHz RF waves to 194 THz (1550 nm) optical waves, through coupling to propagating and localized 2.4 GHz acoustic waves. We demonstrate acousto-optic modulation, resonant in both the optical and mechanical domains, in which waveforms encoded on the RF carrier are mapped to the optical field. We also show opto-acoustic gating, in which the application of modulated optical pulses interferometrically gates the transmission of propagating acoustic pulses. The time-domain characteristics of this system under both pulsed RF and pulsed optical excitation are considered in the context of the different physical pathways involved in driving the acoustic waves, and modelled through the coupled mode equations of cavity optomechanics.

We present a wide-field, high-throughput optical technique for locating solid-state quanutm emitters with

Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, since they benefit from enormous coulomb correlations between electrons and holes. Especially in WSe2, sharp emission features have been observed at cryogenic temperatures, which act as single photon sources . Tight exciton localization has been assumed to induce an anharmonic excitation spectrum, however, the evidence of the hypothesis, namely the demonstration of a localized biexciton, is elusive. Here, we unambiguously demonstrate the existence of a localized biexciton in a monolayer of WSe2, which triggers an emission cascade of single photons. The biexciton is identified by its time-resolved photoluminescence, superlinearity and distinct polarization in micro-photoluminescence experiments. We evidence the cascaded nature of the emission process in a cross-correlation experiment, which yields a strong bunching behavior. Our work paves the way to a new generation of quantum optics experiments with two-dimensional semiconductors., Comment: 13 pages, 3 Figures

We have developed a platform-independent software package for designing nanometer scaled device architectures. The Nanolithography Toolbox is applicable to a broad range of design tasks in the fabrication of microscale and nanoscale devices.

We develop a heterogeneous III-V/Si3N4 integration platform for photonic integrated circuits incorporating on-chip, InAs quantum dot-based single-photon sources.

We report a photoluminescence imaging system for locating single quantum emitters with respect to alignment features. Samples are interrogated in a 4~K closed-cycle cryostat by a high numerical aperture (NA=0.9, 100$\times$ magnification) objective that sits within the cryostat, enabling high efficiency collection of emitted photons without image distortions due to the cryostat windows. The locations of single InAs/GaAs quantum dots within a $>50$~$��$m~$\times$~50~$��$m field of view are determined with $\approx4.5$~nm uncertainty (one standard deviation) in a 1~s long acquisition. The uncertainty is determined through a combination of a maximum likelihood estimate for localizing the quantum dot emission, and a cross-correlation method for determining the alignment mark center. This location technique can be an important step in the high-throughput creation of nanophotonic devices that rely upon the interaction of highly confined optical modes with single quantum emitters., 8 pages, 4 figures, two tables. Comments are welcome