Integrated Quantum Photonic Devices Research Articles

High-uniformity atomic layer deposition of superconducting niobium nitride thin films for quantum photonic integration

Atomic layer deposition (ALD) has been identified as a promising growth method for high-uniformity superconducting thin films for superconducting quantum photonic applications, offering superior uniformity, thickness control and conformality to techniques such as reactive sputtering. The potential scalability of ALD makes this method especially appealing for fabrication of superconducting nanowires and resonators across large areas. We report on the growth of highly uniform superconducting NbN thin films via plasma-enhanced atomic layer deposition (PEALD) with radio frequency substrate biasing, on a 200 mm (8 inch) Si wafer, specifically for superconducting nanowire single-photon detector applications. Niobium nitride films were grown using (tert-butylimido)-tris(diethylamido)-niobium(V) precursor and an H2/Ar plasma. The superconducting properties of a variable thickness series of films (5.9–29.8 nm) show critical temperature (T c) of 13.5 K approaching bulk thickness (28.8 nm) with low suppression down to the ultrathin regime (5.9 nm), with T c = 10.2 K. T c across the 200 mm wafer with 8 nm thick NbN, measured in 15 mm intervals, exhibits minimal variation (<7%). Microbridge structures fabricated on 8 nm thick NbN films also exhibit high critical current densities (J c), > 10 MA cm−2 at 2.6 K. PEALD could therefore be a pivotal technique in enabling large-scale fabrication of integrated quantum photonic devices across a variety of applications.

Multi‐Wavelength Quantum Light Sources on Silicon Nitride Micro‐Ring Chip

AbstractMulti‐wavelength quantum light sources are extremely desired in establishing communication links among multiple users for realizing quantum networks. Despite recent impressive advances, developing such a quantum light source with high quality remains challenging. Here a multi‐wavelength quantum light source using a silicon nitride micro‐ring with a free spectral range of 200 GHz is demonstrated. The generation of eight‐wavelength‐paired photon pairs is ensured in a wavelength range of 25.6 nm. With device optimization and noise‐rejecting filters, this source enables the generation of heralded single‐photons at a rate of 62 kHz with and the generation of energy‐time entangled photons with a visibility of in the Franson interferometer. These results, at room temperature and telecom wavelength, in a CMOS‐compatible platform, represent an important step toward integrated quantum photonic devices, which pave the way for realizing a large‐scale quantum network.

Integrated Reconfigurable Photon-Pair Source Based on High-Q Nonlinear Chalcogenide Glass Microring Resonators.

Chalcogenide glasses (ChGs) have recently emerged as enabling materials for building reconfigurable nanophotonic devices by employing their refractive index changes associated with photosensitive effects. In particular, the availability of low-loss thin-film ChGs and the realization of high-Q microresonators provide exciting opportunities for integrated photonics. So far, the ChG photonic devices are predominately operated in the classical optics regime. In this work, we present the realization on-chip bright photon-pair quantum light sources via spontaneous four-wave mixing in a high-Q microring resonator fabricated on the newly developed ChG Ge25Sb10S65 platform. The emission wavelength of the photon-pair source can be continuously tuned across a double-free spectral range in a reconfigurable manner. Our work serves as a starting point to fully unleash the potential of exploiting ChGs for developing reconfigurable integrated quantum photonic devices.

Cathodoluminescence monitoring of quantum emitter activation in hexagonal boron nitride

The ability to locally activate or generate quantum emitters in two-dimensional materials is of major interest for the realization of integrated quantum photonic devices. In particular, hexagonal boron nitride (hBN) has recently been shown to allow a variety of techniques for obtaining quantum emitters at desired locations. Here, we use cathodoluminescence (CL) to monitor in situ the local activation of color centers by an electron beam in hBN. We observe that the CL signal saturates at a given surface dose, independently of the electron current density. Based on photoluminescence and photon correlations, we show that the number of photoactive color centers is proportional to the CL signal, and we estimate the maximum density of quantum emitters that can be generated by our technique. Our results provide insight about the activation mechanism and could help to optimize the controlled generation of single photon sources in hexagonal boron nitride.

Chip-based quantum communications

Quantum communications aim to share encryption keys between the transmitters and receivers governed by the laws of quantum mechanics. Integrated quantum photonics offers significant advantages of dense integration, high stability and scalability, which enables a vital platform for the implementation of quantum information processing and quantum communications. This article reviews recent experimental progress and advances in the development of integrated quantum photonic devices and systems for quantum communications and quantum networks.

Dual-resonance enhanced quantum light-matter interactions in deterministically coupled quantum-dot-micropillars

Optical microcavities have widely been employed to enhance either the optical excitation or the photon emission processes for boosting light-matter interactions at the nanoscale. When both the excitation and emission processes are simultaneously facilitated by the optical resonances provided by the microcavities, as referred to the dual-resonance condition in this article, the performances of many nanophotonic devices approach to the optima. In this work, we present versatile accessing of dual-resonance conditions in deterministically coupled quantum-dot (QD)-micropillars, which enables emission from neutral exciton (X)—charged exciton (CX) transition with improved single-photon purity. In addition, the rarely observed up-converted single-photon emission process is achieved under dual-resonance conditions. We further exploit the vectorial nature of the high-order cavity modes to significantly improve the excitation efficiency under the dual-resonance condition. The dual-resonance enhanced light-matter interactions in the quantum regime provide a viable path for developing integrated quantum photonic devices based on cavity quantum electrodynamics (QED) effect, e.g., highly efficient quantum light sources and quantum logical gates.

Bright room temperature near-infrared single-photon emission from single point defects in the AlGaN film

Near-infrared (NIR) single-photon source plays a key role in a wide range of applications in quantum technology. In particular, in quantum communication, the NIR wavelength operation perfectly matches the relatively low-attenuation transmission window of the optical fiber, which attracts more and more research interest. Here, we report the room temperature single-photon emission from single point defects in the aluminum gallium nitride (AlGaN) film. The obtained single-photon emission covers from 720 to 930 nm and exhibits highly linear polarization and high photon brightness. This may provide a platform for future integrated on-chip quantum photonic devices.

Bright solid-state sources for single photons with orbital angular momentum.

Photons that have a helical phase front, that is, twisted photons, can carry a discrete, in principle, unlimited, but quantized amount of orbital angular momentum (OAM). Hence, twisted single photons constitute a high-dimensional quantum system with information-processing abilities beyond those of two-level single-photon qubits. To date, the generation of single photons carrying OAM has relied on a non-linear process in bulk crystals, for example, spontaneous parametric down-conversion, which limits both the efficiency and the scalability of the source. Here, we present a bright solid-state source of single photons in an OAM superposition state with a single-photon purity of g(2)(0) = 0.115(1) and a collection efficiency of 23(4)%. The mode purity of the single-photon OAM states is further examined via projection measurements. Future developments of integrated quantum photonic devices with pure OAM states as an additional degree of freedom may enable high-dimensional quantum information processing.

Quantum Photonic Simulation of Spin-Magnetic Field Coupling and Atom-Optical Field Interaction

In this work, we present the physical simulation of the dynamical and topological properties of atom-field quantum interacting systems by means of integrated quantum photonic devices. In particular, we simulate mechanical systems used, for example, for quantum processing and requiring a very complex technology such as a spin-1/2 particle interacting with an external classical time-dependent magnetic field and a two-level atom under the action of an external classical time-dependent electric (optical) field (light-matter interaction). The photonic device consists of integrated optical waveguides supporting two collinear or codirectional modes, which are coupled by integrated optical gratings. We show that the single-photon quantum description of the dynamics of this photonic device is a quantum physical simulation of both aforementioned interacting systems. The two-mode photonic device with a single-photon quantum state represents the quantum system, and the optical grating corresponds to an external field. Likewise, we also present the generation of Aharonov–Anandan geometric phases within this photonic device, which also appear in the simulated systems. On the other hand, this photonic simulator can be regarded as a basic brick for constructing more complex photonic simulators. We present a few examples where optical gratings interacting with several collinear and/or codirectional modes are used in order to illustrate the new possibilities for quantum simulation.

Integrated single photon emitters

The realization of scalable systems for quantum information processing and networking is of utmost importance to the quantum information community. However, building such systems is difficult because of challenges in achieving all the necessary functionalities on a unified platform while maintaining stringent performance requirements of the individual elements. A promising approach that addresses this challenge is based on the consolidation of experimental and theoretical capabilities in quantum physics and integrated photonics. Integrated quantum photonic devices allow efficient control and read-out of quantum information while being scalable and cost effective. Here, the authors review recent developments in solid-state single photon emitters coupled with various integrated photonic structures, which form a critical component of future scalable quantum devices. Their work contributes to the further development and realization of quantum networking protocols and quantum logic on a scalable and fabrication-friendly platform.

Low‐Temperature Silicon‐Vacancy Luminescence of Individual Chemical Vapor Deposition Nanodiamonds Grown by Seeding and Spontaneous Nucleation

Diamond nanoparticles with optically active color centers can be used in nanoscale devices for quantum networking and sensing. A particular interest is focused on nanodiamonds (NDs) containing a small ensemble of negatively charged silicon‐vacancy (SiV) centers. Such NDs can be integrated with on‐chip optical structures. Here, chemical vapor deposition (CVD) is used to synthesize diamond particles of less than 100 nm in size containing 10–20 centers per ND. Two types of NDs grown on a Si substrate are studied, seeded with detonation NDs and without any seeding. The SiV luminescence under off‐resonant and resonant laser excitation at the temperature of 15 K is investigated. The emission lines of SiVs of individual NDs are well resolved and found to be spread in the range of 730–750 nm. The typical SiV linewidth is within 1–2 GHz for spontaneous NDs, which is only a factor of 2.5–5 broader than the lifetime limited linewidth of the SiV at 15 K. The emission of a single SiV is highly stable for both types of samples. This work is a critical step toward the synthesis of SiVs suitable for the realization of integrated quantum photonic devices.

Advanced technologies for quantum photonic devices based on epitaxial quantum dots.

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.

Tilted-potential photonic crystal cavities for integrated quantum photonics.

We propose and investigate a new type of photonic crystal (PhC) cavity for integrated quantum photonics, which provides tailored optical modes with both confined and extended spatial components. The structures consist of elongated PhC cavities in which the effective index of refraction is varied quasi-linearly along their axis, implemented by systematic lateral shifts of the PhC holes. The confined modes have approximately Airy-function envelopes, exhibiting single peaks and extended tails, which is useful for optimizing single photon extraction and transmission in integrated quantum photonic devices. The measured spectrally resolved near-field patterns of such devices show the expected spatial and resonance wavelength behavior, in agreement with numerical simulations of the Airy-Bloch modes. The effects of fabrication-induced disorder on the mode features are also analyzed and discussed. Selective excitation of specific Airy-Bloch modes using integrated, site-controlled quantum dots as localized light sources is demonstrated. Based on the tilted-potential cavity, multiple-QD single photon emitters exploiting wavelength division multiplexing are proposed.

Combined metallic nano-rings and solid-immersion lenses for bright emission from single InAs/GaAs quantum dots

Solid-state single-photon emitters are key components for integrated quantum photonic devices. However, they can suffer from poor extraction efficiencies, caused by the large refractive index contrast between the bulk material they are embedded in and air: this results in a small fraction (that can be as low as ∼0.1%) of the emitted photons reaching free-space collection optics. To overcome this issue, we present a device that combines a metallic nano-ring, positioned on the sample surface and centered around the emitter, and an epoxy-based super-solid immersion lens, deposited above the ring devices. We show that the combined broadband lensing effect of the nano-ring and the super-solid immersion lens significantly increases the extraction of light emitted by single InAs/GaAs quantum dots into free space: we observe cumulative enhancements that allow us to estimate photon fluxes on the first collecting lens approaching 1 × 106 counts per second, from a single quantum dot in bulk. The combined broad-band enhancement in the extraction of light can be implemented with any kind of classical and quantum solid-state emitter and opens the path to the realisation of scalable bright devices. The same approach can also be implemented to improve the absorption of light, for instance, for small-area broadband photo-detectors.

Hybrid Integration of Solid-State Quantum Emitters on a Silicon Photonic Chip.

Scalable quantum photonic systems require efficient single photon sources coupled to integrated photonic devices. Solid-state quantum emitters can generate single photons with high efficiency, while silicon photonic circuits can manipulate them in an integrated device structure. Combining these two material platforms could, therefore, significantly increase the complexity of integrated quantum photonic devices. Here, we demonstrate hybrid integration of solid-state quantum emitters to a silicon photonic device. We develop a pick-and-place technique that can position epitaxially grown InAs/InP quantum dots emitting at telecom wavelengths on a silicon photonic chip deterministically with nanoscale precision. We employ an adiabatic tapering approach to transfer the emission from the quantum dots to the waveguide with high efficiency. We also incorporate an on-chip silicon-photonic beamsplitter to perform a Hanbury-Brown and Twiss measurement. Our approach could enable integration of precharacterized III-V quantum photonic devices into large-scale photonic structures to enable complex devices composed of many emitters and photons.

Optimal antibunching in passive photonic devices based on coupled nonlinear resonators

We propose the use of weakly nonlinear passive materials for prospective applications in integrated quantum photonics. It is shown that strong enhancement of native optical nonlinearities by electromagnetic field confinement in photonic crystal resonators can lead to single-photon generation only exploiting the quantum interference of two coupled modes and the effect of photon blockade under resonant coherent driving. For realistic system parameters in state of the art microcavities, the efficiency of such a single-photon source is theoretically characterized by means of the second-order correlation function at zero-time delay as the main figure of merit, where major sources of loss and decoherence are taken into account within a standard master equation treatment. These results could stimulate the realization of integrated quantum photonic devices based on non-resonant material media, fully integrable with current semiconductor technology and matching the relevant telecom band operational wavelengths, as an alternative to single-photon nonlinear devices based on cavity quantum electrodynamics with artificial atoms or single atomic-like emitters.