Photonic Quantum Networks formed from NV(-) centers

Room-Temperature Fiber-Coupled Single-Photon Sources based on Colloidal Quantum Dots and SiV Centers in Back-Excited Nanoantennas

We demonstrate an important step toward on-chip integration of single-photon sources at room temperature. Excellent photon directionality is achieved with a hybrid metal-dielectric bullseye antenna, while back-excitation is permitted by placement of the emitter in a subwavelength hole positioned at its center. The unique design enables a direct back-excitation and very efficient front coupling of emission either to a low numerical aperture (NA) optics or directly to an optical fiber. To show the versatility of the concept, we fabricate devices containing either a colloidal quantum dot or a nanodiamond containing silicon-vacancy centers, which are accurately positioned using two different nanopositioning methods. Both of these back-excited devices display front collection efficiencies of ∼70% at NAs as low as 0.5. The combination of back-excitation with forward directionality enables direct coupling of the emitted photons into a proximal optical fiber without any coupling optics, thereby facilitating and simplifying future integration.

Large-scale optical characterization of solid-state quantum emitters

Solid-state quantum emitters have emerged as a leading quantum memory for quantum networking applications. However, standard optical characterization techniques are neither efficient nor repeatable at scale. Here we introduce and demonstrate spectroscopic techniques that enable large-scale, automated characterization of colour centres. We first demonstrate the ability to track colour centres by registering them to a fabricated machine-readable global coordinate system, enabling a systematic comparison of the same colour centre sites over many experiments. We then implement resonant photoluminescence excitation in a widefield cryogenic microscope to parallelize resonant spectroscopy, achieving two orders of magnitude speed-up over confocal microscopy. Finally, we demonstrate automated chip-scale characterization of colour centres and devices at room temperature, imaging thousands of microscope fields of view. These tools will enable the accelerated identification of useful quantum emitters at chip scale, enabling advances in scaling up colour centre platforms for quantum information applications, materials science and device design and characterization.

Nanothermometry in rarefied gas using optically levitated nanodiamonds

Heat transfer in gases in the continuum regime follows Fourier's law and is well understood. However, it has been long understood that in the subcontinuum, rarefied gas regime Fourier's law is no longer valid and various models have been proposed to describe heat transfer in these systems. These models have very limited experimental exploration for spherical geometries due to the difficulties involved. Optically levitated nanoparticles are presented as the ideal experimental system to study heat transfer in rarefied gases due to their isolation from their environment. Nanodiamonds with nitrogen-vacancy centers are used to measure temperature. As the pressure decreases so does the heat transfer to the rarefied gas and the nanodiamond temperature increases by over 200 K. These experiments demonstrate the utility of optically levitated nanoparticles to study heat transfer in any gas across a wide range of pressures. In the future, these measurements can be combined with models to empirically determine the energy accommodation coefficient of any gas.

Sub-10 nm Precision Engineering of Solid-State Defects via Nanoscale Aperture Array Mask

Engineering a strongly interacting uniform qubit cluster would be a major step toward realizing a scalable quantum system for quantum sensing and a node-based qubit register. For a solid-state system that uses a defect as a qubit, various methods to precisely position defects have been developed, yet the large-scale fabrication of qubits within the strong coupling regime at room temperature continues to be a challenge. In this work, we generate nitrogen vacancy (NV) color centers in diamond with sub-10 nm scale precision using a combination of nanoscale aperture arrays (NAAs) with a high aspect ratio of 10 and a secondary E-beam hole pattern used as an ion-blocking mask. We perform optical and spin measurements on a cluster of NV spins and statistically investigate the effect of the NAAs during an ion-implantation process. We discuss how this technique is effective for constructing a scalable system.

Laser refrigeration of optically levitated sodium yttrium fluoride nanocrystals

Solid state laser refrigeration can cool optically levitated nanocrystals in an optical dipole trap, allowing for internal temperature control by mitigating photothermal heating. This work demonstrates cooling of ytterbium-doped cubic sodium yttrium fluoride nanocrystals to 252 K on average with the most effective crystal cooling to 241 K. The amount of cooling increases linearly with the intensity of the cooling laser and is dependent on the pressure of the gas surrounding the nanocrystal. Cooling optically levitated nanocrystals allows for crystals prone to heating to be studied at lower pressures than currently achievable and for temperature control and stabilization of trapped nanocrystals.

Algorithmic decomposition for efficient multiple nuclear spin detection in diamond

Efficiently detecting and characterizing individual spins in solid-state hosts is an essential step to expand the fields of quantum sensing and quantum information processing. While selective detection and control of a few ¹³C nuclear spins in diamond have been demonstrated using the electron spin of nitrogen-vacancy (NV) centers, a reliable, efficient, and automatic characterization method is desired. Here, we develop an automated algorithmic method for decomposing spectral data to identify and characterize multiple nuclear spins in diamond. We demonstrate efficient nuclear spin identification and accurate reproduction of hyperfine interaction components for both virtual and experimental nuclear spectroscopy data. We conduct a systematic analysis of this methodology and discuss the range of hyperfine interaction components of each nuclear spin that the method can efficiently detect. The result demonstrates a systematic approach that automatically detects nuclear spins with the aid of computational methods, facilitating the future scalability of devices.

Resource Reduction for Distributed Quantum Information Processing Using Quantum Multiplexed Photons

Distributed quantum information processing is based on the transmission of quantum data over lossy channels between quantum processing nodes. These nodes may be separated by a few microns or on planetary scale distances, but transmission losses due to absorption and/or scattering in the channel are the major source of error for most distributed quantum information tasks. Of course, quantum error correction (QEC) and detection techniques can be used to mitigate such effects, but error detection approaches have severe performance limitations due to the signaling constraints between nodes, and so error correction approaches are preferable-assuming one has sufficient high quality local operations. Typically, performance comparisons between loss-mitigating codes assume one encoded qubit per photon. However, single photons can carry more than one qubit of information and so our focus in this Letter is to explore whether loss-based QEC codes utilizing quantum multiplexed photons are viable and advantageous, especially as photon loss results in more than one qubit of information being lost. We show that quantum multiplexing enables significant resource reduction, in terms of the number of single-photon sources, while at the same time maintaining (or even lowering) the number of 2-qubit gates required. Further, our multiplexing approach requires only conventional optical gates already necessary for the implementation of these codes.

Electron-Induced State Conversion in Diamond NV Centers Measured with Pump-Probe Cathodoluminescence Spectroscopy

Nitrogen-vacancy (NV) centers in diamond are reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers, NV⁰ and NV^-, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, an understanding of the dynamics between the different states still remains challenging. Here, conversion from NV^- to NV⁰ due to electron-induced carrier generation is shown. Ultrafast pump-probe cathodoluminescence spectroscopy is presented for the first time, with electron pulses as pump and laser pulses as probe, to prepare and read out the NV states. The experimental data are explained with a model considering carrier dynamics (0.8 ns), NV⁰ spontaneous emission (20 ns), and NV⁰ → NV^- back transfer (500 ms). The results provide new insights into the NV^- → NV⁰ conversion dynamics and into the use of pump-probe cathodoluminescence as a nanoscale NV characterization tool.

Collective Effects in Casimir-Polder Forces

We study cooperative phenomena in the fluctuation-induced forces between a surface and a system of neutral two-level quantum emitters prepared in a coherent collective state, showing that the total Casimir-Polder force on the emitters can be modified via their mutual correlations. Particularly, we find that a one-dimensional chain of emitters prepared in a super- or subradiant state experiences an enhanced or suppressed collective vacuum-induced force, respectively. The collective nature of dispersion forces can be understood as resulting from the interference between the different processes contributing to the surface-modified resonant dipole-dipole interaction. Such cooperative fluctuation forces depend singularly on the surface response at the resonance frequency of the emitters, thus being easily maneuverable. Our results demonstrate the potential of collective phenomena as a new tool to selectively tailor vacuum forces.

Advances in diamond nanofabrication for ultrasensitive devices

This paper reviews some of the major recent advances in single-crystal diamond nanofabrication and its impact in nano- and micro-mechanical, nanophotonics and optomechanical components. These constituents of integrated devices incorporating specific dopants in the material provide the capacity to enhance the sensitivity in detecting mass and forces as well as magnetic field down to quantum mechanical limits and will lead pioneering innovations in ultrasensitive sensing and precision measurements in the realm of the medical sciences, quantum sciences and related technologies.

Efficient Single-Photon Coupling from a Nitrogen-Vacancy Center Embedded in a Diamond Nanowire Utilizing an Optical Nanofiber

Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.

Quantum information processing with superconducting circuits: a review

During the last ten years, superconducting circuits have passed from being interesting physical devices to becoming contenders for near-future useful and scalable quantum information processing (QIP). Advanced quantum simulation experiments have been shown with up to nine qubits, while a demonstration of quantum supremacy with fifty qubits is anticipated in just a few years. Quantum supremacy means that the quantum system can no longer be simulated by the most powerful classical supercomputers. Integrated classical-quantum computing systems are already emerging that can be used for software development and experimentation, even via web interfaces. Therefore, the time is ripe for describing some of the recent development of superconducting devices, systems and applications. As such, the discussion of superconducting qubits and circuits is limited to devices that are proven useful for current or near future applications. Consequently, the centre of interest is the practical applications of QIP, such as computation and simulation in Physics and Chemistry.