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.

Cooling of an integrated Brillouin laser below the thermal limit.

Photonically integrated resonators are promising as a platform for enabling ultranarrow linewidth lasers in a compact form factor. Owing to their small size, these integrated resonators suffer from thermal noise that limits the frequency stability of the optical mode to ∼100 kHz. Here, we demonstrate an integrated stimulated Brillouin scattering (SBS) laser based on a large mode-volume annulus resonator that realizes an ultranarrow thermal-noise-limited linewidth of 270 Hz. In practice, yet narrower linewidths are required before integrated lasers can be truly useful for applications such as optical atomic clocks, quantum computing, gravitational wave detection, and precision spectroscopy. To this end, we employ a thermorefractive noise suppression technique utilizing an auxiliary laser to reduce our SBS laser linewidth to 70 Hz. This demonstration showcases the possibility of stabilizing the thermal motion of even the narrowest linewidth chip lasers to below 100 Hz, thereby opening the door to making integrated microresonators practical for the most demanding future scientific endeavors.

High-Fidelity Ion State Detection Using Trap-Integrated Avalanche Photodiodes.

Integrated technologies greatly enhance the prospects for practical quantum information processing and sensing devices based on trapped ions. High-speed and high-fidelity ion state readout is critical for any such application. Integrated detectors offer significant advantages for system portability and can also greatly facilitate parallel operations if a separate detector can be incorporated at each ion-trapping location. Here, we demonstrate ion quantum state detection at room temperature utilizing single-photon avalanche diodes (SPADs) integrated directly into the substrate of silicon ion trapping chips. We detect the state of a trapped Sr^{+} ion via fluorescence collection with the SPAD, achieving 99.92(1)% average fidelity in 450 µs, opening the door to the application of integrated state detection to quantum computing and sensing utilizing arrays of trapped ions.

Cavity-enhanced microwave readout of a solid-state spin sensor.

Overcoming poor readout is an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. However, in spite of experimental progress in specific systems, solid-state spin sensors still lack a universal, high-fidelity readout technique. Here we demonstrate high-fidelity, room-temperature readout of an ensemble of nitrogen-vacancy centers via strong coupling to a dielectric microwave cavity, building on similar techniques commonly applied in cryogenic circuit cavity quantum electrodynamics. This strong collective interaction allows the spin ensemble's microwave transition to be probed directly, thereby overcoming the optical photon shot noise limitations of conventional fluorescence readout. Applying this technique to magnetometry, we show magnetic sensitivity approaching the Johnson-Nyquist noise limit of the system. Our results pave a clear path to achieve unity readout fidelity of solid-state spin sensors through increased ensemble size, reduced spin-resonance linewidth, or improved cavity quality factor.

Operation of an optical atomic clock with a Brillouin laser subsystem.

Microwave atomic clocks have traditionally served as the 'gold standard' for precision measurements of time and frequency. However, over the past decade, optical atomic clocks1-6 have surpassed the precision of their microwave counterparts by two orders of magnitude or more. Extant optical clocks occupy volumes of more than one cubic metre, and it is a substantial challenge to enable these clocks to operate in field environments, which requires the ruggedization and miniaturization of the atomic reference and clock laser along with their supporting lasers and electronics4,7,8,9. In terms of the clock laser, prior laboratory demonstrations of optical clocks have relied on the exceptional performance gained through stabilization using bulk cavities, which unfortunately necessitates the use of vacuum and also renders the laser susceptible to vibration-induced noise. Here, using a stimulated Brillouin scattering laser subsystem that has a reduced cavity volume and operates without vacuum, we demonstrate a promising component of a portable optical atomic clock architecture. We interrogate a 88Sr+ ion with our stimulated Brillouin scattering laser and achieve a clock exhibiting short-term stability of 3.9 × 10-14 over one second-an improvement of an order of magnitude over state-of-the-art microwave clocks. This performance increase within a potentially portable system presents a compelling avenue for substantially improving existing technology, such as the global positioning system, and also for enabling the exploration of topics such as geodetic measurements of the Earth, searches for dark matter and investigations into possible long-term variations of fundamental physics constants10-12.

On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries.

We propose the use of a diamond waveguide structure to enhance the sensitivity of magnetometers relying on the detection of the spin state of nitrogen-vacancy ensembles in diamond by infrared optical absorption. An optical waveguide structure allows for enhanced optical path-lengths avoiding the use of optical cavities and complicated setups. The presented design for diamond-based magnetometers enables miniaturization while maintaining high sensitivity and forms the basis for magnetic field sensors applicable in biomedical, industrial and space-related applications.

Brillouin-enhanced hyperparametric generation of an optical frequency comb in a monolithic highly nonlinear fiber cavity pumped by a cw laser.

We demonstrate self-seeded generation of a broadband comb in a highly nonlinear fiber resonator. When pumped with a cw laser, the fiber cavity generates a comb with two characteristic spacings. Hyperparametric modes spaced by approximately 2 THz create the base structure of the comb, while commensurate Brillouin modes spaced by approximately 10 GHz populate the intermediate frequency gaps. The frequency modes are coherent, and the repetition rate of the comb has been locked to a microwave standard.

Generation of paired photons with controllable waveforms.

We describe experiments and theory showing the generation of counterpropagating paired photons with coherence times of about 50 ns and waveforms that are controllable at a rudimentary level. Using cw lasers, electromagnetically induced transparency and cold 87Rb atoms we generate paired photons into opposing single-mode optical fibers at a rate of approximately 12 000 pairs per second.

Frequency mixing using electromagnetically induced transparency in cold atoms.

We report the first experimental demonstration of four-wave mixing using electromagnetically induced transparency in cold atoms. Backward-wave, phase-matched difference-frequency conversion is achieved at optical powers of a few nanowatts and at energies of less than a picojoule.