Spontaneously emitted photons are entangled with the electronic and nuclear degrees of freedom of the emitting atom, so interference and measurement of these photons can entangle separate matter-based quantum systems as a resource for quantum information processing. Since confinement in a single-mode facilitates the photon interference needed for generating entanglement, the dipole emission patterns relevant in spontaneous emission present a mode-matching challenge. Current demonstrations rely on bulk photon-collection and manipulation optics that suffer from large component size and system-to-system variability-factors that impede scaling to the large numbers of entangled pairs needed for quantum information processing. To address these limitations, we demonstrate a collection method that enables passive phase stability, straightforward photonic manipulation, and intrinsic reproducibility. Specifically, we engineer a waveguide-integrated grating to couple photons emitted from a trapped ion into a single optical mode within a microfabricated ion-trap chip. Using the integrated collection optic, we characterize the collection efficiency, image the ion, and detect the ion's quantum state. The integrated optic covers 2.18% of the solid angle and collects 1.97 ± 0.3% of the spontaneously emitted light incident on the grating for a total collection efficiency of 0.043% into a single-mode waveguide. This proof-of-principle demonstration lays the foundation for leveraging the inherent stability and reproducibility of integrated photonics to create, manipulate, and measure multipartite quantum states in arrays of quantum emitters.

Trapped ions are a promising modality for quantum systems, with demonstrated utility as the basis for quantum processors and optical clocks. However, traditional trapped-ion systems are implemented using complex free-space optical configurations, whose large size and susceptibility to vibrations and drift inhibit scaling to large numbers of qubits. In recent years, integrated-photonics-based systems have been demonstrated as an avenue to address the challenge of scaling trapped-ion systems while maintaining high fidelities. While these previous demonstrations have implemented both Doppler and resolved-sideband cooling of trapped ions, these cooling techniques are fundamentally limited in efficiency. In contrast, polarization-gradient cooling can enable faster and more power-efficient cooling and, therefore, improved computational efficiencies in trapped-ion systems. While free-space implementations of polarization-gradient cooling have demonstrated advantages over other cooling mechanisms, polarization-gradient cooling has never previously been implemented using integrated photonics. In this paper, we design and experimentally demonstrate key polarization-diverse integrated-photonics devices and utilize them to implement a variety of integrated-photonics-based polarization-gradient-cooling systems, culminating in the first experimental demonstration of polarization-gradient cooling of a trapped ion by an integrated-photonics-based system. By demonstrating polarization-gradient cooling using an integrated-photonics-based system and, in general, opening up the field of polarization-diverse integrated-photonics-based devices and systems for trapped ions, this work facilitates new capabilities for integrated-photonics-based trapped-ion platforms.

Trapped ions provide a highly controlled platform for quantum sensors, clocks, simulators, and computers, all of which depend on cooling ions close to their motional ground state. Existing methods like Doppler, resolved sideband, and dark resonance cooling balance trade-offs between the final temperature and cooling rate. A traveling polarization gradient has been shown to cool multiple modes quickly and in parallel, but utilizing a stable polarization gradient can achieve lower ion energies, while also allowing tailorable light-matter interactions in the sub-wavelength regime. In this Letter, we demonstrate cooling of a trapped ion below the Doppler limit using a phase-stable polarization gradient created using trap-integrated photonic devices. At an axial frequency of 2π×1.45  MHz we achieve ⟨n⟩=1.56±0.07 in 150  μs and cooling rates of ∼0.3  quanta/μs. We examine ion dynamics under different polarization gradient phases, detunings, and intensities, showing reasonable agreement between experimental results and a multilevel model. Cooling is fast and power efficient, with lower average motional Fock state occupation when compared to simulated operation under the corresponding running wave configuration. Our results demonstrate a well-controlled test bed for studying the dynamics of multilevel atomic systems in a phase-stable polarization gradient.

We statistically characterize waveguide index and thickness variations in integrated silicon nitride directional couplers. Combining limited experimental measurement results with prior probability distributions, we demonstrate a maximum likelihood estimation approach for index and thickness estimation.

We demonstrate the first collection of ion fluorescence into a trap-integrated waveguide by using a tightly-focusing, $30\times 34\ \mu \mathrm{m}$ diffraction grating. This proof-of-principle demonstration charts a path to scalable quantum-state measurement of trapped ions.

Similar to electronic multi-chip modules (MCMs), photonic MCMs (P-MCMs) integrate multiple chips onto a common substrate to provide benefits (e.g., performance, size, power consumption, yield) that cannot be achieved through monolithic, single-chip integration. We report the development of a novel P-MCM platform that integrates best-in-class photonic components (e.g., external-cavity lasers, thin-film lithium-niobate (TFLN) optical modulators, high-Q optical filters, balanced-waveguide photodiodes) onto a silicon-wafer “intermount” that facilitates efficient optical coupling between components and provides environmentally stable mechanical support. The performance demonstrated from the integrated components make the P-MCM platform a strong candidate for realizing microwave photonic (MWP) subsystems having radio-frequency (RF) performance superior to what can be achieved from discrete, fiber-pigtailed photonic components or other photonic integrated circuit (PIC) technologies. Other potential applications include optical interfaces for atom-based quantum computers and optical clocks, free-space lasercom, and remote optical sensing.

This talk reviews photonic integrated circuit materials, devices and integration techniques developed at MIT Lincoln Laboratory to support the needs of next generation quantum systems across the wavelength spectrum from the near-ultraviolet to the midwave-infrared.

In this work, we design and experimentally demonstrate the first, to the best of our knowledge, integrated polarization splitters and rotators at blue wavelengths. We develop compact and efficient designs for both a polarization splitter and rotator at a 422-nm wavelength, an important laser-cooling transition for 88Sr+ ions. These devices are fabricated in a 200-mm wafer-scale process and experimentally demonstrated, resulting in a measured polarization-splitter transverse-electric thru-port coupling of 98.0% and transverse-magnetic tap-port coupling of 77.6% for a compact 16-µm-long device and a polarization-rotator conversion efficiency of 92.2% for a separate compact 111-µm-long device. This work paves the way for more sophisticated integrated control of trapped-ion and neutral-atom quantum systems.

This talk will cover photonics integrated circuits (PICs) being developed at MIT Lincoln Laboratory for quantum applications, especially trapped-ion based quantum computers and optical clocks. We discuss optical signal routing, light collection for direct readout or remote entanglement generation, and laser and active component development.

Compact, low-loss mode-expansion tapers for red light are demonstrated. Inverse design methods enable 50 μm long tapers from single-mode to 8- and 18 μm wide waveguides with measured losses of 0.05 and 1.05 dB/taper respectively.

We design and experimentally demonstrate the first pair of integrated TE- and TM- emitting gratings at a wavelength of 422nm, targeting the 52s1/2-52p1/2 transition of 88Sr+ ions, to enable operations requiring diverse polarizations for integrated-photonics-based trapped-ion quantum systems.

We develop a framework for two advanced trapped-ion cooling schemes, polarization-gradient and electromagnetically-induced-transparency cooling, for 88Sr+ ions using a visible-wavelength integrated-photonics platform and present the design of the key integrated devices.

I discuss MIT Lincoln Laboratory’s development of integrated photonics and detectors for trapped-ion-array optical clocks, as well as compact, narrow-linewidth lasers to serve as clock oscillators. These technologies will help enable liter-scale, high- performance optical clocks.

Integrated photonic technologies for quantum applications are discussed with emphasis on those supporting trapped-ion-based systems. A long-term vision of a fully integrated trapped- ion chip and current work towards its realization are presented.

We present a CMOS-compatible, Q-switched mode-locked integrated laser operating at 1.9 µm with a compact footprint of 23.6 × 0.6 × 0.78mm. The Q-switching rate is 720 kHz, the mode-locking rate is 1.2 GHz, and the optical bandwidth is 17nm, which is sufficient to support pulses as short as 215 fs. The laser is fabricated using a silicon nitride on silicon dioxide 300-mm wafer platform, with thulium-doped Al2O3 glass as a gain material deposited over the silicon photonics chip. An integrated Kerr-nonlinearity-based artificial saturable absorber is implemented in silicon nitride. A broadband (over 100 nm) dispersion-compensating grating in silicon nitride provides sufficient anomalous dispersion to compensate for the normal dispersion of the other laser components, enabling femtosecond-level pulses. The laser has no off-chip components with the exception of the optical pump, allowing for easy co-integration of numerous other photonic devices such as supercontinuum generation and frequency doublers which together potentially enable fully on-chip frequency comb generation.

We demonstrate a silicon photonics optical frequency synthesizer (SPOFS). The frequency instability obtained in the telecom band is 1×10−12 at 1s level, comparable to a bench-top commercial optical frequency synthesizer system.

Efficient complementary metal-oxide semiconductor-based nonlinear optical devices in the near-infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared. With input pulses of 18 pJ in energy, the generated signal spans the wavelength range from the edge of the silicon transmission window, approximately 1.06 to beyond 2.4 μm, with a -20 dB bandwidth covering 1.124-2.4 μm. An octave-spanning supercontinuum was also observed at the energy levels as low as 4 pJ (-35 dB bandwidth). We also measured the coherence over an octave, obtaining , in good agreement with the simulations. In addition, we demonstrate optimization of the third-order dispersion of the waveguide to strengthen the dispersive wave and discuss the advantage of having a soliton at the long wavelength edge of an octave-spanning signal for nonlinear applications. This research paves the way for applications, such as chip-scale precision spectroscopy, optical coherence tomography, optical frequency metrology, frequency synthesis and wide-band wavelength division multiplexing in the telecom window.

Laser sources in the mid-infrared are of great interest due to their wide applications in detection, sensing, communication and medicine. Silicon photonics is a promising technology which enables these laser devices to be fabricated in a standard CMOS foundry, with the advantages of reliability, compactness, low cost and large-scale production. In this paper, we demonstrate a holmium-doped distributed feedback laser monolithically integrated on a silicon photonics platform. The Al2O3:Ho3+ glass is used as gain medium, which provides broadband emission around 2 µm. By varying the distributed feedback grating period and Al2O3:Ho3+ gain layer thickness, we show single mode laser emission at wavelengths ranging from 2.02 to 2.10 µm. Using a 1950 nm pump, we measure a maximum output power of 15 mW, a slope efficiency of 2.3% and a side-mode suppression ratio in excess of 50 dB. The introduction of a scalable monolithic light source emitting at > 2 µm is a significant step for silicon photonic microsystems operating in this highly promising wavelength region.

We demonstrate holmium-doped DFB lasers monolithically integrated on silicon. Single mode lasing at wavelength from 2.02 to 2.10 μm with 15 mW maximum output power are reported. This work extends silicon-photonic microsystems beyond 2 μm.