arXiv subjects

Michael Gehl

Publications and source records attributed to Michael Gehl.

At least 19 recordsLinked to original sources

arXiv2026

A heterogeneously integrated coupled-cavity frequency beam splitter

Frequency encoded photonic qubits promise a scalable path towards high-dimensional quantum information processing, but require efficient components for coherently mixing frequency modes. Coupled cavity modulators provide this functionality by using only a single driving microwave tone to couple hybridized optical supermodes. Here, we demonstrate a heterogeneously integrated thin-film lithium-niobate-on-silicon coupled-cavity modulator that realizes tunable bidirectional frequency mode transformations, including $50/50$ beam splitting and near complete frequency swapping with $>20~\mathrm{dB}$ pump extinction at a $10~\mathrm{GHz}$ supermode splitting. Because the electro-optic film is bonded onto a foundry fabricated silicon photonics platform, the approach is compatible with co-integration of photon pair sources, spectral filters, active tuning elements, and single photon detectors. We also bond thin-film lithium tantalate onto the same coupled-cavity platform, demonstrating material flexibility for scalable integrated frequency bin quantum photonic circuits.

quant-ph↗

arXiv2026

Ultra-low loss piezo-optomechanical low-confinement silicon nitride platform for visible wavelength quantum photonic circuits

Realizing photonic quantum computing at scale requires integrated circuits that combine ultra-low loss with fast, low-power, low-hysteresis, and low-crosstalk reconfiguration. These requirements are particularly challenging at visible wavelengths, where many quantum resource-state generators, including single-photon sources and quantum memories, naturally operate. Low-confinement silicon nitride waveguides offer the requisite loss performance, but conventional thermo-optic modulators dissipate significant static power, driving thermal crosstalk and precluding cryogenic operation. Visible-wavelength piezo-optomechanical circuits avoid these drawbacks, but existing demonstrations rely either on high-confinement waveguides with propagation losses of 35-100 dB/m, or on low-confinement platforms using foundry-incompatible PZT. Here we combine piezo-optomechanical actuation with a CMOS-foundry-fabricated, low-confinement silicon nitride platform, achieving 2.6 dB/m propagation loss at 780 nm, megahertz-scale modulation bandwidth, a half-wave voltage-length product of 2.8 Vm, and negligible hysteresis. We demonstrate reconfigurable Mach-Zehnder interferometers with 0.63 dB loss per spiral phase shifter, enabling deep, actively reconfigurable visible-wavelength quantum photonic circuits.

physics.optics↗

arXiv2026

Frequency-Time Multiplexing for Near-Deterministic Generation of n-Photon Frequency-Bin States

One of the primary challenges of photonic quantum information processing is the on-demand preparation of multiple single-photon-level quantum states from probabilistic photon pair sources. Motivated by recent developments in frequency-bin-encoded photonic quantum information processing, here we consider active time multiplexing to generate n-photon states, where n single photons with n distinct frequencies occupy the same spatiotemporal mode. We devise an approach that uses optical quantum memories to manipulate the temporal mode of heralded single photons and an array of fiber Bragg grating reflectors to jointly manipulate the frequency and temporal modes of the photons, overlapping n photons in n separate frequency bins into a single spatiotemporal mode. We calculate multiphoton state generation rates that, accounting for loss, are realistically achievable with commercially available hardware. Using only a single free-space switchable delay loop for an optical quantum memory, this scheme could feasibly produce 8-photon states at an average rate of 1 kHz.

quant-ph↗

arXiv2026

Modeling integrated frequency shifters and beam splitters

Photonic quantum computing is a strong contender in the race to fault-tolerance. Recent proposals using qubits encoded in frequency modes promise a large reduction in hardware footprint, and have garnered much attention. In this encoding, linear optics, i.e., beam splitters and phase shifters, is necessarily not energy-conserving, and is costly to implement. In this work, we present designs of frequency-mode beam splitters based on modulated arrays of coupled resonators. We develop a methodology to construct their effective transfer matrices based on the SLH formalism for quantum input-output networks. Our methodology is flexible and highly composable, allowing us to define $N$-mode beam splitters either natively based on arrays of $N$-resonators of arbitrary connectivity or as networks of interconnected $l$-mode beam splitters, with $l<N$. We apply our methodology to analyze a two-resonator device, a frequency-domain phase shifter and a Mach-Zehnder interferometer obtained from composing these devices, a four-resonator device, and present a formal no-go theorem on the possibility of natively generating certain $N$-mode frequency-domain beam splitters with arrays of $N$-resonators.

quant-ph↗

arXiv2026

A paradigm for universal quantum information processing with integrated acousto-optic frequency beamsplitters

Frequency-bin encoding offers tremendous potential in quantum photonic information processing, in which a single waveguide can support hundreds of lightpaths in a naturally phase-stable fashion. This stability, however, comes at a cost: arbitrary unitary operations can be realized by cascaded electro-optic phase modulators and pulse shapers, but require nontrivial numerical optimization for design and have thus far been limited to discrete tabletop components. In this article, we propose, formalize, and computationally evaluate a new paradigm for universal frequency-bin quantum information processing using acousto-optic scattering processes between distinct transverse modes. We show that controllable phase matching in intermodal processes enables 2$\times$2 frequency beamsplitters and transverse-mode-dependent phase shifters, which together comprise cascadable FRequency-transverse-mODe Operations (FRODOs) that can synthesize any unitary via analytical decomposition procedures. Modeling the performance of both random gates and discrete Fourier transforms, we demonstrate the feasibility of high-fidelity quantum operations with existing integrated photonics technology, highlighting prospects of parallelizable operations achieving 100\% bandwidth utilization. Our approach is realizable with CMOS technology, opening the door to scalable on-chip quantum information processing in the frequency domain.

quant-ph↗

arXiv2025

Autonomous multi-ion optical clock with on-chip integrated photonic light delivery

Integrated photonics in trapped-ion systems are critical for the realization of applications such as portable optical atomic clocks and scalable quantum computers. However, system-level integration of all required functionalities remains a key challenge. In this work, we demonstrate an autonomously operating optical clock having a short-term frequency instability of $3.14(5)\times 10^{-14} / \sqrt{\tau}$ using an ensemble of four $^{171}\textrm{Yb}^{+}$ ions trapped in a multi-site surface-electrode trap at room temperature. All clock operations are performed with light delivered via on-chip waveguides. We showcase the system's resilience through sustained, autonomous operation featuring automated ion shuttling and reloading to mitigate ion loss during interleaved clock measurements. This work paves the way beyond component-level functionality to establish a viable and robust architecture for the next generation of portable, multi-ion quantum sensors and computers.

quant-ph↗

arXiv2024

CMOS-fabricated ultraviolet light modulators using low-loss alumina piezo-optomechanical photonic circuits

Ultra-violet (UV) and near-UV wavelengths are necessary for many important optical transitions for quantum technologies and various sensing mechanisms for biological and chemical detection. However, all well-known photonic platforms have excessively high losses in the UV, which has prevented photonic integrated circuits (PICs) being used to address these and other important application spaces. Photonic waveguides using low-loss alumina cores have emerged as a promising solution because of almunia's large optical bandgap and the high quality of films enabled by atomic layer deposition. However, to the best of our knowledge, active alumina PICs have only been realized using thermo-optic tuning, which precludes switching speeds shorter than one microsecond, high circuit densities, and cryogenically compatible operation. Here, we introduce a CMOS-fabricated, piezo-optomechanical PIC platform using alumina waveguides with low optical losses at UV wavelengths and aluminum nitride piezoelectric strain actuators, which solves the issues associated with thermal tuning. We demonstrate a high-performance, reconfigurable optical filter operating at wavelengths as low as 320 nm. The filter has a 6 nanosecond switching time, a loaded linewidth of 3.3 GHz, tuning rate of -120 MHz/V, and a hold power less than 20 nW.

physics.optics↗

arXiv2024

A Terahertz Bandwidth Nonmagnetic Isolator

Integrated photonics could bring transformative breakthroughs in computing, networking, imaging, sensing, and quantum information processing, enabled by increasingly sophisticated optical functionalities on a photonic chip. However, wideband optical isolators, which are essential for the robust operation of practically all optical systems, have been challenging to realize in integrated form due to the incompatibility of magnetic media with these circuit technologies. Here, we present the first-ever demonstration of an integrated non-magnetic optical isolator with terahertz-level optical bandwidth. The system is comprised of two acousto-optic frequency-shifting beam splitters which create a non-reciprocal multimode interferometer exhibiting high-contrast, nonreciprocal light transmission. We dramatically enhance the isolation bandwidth of this system by precisely dispersion balancing the paths of the interferometer. Using this approach, we demonstrate integrated nonmagnetic isolators with an optical contrast as high as 28 dB, insertion losses as low as -2.16 dB, and optical bandwidths as high as 2 THz (16 nm). We also show that the center frequency and direction of optical isolation are rapidly reconfigurable by tuning the relative phase of the microwave signals used to drive the acousto-optic beam splitters. With their CMOS compatibility, wideband operation, low losses, and rapid reconfigurability, such integrated isolators could address a key barrier to the integration of a wide range of photonic functionalities on a chip. Looking beyond the current demonstration, this bandwidth-scalable approach to nonmagnetic isolation opens the door to ultrawideband (>10 THz) isolators, which are needed to shrink state-of-the-art imaging, sensing, and communications systems into photonic integrated circuits.

physics.optics↗

arXiv2024

Non-resonant Bragg scattering four-wave-mixing at near visible wavelengths in low-confinement silicon nitride waveguides

Quantum state coherent frequency conversion processes-such as Bragg scattering four wave mixing (BSFWM)-hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near unity quantum coherent frequency conversion in visible and near-visible wavelength ranges. Using sensitive heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (~1.55 W^{-1} m^{-1}) and linear propagation loss (~0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = gamma/alpha is approximately equal to 3.85 W^{-1}) for BSFWM of near visible light in non-resonant silicon nitride waveguides. We demonstrate how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.

physics.optics↗

arXiv2023

Optical Nanofiber Testbeds for Benchmarking Membrane-Waveguide Photonic Integrated Circuit Platforms toward On-Chip Quantum Inertial Sensing

Recent advances in cold atom interferometry with optical and magnetic atom guides have set the stage for quantum inertial sensors capable of operating in dynamic environments. In this work, we present three key innovations, such as evanescent-field (EF) atom guides, optical nanofiber testbeds, and membrane-waveguide photonic integrated circuit (PIC) platforms, to advance EF-guided atom interferometry. First, we demonstrate EF atom guides on optical nanofiber testbeds, which serve as performance benchmarks for our membrane-waveguide PIC platforms. Second, we achieve low-power (~5 mW) guiding of freely moving, laser-cooled 133Cs atoms in two-color, traveling-wave EF optical dipole traps at the novel, heat-efficient magic wavelengths of 793 nm and 937 nm (i.e. "793/937-nm EF atom guides"). We designed and fabricated membrane-waveguide PIC platforms for these EF atom guides; in our prior work we showed that they safely handle up to 4-6x times the minimum trap power under vacuum and enable dense cold atom generation for efficient loading. Third, we verify preserved atomic coherence via microwave fields and EF-coupled Doppler-free Raman beams; to our knowledge, this is the first report of coherence fringes driven by co-propagating EF-coupled Raman beams with only 150 nW of total optical power. By providing a direct comparison between optical nanofiber testbeds and membrane-waveguide PIC platforms, our results lay critical groundwork for the on-chip realization of EF-guided atom interferometry and the development of for fully integrated, low-SWaP (size, weight, and power) quantum accelerometers and gyroscopes.

physics.atom-ph↗

arXiv2023

Multi-site Integrated Optical Addressing of Trapped Ions

One of the most effective ways to advance the performance of quantum computers and quantum sensors is to increase the number of qubits or quantum resources in the system. A major technical challenge that must be solved to realize this goal for trapped-ion systems is scaling the delivery of optical signals to many individual ions. In this paper we demonstrate an approach employing waveguides and multi-mode interferometer splitters to optically address multiple $^{171}\textrm{Yb}^+$ ions in a surface trap by delivering all wavelengths required for full qubit control. Measurements of hyperfine spectra and Rabi flopping were performed on the E2 clock transition, using integrated waveguides for delivering the light needed for Doppler cooling, state preparation, coherent operations, and detection. We describe the use of splitters to address multiple ions using a single optical input per wavelength and use them to demonstrate simultaneous Rabi flopping on two different transitions occurring at distinct trap sites. This work represents an important step towards the realization of scalable integrated photonics for atomic clocks and trapped-ion quantum information systems.

quant-ph↗

arXiv2023

Electrically interfaced Brillouin-active waveguide for multi-domain transduction

New strategies to convert signals between optical and microwave domains could play a pivotal role in advancing both classical and quantum technologies. Through recent studies, electro-optomechanical systems have been used to implement microwave-to-optical conversion using resonant optical systems, resulting in transduction over limited optical bandwidth. Here, we present an optomechanical waveguide system with an integrated piezoelectric transducer that produces electro-optomechanical transduction over a wide optical bandwidth through coupling to a continuum of optical modes. Efficient electromechanical and optomechanical coupling within this system enables bidirectional optical-to-microwave conversion with a quantum efficiency of up to $-$54.16 dB. When electrically driven, this system produces a low voltage acousto-optic phase modulation over a wide ($>$100 nm) wavelength range. Through optical-to-microwave conversion, we show that the amplitude-preserving nature inherent to forward Brillouin scattering is intriguing and has the potential to enable new schemes for microwave photonic signal processing. We use these properties to demonstrate a multi-channel microwave photonic filter by transmitting an optical signal through a series of electro-optomechanical waveguide segments having distinct resonance frequencies. Building on these demonstrations, such electro-optomechanical systems could bring flexible strategies for modulation, channelization, and spectrum analysis in microwave photonics.

physics.optics↗

arXiv2022

Intermodal strong coupling and wideband, low-loss isolation in silicon

Strong coupling enables a diverse set of applications that include optical memories, non-magnetic isolators, photonic state manipulation, and signal processing. To date, strong coupling in integrated platforms has been realized using narrow-linewidth high-Q optical resonators. In contrast, here we demonstrate wideband strong coupling between two photonic bands. The indirect interband photonic transition is controlled by electrically driving phonons in a linear silicon waveguide. Under large acoustic drive, the system features a Rabi-like energy exchange between two waveguide modes, demonstrating strong coupling. When tuned to unity energy conversion, our system unlocks a set of powerful applications, including optical modulators, routers and filters. In particular, we demonstrate a low loss (-2.08 dB) acousto-optic modulator (AOM) with pump suppression ratio > 55 dB. We also reconfigure our system to demonstrate a non-magnetic, low-loss (< 1 dB) and broadband (59 GHz 10 dB isolation bandwidth) optical isolator.

physics.optics↗

arXiv2022

High-Performance Silicon Photonic Single-Sideband Modulators for Cold Atom Interferometry

The most complicated and challenging system within a light-pulse atom interferometer (LPAI) is the laser system, which controls the frequencies and intensities of multiple laser beams over time to configure quantum gravity and inertial sensors. The main function of an LPAI laser system is to perform cold-atom generation, state-preparation, state-selective detection and to generate coherent two-photon process for the light-pulse sequence. Substantial miniaturization and ruggedization of the laser system can be achieved by bringing most key functions of the laser system onto photonic integrated circuit (PIC). We demonstrate a high-performance silicon photonic suppressed-carrier single-sideband (SC-SSB) modulator at 1560 nm, which can dynamically frequency shift within the LPAI. With independent RF-channel control, we study the imbalances in both the optical and RF phases/amplitudes to reach 30 dB carrier-suppression, unprecedented 47.8 dB sideband-suppression at peak conversion-efficiency: -6.846 dB (20.7 %). Using a silicon photonic SSB-modulator, we demonstrate cold-atom generation, state-selective detection, and atom interferometer fringes to estimate gravitational acceleration, $g \approx 9.77 \pm 0.01 \,\rm{m/s^2}$, in a Rubidium ($^{87}$Rb) atom system.

physics.optics↗

arXiv2021

A Compact Cold-Atom Interferometer with a High Data-Rate Grating Magneto-Optical Trap and a Photonic-Integrated-Circuit-Compatible Laser System

The extreme miniaturization of a cold-atom interferometer accelerometer requires the development of novel technologies and architectures for the interferometer subsystems. Here we describe several component technologies and a laser system architecture to enable a path to such miniaturization. We developed a custom, compact titanium vacuum package containing a microfabricated grating chip for a tetrahedral grating magneto-optical trap (GMOT) using a single cooling beam. In addition, we designed a multi-channel photonic-integrated-circuit-compatible laser system implemented with a single seed laser and single sideband modulators in a time-multiplexed manner, reducing the number of optical channels connected to the sensor head. In a compact sensor head containing the vacuum package, sub-Doppler cooling in the GMOT produces 15 uK temperatures, and the GMOT can operate at a 20 Hz data rate. We validated the atomic coherence with Ramsey interferometry using microwave spectroscopy, then demonstrated a light-pulse atom interferometer in a gravimeter configuration for a 10 Hz measurement data rate and T = 0 - 4.5 ms interrogation time, resulting in $\Delta$ g / g = 2.0e-6. This work represents a significant step towards deployable cold-atom inertial sensors under large amplitude motional dynamics.

physics.atom-ph↗

arXiv2021

Roadmap on Integrated Quantum Photonics

Integrated photonics is at the heart of many classical technologies, from optical communications to biosensors, LIDAR, and data center fiber interconnects. There is strong evidence that these integrated technologies will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying laser and optical quantum technologies, with the required functionality and performance, 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 and a dramatic reduction in optical losses have enabled benchtop experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. The reduction in size, weight, power, and improvement in stability that will be enabled by QPICs will play a key role in increasing the degree of complexity and scale in quantum demonstrations. In the next decade, with sustained research, development, and investment in the quantum photonic ecosystem (i.e. PIC-based platforms, devices and circuits, fabrication and integration processes, packaging, and testing and benchmarking), we will witness the transition from single- and few-function prototypes to the large-scale integration of multi-functional and reconfigurable QPICs that will define how information is processed, stored, transmitted, and utilized for quantum computing, communications, metrology, and sensing. This roadmap highlights the current progress in the field of integrated quantum photonics, future challenges, and advances in science and technology needed to meet these challenges.

quant-ph↗

arXiv2021

Characterization of Suspended Membrane Waveguides towards a Photonic Atom Trap Integrated Platform

We demonstrate an optical waveguide device, capable of supporting the high, in-vacuum, optical power necessary for trapping a single atom or a cold atom ensemble with evanescent fields. Our photonic integrated platforms, with suspended membrane waveguides, successfully manages optical powers of 6 mW (500 um span) to nearly 30 mW (125 um span) over an un-tethered waveguide span. This platform is compatible with laser cooling and magneto-optical traps (MOTs) in the vicinity of the suspended waveguide, called the membrane MOT and the needle MOT, a key ingredient for efficient trap loading. We evaluate two novel designs that explore critical thermal management features that enable this large power handling. This work represents a significant step toward an integrated platform for coupling neutral atom quantum systems to photonic and electronic integrated circuits on silicon.

quant-ph↗

arXiv2020

Back-scatter immune injection-locked Brillouin laser in silicon

As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser's frequency and phase can be controlled by an injected signal. Due to its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection locking dynamics remain relatively untapped--despite significant potential for technological and scientific impact. Here, we demonstrate injection locking in a silicon photonic Brillouin laser for the first time. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the Brillouin gain bandwidth. Harnessing these dynamics, we demonstrate amplification of small signals by more than 23 dB. Moreover, we demonstrate that the injection locking dynamics of this system are inherently nonreciprocal, yielding unidirectional control and back-scatter immunity in an all-silicon system. This device physics opens the door to new strategies for phase noise reduction, low-noise amplification, and back-scatter immunity in silicon photonics.

physics.optics↗