The electro-optic effect, in which an applied electric field changes a material’s refractive index, provides a direct bridge between electronic and optical signals. Spurred by recent advances in nanofabrication, integrated electro-optics has had great success revolutionizing commercial markets for telecommunications and is expected to play a critical role in emerging applications such as quantum networks and photonic quantum computing. In this dissertation, I present two perspectives on leveraging the strong electro-optic coupling in a characteristic material platform, thin-film lithium niobate (TFLN). In Chapter 1, I provide a philosophical overview of the structure-property-performance relationships that govern materials science, and what it means for engineering to be "materials-motivated". In Chapter 2, I summarize the background theory of electro-optics required for the studies in this dissertation. In Chapters 3 and 4, I will describe the development of cavity-based electro-optic devices inspired by atomic and solid-state physics and their application to efficient spectral manipulation of light for quantum optics experiments such as two-photon interference. In Chapters 5 and 6, I will discuss materials challenges facing the stable dc biasing of such electro-optic devices, and progress toward sensing characteristic sources of drift and instability at material interfaces. By simply changing perspectives to a defect-oriented interpretation more characteristic of well-established semiconductor engineering, we can gain fundamental insights and new approaches into the microscopic origins and possible mitigation techniques for these nonidealities.
The electro-optic effect, in which an applied electric field changes a material’s refractive index, provides a direct bridge between electronic and optical signals. Spurred by recent advances in nanofabrication, integrated electro-optics has had great success revolutionizing commercial markets for telecommunications and is expected to play a critical role in emerging applications such as quantum networks and photonic quantum computing. In this dissertation, I present two perspectives on leveraging the strong electro-optic coupling in a characteristic material platform, thin-film lithium niobate (TFLN). In Chapter 1, I provide a philosophical overview of the structure-property-performance relationships that govern materials science, and what it means for engineering to be "materials-motivated". In Chapter 2, I summarize the background theory of electro-optics required for the studies in this dissertation. In Chapters 3 and 4, I will describe the development of cavity-based electro-optic devices inspired by atomic and solid-state physics and their application to efficient spectral manipulation of light for quantum optics experiments such as two-photon interference. In Chapters 5 and 6, I will discuss materials challenges facing the stable dc biasing of such electro-optic devices, and progress toward sensing characteristic sources of drift and instability at material interfaces. By simply changing perspectives to a defect-oriented interpretation more characteristic of well-established semiconductor engineering, we can gain fundamental insights and new approaches into the microscopic origins and possible mitigation techniques for these nonidealities.
Quantum networks of superconducting qubits linked by optical channels could leverage both the quantum information processing capabilities of superconducting circuits and the long communication distances provided by optical photons. Such networks would require high efficiency, low noise, and wide bandwidth transducers between microwave and optical frequencies. Transducers based on the Pockels electro-optic (EO) effect are particularly promising in this application for their direct conversion mechanism and potential for strong performance. EO transducers could also be used for sensitive optical modulators and low-noise detection of microwave and millimeter-wave signals. This dissertation presents recent work to create cavity EO transducers in thin-film lithium niobate, an integrated photonics platform that provides low optical loss and strong EO coupling. I first describe the theory of cavity electro-optics and how it can be used to generate high-efficiency transduction between microwave and optical fields. An initial device is presented and characterized, demonstrating per-photon on-chip transduction efficiencies of up to (2.7 ± 0.3) × 10^−5. A key benefit of the device described here, which is based on photonic molecule modes, is the ability to use a static electro-optic bias to trim the transducer into resonance. However, we find the migration of free carriers in thin-film lithium niobate reduces the EO response of the device to static fields, making such trimming ineffective. This carrier migration is a key challenge for enabling the promise of low-power electro-optics provided by thin-film lithium niobate devices. I characterize the low-frequency electro-optic response, which suggests that conduction occurs on the etched surface of lithium niobate. I show how this conduction can be reduced – and low-frequency EO performance improved – by changing the electrode design and annealing the devices. Following this, I describe the design and initial characterization of an improved transducer device. Finally, I describe a scheme by which even relatively low-efficiency transducers could be used to generate remote entanglement using an optically heralding scheme. Demonstration of such a system appears possible with current devices, suggesting that small opticallymediated quantum networks of superconducting qubits may be feasible soon.
Photonics has proven to be a very attractive platform for quantum technologies, offering key features such as high-fidelity qubits and room-temperature signal processing. Advancements in integrated photonics are expected to further enhance these capabilities as the technology evolves from few-photon architectures to systems capable of generating and processing tens, possibly hundreds, of photons, marking critical progress toward scalable quantum information processing. Although each integrated platform has its own unique advantages and limitations, thin-film lithium niobate (TFLN) photonics has recently emerged as a strong contender thanks to its low-loss characteristics, large electro-optic and nonlinear coefficients, broad transparency window, and ultra-fast modulation capabilities. In this review, we examine the latest developments in TFLN quantum photonics and identify promising directions and challenges for future research in this field.
Integrated quantum photonics requires material platforms that can combine photon generation, spectral control, and electro-optic reconfiguration with low loss and operational stability. Thin-film lithium niobate (TFLN) is a promising platform for this purpose because its second-order nonlinearity and Pockels effect support nonlinear optical processes and active phase control within compact photonic circuits. This dissertation develops TFLN integrated photonic devices and, through collaborative experiments, demonstrates methods toward a frequency-bin quantum information processing platform in which quantum states are represented by discrete optical frequency modes. The work focuses on the design and validation of chip-scale building blocks for frequency-bin operation, including spectral selection, electro-optic tuning, and programmable phase control. Device design, process development, packaging, and experimental characterization led to functional TFLN hardware with resonator-based frequency selectivity, electrically controlled channel tuning, and stable optical and electrical access. Measurements demonstrate stable and programmable frequency-bin control: drift-compensated bias control mitigates electro-optic relaxation and stabilizes multiple frequency channels, while dual-comb spectroscopy verifies repeatable spectral phase programming and waveform reconstruction. These results establish a foundation for future integration of a complete frequency-bin quantum photonic system on TFLN. To support artificial-intelligence-assisted design of photonic and electromagnetic systems, this dissertation further develops a data-driven framework for electromagnetic wave modeling. The EM-OmniVerse dataset and foundation-model framework organize simulated field dynamics together with material, source, geometry, and language information. Across seven out-of-distribution transfer domains, the jointly trained foundation model gives the lowest prediction error in five cases and the second-lowest in two. A representative autoregressive test also shows improved long-horizon stability relative to a single-domain baseline. These results connect experimental photonic-platform development with scalable computational tools for electromagnetic design.
Integrated thin-film lithium niobate (TFLN) photonics has emerged as a powerful platform for quantum information science, offering its outstanding nonlinear, electro-optic (EO), and integration capabilities. In this review, we present the latest advances in TFLN-based integrated photonics tailored to quantum technologies. We first explore state-of-the-art quantum light sources realized in both straight waveguide and resonator configuration, including high-brightness photon pair generations, squeezed light, and versatile entanglement schemes. Next, we detail progress in integrated photonic processors, with a focus on programmable interferometric networks, ultrafast EO modulators, and essential passive components for photonic qubit processing. We then address critical challenges in optical interfacing and detection technologies, discussing recent innovations in low-loss fiber-to-chip and grating coupler designs, as well as the integration of on-chip single photon detectors. This review provides a forward-looking perspective on scalable quantum photonic systems that could underpin future advances in quantum communication, computing, and sensing.
Radio frequency (RF) radiation is a powerful tool in computing, communication, and sensing due to the ability to engineer strong electrical interactions. Within cryogenic systems, in particular, microwave (MW) frequency superconducting qubits have demonstrated promise as a platform for quantum computing, and MW and millimeter-wave (mmW) systems have been valuable tools in sensing. However, owing to their low energy, the weak, single-photon level signals employed by these systems suffer high sensitivity to thermal noise when they exit the thermal bath, as well as short attenuation lengths due to absorption and scattering in cables. Telecommunication frequency optical photons, meanwhile, have long propagation lengths and can be supported by low-loss optical fibers. The high photon energy makes signals insensitive to thermal noise, and the high frequency can allow many RF signals to be multiplexed onto a single optical carrier. Interfacing RF and optical radiation to leverage both strong interactions with macroscopic systems characteristic of electrical interactions and low-loss propagation characteristic of optical photons has been critical to realizing our global communication system. Leveraging the infrastructure developed to support this industry, such as single photon detectors, is attractive for scaling cryogenic RF systems. Coherent conversion processes, especially, can benefit a wide range of applications, especially in computing and sensing, by preserving quantum states, and retaining phase information necessary for quantum gates, and enable the use of measurement techniques that can increase detection sensitivity. This dissertation focuses on using the electro-optic effect in thin-film lithium niobate to form an efficient, coherent interface between radio- and telecommunication-frequency photons. Lithium niobate is an attractive platform due to its high electro-optic coefficient (approx. 30 pm/V), wide transparency window (DC to 400 THz), and ability to support low-loss optical waveguides (.2 dB/m), all of which deviate little from room temperature down to near-zero Kelvin environments. First, I explore the development of low-loss lithium niobate optical cavities and operation of lithium niobate waveguides at low temperatures. While lithium niobate is an electro-optic material with a DC response, using the electro-optic response at room temperature for stable biasing and low-frequency operation has remained a challenge. A temperature- and frequency-dependent study is conducted to identify lithium charge migration as a potential screening mechanism suppressed at low temperatures. Next, I explore the use of RF-cavity enhanced, triply resonant photonic molecules (created from two coupled low-loss optical cavities) for forming efficient electro-optic interfaces with microwave (3-10 GHz) and millimeter wave (100 GHz) radiation. In the microwave regime, I explore microwave-optical transduction for forming optical interfaces with microwave qubits, specifically focusing on superconducting qubits. The characterization of one such transducer is demonstrated, and the device is used to optically synthesize microwave signals at low temperatures, bypassing the need for input microwave control lines. Outlook for other interfaces, including optical photon mediated quantum information transfer, is discussed. At mmW frequencies, the triply resonant photonic molecule is explored for low-power ( mW) optical-frequency shifting.
Efficient and stable microwave-optical transduction is a key enabling technology for distributed superconducting quantum computing and heterogeneous quantum networks. Electro-optic transducers based on thin-film lithium niobate (TFLN) have shown strong promise, but demonstrations to date have been limited by various factors such as low frequency bias drift, low efficiency, fabrication complexity, and scalability. Here we demonstrate the first integrated electro-optic microwave-optical transducers realized in thin-film lithium tantalate (TFLT), a material platform offering Pockels nonlinearity comparable to TFLN together with improved bias stability and high-power handling. We fabricate superconducting microwave resonators coupled to tunable photonic-molecule optical resonators using wafer-scale deep ultraviolet lithography, offering high-throughput production of hundreds of devices per wafer. Across six devices we observe coherent bidirectional conversion between C-band optical photons and 4.9-5.5 GHz microwave photons, with measured on-chip efficiencies and inferred single-photon coupling rates g_0/2π ~ 1 kHz consistent with theory. Continuous operation over multiple days is achieved using a static bias field with minimal feedback, demonstrating a major operational advantage. We further characterize optical loss statistics, microwave resonator performance, and optically induced added noise under pulsed pumping, finding less than one added photon for 100 microsecond pulses at the highest measured efficiencies. These results establish TFLT as a scalable and robust electro-optic platform for future quantum interconnects and modular quantum processors.