arXiv subjects

Young-Ik Sohn

Publications and source records attributed to Young-Ik Sohn.

17 recordsLinked to original sources

arXiv2026

Generalized model of anisotropic thermo-optic response on thin-film lithium niobate platform

Thermo-optic (TO) control is crucial for thin-film lithium niobate (TFLN) photonic integrated circuits (PICs), offering a simple and practical method for low-frequency and DC tuning while remaining compatible with high-frequency electro-optic (EO) modulation. In x-cut TFLN, the TO response is inherently anisotropic, depending on both waveguide propagation angle and polarization due to the mode-specific overlap of the electric field with the ordinary and extraordinary refractive index axes of the crystal. Despite its significance, a systematic and quantitative analysis of this anisotropy has remained elusive. Here, we present the first generalized analytical model that describes the anisotropic TO response as a function of polarization and arbitrary waveguide orientation, and rigorously validate it through numerical simulations and experiments. This study provides foundational insight into anisotropic thermal tuning and enables new opportunities for engineering energy-efficient and scalable photonic design in next-generation TFLN PICs.

physics.optics↗

arXiv2025

Rapid adiabatic couplers with arbitrary split ratios for broadband DWDM interleaver application

We experimentally demonstrate a compact and broadband rapid adiabatic couplers (RACs) with arbitrary power split ratios, achieved through the combination of translational offset and waveguide width control. Fabricated RACs of four different target split ratios show power splitting within $\pm$3% of the design target over a 160 nm wavelength range. Using these RACs, we implement an 8-channel dense wavelength division multiplexing (DWDM) interleaver exhibiting < -20 dB crosstalk for the center 8 channels with flat-top passbands. Over a broader wavelength range, the design maintains crosstalk below -10 dB across more than 40 channels with 100 GHz spacing, demonstrating the broadband capability and scalability of RAC-based photonic integrated circuits.

physics.optics↗

arXiv2025

Ultra-fast and accurate multimode waveguide design based on dataset-based eigenmode expansion method

We propose a dataset-based photonic simulation framework for multimode waveguide design, enabling ultra-fast simulations with high accuracy. Compared to conventional approaches, our method offers two to three orders of magnitude speed-up in complex multimode waveguide designs. Based on this approach, we demonstrate a silicon multimode waveguide bend with an effective radius of $30\,μ\mathrm{m}$ under one second, with accuracy validated against commercial 3D finite-difference time-domain method. We further explore its utility for device optimization by designing a $20\,μ\mathrm{m}$-radius, arbitrary power splitting ratio bends through thousands of optimization iterations, completed in just 68 minutes on a standard desktop CPU. This framework enables the rapid design and engineering of large-scale multimode photonic devices, making computationally intensive simulations more accessible to many photonic circuit designers.

physics.optics↗

arXiv2025

Simulating Quantum Light in Lossy Microring Resonators Driven by Strong Pulses

In this work, we present a quantum theory for pulsed photon pair generation in a single ring resonator. Our approach combines the Heisenberg picture input-output formalism with the Ikeda mapping from classical nonlinear optics. In doing so, we address the high-gain regime by incorporating non-perturbative effects, including self-phase modulation, cross-phase modulation, and time-ordering, which are roots for significantly different behaviors in the low-gain regime. We also account for optical losses by introducing an auxiliary waveguide, allowing for a more accurate representation of experimentally viable scenarios. Numerical simulations reveal that non-perturbative effects significantly distort transfer functions, making desirable operations challenging without careful optimization. We show that appropriate detuning of the pump frequency can mitigate these issues, leading to enhanced brightness and higher spectral purity in the high-gain regime. We further investigate the performance of a single ring resonator as a two-mode squeezer by analyzing various performance metrics under experimentally relevant optical loss conditions.

quant-ph↗

arXiv2024

Simulation of integrated nonlinear quantum optics: from nonlinear interferometer to temporal walk-off compensator

Nonlinear quantum photonics serves as a cornerstone in photonic quantum technologies, such as universal quantum computing and quantum communications. The emergence of integrated photonics platform not only offers the advantage of large-scale manufacturing but also provides a variety of engineering methods. Given the complexity of integrated photonics engineering, a comprehensive simulation framework is essential to fully harness the potential of the platform. In this context, we introduce a nonlinear quantum photonics simulation framework which can accurately model a variety of features such as adiabatic waveguide, material anisotropy, linear optics components, photon losses, and detectors. Furthermore, utilizing the framework, we have developed a device scheme, chip-scale temporal walk-off compensation, that is useful for various quantum information processing tasks. Applying the simulation framework, we show that the proposed device scheme can enhance the squeezing parameter of photon-pair sources and the conversion efficiency of quantum frequency converters without relying on higher pump power.

quant-ph↗

arXiv2024

A manufacturable platform for photonic quantum computing

Whilst holding great promise for low noise, ease of operation and networking, useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions. Here we introduce a manufacturable platform for quantum computing with photons. We benchmark a set of monolithically-integrated silicon photonics-based modules to generate, manipulate, network, and detect photonic qubits, demonstrating dual-rail photonic qubits with $99.98\% \pm 0.01\%$ state preparation and measurement fidelity, Hong-Ou-Mandel quantum interference between independent photon sources with $99.50\%\pm0.25\%$ visibility, two-qubit fusion with $99.22\%\pm0.12\%$ fidelity, and a chip-to-chip qubit interconnect with $99.72\%\pm0.04\%$ fidelity, not accounting for loss. In addition, we preview a selection of next generation technologies, demonstrating low-loss silicon nitride waveguides and components, fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors, low-loss chip-to-fiber coupling, and barium titanate electro-optic phase shifters.

quant-ph↗

arXiv2024

Do different kinds of photon-pair sources have the same indistinguishability in quantum silicon photonics?

In the same silicon photonic integrated circuit, we compare two types of integrated degenerate photon-pair sources (microring resonators or waveguides) by means of Hong-Ou-Mandel (HOM) interference experiments. Two nominally identical microring resonators are coupled to two nominally identical waveguides which form the arms of a Mach-Zehnder interferometer. This is pumped by two lasers at two different wavelengths to generate, by spontaneous four-wave mixing, degenerate photon pairs. In particular, the microring resonators can be thermally tuned in or out of resonance with the pump wavelengths, thus choosing either the microring resonators or the waveguides as photon-pair sources, respectively. In this way, an on-chip HOM visibility of 94% with microring resonators and 99% with straight waveguides is measured upon filtering. We compare our experimental results with theoretical simulations of the joint spectral intensity and the purity of the degenerate photon pairs. We verify that the visibility is connected to the sources' indistinguishability, which can be quantified by the overlap between the joint spectral amplitudes (JSA) of the photon pairs generated by the two sources. We estimate a JSAs overlap of 98% with waveguides and 89% with microring resonators.

quant-ph↗

arXiv2019

Coherent Acoustic Control of a Single Silicon Vacancy Spin in Diamond

Phonons are considered to be universal quantum transducers due to their ability to couple to a wide variety of quantum systems. Among these systems, solid-state point defect spins are known for being long-lived optically accessible quantum memories. Recently, it has been shown that inversion-symmetric defects in diamond, such as the negatively charged silicon vacancy center (SiV), feature spin qubits that are highly susceptible to strain. Here, we leverage this strain response to achieve coherent and low-power acoustic control of a single SiV spin, and perform acoustically driven Ramsey interferometry of a single spin. Our results demonstrate a novel and efficient method of spin control for these systems, offering a path towards strong spin-phonon coupling and phonon-mediated hybrid quantum systems.

quant-ph↗

arXiv2019

Phononic band structure engineering for high-Q gigahertz surface acoustic wave resonators on lithium niobate

Phonons at gigahertz frequencies interact with electrons, photons, and atomic systems in solids, and therefore have extensive applications in signal processing, sensing, and quantum technologies. Surface acoustic wave (SAW) resonators that confine surface phonons can play a crucial role in such integrated phononic systems due to small mode size, low dissipation, and efficient electrical transduction. To date, it has been challenging to achieve high quality (Q) factor and small phonon mode size for SAW resonators at gigahertz frequencies. Here, we present a methodology to design compact high-Q SAW resonators on lithium niobate operating at gigahertz frequencies. We experimentally verify out designs and demonstrate Q factors in excess of $2\times10^4$ at room temperature ($6\times10^4$ at 4 Kelvin) and mode area as low as $1.87 λ^2$. This is achieved by phononic band structure engineering, which provides high confinement with low mechanical loss. The frequency-Q products (fQ) of our SAW resonators are greater than $10^{13}$. These high-fQ and small mode size SAW resonators could enable applications in quantum phononics and integrated hybrid systems with phonons, photons, and solid-state qubits.

cond-mat.mes-hall↗

arXiv2019

Quantum interference of electromechanically stabilized emitters in nanophotonic devices

Photon-mediated coupling between distant matter qubits may enable secure communication over long distances, the implementation of distributed quantum computing schemes, and the exploration of new regimes of many-body quantum dynamics. Nanophotonic devices coupled to solid-state quantum emitters represent a promising approach towards realization of these goals, as they combine strong light-matter interaction and high photon collection efficiencies. However, the scalability of these approaches is limited by the frequency mismatch between solid-state emitters and the instability of their optical transitions. Here we present a nano-electromechanical platform for stabilization and tuning of optical transitions of silicon-vacancy (SiV) color centers in diamond nanophotonic devices by dynamically controlling their strain environments. This strain-based tuning scheme has sufficient range and bandwidth to alleviate the spectral mismatch between individual SiV centers. Using strain, we ensure overlap between color center optical transitions and observe an entangled superradiant state by measuring correlations of photons collected from the diamond waveguide. This platform for tuning spectrally stable color centers in nanophotonic waveguides and resonators constitutes an important step towards a scalable quantum network.

physics.app-ph↗

arXiv2018

Spectral alignment of single-photon emitters in diamond using strain gradient

Solid-state single-photon emitters are attractive for realization of integrated quantum systems due to their experimental convenience and scalability. Unfortunately, however, their complex mesoscopic environments cause photons from different emitters to be spectrally distinguishable. Here we demonstrate spectral alignment of two solid-state single-photon emitters by utilizing the strain gradient. Multiple germanium vacancy (GeV) color centers in diamond are created in fabricated diamond microcantilevers using focused ion beam implantation. The strain response of the electronic energy levels of the GeV is measured by inducing an electrically controlled strain in the device. Leveraging the large strain gradient, we tune two GeVs in the spot to emit at the same optical wavelength. Simultaneous resonant excitation of two spectrally aligned GeVs is demonstrated using a narrow linewidth laser. This strain gradient tuning can be used to realize spectrally identical quantum emitters for on-chip integrated quantum systems.

cond-mat.mes-hall↗

arXiv2018

Controlling the coherence of a diamond spin qubit through strain engineering

The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. In the context of solid-state qubits, techniques to mitigate the impact of fluctuating electric and magnetic fields from the environment are well-developed. In contrast, suppression of decoherence from thermal lattice vibrations is typically achieved only by lowering the temperature of operation. Here, we use a nano-electro-mechanical system (NEMS) to mitigate the effect of thermal phonons on a solid-state quantum emitter without changing the system temperature. We study the silicon-vacancy (SiV) colour centre in diamond which has optical and spin transitions that are highly sensitive to phonons. First, we show that its electronic orbitals are highly susceptible to local strain, leading to its high sensitivity to phonons. By controlling the strain environment, we manipulate the electronic levels of the emitter to probe, control, and eventually, suppress its interaction with the thermal phonon bath. Strain control allows for both an impressive range of optical tunability and significantly improved spin coherence. Finally, our findings indicate that it may be possible to achieve strong coupling between the SiV spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics.

quant-ph↗

arXiv2018

Strain engineering of the silicon-vacancy center in diamond

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multi-qubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain suseptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.

quant-ph↗

arXiv2017

Mechanical and optical nanodevices in single-crystal quartz

Single-crystal α-quartz, one of the most widely used piezoelectric materials, has enabled a wide range of timing applications. Owing to the fact that integrated thin-film based quartz platform is not available, most of these applications rely on macroscopic, bulk crystal-based devices. Here we show that the Faraday cage angled-etching technique can be used to realize nanoscale electromechanical and photonic devices in quartz. Using this approach, we demonstrate quartz nanomechanical cantilevers and ring resonators featuring Qs of 4,900 and 8,900, respectively.

cond-mat.mes-hall↗

arXiv2016

Faraday cage angled-etching of nanostructures in bulk dielectrics

For many emerging optoelectronic materials, heteroepitaxial growth techniques do not offer the same high material quality afforded by bulk, single-crystal growth. However, the need for optical, electrical, or mechanical isolation at the nanoscale level often necessitates the use of a dissimilar substrate, upon which the active device layer stands. Faraday cage angled-etching (FCAE) obviates the need for these planar, thin-film technologies by enabling in-situ device release and isolation through an angled-etching process. By placing a Faraday cage around the sample during inductively-coupled plasma reactive ion etching (ICP-RIE), the etching plasma develops an equipotential at the cage surface, directing ions normal to its face. In this Article, the effects Faraday cage angle, mesh size, and sample placement have on etch angle, uniformity, and mask selectivity are investigated within a silicon etching platform. Simulation results qualitatively confirm experiments and help to clarify the physical mechanisms at work. These results will help guide FCAE process design across a wide range of material platforms.

cond-mat.mes-hall↗

arXiv2015

Dynamic Actuation of Single-Crystal Diamond Nanobeams

We show the dielectrophoretic actuation of single-crystal diamond nanomechanical devices. Gradient radio-frequency electromagnetic forces are used to achieve actuation of both cantilever and doubly clamped beam structures, with operation frequencies ranging from a few MHz to ~50MHz. Frequency tuning and parametric actuation are also studied.

cond-mat.mes-hall↗

arXiv2015

Enhanced strain coupling of nitrogen vacancy spins to nanoscale diamond cantilevers

Nitrogen vacancy (NV) centers can couple to confined phonons in diamond mechanical resonators via the effect of lattice strain on their energy levels. Access to the strong spin-phonon coupling regime with this system requires resonators with nanoscale dimensions in order to overcome the weak strain response of the NV ground state spin sublevels. In this work, we study NVs in diamond cantilevers with lateral dimensions of a few hundred nm. Coupling of the NV ground state spin to the mechanical mode is detected in electron spin resonance (ESR), and its temporal dynamics are measured via spin echo. Our small mechanical mode volume leads to a 10-100X enhancement in spin-phonon coupling strength over previous NV-strain coupling demonstrations. This is an important step towards strong spin-phonon coupling, which can enable phonon-mediated quantum information processing and quantum metrology.

quant-ph↗