Nonlinear Electro-Optic Visible Photonic Circuits for Solid-State Quantum Defects

Abstract

Integrated visible photonic engines for solid-state quantum defects provide a foundation for scalable quantum networks. While miniaturization is advancing, active manipulation remains limited by the difficulty of achieving simultaneous milliwatt-scale visible light generation and high-contrast modulation. Despite extensive efforts, the concurrent chip-scale realization of nonlinear frequency conversion and fast temporal gating for high-fidelity quantum control has remained elusive. Here, we demonstrate a monolithic thin-film lithium niobate (TFLN) platform integrating periodically poled frequency conversion with GHz-bandwidth electro-optic (EO) switching. The device delivers off-chip green-light power exceeding 1 mW with an extinction ratio (ER) of 42.2 dB, enabling coherent spin control and time-resolved lifetime measurements of individual nitrogen-vacancy (NV) centers in diamond through nanosecond gating. System performance is validated through pulsed optically detected magnetic resonance (ODMR), Rabi oscillations, and Ramsey interference, supported by time-tagged photon counting with nanosecond resolution. By unifying sufficient nonlinear light generation with high-speed active manipulation, this platform establishes a scalable framework for the realization of high-rate quantum communication nodes.

Figures (5)

• Figure 1: Integrated thin-film lithium niobate nonlinear photonic circuits for high-speed green-light switching and optical addressing of an NV center in diamond.a Conceptual schematic of the integrated device and the quantum measurement. Continuous wave (CW) near-infrared pump light is modulated by an EO modulator and frequency-doubled to 532 nm in a PPLN waveguide, enabling milliwatt-level green light generation with fast on/off control and high extinction. The green light from the chip optically addresses an NV center in diamond for spin initialization and readout under microwave (MW) control. b Photographs of the fabricated device generating the green light guided on the chip in the ON (top) and OFF (bottom) states. c Top-view schematic layout of the device (top) and corresponding optical microscope images of the fabricated chip (bottom), showing the EO MZI switch and the PPLN waveguide sections.
• Figure 2: Efficient green light generation in a PPLN waveguide.a Conceptual schematic of the PPLN section, where the near-infrared fundamental pump light is converted to the green light via domain-inverted QPM. $\Lambda$ denotes the poling period. b Calculated phase mismatch ($\Delta k$) map versus waveguide top width and etch depth. The marked point indicates the designed geometry used for the device. c Scanning electron microscopy (SEM) image of the fabricated PPLN waveguide (scale bar: 3 $\mu$m). Inset shows the SHG microscopy image of the domain pattern before waveguide fabrication (scale bar: 5 $\mu$m). d Schematic of the experimental setup utilizing a fiber-amplified pump source and lensed fiber coupling. Temperature stabilization via a TEC is applied to maintain the optimal QPM condition. Active fiber alignment stabilization is also performed by monitoring the output power. e Temperature-dependent SHG response showing the QPM tuning curve. The dashed line is a sinc$^2$ fit used to identify the optimum phase-matching temperature. f Off-chip measured SHG power as a function of the squared pump power. The green dashed line shows the expected quadratic scaling, corresponding to a normalized conversion efficiency of $\sim$0.46%/W.
• Figure 3: Dynamic modulation of the fundamental (1064 nm) and second-harmonic (532 nm) signals.a Operational principle and measurement flow. The 1064 nm pump light is intensity-modulated by an EO MZI and frequency-doubled to 532 nm in the PPLN section. This allows for simultaneous characterization of the extinction ratios for the pump ($ER_{pump}$) and the second-harmonic ($ER_{SH}$) signals. b, c Normalized transmission versus DC bias voltage. This yields $V_{\pi} = 3.98$ V for 1064 nm and $V_{\pi} = 3.98$ V for 532 nm. Dashed curves indicate model fits reflecting the sinusoidal MZI response and quadratic scaling of SH. d, e Transmission in logarithmic scale. The data demonstrate extinction ratios of 23.2 dB for the pump and 42.2 dB for the SH signal. f, g Time-domain switching measured with a photodetector. Measured $10\text{--}90\%$ rise and fall transition times are $0.612~\text{ns}$ and $0.669~\text{ns}$, respectively, approaching the $1.2~\text{GHz}$ bandwidth limit of the photodetector.
• Figure 4: Photonic chip-based confocal imaging and CW-ODMR measurements of NV centers.a Schematic of the experimental setup. A 1064 nm pump laser is frequency-converted in the PPLN nonlinear device to generate 532 nm excitation light. This is delivered to a confocal microscopy setup for NV excitation and fluorescence collection. The performance is benchmarked against a conventional 532 nm laser under the same optical configuration (green box: PPLN-generated 532 nm source; grey box: conventional 532 nm laser). b Confocal fluorescence images of NV centers acquired under identical conditions. c CW-ODMR spectrum measured using the on-chip generated 532 nm excitation. A resonance dip in fluorescence is observed as the microwave frequency is scanned across the spin transition.
• Figure 5: High-speed EO pulse gating for coherent spin measurements of NV centers.a Schematic of the FPGA-synchronized pulse control scheme. Voltage-driven PPLN switching enables nanosecond-scale optical pulse delivery to NV centers combined with time-tagged photon counting. This configuration facilitates pulsed ODMR, Rabi oscillations, Ramsey interference, and time-resolved fluorescence measurements. b Pulsed ODMR spectrum of a single NV center. Multiple resonance dips are resolved as the microwave frequency is scanned. c Rabi oscillations obtained by varying the microwave pulse duration. d Ramsey interference fringes. These are used to extract the spin dephasing time $T_2^*$ and detuning-dependent phase evolution. The inset shows the FFT of the Ramsey trace highlighting dominant frequency components. e Time-resolved fluorescence trace following pulsed excitation. The black line indicates the PPLN-generated optical pulse profile , while the red dashed line shows the NV fluorescence decay triggered by the pulse. The inset displays a magnified view of the PPLN-generated green light pulse.