Quantum photonic frequency processor on thin-film lithium niobate

Abstract

The rapid development of photonic quantum information processing necessitates precise and programmable control over optical frequency, a capability critical not only for achieving photon indistinguishability but also for exploiting a virtually unbounded frequency dimension. However, efficient and scalable processing of frequency-encoded photon states remains challenging, primarily due to the limited nonlinear optical interaction in most photonic materials. Here, by harnessing the high-performance thin-film lithium niobate electro-optic (EO) platform, we demonstrate an integrated quantum photonic frequency processor that enables coherent and programmable control of photon frequency with high precision. We establish a scalable architecture for frequency-encoded quantum information processing. Using a fully integrated photonic chip, we realize a universal set of frequency-encoded quantum logic gates, including arbitrary single-qubit rotation gates and the two-qubit controlled-phase gate. Furthermore, we demonstrate its application in high fidelity characterization of frequency-bin entangled states. Our work reveals the unprecedented potential of utilizing the frequency degree of freedom in integrated quantum photonic systems.

Figures (4)

• Figure 1: Description of the Quantum Photonic frequency processor chip.a, Schematic and operating principle of microwave-driven coupled double resonators (DR). b, Schematic diagram of the chip design. c, Optical microscope images of the chip and the test setup. FA, fiber array; DC, direct-current source; R, microring resonator; GC, grating coupler.
• Figure 2: Chip characterization.a, Experimental setup for characterizing the chip. ECDL, external cavity diode laser; MSG, microwave signal generator; EA, electrical amplifier; FFP, fiber Fabry-Pérot cavity; PD, photodetector; OSC, oscilloscope. b, Transmission spectrum of DR1 against the thermal tuning power. The minimum frequency mode splitting is 13.49 GHz, with balanced transmission of the two modes. c, Performance of three DRs, including (i) frequency mode splitting, (ii) linewidth, and (iii) transmission-dip depth. d, The resonance shift under DC voltages, with the corresponding EO-response values, obtained from linear fits, listed at lower right corner. e, Splitting ratio and total efficiency $\eta$ of the f-BS for DR1 with input $\omega_1$ (i) and $\omega_2$ (ii). f, Frequency distribution at maximal interconversion efficiency, measured by scanning the resonant frequency of a FFP cavity (FSR, 10 GHz). g, Transmission spectra of the add-drop microring filters.
• Figure 3: Frequency domain photonic interferences.a, Characterization of f-MZI using CW light. b, Demonstration of f-MZI using heralded single photon. c, Histogram of time-correlated coincidence counts. d, Hong-Ou-Mandel interference at different reflectivities.
• Figure 4: Frequency qubits manipulation.a, Encoding of qubits in photonic frequency-bins. b, Measured probability distributions of CZ gate with different input states. c, Generation of frequency entangled state through SPDC. d, Measured entanglement curves.