Quantum-coherent optical isolation and circulation using frequency conversion on a chip

Abstract

Breaking optical reciprocity enables new regimes of light--matter interaction with broad implications for fundamental physics and emerging quantum technologies. Although various approaches have been explored to achieve optical nonreciprocity, realizing it at the single-photon level has remained a major challenge. Here, we demonstrate nonmagnetic optical nonreciprocity -- including both isolation and circulation -- in the quantum regime, enabled by efficient and noiseless all-optical frequency conversion on an integrated III-V photonic chip. Our device preserves the quantum coherence and entanglement of the input photons while delivering exceptional performance parameters, including a high extinction ratio of 34 dB, low insertion loss of 0.8 dB, broad bandwidth of 44 GHz, high operational fidelity of 97%, and widely tunable operation wavelength. This realization of quantum optical nonreciprocity in a scalable photonic platform opens a pathway toward directional quantum communication and noise-resilient quantum networks.

Figures (4)

• Figure 1: Optical nonreciprocity via noiseless optical frequency conversion.a. Illustration of optical isolation via optical frequency conversion in a $\chi^{(2)}$ nonlinear waveguide. b. Representation of $\chi^{(2)}$-mediated optical frequency conversion in the band diagram. Only the forward direction satisfies the frequency- and phase-matching conditions for the frequency conversion. c. Optical circulation utilizing the full mode space of a parametrically-pumped $\chi^{(2)}$ waveguide. d. InGaP photonic chip. e. 3D illustration of the phase-matching tunable waveguide device (not to scale). f. Optical microscope image of an InGaP nanophotonic waveguide integrated with a nanoheater array. g. Scanning electron microscope image of a portion of the device and simulated field profile of the waveguide modes.
• Figure 2: Isolator performance.a. Backward and forward transmissions of the 6-mm isolator for pump on and off with pump power of 21.3 mW. b. Measured and theoretical isolation versus pump power. c. Peak isolation ratio versus pump power. d. Tunable isolation by changing the pump wavelength. Two isolation spectra are shown for pump wavelength of 1562 nm and 1543 nm, respectively. The 3-dB and 10-dB isolation bandwidths are indicated. Measured isolation wavelength range is 1538 nm$-$1570 nm due to the available laser wavelengths while the simulated isolation range is $> 1000$ nm for the same device.
• Figure 3: Quantum optical isolator and circulator.a. Forward and backward on-chip noise flux in the 1550-nm band at the wavelength separated from the pump by 20 nm ($-2.5$ THz) versus the pump power of the 6-mm waveguide. The line is a linear fitting. b. Normalized correlation function $g^{(2)}(\tau)$ of non-degenerate correlated photon pairs in the forward direction for pump on and off. EPS: entangled-photon source. Line is fitting. c. Two-photon interference fringe of degenerate correlated photon pairs after transmission through the optical isolator in the backward direction. Time-resolved coincidence counts are collected in 250-ps time-bins and for 180 s. The visibility of the fringe is $91.7\%$. d. Measured transmission matrix in the counterclockwise direction. The operational fidelity is $\mathcal{F}=0.962(4)$. e. Measured transmission matrix in the clockwise direction. The operational fidelity is $\mathcal{F}=0.970(3)$. f. Total and noise-subtracted coincidence counts in 2.3 GHz bandwidth in 60 s versus entangled photon pair rate after the signal is transmitted from port 1 to port 4 in the counterclockwise circulator.
• Figure 4: Comparison of integrated nonmagnetic isolators.a. Isolation vs. pump power. b. 3-dB isolation bandwidth vs. insertion loss. Acousto-optic effect: cheng2025terahertztian2021magneticsohn2021electricallykittlaus2021electricallykittlaus2018non. Electro-optic effect: shah2023visibleyu2023integratedherrmann2022mirror. Passive Kerr nonlinearity: white2023integrated.