Photon Conversion and Interaction in a Quasi-Phase-Matched Microresonator

The conversion and interaction between quantum signals at the single-photon level are essential for scalable quantum photonic information technology. Using a fully optimized periodically poled lithium niobate microring, we demonstrate ultraefficient sum-frequency generation on a chip. The external quantum efficiency reaches $(65\pm 3)\mathrm{\%}$ with only $(104\pm 4)$-$\mu \mathrm{W}$ pump power. At peak conversion, $3\times {10}^{-5}$-noise photon is created during the cavity lifetime, which meets the requirement of quantum applications using single-photon pulses. Using a pump and signal in single-photon coherent states, we directly measure the conversion probability produced by a single pump photon to be ${10}^{-5}$, which is a significant improvement from the state of the art, and the photon-photon coupling strength to be 9.1 MHz. Our results mark steady progress toward quantum nonlinear optics at the ultimate single-photon limit, with potential applications in highly integrated photonics and quantum optical computing.

Figure 1

Integrated TFLN circuits for photon conversion and interaction. Schematic of the $Z$-cut periodically poled microring, where the pump, ${\omega }_p$, and signal, ${\omega }_s$, couple into the microring and generate SF light, ${\omega }_f$, via a ${\chi }^{(2)}$ process. Pulley coupler is designed for overcoupling all light waves, for high photon-extraction efficiency. Insets illustrate triply resonant and quasi-phase-matching conditions. (b) Optical spectra of interacting ${\mathrm{TM}}_{00}$ cavity modes at (i) 1560.15 nm, (ii) 1551.85 nm, and (iii) 778.00 nm.

Figure 2

Original optical spectrum before any optical filtering when strong pump and weak signal are applied. In high-conversion region, signal starts to be depleted. Inset shows magnified spectrum around the SF band. After correcting for coupling loss, on-chip powers of pump, signal, and SF waves are $-13.8$, $-44.3$, and $-44.0$ dBm, respectively.

Figure 3

Quantum efficiency, ${\eta }_{\mathrm{QE}}$ (left axis, red squares), and noise photon flux, $N_{\mathrm{noise}}$(right axis, black squares), plotted against on-chip pump power. ${\eta }_{\mathrm{QE}}$ = $65\mathrm{\%}$ is obtained at pump power around $100\mu \mathrm{W}$. Error bars for left axis and $x$ axis are estimated according to coupling instability. Error bars of noise photon on right axis are estimated by uncertainty assuming Poissonian photon-counting statistics.

Figure 4

Quantum efficiency, ${\eta }_{\mathrm{QE}}$, versus intracavity mean pump-photon number. Inset is a magnification to show that a quantum efficiency of ${\eta }_{\mathrm{QE}}={10}^{-5}$ is achieved at one intracavity pump photon (corresponding to photon flux $N_p=2.8\mathrm{GHz}$), where the intracavity signal photon number is fixed at 0.25 (corresponding to photon flux $N_s=0.7\mathrm{GHz}$). All error bars are estimated assuming Poissonian photon-counting statistics.

Figure 5

(a),(b) SEM images of etched pulley coupler before poling process and periodic poled microring after removing poling electrodes, respectively.

Figure 6

Setups for classical (a) and quantum (b) experiments. Blue and red lines denote the telecom light path and visible path, respectively. FPC, fiber-polarization controller; TEC, thermoelectric cooler; WDM, wavelength-division multiplexing module; PD, photodetector; DUT, device under test; VOA, variable optical attenuator; ATT, optical attenuator; FC, fiber collimator; SP, short-pass filter; BP, band-pass filter; NBP, narrow-band-pass filter.