Quantum frequency conversion (QFC) is essential for bridging the spectral gap between stationary qubits and low-loss optical communication channels. Practicable QFC interfaces connecting ultraviolet and telecommunication bands are of great significance but have remained elusive, constrained by the dual challenges of a high-performance frequency converter and effective noise suppression in short-wavelength pumping configurations. We address this by demonstrating the phase-matching mechanism with domain defects and differential-tuning behavior of the spontaneous parametric down-conversion noises. Based on a quantitative analysis of performance degradation induced by domain defects, we propose specific fabrication guidelines and experimentally achieve an ultrahigh normalized conversion efficiency of 839%/(W cm^{2}) for the fundamental guided mode in thin-film lithium niobate waveguides. Meanwhile, we reveal a new noise control mechanism for short-wavelength pumping by utilizing the differential-tuning behaviors of difference-frequency generation and spontaneous parametric down-conversion processes. Then a single-stage QFC from 393 nm to the telecom C band with a record-high external efficiency of 28.8% and an ultralow noise level of 35 counts per second is achieved experimentally. The proposed mechanisms would enable other QFCs with higher efficiency and lower noise, advancing the development of scalable quantum networks. Furthermore, it holds significant potential for driving progress in both classical and integrated nonlinear photonics.
Quantum frequency conversion (QFC) is essential for bridging the spectral gap between stationary qubits and low-loss optical communication channels. Practicable QFC interfaces connecting ultraviolet and telecommunication bands are of great significance but have remained elusive, constrained by the dual challenges of a high-performance frequency converter and effective noise suppression in short-wavelength pumping configurations. We address this by demonstrating the phase-matching mechanism with domain defects and differential-tuning behavior of the spontaneous parametric down-conversion noises. Based on a quantitative analysis of performance degradation induced by domain defects, we propose specific fabrication guidelines and experimentally achieve an ultrahigh normalized conversion efficiency of 839%/(W cm^{2}) for the fundamental guided mode in thin-film lithium niobate waveguides. Meanwhile, we reveal a new noise control mechanism for short-wavelength pumping by utilizing the differential-tuning behaviors of difference-frequency generation and spontaneous parametric down-conversion processes. Then a single-stage QFC from 393 nm to the telecom C band with a record-high external efficiency of 28.8% and an ultralow noise level of 35 counts per second is achieved experimentally. The proposed mechanisms would enable other QFCs with higher efficiency and lower noise, advancing the development of scalable quantum networks. Furthermore, it holds significant potential for driving progress in both classical and integrated nonlinear photonics.
Quantum frequency conversion (QFC) is essential for bridging the spectral gap between stationary qubits and low-loss optical communication channels. In this work, we demonstrate a short-wavelength-pumping QFC with the first-order quasi-phase matching period of 3.07 um on thin-film lithium niobate, converting ultraviolet photons to the telecom C-band. By constructing a theoretical model that correlates the normalized conversion efficiency with domain defects in the short-period phase-matched waveguide, we found the critical tolerance of domain defects along the waveguide should be ≤2 (excluding the ends). Based on this, we achieved a theoretical limit normalized conversion efficiency of 839%/(W*cm^2) for the fundamental guided mode through fabrication optimization. Furthermore, we propose a robust noise suppression strategy for short-wavelength pumping by utilizing the counter-tuning behaviors of difference-frequency generation and spontaneous parametric down-conversion. By combining these advances with ultra-narrowband filtering, we achieve a record-high external efficiency of 28.8% and an ultra-low noise of 35 counts per second. This high-performance QFC connecting ultraviolet and telecom bands satisfies the stringent requirements for long-lived remote ion-ion entanglement in scalable quantum networks [W.-Z. Liu et al., Nature (2026)].
Signal photons emitted by quantum nodes typically fall outside the low-loss telecom window of optical fibers, leading to severe transmission losses. Quantum frequency conversion (QFC) offers an effective optical interface that bridges quantum nodes with telecom-band channels, enabling long-distance quantum communication. In this work, we demonstrate a compact, fiber-integrated QFC system with low noise and a high signal-to-noise ratio (SNR). Using a periodically poled lithium niobate (PPLN) waveguide, input photons at 637.2 nm are down-converted to telecom photons at 1588.3 nm. Our system achieves a total conversion efficiency of approximately 9%, with pump-induced noise suppressed to 154 Hz. For input photon rates of 32.7, 118.0, and 327.7 kHz, the corresponding SNRs are 12.3, 43.9, and 117.8, respectively. We further develop a theoretical model to simulate the entanglement fidelity between nitrogen-vacancy (NV) center spins and the frequency-converted telecom photons. At the emission rate of an NV center, our QFC system maintains an expected fidelity exceeding 52% over a transmission distance of 100 km. These findings highlight the potential of our QFC system for scalable, long-distance quantum networking.
Quantum frequency conversion (QFC) is essential for interfacing quantum systems operating at different wavelengths and for realizing scalable quantum networks. Despite extensive progress, achieving QFC with simultaneous high efficiency, low pump power, minimal noise, broad bandwidth, and pump-wavelength flexibility remains challenging. Here, we demonstrate efficient, low-noise, and bidirectional QFC between the telecom (1550-nm) and visible (780-nm) bands using unpoled indium gallium phosphide (InGaP) χ(2) nanophotonic waveguides, eliminating the need for a long-wavelength pump. Leveraging the large nonlinear susceptibility of InGaP together with programmable modal-phase-matching control, we obtain record-low pump power (20 mW) -- an order of magnitude lower than that in previous demonstrations using integrated thin-film waveguides -- and record-high loss-inclusive normalized conversion efficiency among non-resonant QFC implementations. The platform maintains quantum coherence and entanglement of input photons with noise well below the single-photon level. These results mark a significant advance in integrated nonlinear photonics for high-performance QFC, facilitating the development of versatile and scalable quantum networks.
In this paper, we present a novel single stage quantum frequency conversion (QFC) scheme based on an enhancement cavity, which allows for high conversion efficiencies with record low noise levels, 100 times smaller than in previous systems and close to the thermal background. Our approach represents a significant improvement over traditional QFC methods that rely on periodically poled waveguide crystals, which typically produce high levels of noise with input wavelengths in the visible spectrum. One of the key challenges in QFC is the generation of noise photons - photons that are not part of the desired output state. Those noise photons are one of the major limitations of today’s quantum network experiments. It has been widely believed that single stage QFC of qubit photons in the visible range would result in too many noise photons in the telecom band, because of SPDC induced by the short wavelength driver laser. However, using the enhancement cavity design, we are able to overcome this challenge and demonstrate high-fidelity QFC from the visible to telecom band. Our results have important implications for the development of practical QFC devices for a range of applications, including quantum communication and quantum networks, where low noise levels are critical.
Quantum frequency conversion (QFC) plays a critical role in practical quantum information technology as it provides a bridge among different quantum devices, which usually operate at different optimal wavelength. Photons with longer wavelength feature lower propagation loss and lower solar radiation noise in free space, hence hold promise for daylight long distance quantum communication. Besides, wavelength over 2 μ m also overlap with the absorption band of many important molecules, hence is of great importance for gases and molecules detection. Yet development of technology in this region has been hindered primarily by the spectral mismatch with other quantum devices, notably quantum detection and memories, which optimally operate in the visible band. Here, we demonstrate the first QFC of 2 μ m photons to the visible region on domain-engineered thin-film lithium niobate (TFLN) platform. Benefiting from the strong nonlinearity in such integrated platform, the highest internal quantum conversion efficiency of 42% is achieved at an exceptionally low pump saturation power of only 58 mW . This work provides an efficient interconnection between photons operating at the visible and 2 μ m bands in the integrated platform, pushing forward the development of practical quantum chips for application of quantum communication, sensing and metrology in the future. • Strong mode confinement and domain-engineered thin film lithium niobate (TFLN), combined with large χ ( 2 ) , enable efficient on-chip nonlinear conversion. • First demonstration of quantum frequency conversion (QFC) of 2 μ m band photon on thin film lithium niobate.
Quantum frequency conversion (QFC) plays a crucial role in constructing seamless interconnection between quantum systems operating at different wavelengths. To advance future quantum technology, chip-scale integrated QFC components, featuring high efficiency, small footprint, low power consumption, and high scalability, are indispensable. In this work, we demonstrate the first hybrid integrated QFC chip on a thin-film lithium niobate platform that connects the telecom and visible bands. Benefiting from the periodically poled microring resonator with ultra-high normalized conversion efficiency of 386,000%/W, an ultra-low pump power of 360 μW is achieved, which is more than two orders of magnitude lower than the traditional straight waveguide scheme. By injecting current into the chip, an on-chip quantum efficiency of 57% and a noise count of ∼7000 counts per second are achieved. Such an electrically pumped, integrated, and scalable QFC chip would significantly advance the integration of quantum networks and the development of chip-scale quantum optical systems.