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arXiv:2608.09346

A high-performance quantum pulse gate in thin-film lithium niobate

Silia Babel, Alejandra Alarcón, Laura Serino, Christian Golla, Laura Bollmers, Sebastian Lengeling, Jiayu Yang, Bernhard Reineke, Christof Eigner, Benjamin Brecht, Marko Lončar, Laura Padberg, Christine Silberhorn

quant-phSubmitted Aug 10, 2026• Announced Aug 11, 2026• 0 citations
arXivHTMLPDF

Abstract

In this work, we demonstrate a quantum pulse gate (QPG) in thin-film lithium niobate. QPGs enable the selective manipulation and detection of temporal modes of quantum light and form the basis of numerous applications in photonic quantum technologies. To date, their widespread adaption is held back by two main limitations: restricted wavelength and polarization combinations of the involved fields and low normalized conversion efficiencies. We overcome these limitations through developing a QPG in thin-film lithium niobate. We design a waveguide geometry that provides the required dispersion properties for a highly efficient type-0 sum-frequency generation.We verify our design through mapping of the phase matching intensity, and demonstrate high-quality QPG operation by measuring a temporal-mode selectivity of (96.8$\pm$1.7)% on par with existing QPGs. Thanks to the strong confinement in thin-film lithium niobate, we succeed in demonstrating an internal conversion efficiency of (89.6$\pm$0.1)% for a pump power of only 20mW in front of our sample. This yields a lower-bound estimate for the normalized conversion efficiency of (1810$\pm$10)$\mathrm{W}^{-1}\mathrm{cm}^{-2}$, three orders of magnitude higher than in previous QPGs. Our results establish thin-film lithium niobate as ideal platform for high-performance QPGs and are a major step towards practical QPGs for photonic quantum technologies.

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In this work, we demonstrate a quantum pulse gate (QPG) in thin-film lithium niobate. QPGs enable the selective manipulation and detection of temporal modes of quantum light and form the basis of numerous applications in photonic quantum technologies. To date, their widespread adaption is held back by two main limitations: restricted wavelength and polarization combinations of the involved fields and low normalized conversion efficiencies. We overcome these limitations through developing a QPG in thin-film lithium niobate. We design a waveguide geometry that provides the required dispersion properties for a highly efficient type-0 sum-frequency generation.We verify our design through mapping of the phase matching intensity, and demonstrate high-quality QPG operation by measuring a temporal-mode selectivity of (96.8±\pm±1.7)% on par with existing QPGs. Thanks to the strong confinement in thin-film lithium niobate, we succeed in demonstrating an internal conversion efficiency of (89.6±\pm±0.1)% for a pump power of only 20mW in front of our sample. This yields a lower-bound estimate for the normalized conversion efficiency of (1810±\pm±10)W−1cm−2\mathrm{W}^{-1}\mathrm{cm}^{-2}W−1cm−2, three orders of magnitude higher than in previous QPGs. Our results establish thin-film lithium niobate as ideal platform for high-performance QPGs and are a major step towards practical QPGs for photonic quantum technologies.
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.
Within the last decade, thin-film lithium niobate (TFLN) has emerged as a leading integrated photonics platform with immediate applications in classical communications. Concurrently, TFLN components tailored to the requirements of photonic quantum information processing have also garnered considerable interest. Chief among these is the quasi-phase matched (QPM) nonlinear frequency mixer—implemented via periodic domain inversion in ferroelectric lithium niobate—which can be used to generate photon pairs, squeezed states of light, and to perform single photon frequency conversion. Here, we demonstrate progress towards realizing a spectrally separable photon pair source in lithium niobate via waveguide dispersion engineering—a technique uniquely enabled by sub-wavelength optical mode confinement in the thin-film platform. Subsequently, we design optimize a scalable fabrication process to produce QPM TFLN devices for applications that require strict adherence to a specified operating wavelength, such as quantum frequency conversion in a quantum communications network. Finally, we explore how high-performance electro-optic devices can be combined with these nonlinear optical devices to realize a multi-functional platform in which quantum states of light can be generated and manipulated within a single, compact photonic integrated circuit.
Photonic temporal modes (TMs) form a field-orthogonal basis set representing a continuous-variable degree of freedom that is in principle infinite dimensional, and create a promising resource for quantum information science and technology. The ideal quantum pulse gate (QPG) is a device that multiplexes and demultiplexes temporally orthogonal optical pulses that have the same carrier frequency, spatial mode, and polarization. The QPG is the chief enabling technology for usage of orthogonal temporal modes as a basis for high-dimensional quantum information storage and processing. The greatest hurdle for QPG implementation using nonlinear-optical, parametric processes with time-varying pump or control fields is the limitation on achievable temporal mode selectivity, defined as perfect TM discrimination combined with unity efficiency. We propose the use of pulsed nonlinear frequency conversion in an optical cavity having greatly different finesses for different frequencies to implement a nearly perfectly TM-selective QPG in a low-loss integrated-optics platform.
A new, and thus far only, method to overcome a selectivity barrier in parametrically pumped quantum pulse gates is proposed and experimentally demonstrated for the first time, using frequency conversion of optical temporal modes in second-order nonlinear waveguides. Temporal modes and quantum pulse gates are defined and their utilities are explored. Pulsed operation of three-field and four-field, parametric, optical processes are modeled and numerically investigated. A maximum limit to achievable selectivity for quantum pulse gating in uniform media is discovered and theoretically explained. An interferometric means of overcoming said limit and asymptotically approaching unit selectivity is proposed. The principle is experimentally verified by double-passing specifically shaped optical pulses derived from an ultrafast Ti:sapphire laser through a periodically-poled lithium niobate waveguide phasematched for sum-frequency generation. Further improvements and future implications for quantum technologies are discussed.
Thin-film lithium niobate (TFLN) waveguides provide a flexible platform for classical and quantum photonics. Their tight optical confinement enables strong nonlinear coupling, dispersion engineering for broadband interactions, passive components such as filters and high-Q resonators, low-voltage high-speed electro-optic devices, and tight-radius bends for dense integration. The performance of TFLN devices will be compared with that obtained in conventional weakly guiding waveguides, with a focus on quantum frequency conversion, heralded single photon sources, and progress towards few-photon nonlinear interactions.
Abstract Broadband photon pairs are highly desirable for quantum metrology, quantum sensing, and quantum communication. Such sources are usually designed through type-0 phase-matching spontaneous parametric down-conversion (SPDC) that makes the photon pairs hard to separate in the frequency-degenerate case and thus limits their applications. In this paper, we design a broadband frequency-degenerate telecom-band photon pair source via the type-II SPDC in a dispersion-engineered thin-film lithium niobate waveguide, where the polarization modes of photon pairs are orthogonal and thus are easily separated deterministically. With a 5-mm-long waveguide, our design can achieve a bandwidth of 5.56 THz (44.8 nm), which is 8.6 times larger than that of the bulk lithium niobate, and the central wavelength can be flexibly adjusted. Our design is a promising approach towards high-quality integrated photon sources and may have wide applications in photonic quantum technologies.