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arXiv:2007.07411 · Optica

Toward 1% single-photon anharmonicity with periodically poled lithium niobate microring resonators

Juanjuan Lu, Ming Li, Chang-Ling Zou, Ayed Al Sayem, Hong X. Tang

Published Oct 23, 2020• 221 citations
arXivHTMLPDF

Abstract

The absence of the single-photon nonlinearity has been a major roadblock in developing quantum photonic circuits at optical frequencies. In this paper, we demonstrate a periodically poled thin film lithium niobate microring resonator (PPLNMR) that reaches 5,000,000%/W second-harmonic conversion efficiency—almost 20-fold enhancement over the state-of-the-art—by accessing its largest χ ( 2 ) tensor component d 33 via quasi-phase matching. The corresponding single-photon coupling rate g / 2 π is estimated to be 1.2 MHz, which is an important milestone as it approaches the dissipation rate κ / 2 π of best-available lithium niobate microresonators developed in the community. Using a figure of merit defined as g / κ , our device reaches a single-photon nonlinear anharmonicity approaching 1%. We show that, by further scaling of the device, it is possible to improve the single-photon anharmonicity to a regime where photon blockade effect can be manifested.

DOI
10.1364/optica.403931

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The absence of the single-photon nonlinearity has been a major roadblock in developing quantum photonic circuits at optical frequencies. In this paper, we demonstrate a periodically poled thin film lithium niobate microring resonator (PPLNMR) that reaches 5,000,000%/W second-harmonic conversion efficiency—almost 20-fold enhancement over the state-of-the-art—by accessing its largest χ ( 2 ) tensor component d 33 via quasi-phase matching. The corresponding single-photon coupling rate g / 2 π is estimated to be 1.2 MHz, which is an important milestone as it approaches the dissipation rate κ / 2 π of best-available lithium niobate microresonators developed in the community. Using a figure of merit defined as g / κ , our device reaches a single-photon nonlinear anharmonicity approaching 1%. We show that, by further scaling of the device, it is possible to improve the single-photon anharmonicity to a regime where photon blockade effect can be manifested.
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 $(65\ifmmode\pm\else\textpm\fi{}3)\mathrm{%}$ with only $(104\ifmmode\pm\else\textpm\fi{}4)$-$\ensuremath{\mu}\mathrm{W}$ pump power. At peak conversion, $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$-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 ${10}^{\ensuremath{-}5}$, 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.
Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process, but currently the types of atoms used for quantum information processing and storage are limited by the narrow bandwidth of up-conversion available. Here we present the first experimental demonstration of broadband and high-efficiency quasi-phase matching second harmonic generation (SHG) in a chip-scale periodically poled lithium niobate thin film. We achieve large bandwidth of up to 2 THz for SHG by satisfying quasi-phase matching and group-velocity matching simultaneously. Furthermore, by changing film thickness, the central wavelength of quasi-phase matching SHG bandwidth can be modulated from 2.70 um to 1.44 um. The reconfigurable quasi-phase matching lithium niobate thin film provides a significant on-chip integrated platform for photonics and quantum optics.
Abstract Integrated photon-pair sources are crucial for scalable photonic quantum systems. Thin-film lithium niobate is a promising platform for on-chip photon-pair generation through spontaneous parametric down-conversion (SPDC). However, the device implementation faces practical challenges. Periodically poled lithium niobate (PPLN), despite enabling flexible quasi-phase matching, suffers from poor fabrication reliability and device repeatability, while conventional modal phase matching (MPM) methods yield limited efficiencies due to inadequate mode overlaps. Here, we introduce a layer-poled lithium niobate (LPLN) nanophotonic waveguide for efficient photon-pair generation. It leverages layer-wise polarity inversion through electrical poling to break spatial symmetry and significantly enhance nonlinear interactions for MPM, achieving a notable normalized second-harmonic generation (SHG) conversion efficiency of 4615% W-1 cm-2. Through a cascaded SHG and SPDC process, we demonstrate photon-pair generation with a normalized brightness of 3.1×106 Hz nm-1 mW-2 in a 3.3 mm long LPLN waveguide, surpassing existing on-chip sources under similar operating configurations. Crucially, our LPLN waveguides offer enhanced fabrication reliability and reduced sensitivity to geometric variations and temperature fluctuations compared to PPLN devices. We expect LPLN to become a promising solution for on-chip nonlinear wavelength conversion and non-classical light generation, with immediate applications in quantum communication, networking, and on-chip photonic quantum information processing.
Future quantum information networks operated on telecom channels require qubit transfer between different wavelengths while preserving quantum coherence and entanglement. Qubit transfer is a nonlinear optical process, but currently the types of atoms used for quantum information processing and storage are limited by the narrow bandwidth of upconversion available. Here we present the first experimental demonstration of broadband and high-efficiency quasi-phase matching second-harmonic generation (SHG) in a chip-scale periodically poled lithium niobate thin film. We achieve a large bandwidth of up to 2 THz for SHG by satisfying quasi-phase matching and group-velocity matching simultaneously. Furthermore, by changing the film thickness, the central wavelength of the quasi-phase matching SHG bandwidth can be modulated from 2.70 μm to 1.44 μm. The reconfigurable quasi-phase matching lithium niobate thin film provides a significant on-chip integrated platform for photonics and quantum optics.
Abstract Quantum noise limits the sensitivity of optical measurements, but squeezed states of light enable quantum-enhanced metrology, sensing, and information processing. Most on-chip squeezed-light sources rely on Kerr (χ(3)) nonlinearities, remain limited by pump power and excess loss constraints. Quadratic (χ(2)) platforms instead provide stronger parametric interactions, lower pump power requirements, and greater spectral engineering flexibility. Here, we demonstrate strong, broadband squeezed-light generation on a thin-film lithium niobate (TFLN) photonic chip using a dual-resonant optical parametric amplifier implemented in a single periodically poled LN (PPLN) microresonator. Near-full-depth domain inversion is achieved simultaneously with highly over-coupled resonances, exhibiting escape efficiencies exceeding 90% and intrinsic quality factors above 2.5 million in a 0.6mm2 X-cut TF-PPLN resonator, enabling efficient squeezing at 1587nm when pumped at 793.5 nm. Operating in the continuous-wave regime, we directly measure −0.81 dB of squeezing below the shot-noise limit with a pump power of 27mW, together with +4.29 dB of anti-squeezing. From these measurements, we infer an on-chip squeezing level of −7.52 dB±0.22 dB (95% confidence interval: [−7.96,−7.10] dB), and an on-chip anti-squeezing level of +9.62 dB±0.25 dB . We demonstrate single-mode squeezing at degeneracy with a squeezed-light spectrum exceeding 10.3 THz. This work reports the highest squeezing ratio among integrated χ(2) cavity platforms and the first quasi-phase matched, fully resonant χ(2) cavity squeezer on chip, establishing a scalable route to fully integrated power-efficient squeezed-light sources for quantum-enhanced sensing and metrology.
Spontaneous parametric down conversion in nonlinear material is widely exploited to generate entangled photon pairs in quantum optics experiments and applications, including quantum computing and communication. Periodically poled thin film lithium niobate (PPTFLN) has emerged as a promising platform for efficient entangled photon pair generation, offering enhanced nonlinear interaction through quasi-phase matching (QPM) and tight confinement of light. However, achieving optimal performance requires careful control of the QPM condition since the waveguide in TFLN is highly dispersive to changes in the geometric parameter. In this study, we fabricate PPTFLN rib waveguides to generate entangled photon pairs at telecommunication wavelengths, varying geometric parameters. QPM condition is confirmed with the second harmonic generation experiments and Pair generation rate and coincidence-to-accidental count ratio are also estimated by temporal coincidence measurement. Digital etching process is introduced to control the QPM condition, resulting in incremental peak wavelength shift by discrete etching step. This is expected to contribute to synchronizing wavelength of quantum nodes.