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Physical Review A

Parity-time-symmetry-enabled broadband quantum frequency-comb generation

Nuo Chen, Wu-Qiang Chi, Yunru Fan, Hanghang Li, Zijie Wang, Qiang Zhou, Jing Ming Xu, Xinliang Zhang

Published Aug 13, 2024• 4 citations
Publisher

Abstract

Microcavities stand out as competitive tools in the development of quantum frequency combs (QFCs) for multiphoton entanglement sources, frequency-multiplexed single-photon sources, and the generation of high-dimensional entangled states. However, the presence of waveguide dispersion hinders the creation of broadband QFCs, an issue that becomes increasingly critical as the quality factor of the microcavity increases. Here, we present a scheme to enhance the spectral range of QFCs by selectively manipulating the pump resonance via parity-time symmetry. We show that by using pulsed pump light to cover the pump resonance, frequency-matching conditions can be relaxed and the spectral range of QFCs can thus be significantly extended near the exceptional point. The proposed method offers a simple, effective, and robust approach to increase the dimension of QFCs, without severely sacrificing nonlinear efficiency.

DOI
10.1103/physreva.110.023714

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Microcavities stand out as competitive tools in the development of quantum frequency combs (QFCs) for multiphoton entanglement sources, frequency-multiplexed single-photon sources, and the generation of high-dimensional entangled states. However, the presence of waveguide dispersion hinders the creation of broadband QFCs, an issue that becomes increasingly critical as the quality factor of the microcavity increases. Here, we present a scheme to enhance the spectral range of QFCs by selectively manipulating the pump resonance via parity-time symmetry. We show that by using pulsed pump light to cover the pump resonance, frequency-matching conditions can be relaxed and the spectral range of QFCs can thus be significantly extended near the exceptional point. The proposed method offers a simple, effective, and robust approach to increase the dimension of QFCs, without severely sacrificing nonlinear efficiency.
We demonstrate the generation of multiphoton quantum states of light by cavity-enhanced parametric down-conversion in the high-repetition-rate pulsed regime. An external enhancement cavity resonant with the spectral comb of modes of a mode-locked pump laser provides a coherent buildup of the pump intensity and greatly enhances the parametric gain without sacrificing its high repetition rate and comb structure. We probe the parametric gain enhancement by the conditional generation and tomographic analysis of two-photon Fock states. Besides its potential impact for efficiently generating highly nonclassical or entangled multiphoton states in many existing experimental setups, this scheme opens exciting perspectives toward the combination of quantum and comb technologies for enhanced measurements and advanced quantum computation protocols.
The development of quantum technologies for quantum information science demands the realization and precise control of complex (multipartite and high dimensional) entangled systems on practical and scalable platforms. Quantum frequency combs (QFCs) generated via spontaneous four-wave mixing in integrated microring resonators represent a powerful tool towards this goal. They enable the generation of complex photon states within a single spatial mode as well as their manipulation using standard fiber-based telecommunication components. Here, we review recent progress in the development of QFCs, with a focus on our results that highlight their importance for the realization of complex quantum states. In particular, we outline our work on the use of integrated QFCs for the generation of high-dimensional multipartite optical cluster states and their unidirectional processing, being at the core of measurement-based quantum computation. These results confirm that engineering the time-frequency entanglement properties of QFC may provide a stable, practical, low-cost, and established platform for the development of near-future quantum devices for out-of-the-lab applications, ranging from practical quantum computing to more secure communications.
Frequency combs are multimode photonic systems that underlie countless precision sensing and metrology applications. Since their invention over two decades ago, numerous efforts have pushed frequency combs to broader bandwidths and more stable operation. More recently, quantum squeezing and entanglement have been explored in single frequency comb systems for quantum advantages in sensing and signal multiplexing. However, the production of quantum light across multiple frequency combs remains unexplored. In this work, we theoretically explore a mechanism that generates a series of nonlinearly coupled frequency combs through cascaded three-wave upconversion and downconversion processes mediated by a single idler comb. We show how this system generates inter- and intracomb two-mode squeezing and entanglement spanning a very large spectral range, from ultraviolet to mid-IR frequencies. Finally, we show how this system can be engineered to produce on-demand multimode quantum light through covariance matrix optimization. Our findings could enable tunable broadband ghost spectroscopy protocols, squeezing-enhanced pump-probe measurements, and broadband entanglement between spectrally-multiplexed quanta of information.
The investigation of integrated frequency comb sources characterized by equidistant spectral modes was initially driven by considerations toward classical applications, seeking a more practical and miniaturized way to generate stable broadband sources of light. Recently, in the context of scaling the complexity of optical quantum circuits, these on-chip approaches have provided a new framework to address the challenges associated with non-classical state generation and manipulation. For example, multi-photon and high-dimensional states were to date either inaccessible, lacked scalability, or were difficult to manipulate, requiring elaborate approaches. The emerging field of quantum frequency combs studying spectral multimode sources based on the judicious excitation of (typically) third-order nonlinear optical micro-cavities has begun to address these issues. Several quantum sources based on this concept have already been demonstrated, among them are combs of correlated photons, cross-polarized photon pairs, entangled photon pairs, multi-photon states, and high-dimensional entangled states. While sources have achieved increasing complexity, so have coherent state processing operations, demonstrated in a practical manner using standard telecommunications components. Here, we review our recent work in the development of this framework, with a focus on multi-photon and high-dimensional states. The integrated frequency comb platform thus demonstrates significant potential for the development of meaningful quantum optical technologies.
Quantum frequency combs (QFCs) are essential to quantum photonic systems, enabling high dimensional entanglement in both temporal and frequency domains. Silicon photonics offers a promising platform for scalable and monolithic quantum photonic integrated circuits. However, its performance in QFC generation has been hindered by nonlinear losses and restricted phase-matching bandwidth. To overcome these challenges, we introduce a novel design strategy that combines high-order spatial mode engineering with an optimized free-carrier loss suppression structure in a silicon micro-ring resonator. This approach enables a broadband QFC spanning 150 nm, along with a high single pair photon brightness of 6.43 × 109 Hz/mW2/GHz and photon efficiency of 19.9 GHz/mW2 with the collection of 11 frequency bins. The generated QFCs produce heralded single photons with low heralded second-order correlation gh20=0.0024 and energy-time entangled photon pairs with high visibility of 98.19%. Consistent performance across wafer-scale multiple dies confirms the robustness and manufacturability of the designed device. This work establishes a scalable and high-yield pathway toward monolithic quantum photonic integrated circuits.
We reveal the generation of a broadband (> 1.9 THz) bi-photon quantum frequency comb (QFC) in a silicon-on-insulator (SOI) Fabry–Pérot micro-cavity and the control of its spectral correlation properties. Correlated photon pairs are generated through three spontaneous four-wave mixing (SFWM) processes by using a co-polarized bi-chromatic coherent input with power P 1 and P 2 on adjacent resonances of the nonlinear cavity. Adjusting the spectral power ratio r = P 1 /( P 1 + P 2 ) allows control over the influence of each process leading to an enhancement of the overall photon pair generation rate (PGR) μ ( r ) by a maximal factor of μ ( r = 0.5)/ μ ( r = 0) ≈ 1.5, compared to the overall PGR provided by a single-pump configuration with the same power budget. We demonstrate that the efficiency a ND of the non-degenerate excitation SFWM process (NDP) doubles the efficiency a 1 ≈ a 2 of the degenerate excitation SFWM processes (DP), showing a good agreement with the provided model.