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Physical Review Applied

Platform for designing bipartite entangled quantum frequency combs based on silicon nitride microring resonators

Nianqin Li, Bo Ji, Yang Shen, Guangqiang He

Published May 29, 2024• 7 citations
Publisher

Abstract

Integrated Kerr quantum frequency combs (QFCs), with the potential to generate multiple and scalable quantum states, have emerged as a compact, stable, and fundamental resource for broadband entanglement. Here, we build a platform for designing bipartite entangled QFCs via an on-chip silicon nitride microring resonator. By establishing the system quantum dynamics of Kerr nonlinear microresonators, our platform can support up to 12 continuous-variable quantum modes, in the form of six simultaneously two-mode squeezed pairs under the influence of hysteresis. The entanglement degree of frequency-mode pairs is dependent on the resonator structure and ambient temperature. By adjusting the cavity temperature, we can optimize the performance of entanglement under certain injected pump power and pump detuning. Our comprehensive QFC designing process and entanglement distribution control may ameliorate the generation and optimization of entanglement.

DOI
10.1103/physrevapplied.21.054058

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Integrated Kerr quantum frequency combs (QFCs), with the potential to generate multiple and scalable quantum states, have emerged as a compact, stable, and fundamental resource for broadband entanglement. Here, we build a platform for designing bipartite entangled QFCs via an on-chip silicon nitride microring resonator. By establishing the system quantum dynamics of Kerr nonlinear microresonators, our platform can support up to 12 continuous-variable quantum modes, in the form of six simultaneously two-mode squeezed pairs under the influence of hysteresis. The entanglement degree of frequency-mode pairs is dependent on the resonator structure and ambient temperature. By adjusting the cavity temperature, we can optimize the performance of entanglement under certain injected pump power and pump detuning. Our comprehensive QFC designing process and entanglement distribution control may ameliorate the generation and optimization of entanglement.
Integrated microresonator facilitates the realization of quantum frequency comb (QFC), which provides a large number of discrete frequency modes with broadband spectral range and narrow linewidth. However, all previous demonstrations have focused on the generation of energy-time or time-bin entangled photons from QFC. Realizing polarization-entangled quantum frequency comb, which is a useful resource for the fundamental study of quantum mechanics and quantum information applications, remains challenging. Here, we demonstrate a broadband polarization-entangled quantum frequency comb by combining an integrated silicon-nitride microresonator with a Sagnac interferometer. With a free spectral range of about 99 GHz and a narrow linewidth of about 190 MHz, our source provides 22 polarization-entangled photon pairs with frequency covering the whole telecom C-band. The entanglement fidelities for all 22 pairs are above 81%, including 17 pairs with fidelities higher than 90%. Our demonstration paves the way for employing the polarization-entangled quantum frequency comb in quantum network using CMOS technology as well as standard dense wavelength division-multiplexing technology.
Abstract Considerable efforts have been devoted to augmenting the performance of displacement sensors constrained by quantum noise, particularly within high‐precision applications such as gravitational wave detection. Frequency‐dependent squeezing methodologies have adeptly exceeded the standard quantum limit in optomechanical force measurements, catalyzing profound advancements in the field. Concurrently, notable strides in integrated photonics have paved the way for the realization of integrated Kerr quantum frequency combs (QFCs). In this work, a sophisticated platform designed for the creation of Einstein–Podolsky–Rosen (EPR)‐entangled QFCs utilizing on‐chip silicon nitride microring resonators is presented. This platform facilitates an exhaustive analysis and optimization of entanglement performance, establishing a robust framework for noise mitigation. By incorporating the quantum dynamics of Kerr nonlinear microresonators, the system accommodates at least 12 continuous‐variable quantum modes, including 6 pairs of concurrently EPR‐entangled states. Moreover, through precise tuning of the detection angle of the idler mode, the signal mode transitions into a single‐mode squeezed state. Harnessing the frequency‐dependent nature of this detection angle enables the achievement of frequency‐dependent squeezing. A comparative analysis under different dispersion conditions is also presented.
Simultaneous Generation of Quantum Frequency Combs across Distinct Modal Families in a Single Si3N4Si_3 N_4Si3​N4​ Whispering Gallery Mode Resonator
Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal families. It presents a micro-ring resonator with a radius of 240 μm\mathrm{μm}μm, capable of supporting four modal families within the 130 to 260 THz\mathrm{THz}THz frequency range for consistency regulation. The results indicate that, by carefully designing the structure of silicon nitride WGMRs, it is possible to generate quantum entangled frequency combs across distinct modal families simultaneously using monochromatic pump light. It is achieved by modulating the pump mode profiles with a spatial light modulator (SLM) or an on-chip inverse-designed mode converter. This approach offers a simple and low-cost method to achieve higher-density entanglement integration on-chip.
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High-dimensional entanglement provides valuable resources for quantum technologies, including quantum communication, quantum optical coherence tomography, and quantum computing. Obtaining a high brightness and dimensional entanglement source has significant value. Here we utilize a tunable asymmetric Mach–Zehnder interferometer coupled silicon microring resonator with 100 GHz free spectral range to achieve this goal. With the strategy of the tunable coupler, the dynamical and extensive tuning range of quality factors of the microring can be obtained, and then the biphoton pair generation rate can be optimized. By selecting and characterizing 28 pairs from a more than 30-pair modes biphoton frequency comb, we obtain a Schmidt number of at least 23.4 and on-chip pair generation rate of 19.9 MHz/mW2 under a low on-chip pump power, which corresponds to 547 dimensions Hilbert space in frequency freedom. These results will prompt the wide applications of quantum frequency comb and boost the further large density and scalable on-chip quantum information processing.