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International Conference on Transparent Optical Networks

Generation of hyperentangled photon pairs encoded in the time-bin and frequency-bin degree of freedom from silicon microrings

Sara Congia, Massimo Borghi, Emanuele Brusaschi, Marco Liscidini, Johan Rothman, S. Olivier, Mattéo Galli, Daniele Bajoni

Published Jul 6, 2025• 0 citations
Publisher

Abstract

Multidimensional entangled photon states represent a useful resource for large-scale quantum communication networks. Among them, hyperentangled (HE) states, i.e. presenting simultaneous entanglement in several degrees of freedom (DoFs), stand out for their noise resilience. In this work, we demonstrate the generation of HE photon pairs in the time-bin and the frequency-bin DoFs through Spontaneous Four-Wave Mixing (SFWM) from two silicon-on-insulator high-brightness microring resonators.

DOI
10.1109/icton67126.2025.11125030

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Multidimensional entangled photon states represent a useful resource for large-scale quantum communication networks. Among them, hyperentangled (HE) states, i.e. presenting simultaneous entanglement in several degrees of freedom (DoFs), stand out for their noise resilience. In this work, we demonstrate the generation of HE photon pairs in the time-bin and the frequency-bin DoFs through Spontaneous Four-Wave Mixing (SFWM) from two silicon-on-insulator high-brightness microring resonators.
Multi-dimensional entangled photon states represent an important resource in quantum communication networks. Specifically, hyperentangled states presenting simultaneous entanglement in several degrees of freedom (DoF) stand out for their noise resilience and information capacity. In this work, we demonstrate the generation of hyperentangled photon pairs in the time and frequency-bin domain by spontaneous four-wave mixing from the coherent driving of two integrated silicon microresonators. We demonstrate entanglement in each DoF by proving the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality by more than 27 standard deviations (STDs) in each reduced space. Genuine hyperentanglement is then assessed from the negativity of a hyperentanglement witness, which is verified by more than 60 STDs. These results mark the first, to the best of our knowledge, demonstration of time-frequency bin hyperentanglement in an integrated silicon photonic device.
Multidimensional entangled photon states represent a useful resource for large-scale quantum communication networks. By leveraging multiple degrees of freedom (DoFs) of photons, the dimensionality of the Hilbert space can be expanded without increasing the number of particles, enhancing the efficiency of quantum information processing. Specifically, hyperentanglement, i.e. simultaneous entanglement across multiple DoFs, is robust against decoherence, thus providing strengthened performance in noisy quantum communication protocols with respect to n-photon quantum states [1].
Abstract Optical losses and environmental noise present significant challenges for the coherent propagation of entangled states of light over large distances in quantum communication protocols. To cope with optical losses, one possible strategy is to increase the emission rate as much as possible. Decoherence, related to thermal and pressure fluctuation and to the presence of parasitic processes, can be overcome by encoding information via hyper-entanglement, i.e. entanglement over multiple degrees of freedom (DoFs). In this work we experimentally demonstrate a silicon-integrated device implementing both strategies, demonstrating the emission of spectrally multiplexed and hyper-entangled photon pairs. The pair generation rate exceeds 10 9 pairs per second at the output of the device over an 8 THz-wide comb of multiplexed frequency modes. Hyperentanglement is proved by showing entanglement in the frequency-bin and time-energy DoFs, along with high purity of the states when tracing over the time-energy degree of freedom. Quantum state tomography shows both fidelity and purity to be greater than 95% in the frequency domain, while, in the time-domain encoding, Bell’s inequality is violated by more than 10 standard deviations.
Entanglement and encoding in discrete frequency bins – essentially a quantum analogue of wavelength-division multiplexing – represents a relatively new degree of freedom for quantum information with photons. In this talk I discuss biphoton frequency combs, generated either by spontaneous four-wave mixing (SFWM) from on-chip microring resonators or by spectral filtering of spontaneous parametric down conversion (SPDC) in second order nonlinear crystals. Potential advantages include generation of high dimensional units of quantum information (qudits), which can carry multiple qubits per photon, robust transmission over fiber, frequency parallelism and routing, and compatibility with on-chip implementations, as well as hyperentanglement with other photonic degrees, e.g., time-frequency hyperentanglement. Since the initial experiments less than two years ago, frequency bin quantum photonics has been advancing rapidly [1-8]. In this talk I will discuss a method using pulse shapers and phase modulators in order to mix different frequencies and perform two photon interference experiments for characterization of the frequency-bin entanglement. Similar components (pulse shapers and phase modulators) may be used to manipulate the frequency-encoded quantum states; this will be described in another talk by our collaborators at Oak Ridge National Labs. I will also discuss the use of time bins and frequency bins as independent degrees of freedom in a quantum encoding fashion to realize what we believe to be the first deterministic two qudit gates. Finally, I comment briefly on potential applications and on prospects for realization of integrated frequency bin quantum photonics.