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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Generation of Hyperentangled Photon Pairs in the Frequency-Bin and Time-Bin Domains with a Silicon Photonic Chip

Sara Congia, Massimo Borghi, Federico Andrea Sabattoli, Houssein El Dirani, Laurène Youssef, Camille Petit-Étienne, E. Pargon, Marco Liscidini, Corrado Sciancalepore, Johan Rothman, S. Olivier, Mattéo Galli, Daniele Bajoni

Published Jun 23, 2025• 0 citations
Publisher

Abstract

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].

DOI
10.1109/cleo/europe-eqec65582.2025.11109958

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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].
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.
Quantum communication is based on the generation of quantum states and exploitation of quantum resources for communication protocols. Currently, photons are considered as the optimal carriers of information, because they enable long-distance transition with resilience to decoherence and they are relatively easy to create and detect. Entanglement is a fundamental resource for quantum communication and information processing, and it is of particular importance for quantum repeaters. Hyperentanglement, a state where parties are entangled with two or more degrees of freedom (DoFs) simultaneously, provides an important additional resource because it increases data rates and enhances error resilience. However, in photonics, the channel capacity, i.e., the ultimate throughput, is fundamentally limited when dealing with linear elements. We propose a technique for achieving higher transmission rates for quantum communication by using hyperentangled states, based on multiplexing multiple DoFs on a single photon, transmitting the photon, and eventually demultiplexing the DoFs to different photons at the destination, using Bell state measurements. Following our scheme, one can generate two entangled qubit pairs by sending only a single photon. The proposed transmission scheme lays the groundwork for novel quantum communication protocols with higher transmission rates and refined control over scalable quantum technologies.
Quantum photonics is increasingly making use of the energy-time degree of freedom (DoF) to encode information. Its inherently high-dimensionality offers higher information capacity and robustness against noise. Most frequently, the energy-time DoF is exploited in the form of time bins and frequency bins, with direct applications in both quantum information processing tasks and quantum communication protocols. More recently, it has been used also in its pulse modes (or temporal modes) form, sets of states overlapping in time and frequency but kept orthogonal considering their temporal and spectral phase, whose difficult manipulation and characterisation made it less appealing for experimental applications. The production of states encoded in pulse modes has been demonstrated through sum frequency generation in waveguides [1] and parametric down conversion in bulk crystals [2], as well as the demonstration of schemes for creating hyper-entanglement among energy-time DoF and other high-dimensional DoFs [3], [4]. However, their implementation is still an area of continuous development and evolution, given the complexity of manipulating and characterising them.
"The field of quantum information science promises incredible enhancements in computing, metrology, simulation, and communication, but the challenge of creating, manipulating, and measuring the large quantum states has limited current implementations of such techniques. Such limitations affect photonic quantum information in particular, because photons lack the strong nonlinear interactions required for building up many-particle entangled states and performing multi-photon gates; nevertheless, because photons are currently the only ""flying qubit"", i.e., qubits that are mobile, they are a required resource for quantum communication protocols. One strategy to partially mitigate this limitation is to encode multiple entangled qubits on the different degrees of freedom of a single pair of photons. Such ""hyperentangled"" quantum states may be created with enough qubits to enable a whole new class of quantum information experiments. Furthermore, while nonlinear interactions are required to implement multi-qubit gates between qubits encoded on different particles, such gates can be implemented between qubits encoded on the same particle using only linear elements, enabling a much broader class of measurements. We use hyperentangled states to implement various quantum communication and quantum metrology protocols. Specifically, we demonstrate that hyperentangled photons can be used to increase the classical channel capacity of a quantum channel, transport quantum information between two remote parties efficiently and deterministically, and efficiently characterize quantum channels. We will discuss how to produce, manipulate, and measure hyperentangled states and discuss how entanglement in multiple degrees of freedom enables each technique. Finally, we discuss the limitations of each of these techniques and how they might be improved as technology advances."