Fiber-optical networks are well established to accommodate global data traffic via coherent information transmission. The next generation of telecommunications will require the integration of quantum information into fiber-optic networks, e.g., for quantum key distribution. A promising and scalable route to enable quantum networking is encoding quantum information into the frequency of photons. While the cointegration of frequency-entangled photons with coherent information transmission is achieved via spectral multiplexing, more resource-efficient approaches are required. In this work, we introduce and experimentally demonstrate a transceiver concept that enables the transmission of coherent and frequency-entangled photons over a single-frequency channel. Our concept leverages the serrodyne technique via electro-optic phase modulation leading to very different dynamics for entangled and coherent photons. This enables temporal multiplexing of the respective signals. We demonstrate the preservation of entanglement over the channel in the presence of coherent light. Our approach reveals a strong potential for efficient bandwidth use in hybrid networks.

Co-transmission of coherent signals and frequency-entangled photons over a single frequency channel is experimentally demonstrated via the serrodyne technique. Our approach preserves entanglement and paves the way towards scalable and efficient hybrid quantum coherent networks.

Today's quantum technology relies on the realization of large-scale non-classical systems in practical formats to enable quantum-accelerated computing, secure communications and enhanced sensing. Optical on-chip quantum frequency combs, characterized by many equidistantly spaced frequency modes, allow the storage of large amounts of quantum information and together with control mechanisms can provide practical large-scale quantum systems. In this contribution, we present recent advances on the controlled generation and use of quantum frequency combs for information processing. First, we demonstrate an electrically-pumped laser-integrated quantum light source of two- and high-dimensional maximally entangled photons. We exploit a hybrid InP-SiN approach which allows to include a filter, a gain section and a parametric photon pair source in a single system. Second, we demonstrate the generation of high-dimensional bi-photon quantum frequency combs with tunable entropies by exploiting a novel excitation technique and spectral filtering. Using this, we reveal unidirectional bosonic quantum walks, asymmetric energy transfer, and directional entanglement transport.

We demonstrate an electrically-pumped laser-integrated quantum light source of entangled photons. The hybrid InP-Si 3 N 4 source emits frequency-bin entangled two- and high-dimensional quantum photonic states in the telecommunication C-band. This source is fully integrated, compact, and field-deployable, bringing the required scalability and stability to the quantum photonic sources for quantum information processing.

We generate high-dimensional bi-photon quantum frequency combs with tunable entropies exploiting the second-order nonlinearity of a periodically-poled lithium niobate waveguide through a novel pumping and filtering scheme. Using these quantum states with varying degrees of entanglement, we demonstrate unidirectional bosonic quantum walks, asymmetric energy transfer, and entanglement transport. Our non-maximally entangled quantum states can serve as excellent testbeds for several computational protocols. Moreover, we achieve the steering of the directionality in a scalable format, which enables a new control mechanism for quantum walks as well as novel modification means of joint probability distributions.

Integrated quantum photonics can realize and process optical entangled quantum states in highly compact, robust, and scalable chips thereby enabling chip scale implementations of long-distance quantum-secured communication, quantum-accelerated information processing, and non-classical metrology [1]. Notably, all previous on-chip entangled quantum photonic sources have relied on an external laser to excite nonlinear parametric processes, thereby making these systems overall non-reproducible, bulky, impractical, and thus unsuitable for out-of-lab use as well as production at large scale [2]. To date, the major challenge inhibiting a fully on-chip quantum light system is to integrate a stable, tunable laser together with a high rejection filter that eliminates laser sideband noise [3], [4] and a nonlinear parametric source of entangled photons. Fig. 1 A) laser-integrated photonic quantum light source of frequency-bin entangled photon states: an electrically pumped inp gain-section, i.e. A reflective semiconductor optical amplifier (rsoa) providing optical gain, is coupled to a si3n4 chip containing a three microring resonator (r1, r2, and r3) vernier filter and a mach-zehnder interferometer (mzi) with a sagnac loop mirror. B) measurements utilizing single photon detectors allowed to determine an smsr≈ 112 db, and an ase suppression of> 56 db. C) car for respective frequency pairs for an excitation power of 3.9 mw. D) density matrices of two-dimensional (qubit) and three-dimensional (qutrit) frequency-bin entangled states reconstructed via quantum state tomography (qst).

Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter ($> 55$ dB) exploiting the Vernier effect and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si$_3$N$_4$ low-loss microring filter system, and demonstrates high performance parameters, i.e., a pair emission over four resonant modes in the telecom band (bandwidth $\sim 1$ THz), and a remarkable pair detection rate of $\sim 620$ Hz at a high coincidence-to-accidental ratio of $\sim 80$. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), verified by quantum interference measurements with visibilities up to $96\%$ (violating Bell-inequality) and by density matrix reconstruction through state tomography showing fidelities of up to $99\%$. Our approach, leveraging a hybrid photonic platform, enables commercial-viable, low-cost, compact, light-weight, and field-deployable entangled quantum sources, quintessential for practical, out-of-lab applications, e.g., in quantum processors and quantum satellite communications systems.

We demonstrate an electrically-pumped laser-integrated quantum light source of two and high-dimensional entangled photons. Our hybrid InP-Si 3 N 4 source is fully-integrated, compact, and field-deployable, bringing the required scalability to photonic quantum processing.