Integrated photonic platforms provide a powerful route toward scalable and stable quantum light sources. In this presentation, we explore how quantum correlations can be generated, distributed, and characterized in the frequency domain using integrated photonic frequency combs. Relying on Kerr nonlinear microresonators operated below and above threshold, we demonstrate the generation of discrete entangled photon pairs as well as bright multipartite quantum states involving many spectral modes. We show how frequency multiplexing enables both multi-user quantum communication and enhanced data rates, while remaining fully compatible with integrated photonic circuits. Beyond bipartite entanglement, we report direct signatures of genuine multipartite quantum correlations in bright frequency combs. These results highlight integrated photonics as a versatile and scalable platform for multimode quantum technologies in communication, sensing, and metrology.
Integrated photonic platforms provide a powerful route toward scalable and stable quantum light sources. In this presentation, we explore how quantum correlations can be generated, distributed, and characterized in the frequency domain using integrated photonic frequency combs. Relying on Kerr nonlinear microresonators operated below and above threshold, we demonstrate the generation of discrete entangled photon pairs as well as bright multipartite quantum states involving many spectral modes. We show how frequency multiplexing enables both multi-user quantum communication and enhanced data rates, while remaining fully compatible with integrated photonic circuits. Beyond bipartite entanglement, we report direct signatures of genuine multipartite quantum correlations in bright frequency combs. These results highlight integrated photonics as a versatile and scalable platform for multimode quantum technologies in communication, sensing, and metrology.
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.
This experimental work demonstrates multipartite quantum correlation in bright frequency combs out of a microresonator integrated on silicon nitride operating above its oscillation threshold. Multipartite features, going beyond so far reported two-mode correlation, naturally arise due to a cascade of nonlinear optical processes, making a single-color laser pump sufficient to initiate their generation. Our results show the transition from two-mode to multipartite correlation, witnessed by noise reductions as low as − 2.5 dB and − 2 dB , respectively, compared to corresponding classical levels. A constant of the movement of the nonlinear interaction Hamiltonian is identified and used to asses the multipartite behavior. Reported demonstrations pave the way to next generation on-chip multipartite sources for quantum technologies applications.
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.
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. The combination with control techniques, using accessible state-of-the-art telecommunications infrastructure, can constitute a powerful frequency-domain quantum circuit with new functionalities and represents an approach towards realizing practical large-scale controllable quantum systems. In this presentation, we will review approaches for the efficient realization of quantum frequency combs in on-chip waveguide structures and micro-resonators. We will show their applicability for the realization of quantum systems with considerably enhanced complexity, particularly generating and manipulating on-chip multi-photon and high-dimensional quantum states as well as discrete high-dimensional cluster states, laying at the basis of measurement based-quantum computing. Building on this, the realization of frequency-domain Hong-Ou-Mandel interference of independent photons, fundamental to quantum information processing, as well as an outlook on frequency-domain circuits will be discussed.
Complex optical photon states with entanglement shared among several modes are critical to improving our fundamental understanding of quantum mechanics and have applications for quantum information processing, imaging, and microscopy. We demonstrate that optical integrated Kerr frequency combs can be used to generate several bi- and multiphoton entangled qubits, with direct applications for quantum communication and computation. Our method is compatible with contemporary fiber and quantum memory infrastructures and with chip-scale semiconductor technology, enabling compact, low-cost, and scalable implementations. The exploitation of integrated Kerr frequency combs, with their ability to generate multiple, customizable, and complex quantum states, can provide a scalable, practical, and compact platform for quantum technologies.
The on-chip generation of optical quantum states will enable accessible advances for quantum technologies. We demonstrate that integrated quantum frequency combs (based on high-Q microring resonators made from a CMOS-compatible, high refractive-index doped-glass platform) can enable the generation of pure heralded single photons, cross-polarized photon pairs, as well as bi- and multi-photon entangled qubit states over a broad frequency comb covering the S, C, L telecommunications band, with photon frequencies corresponding to standard telecommunication channels spaced by 200 GHz. Exploiting a self-locked, intra-cavity excitation configuration, a highly-stable source of multiplexed heralded single photons is demonstrated, operating continuously for several weeks with less than 5% fluctuations. The photon bandwidth of 110 MHz is compatible with quantum memories, and high photon purity was confirmed through single-photon auto-correlation measurements. In turn, by simultaneously exciting two orthogonal polarization mode resonances, we demonstrate the first realization of type-II spontaneous FWM (in analogy to type-II spontaneous parametric down-conversion), allowing the direct generation of orthogonally-polarized photon pairs on a chip. By using a double-pulse excitation, we demonstrate the generation of time-bin entangled photon pairs. We measure qubit entanglement with visibilities above 90%, enabling the implementation of quantum information processing protocols. Finally, the excitation field and the generated photons are intrinsically bandwidth-matched due to the resonant characteristics of the ring cavity, enabling the multiplication of Bell states and the generation of a four-photon time-bin entangled state. We confirm the generation of this four-photon entangled state through four-photon quantum interference.