Photons serve as essential carriers of quantum information in quantum computing, quantum networking, and quantum metrology. However, the lack of direct photon-photon interaction poses a fundamental barrier: the inherently probabilistic nature of nonlinear quantum operations. Active multiplexing has emerged as the critical strategy, transforming probabilistic nonlinear processes into deterministic building blocks for large-scale quantum systems. In this review, we explore the recent progress and potential architectures of photonic active multiplexing systems, ranging from the quasi-deterministic generation of single photons and complex entangled states to the realization of measurement-based quantum computing architectures. We also provide an overview of recent advancements in enabling hardware—including basic photon sources, detectors, switches, and their integration. By analyzing the state of the art and identifying key remaining challenges, we highlight how active multiplexing strategies serve as the cornerstone for the next generation of scalable photonic quantum information processing.
Photons serve as essential carriers of quantum information in quantum computing, quantum networking, and quantum metrology. However, the lack of direct photon-photon interaction poses a fundamental barrier: the inherently probabilistic nature of nonlinear quantum operations. Active multiplexing has emerged as the critical strategy, transforming probabilistic nonlinear processes into deterministic building blocks for large-scale quantum systems. In this review, we explore the recent progress and potential architectures of photonic active multiplexing systems, ranging from the quasi-deterministic generation of single photons and complex entangled states to the realization of measurement-based quantum computing architectures. We also provide an overview of recent advancements in enabling hardware—including basic photon sources, detectors, switches, and their integration. By analyzing the state of the art and identifying key remaining challenges, we highlight how active multiplexing strategies serve as the cornerstone for the next generation of scalable photonic quantum information processing.
Nonclassical states of light are an essential resource for many emerging quantum technologies and applications ranging from information processing, encrypted communications, and networking to sensing, metrology, and imaging. Nonlinear optical processes in solid-state materials are widely used for generating quantum light, including single photons, entangled-photon pairs, and quadrature-squeezed states. Recent advances in nonlinear photonics have enabled the functionality of benchtop nonlinear instruments to be scaled down to a single chip without sacrificing efficiency or degrading the key performance metrics. The dramatic improvement in the size, weight, power, cost, and stability enabled by photonic integrated circuits has been essential for enabling the chip-scale generation, manipulation, and detection of quantum light at a steadily increasing degree of complexity and scale. Within the last decade, the authors have seen the progression from few-component photonic circuits operating on two photons to arrays of 18 identical heralded single-photon sources and reconfigurable devices operating with more than 650 components for multidimensional entanglement and arbitrary two-photon quantum gates. In this review, the authors summarize the history and recent key technological developments of chip-scale nonlinear quantum light generation based on integrated nonlinear photonics, recent advances in heterogeneous integrated methods, and approaches for system-level integration and demonstrated applications.
The maturation of many photonic technologies from individual components to next-generation system-level circuits will require exceptional active control of complex states of light. A prime example is in quantum photonic technology: while single-photon processes are often probabilistic, it has been shown in theory that rapid and adaptive feedforward operations are sufficient to enable scalability. Here, we use simple “off-the-shelf” optical components to demonstrate active multiplexing—adaptive rerouting to single modes—of eight single-photon “bins” from a heralded source. Unlike other possible implementations, which can be costly in terms of resources or temporal delays, our new configuration exploits the benefits of both time and space degrees of freedom, enabling a significant increase in the single-photon emission probability. This approach is likely to be employed in future near-deterministic photon multiplexers with expected improvements in integrated quantum photonic technology.
Deterministic generation of single- and multiphoton states is a key requirement for large-scale optical quantum information and communication applications. While heralded single-photon sources (HSPSs) using nonlinear optical processes have enabled proof-of-principle demonstrations in this area of research, they are not scalable as their probabilistic nature severely limits their generation efficiency. We overcome this limitation by demonstrating a substantial improvement in HSPS efficiency via large-scale time multiplexing. Using an ultra-low loss, adjustable optical delay to multiplex 40 conventional HSPS photon generation processes into each operation cycle, we have observed a factor of 9.7(5) enhancement in efficiency, yielding a 66.7(24)% probability of collecting a single photon with high indistinguishability (90%) into a single-mode fiber per cycle. We also experimentally investigate the trade-off between a high single-photon probability and unwanted multiphoton emission. Upgrading our time-multiplexed source with state-of-the-art HSPS and single-photon detector technologies will enable the generation of >30 coincident photons with unprecedented efficiency.
In quantum technology, entanglement is the key resource to perform experiments in quantum computing, quantum communication, quantum sensing and metrology. Generation, characterization and distribution of entanglement deterministically is still an active research area. In contemporary, probabilistic entanglement sources based on parametric down-conversion process remain the workhorse for experimental demonstrations and practical applications, despite their inherent limitations of on-demand entangled photon generation. Over the years, three main technological architectures have evolved for generating probabilistic entangled-photon source; bulk-optics, waveguides and integrated photonic chips, each comprising several distinct architectural approaches tailored to different applications. This review article talks about the state of the art in probabilistic entangled photon source, examining the advancement from free space bulk non-linear optics to fiber based waveguides and scalable photonic chips with their current limitations, presenting a road map for researchers to choose the most appropriate platform for their quantum photonic applications.
In quantum technology, entanglement is the key resource to perform experiments in quantum computing, quantum communication, quantum sensing and metrology. Generation, characterization and distribution of entanglement deterministically is still an active research area. In contemporary, probabilistic entanglement sources based on parametric down-conversion process remain the workhorse for experimental demonstrations and practical applications, despite their inherent limitations of on-demand entangled photon generation. Over the years, three main technological architectures have evolved for generating probabilistic entangled-photon source; bulk-optics, waveguides and integrated photonic chips, each comprising several distinct architectural approaches tailored to different applications. This review article talks about the state of the art in probabilistic entangled photon source, examining the advancement from free space bulk non-linear optics to fiber based waveguides and scalable photonic chips with their current limitations, presenting a road map for researchers to choose the most appropriate platform for their quantum photonic applications.
ABSTRACT The rapid growth of global data traffic and the increasing demand for secure and scalable communication are driving the need for networking paradigms beyond the classical internet. The quantum internet has emerged as a promising solution, leveraging the principles of quantum mechanics to enable intrinsically secure communication, and computation. In this paper, we present a comprehensive review of the fundamental building blocks and system architectures required for large‐scale quantum networks, with a particular focus on photonic hardware platforms. We introduce key concepts of quantum information relevant to networking, including qubits, entanglement, and decoherence, and examine enabling technologies across different qubit platforms, highlighting photonic qubits as the primary carriers for long‐distance communication. We review major deterministic and probabilistic entanglement generation techniques, and analyze entanglement distribution strategies based on fiber, satellite, and quantum repeater architectures. Beyond the physical layer, we provide a system‐level perspective on quantum networking through protocol stack design, as well as challenges in entanglement routing, forwarding, and scheduling. Finally, we discuss experimental testbeds for entanglement distribution in both fiber‐based and free‐space systems, and outline the corresponding challenges and future research directions, including satellite‐assisted architectures for achieving scalable and globally connected quantum networks.