Light carrying orbital angular momentum constitutes an important resource for both classical and quantum information technologies. Its inherently unbounded nature can be exploited to generate high-dimensional quantum states or for channel multiplexing in classical and quantum communication in order to significantly boost the data capacity and the secret key rate, respectively. While the big potentials of light owning orbital angular momentum have been widely ascertained, its technological deployment is still limited by the difficulties deriving from the fabrication of integrated and scalable photonic devices able to generate and manipulate it. Here, we present a photonic integrated chip able to excite orbital angular momentum modes in an 800 m long ring-core fiber, allowing us to perform parallel quantum key distribution using two and three different modes simultaneously. The experiment sets the first steps towards quantum orbital angular momentum division multiplexing enabled by a compact and light-weight silicon chip, and further pushes the development of integrated scalable devices supporting orbital angular momentum modes.
Light carrying orbital angular momentum constitutes an important resource for both classical and quantum information technologies. Its inherently unbounded nature can be exploited to generate high-dimensional quantum states or for channel multiplexing in classical and quantum communication in order to significantly boost the data capacity and the secret key rate, respectively. While the big potentials of light owning orbital angular momentum have been widely ascertained, its technological deployment is still limited by the difficulties deriving from the fabrication of integrated and scalable photonic devices able to generate and manipulate it. Here, we present a photonic integrated chip able to excite orbital angular momentum modes in an 800 m long ring-core fiber, allowing us to perform parallel quantum key distribution using two and three different modes simultaneously. The experiment sets the first steps towards quantum orbital angular momentum division multiplexing enabled by a compact and light-weight silicon chip, and further pushes the development of integrated scalable devices supporting orbital angular momentum modes.
Quantum light sources are one of key devices for quantum information processing, and they are also the important foundation for applications such as in quantum computing, quantum communication, and quantum simulation. Improving the capacity of quantum information coding by using the quantum light source is a major challenge in the development of quantum information technology. Photons with a helical phase front can carry a discrete, unlimited but quantized amount of orbital angular momentum (OAM). The infinite number of states with different OAMs can greatly increase the capacity of optical communication and information processing in quantum regimes. To date photons carrying OAM have mainly been generated by using bulk crystals, which limits the efficiency and the scalability of the source. With the advancement of quantum photonic technology, many significant quantum photonic devices can now be realized on integrated chips. However, creating high-dimensional OAM quantum states at a micro-nano scale is still a challenge. And the research of harnessing high-dimensional OAM mode by using integrated quantum photonic technologies is still in its infancy. Here, the authors review the recent progress and discuss the integrated quantum light sources with OAM. The authors introduce the research progress of using OAM for both single photons and entangled photons and emphasize the exciting work on pushing boundaries in high-dimensional quantum states. This may pave the way for the research and practical applications of high-dimensional quantum light sources.
Orbital angular momentum (OAM) of photons provides a promising approach to enhance the capacity, robustness, and functionality of quantum communication systems in optical fibers. With many twist states available, OAM enables high-dimensional encoding, significantly increasing data rates and noise tolerance. This review explores sources, channels, and system architectures for OAM-based quantum communication in fibers. It compares free-space and integrated emitters, discussing in-fiber pair generation and mode conversion pathways that produce fiber-ready single photons and entangled states. For the channels, it details design principles and trade-offs for step-index and ring-core fibers that minimize intermodal coupling and reviews milestones in kilometer-scale single-photon transmission and high-dimensional entanglement transport. On the system side, the review examines coupling, multiplexing, and detection techniques—including mode (de)multiplexers, lanterns, and programmable sorters—and discusses transmission-matrix-based control methods to mitigate dispersion and bending effects. The review concludes with practical guidance and open challenges, such as improving mode selectivity and stability under real-world conditions; developing compact, efficient detectors for many modes; and integrating co-designed error correction schemes. These directions aim to bridge laboratory demonstrations with the deployment of scalable, high-dimensional fiber networks that harness OAM to significantly boost capacity, resilience, and functionality.
Going beyond two-state qubits, $q\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}d\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}s$ based on quantum states of high dimension constitute a rich resource in quantum information, and their exploitation will play a prominent role in next-generation technologies. Generation and manipulation of qudits have improved strongly over the last decades; their reliable transmission between remote locations remains the central challenge. The authors use an air-core fiber supporting orbital angular momentum (OAM) modes to faithfully transmit qudits. Four OAM quantum states and their superpositions are created, propagated over a 1.2-km fiber, and detected. Moreover, three quantum-key-distribution protocols are implemented.
Genuine random numbers can be produced beyond a shadow of doubt through the intrinsic randomness provided by quantum mechanics theories. While many degrees of freedom have been investigated for randomness generation, adequate attention has not been paid to the orbital angular momentum of light. In this work, we present a quantum random number generator based on the intrinsic randomness inherited from the superposition of orbital angular momentum modes caused by the cross talk inside a ring-core fiber. We studied two possible cases: a first one, device-dependent, where the system is trusted, and a second one, semi-device-independent, where the adversary can control the measurements. We experimentally realized the former, extracted randomness, and, after privacy amplification, we achieved a generation rate higher than 10 Mbit/s. In addition, we presented a possible realization of the semi-device-independent protocol using a newly introduced integrated silicon photonic chip. Our work can be considered as a starting point for novel investigation of quantum random number generators based on the orbital angular momentum of light.
Quantum communication consists of the reliable transmission of quantum states among several parties and looks toward the long-term goal of a Quantum Internet. Quantum Internet could open up a whole universe of new applications, spanning from fundamental physics and secure communications to remote quantum computing. Multiple degrees of freedom can be used for the distribution of the quantum states, such as polarization, frequency, time and space. In particular, Orbital Angular Momentum (OAM) of light is one of the most promising thanks to its unbounded nature, albeit challenging to manipulate. OAM has been largely investigated both for classical and quantum communications, allowing for enhanced data rate in classical links and determining a high-dimensional basis for quantum communication. Here, we report our recent results related to quantum states encoded in the orbital angular momentum of light, proving the capability of preparing, manipulating, transmitting and measuring high-dimensional quantum states through a multimode fibre.
The field of quantum communication is thriving as a complement to conventional telecommunication with its distinctive feature of absolute security. As the core technology for delivering quantum information, substantial advances in quantum communication have already been demonstrated on various platforms, including photonic systems. Among all of them, the orbital angular momentum (OAM) of photons with its infinite Hilbert space has attracted much attention and has been widely employed in both classical and quantum regimes. In particular, many types of fiber have been designed and fabricated to allow transmitting OAM of photons. Here, we review recent progress in transmitting OAM quantum states through different types of fiber, including few-mode fibers, multi-mode fibers, ring-core fibers, and single-mode fibers. We also discuss the challenges and prospects of quantum OAM in fibers.