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Programmable Quantum Networks in Integrated Multimode Waveguides

van der Heide, Leonie, Rothe, Stefan, Pepijn W. H. Pinkse

Published Sep 27, 2025• 0 citations
OpenAlex

Abstract

This Master’s project aims to implement a programmable linear quantum network within a single integrated multimode waveguide slab. Multimode waveguides naturally support strong spatial mode mixing and coupling, enabling high optical connectivity which is critical for scalable quantum computing platforms. Using simulations of traditional wavefront shaping through the multimode waveguide, we show the feasibility of this method.

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This Master’s project aims to implement a programmable linear quantum network within a single integrated multimode waveguide slab. Multimode waveguides naturally support strong spatial mode mixing and coupling, enabling high optical connectivity which is critical for scalable quantum computing platforms. Using simulations of traditional wavefront shaping through the multimode waveguide, we show the feasibility of this method.
Entanglement between large numbers of quantum modes is the quintessential resource for future technologies such as the quantum internet. Conventionally, the generation of multimode entanglement in optics requires complex layouts of beamsplitters and phase shifters in order to transform the input modes into entangled modes. Here we report the highly versatile and efficient generation of various multimode entangled states with the ability to switch between different linear optics networks in real time. By defining our modes to be combinations of different spatial regions of one beam, we may use just one pair of multi-pixel detectors in order to measure multiple entangled modes. We programme virtual networks that are fully equivalent to the physical linear optics networks they are emulating. We present results for N=2 up to N=8 entangled modes here, including N=2, 3, 4 cluster states. Our approach introduces the highly sought after attributes of flexibility and scalability to multimode entanglement. Multi-partite entanglement is essential not only to understand large quantum ensembles but also to build useful quantum technologies. Armstronget al. demonstrate multimode entanglement of up to eight modes using programmable virtual networks based on linear optics that can be switched in real time.
Entanglement is an essential resource at the heart of quantum information processing and quantum metrology. Moreover, multimode entanglement is necessary for the fabrication of complex quantum networks, in which entanglement is distributed among several quantum modes. The nodes of the network are made from quantum modes, which are the fundamental information carriers, and these nodes are interconnected by a series of channels through which the information flows. Multimode entanglement is traditionally viewed as many-body correlations, in which the nodes are spatially separated and can be measured individually. In our multimode resource, all of the modes travel together within a single laser beam [1]. This co-propagation of modes enables us to construct on-demand quantum networks via arbitrary shaping within the measurement process.
The ability to implement reconfigurable linear optical circuits is a fundamental building block for the implementation of scalable quantum technologies. Here, we implement such circuits in a multimode fiber by harnessing its complex mixing using wavefront shaping techniques. We program linear transformations involving spatial and polarization modes of the fiber and experimentally demonstrate their accuracy and robustness using two-photon quantum states. In particular, we illustrate the reconfigurability of our platform by emulating a tunable coherent absorption experiment, where output probabilities of single- and two-photon survivals can be controlled. By demonstrating complex, reprogrammable, reliable, linear transformations, with the potential to scale, our results highlight the potential of complex media driven by wavefront shaping for quantum information processing.
Multiple-scattering has become an exciting platform for quantum optical experiments [1-5]. In wavefront shaping one uses spatial light modulation in combination with strongly scattering materials to achieve control over light in space and time [6]. Recent wavefront-shaping experiments have transformed opaque media in equivalents of waveguides, lenses, waveplates and optical pulse compressors that are inherently robust against disorder and imaging errors. In quantum optics, interference of quantum states is studied in often complicated optical circuits. This requires a close-to-perfect implementation of the setup and provides little flexibility or programmability of the interference. We implement the radically different approach to apply wavefront shaping on quantum light to obtain ample flexibility in optimization and manipulation of the quantum interference. This offers unique opportunities for sample characterization, quantum patterning, secure key generation, or quantum transport through disordered media.
The distribution of entanglement in quantum networks will enable the next generation of technologies in quantum-secured communications, distributed quantum computing and sensing. Future quantum networks will require dense connectivity, allowing multiple users to share entanglement in a reconfigurable and multiplexed manner, while long-distance connections are established through the teleportation of entanglement, or entanglement swapping. Although several recent works have demonstrated fully connected, local multi-user networks based on multiplexing, extending such networks to a global network architecture of interconnected local networks remains an outstanding challenge. Here we demonstrate the next step in the evolution of multiplexed quantum networks-a prototype global reconfigurable network in which entanglement is routed and teleported in a flexible and multiplexed manner between two local four-user networks. At the heart of our network is a programmable 8 × 8-dimensional multi-port circuit that harnesses the natural mode-mixing process inside of a multi-mode fibre to implement on-demand high-dimensional operations on two independent photons carrying eight transverse-spatial modes. Our circuit design allows us to break away from the limited planar geometry and bypass the control and fabrication challenges of conventional integrated photonic platforms. Our demonstration highlights the potential of this architecture for enabling large-scale, global quantum networks that offer versatile connectivity while being fully compatible with an existing communications infrastructure.
Multimode optical interferometers represent the most viable platforms for the successful implementation of several quantum information schemes that take advantage of optical processing. Examples range from quantum communication and sensing, to computation, including optical neural networks, optical reservoir computing, or simulation of complex physical systems. The realization of such routines requires high levels of control and tunability of the parameters that define the operations carried out by the device. This requirement becomes particularly crucial in light of recent technological improvements in integrated photonic technologies, which enable the implementation of progressively larger circuits embedding a considerable amount of tunable parameters. We formulate efficient procedures for the characterization of optical circuits in the presence of imperfections that typically occur in physical experiments, such as unbalanced losses and phase instabilities in the input and output collection stages. The algorithm aims at reconstructing the transfer matrix that represents the optical interferometer without making any strong assumptions about its internal structure and encoding. We show the viability of this approach in an experimentally relevant scenario, defined by a tunable integrated photonic circuit, and we demonstrate the effectiveness and robustness of our method. Our findings can find application in a wide range of optical setups, based on both bulk and integrated configurations.