Spatial modes of photons offer a rich encoding resource for high-dimensional quantum information processing. Multiplane light conversion (MPLC) enables spatial mode transformation and is applicable in both classical and quantum optics. Here, we demonstrate a polymer-based MPLC device, fabricated via femtosecond laser three-dimensional printing, that realizes high-dimensional quantum logic gates in an ultracompact format. Specifically, we design a three-dimensional Hadamard gate by training a diffractive neural network to generate the required phase distribution. The device is evaluated through quantum process tomography at the single-photon level within spatial modes, achieving a fidelity of 90%. Compared to traditional spatial light modulator-based implementations, our approach integrates spatial mode manipulation into a miniaturized photonic platform. These results highlight the feasibility of polymer-based MPLC for compact quantum logic and open possibilities for scalable, high-dimensional quantum information processing on integrated photonic chips.
Spatial modes of photons offer a rich encoding resource for high-dimensional quantum information processing. Multiplane light conversion (MPLC) enables spatial mode transformation and is applicable in both classical and quantum optics. Here, we demonstrate a polymer-based MPLC device, fabricated via femtosecond laser three-dimensional printing, that realizes high-dimensional quantum logic gates in an ultracompact format. Specifically, we design a three-dimensional Hadamard gate by training a diffractive neural network to generate the required phase distribution. The device is evaluated through quantum process tomography at the single-photon level within spatial modes, achieving a fidelity of 90%. Compared to traditional spatial light modulator-based implementations, our approach integrates spatial mode manipulation into a miniaturized photonic platform. These results highlight the feasibility of polymer-based MPLC for compact quantum logic and open possibilities for scalable, high-dimensional quantum information processing on integrated photonic chips.
High-dimensional entanglement offers a variety of advantages for both fundamental and applied applications in quantum information science. A central building block for such applications is a programmable processor of entangled states, which is crucial for the certification, manipulation, and distribution of high-dimensional entanglement. The leading technology for processing photons is integrated multiport interferometers. However, such devices are incompatible with structured light and their scaling is challenging. Here, we unlock these limitations by demonstrating a reconfigurable processor of entangled photons in high dimensions that is based on multiplane light conversion (MPLC), a technology that has recently been developed for multiplexing hundreds of spatial modes for classical communication. We use our programmable MPLC platform to certify three-dimensional entanglement in two mutually unbiased bases, perform 400 arbitrary random transformations on entangled photons, and convert the mode basis of entangled photons for entanglement distribution.
High-dimensional entangled photons are a key resource for advanced quantum information processing. Efficient processing of high-dimensional entangled photons requires the ability to synthesize their state using general unitary transformations. The leading technology for processing photons in high-dimensions is integrated multiport interferometers. However, such devices are incompatible with free-space and fiber-based systems, and their architecture poses significant scaling challenges. Here we unlock these limitations by demonstrating a reconfigurable processor of entangled photons that is based on multi-plane light conversion (MPLC), a technology that was recently developed for multiplexing hundreds of spatial modes for classical free-space and fiber communication. To demonstrate the flexibility of MPLC, we perform four key tasks of quantum information processing using the same MPLC hardware: entanglement certification, tailored two-photon interference, arbitrary state transformations, and mode conversion. Based on the high degree of control we obtain, we expect MPLC will become a leading platform for future quantum technologies.
We present a compact and efficient realization of Multi-Plane Light Conversion (MPLC) for full vectorial light modulation, enabling control over polarization, phase, and amplitude. Conventional MPLC implementations based on phase-only modulation suffer from losses and limited polarization control, while metasurface-based solutions require complex nanofabrication processes. Our approach employs laser-written birefringent waveplates in silica slides, each with fixed retardance and a spatially varying optical axis orientation. The structures are fabricated using direct laser writing of nanogratings in silica, achieving ~90% transmission and ~1–2 µm spatial resolution. We demonstrate high-dimensional quantum gates and a polarization-controlled single-photon CNOT gate using spatial and polarization degrees of freedom. This cleanroom-free platform shows strong potential for high-dimensional quantum processing, optical communication, and beam shaping, with future prospects for extending modulation into the frequency domain.
Abstract While the spatial mode of photons is widely used in quantum cryptography, its potential for quantum computation remains largely unexplored. Here, we showcase the use of the multi-dimensional spatial mode of photons to construct a series of high-dimensional quantum gates, achieved through the use of diffractive deep neural networks (D2NNs). Notably, our gates demonstrate high fidelity of up to 99.6(2)%, as characterized by quantum process tomography. Our experimental implementation of these gates involves a programmable array of phase layers in a compact and scalable device, capable of performing complex operations or even quantum circuits. We also demonstrate the efficacy of the D2NN gates by successfully implementing the Deutsch algorithm and propose an intelligent deployment protocol that involves self-configuration and self-optimization. Moreover, we conduct a comparative analysis of the D2NN gate’s performance to the wave-front matching approach. Overall, our work opens a door for designing specific quantum gates using deep learning, with the potential for reliable execution of quantum computation.
This thesis explores the development and application of multi-plane light conversion (MPLC) technol-ogy, focusing on its integration into experimental setups that push the boundaries of quantum opticsand spatial state tomography. Central to this study is a custom-built, research-grade MPLC devicedesigned around a programmable spatial light modulator (SLM), which facilitates two groundbreak-ing experiments: the manipulation of high-dimensional qudits for quantum gate operations, and thedevelopment of a high-dimensional Stokes-space spatial beam analyser for single-shot spatial statetomography.The first experiment involved implementing quantum gates — specifically the X-gate, Z-gate, andDFT-gate — for a 17-dimensional qudit, represented through the first 17 azimuthal Laguerre-Gaussianspatial modes on a MPLC device. This experiment not only demonstrated MPLC’s capability tohandle complex, high-dimensional quantum states but also underscored its potential to enhance thescalability and efficiency of quantum computing architectures. By leveraging the precise control overspatial modes afforded by MPLC and the programmability of SLM-based MPLC, the experimentdemonstrated high-dimensional gate operations, paving the way for more complex quantum computingoperations for qudits.The second project focused on using MPLC to develop a device capable of performing high-dimensional Stokes-space spatial beam analysis. This innovative instrument marks a significantbreakthrough in optical beam characterisation, providing a reference-free, single-shot technique forconducting spatial state tomography on beams characterisable by a six-mode or six-dimensional system.The device’s capacity to swiftly and precisely characterise the wavefront and coherence of opticalfields renders it an invaluable asset for advancing optical communication technologies and enhancingoptical sensing methodologies.Throughout this thesis, the theoretical foundations of MPLC technology are presented, with adetailed account of the MPLC device design and operational principles. Experimental results arepresented to validate the effectiveness of the MPLC device in both quantum gate operations andspatial state tomography. Comparisons with existing technologies highlight the MPLC’s enhancedperformance and versatility.This work not only expands the understanding and application of MPLC in quantum and opticalsciences but also sets the stage for future innovations in these fields. The continuous refinement andadaptation of MPLC technology promise to unlock new possibilities in both fundamental research andpractical applications.
Integrated quantum photonic circuit is a promising platform for the realization of quantum information processing in the future. To achieve the large-scale quantum photonic circuits, the applied quantum logic gates should be as small as possible for the high-density integration on chips. Here, we report the implementation of super-compact universal quantum logic gates on silicon chips by the method of inverse design. In particular, the fabricated controlled-NOT gate and Hadamard gate are both nearly a vacuum wavelength, being the smallest optical quantum gates reported up to now. We further design the quantum circuit by cascading these fundamental gates to perform arbitrary quantum processing, where the corresponding size is about several orders smaller than that of previous quantum photonic circuits. Our study paves the way for the realization of large-scale quantum photonic chips with integrated sources and can have important applications in the field of quantum information processes.