Title: Variational processing of partially coherent light in photonic integrated circuits
Abstract: Classical and quantum optical fields are naturally described in terms of modes. Modal decompositions underpin our understanding of the generation, propagation, and measurement of multimode light, as exemplified by the Karhunen–Loève expansion for partially coherent fields, density-matrix eigendecompositions, Schmidt decompositions of bipartite states, and the Bloch–Messiah decomposition of Gaussian states. Conventional approaches to such decompositions rely on tomographic measurements and projections onto predefined mode bases, typically requiring substantial prior knowledge of the mode geometry.
Networks of Mach–Zehnder interferometers (MZIs) provide a powerful platform for manipulating and measuring coherent multimode light. Here, we extend self-configuring MZI meshes to the measurement, processing, and generation of partially coherent classical and quantum optical fields. I will introduce a general framework for modal decomposition using variational optical processors: self-configuring interferometric networks in which parameters are optimized sequentially to maximize a chosen output signal. Through this adaptive optimization, the device physically separates the input field into orthogonal components corresponding to the desired decomposition, whether Karhunen–Loève, Schmidt, or Bloch–Messiah, without requiring prior knowledge of the underlying modal structure.
By sequentially training the processor on the largest eigenvalues or singular values, this approach achieves favorable scaling in both hardware complexity and measurement resources, enabling efficient and complete characterization of high-dimensional multimode light. I will also present an experimental realization of a variational optical processor implemented on an integrated photonic chip, designed to process spatial partial coherence. This device demonstrates on-chip coherence tomography and highlights new opportunities for separating and processing optical fields based on their coherence properties, with potential applications in imaging, sensing, and quantum information processing.
Bio: Charles Roques-Carmes is an Assistant Professor at the Institute of Science and Technology Austria (ISTA). His lab studies and engineers subwavelength light–matter interactions to unlock quantum technologies, advanced microscopes, and next-generation communications and computing platforms—combining rigorous theory with ultrafast electron microscopy, X-ray imaging, and quantum sensing to turn insights into devices. Before joining ISTA, Charles was a Stanford Science Fellow at Stanford University and a Visiting Scientist at MIT, where he earned his PhD in Electrical Engineering and Computer Science in 2022. Charles has delivered 40+ invited talks at major venues including APS, CLEO, and SPIE.
In 2025, he received the inaugural Photonics Innovation Award in honor of Federico Capasso for pioneering achievements that broaden photonics’ frontiers and connect fundamentals to real-world impact; Charles is widely regarded as one of the founders of the emerging field of nanophotonic scintillation. His honors include numerous distinctions such as Forbes 30 Under 30 (Science, 2023), the Stanford Science Fellowship, the MathWorks Engineering Fellowship, the Robert B. Guenassia Award, and a Carnot Foundation Fellowship. He holds M.S. degrees from MIT (2018) and École Polytechnique (2016), and a B.S. from École Polytechnique (2015).
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