- Open Access
Variational Processing of Multimode Squeezed Light
PRX Quantum 7, 020311 – Published 20 April, 2026
DOI: https://doi.org/10.1103/mcmq-qf4p
Abstract
Integrated multimode quantum optics is a promising platform for scalable continuous-variable quantum technologies leveraging multimode squeezing in both the spatial and spectral domains. However, on-chip measurement, routing and processing the relevant “supermodes” over which the squeezing resource is distributed still scales quadratically with the number of modes , causing a rapid increase in photonic circuit size and number of required measurements. Here, we introduce a variational scheme, relying on self-configuring photonic networks (SCNs) that learn and extract the most-squeezed supermodes sequentially, reducing both the circuit size and the experimental overhead. Using homodyne measurement as a cost function, a sparse SCN discovers the most significant supermodes using physical elements and optimization steps. We analyze and numerically simulate these architectures for both real-space and frequency-domain implementations, showing a fidelity close to unity between the learned circuit and the supermode decomposition, even in the presence of optical losses and detection noise. In the frequency domain, we show that circuit size can be further reduced by using inverse-designed surrogate networks, which emulate the layers learned thus far. Using two different frequency encoding schemes—uniformly and nonuniformly spaced frequency bins—we reduce an entire network (learning all supermodes) to and even modulated cavities. Our results point toward chip-scale, resource-efficient quantum processing units and demultiplexers for continuous variable processing in multimode quantum optics, with applications ranging from quantum communication, metrology, and computation.
Physics Subject Headings (PhySH)
Popular Summary
Squeezed light—light with reduced quantum noise—is a key resource for quantum technologies such as sensing, communication, and computation. Modern photonic platforms can generate squeezed light distributed across many spatial or spectral modes simultaneously. However, the useful quantum correlations are typically encoded in special superpositions of these modes, called supermodes, which are not directly accessible in experiments. Identifying and extracting these supermodes becomes increasingly difficult as the number of modes grows. In this work, we introduce a method for processing multimode squeezed light using variational photonic circuits. Our approach employs a self-configuring optical network that learns the structure of the quantum state directly from measurement feedback. By optimizing homodyne measurements, the network sequentially identifies the most strongly squeezed supermodes and routes them to specific outputs. This strategy significantly reduces the hardware complexity required to analyze multimode squeezed states and provides a scalable route toward integrated processors for high-dimensional quantum light with applications in sensing, communication, and continuous-variable quantum computing.
Article Text
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