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  • Open Access

Diagnosing Electronic Phases of Matter Using Photonic Correlation Functions

Gautam Nambiar*, Andrey Grankin, and Mohammad Hafezi

  • *Contact author: nambiar@terpmail.umd.edu
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Phys. Rev. X 15, 041020 – Published 4 November, 2025

DOI: https://doi.org/10.1103/67zs-hqf3

Abstract

In the past couple of decades, there have been significant advances in measuring quantum properties of light, such as quadratures of squeezed light and single-photon counting. Here, we explore whether such tools can be leveraged to probe electronic correlations in the many-body quantum regime. Specifically, we show that it is possible to probe certain spin, charge, and topological orders in an electronic system by measuring the correlation functions of scattered photons. We construct a mapping from the correlators of the scattered photons to those of a correlated insulator, particularly for Mott insulators described by a single-band Fermi-Hubbard model at half filling. We show that frequency filtering before photodetection plays a crucial role in determining this mapping. We find that if the ground state of the insulator is a gapped spin liquid, a photon-pair correlation function, i.e., G(2), can detect the presence of anyonic excitations with fractional mutual statistics. Moreover, we show that correlations between electromagnetic quadratures can be used to detect expectation values of static spin chirality operators on both the kagome and triangular lattices, thus being useful in detecting chiral spin liquids. More generally, we show that a series of hitherto unmeasured spin-spin and spin-charge correlation functions of the material can be extracted from photonic correlations. This work opens up access to probe correlated materials, beyond the linear-response paradigm, by detecting quantum properties of scattered light.

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Popular Summary

The remarkable behaviors of materials—such as superconductivity and magnetism—arise from complex correlations among electrons. Much of condensed matter physics focuses on uncovering these correlations experimentally and explaining them theoretically. Traditional measurements, such as electrical conductivity or magnetic susceptibility, each probe a specific type of electronic correlation. Yet, given the vast range of electronic systems that remain poorly understood, researchers need new tools that can access many more types of correlations than current techniques allow. We propose an approach that borrows tools from quantum optics to probe electronic correlations that have so far been out of reach.

Typical optical experiments measure only the intensity of light scattered from a material—that is, how many photons are detected. But in quantum optics, far more detailed measurements are possible, including two-photon correlations and phase-sensitive quadrature correlations. We establish a direct “dictionary” linking each of these optical observables to the electronic correlations they reveal. Using this framework, we show how such measurements could, for instance, access spin chirality—a property describing how spins twist collectively—or detect “anyons,” exotic excitations that obey fractional statistics.

Our work opens a new frontier for exploring quantum materials by showing how the quantum properties of light can encode the quantum properties of matter.

Article Text

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Phys. Rev. X 15, 041020– Published 4 November, 2025
  • Received 23 December 2024
  • Revised 21 July 2025
  • Accepted 9 October 2025
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