Two-Photon Bandwidth of Hyper-Entangled Photons in Complex Media

TL;DR

This paper shows that hyper-entangled photon pairs maintain stable spatial correlations over broad bandwidths in complex media, enabling enhanced quantum imaging and communication.

Contribution

It introduces the concept of two-photon bandwidth, demonstrating that spectral anti-correlation cancels chromatic dispersion, extending the usable bandwidth in complex media.

Findings

Two-photon bandwidth exceeds classical limits.

Chromatic modal dispersion is canceled by spectral anti-correlation.

Broadband wavefront shaping of quantum states is achieved.

Abstract

When light propagates through complex media, its output spatial distribution is highly sensitive to its wavelength. This fundamentally limits the bandwidth of applications ranging from imaging to communication. Here, we demonstrate analytically and numerically that the spatial correlations of hyper-entangled photon pairs, simultaneously entangled spatially and spectrally, remain stable across a broad bandwidth: The chromatic modal dispersion experienced by one photon is canceled to first order by its spectrally anti-correlated twin, defining a "two-photon bandwidth" that can far exceed its classical counterpart. We illustrate this modal dispersion cancellation in multimode fibers, thin diffusers and blazed gratings, and demonstrate its utility for broadband wavefront shaping of quantum states. These findings advance our fundamental understanding of quantum light in complex media with applications in quantum imaging, communication, and sensing.