Unraveling two-photon entanglement via the squeezing spectrum of light traveling through nanofiber-coupled atoms

TL;DR

This paper demonstrates how the squeezing spectrum of light transmitted through nanofiber-coupled atoms reveals detailed information about two-photon entanglement, including phase and amplitude, enabling advanced diagnostics in quantum optics.

Contribution

It introduces a method to directly access and reconstruct the two-photon wavefunction's phase and amplitude from the squeezing spectrum in a nanofiber-atom system.

Findings

Quadrature squeezing observed in transmitted light.

Spectrum shape varies with atomic ensemble size.

Phase of the two-photon wavefunction inferred from detuning.

Abstract

We observe that a weak guided light field transmitted through an ensemble of atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the measured squeezing spectrum we gain direct access to the phase and amplitude of the energy-time entangled part of the two-photon wavefunction which arises from the strongly correlated transport of photons through the ensemble. For small atomic ensembles we observe a spectrum close to the lineshape of the atomic transition, while sidebands are observed for sufficiently large ensembles, in agreement with our theoretical predictions. Furthermore, we vary the detuning of the probe light with respect to the atomic resonance and infer the phase of the entangled two-photon wavefunction. From the amplitude and the phase of the spectrum, we reconstruct the real- and imaginary part of the time-domain wavefunction. Our characterization of the entangled two-photon component constitutes a diagnostic tool for quantum optics devices.