Development of Biphoton Entangled Light Spectroscopy (BELS) using Bell pairs

TL;DR

Biphoton Entangled Light Spectroscopy (BELS) uses polarization-entangled Bell pairs and two-photon interference to probe material properties through changes in joint polarization and path correlations, offering a quantum-enhanced spectroscopic method.

Contribution

This work introduces BELS, a novel quantum spectroscopy technique that maps polarization transformations to Bell state changes, enabling new insights into material properties using entangled photons.

Findings

Successfully measured birefringence in an anisotropic dielectric.

Demonstrated Faraday rotation measurement in Tb3Ga5O12.

Mapped optical element effects to Bell state transformations.

Abstract

We introduce Biphoton Entanglement Light Spectroscopy (BELS), a quantum spectroscopic technique that employs polarization entangled Bell pairs and two photon interference to probe material properties. In BELS, the measured signal arises not from single photon intensities but from changes in the joint polarization and path correlations of biphoton Bell pairs transmitted through or scattered by a sample and analyzed via cross channel coincidences. A key concept of BELS is the explicit mapping between Jones matrix operations and transformations within the Bell state manifold. Optical elements that are equivalent under classical polarization optics can produce qualitatively distinct signatures in the coincidence landscape when interrogated with entangled photons. We demonstrate that linear birefringence and Faraday rotation generate orthogonal admixtures of Bell states, yielding experimentally distinguishable coincidence channels within a single measurement. We measure birefringence in an anisotropic dielectric and Faraday rotation in $\text{Tb}_3\text{Ga}_5\text{O}_{12}$. By mapping the changes to the photonic entanglement, BELS establishes a new framework for future entanglement enhanced spectroscopy, a potentially powerful approach in characterizing quantum materials, nanophotonic devices, and light matter interactions perhaps eventually at a fundamentally quantum level.