Eigenstate-Selective Entangled Two-Photon Absorption in Monolayer WSe$_2$

TL;DR

This study demonstrates that the Bell-state phase of polarization-entangled photons controls the distribution of biexciton eigenstates in monolayer WSe$_2$, enabling phase-dependent selective excitation of quantum states.

Contribution

It reveals a novel phase-controlled mechanism for eigenstate selection in entangled two-photon absorption in 2D materials, distinct from classical polarization effects.

Findings

Bell-state phase controls biexciton eigenstate distribution.

Symmetric and antisymmetric Bell states selectively excite different eigenstates.

Phase-scan visibility exceeds 0.97 at 4 K with broadband SPDC.

Abstract

We show that the Bell-state phase of a polarization-entangled photon pair controls the biexciton eigenstate distribution produced by entangled two-photon absorption (ETPA) in monolayer WSe$_2$. In a frequency-nondegenerate ladder scheme, two independent valley pathways ($K$ and $K'$) share no intermediate state, so the biphoton phase sets the relative amplitude between them. Within the valley-symmetric limit this phase factorizes from the material response, and the resulting selection rule partitions the excitation among biexciton eigenstates according to the Bell-state phase $\varphi$. The symmetric Bell state ($\varphi = 0$) selectively drives bright eigenstates, while the antisymmetric state ($\varphi = \pi$) drives the exchange-dark eigenstate. No classical polarization source reproduces this $\varphi$-dependent eigenstate distribution. Including valley dephasing and intervalley scattering at 4~K, the phase-scan visibility exceeds $0.97$ for broadband SPDC ($T_e \sim 100$~fs) with high source purity.