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 WSe2. 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 φ. The symmetric Bell state (φ=0) selectively drives bright eigenstates, while the antisymmetric state (φ=π) drives the exchange-dark eigenstate. No classical polarization source reproduces this φ-dependent eigenstate distribution. Including valley dephasing and intervalley scattering at 4~K, the phase-scan visibility exceeds 0.97 for broadband SPDC (Te∼100~fs) with high source purity.
Cite
@article{arxiv.2605.05633,
title = {Eigenstate-Selective Entangled Two-Photon Absorption in Monolayer WSe$_2$},
author = {Minseok A. Jang and Hongki Yoo},
journal= {arXiv preprint arXiv:2605.05633},
year = {2026}
}