Interference of Driven Quantum Wave Functions Measured through Stokes Polarimetry of High Order Sidebands

Interferometry is often used to measure the difference in phase between two waves, including phases of quantum wave functions. Here we present measurements of the interference between the wave functions two hole species in Gallium Arsenide (GaAs) as they are driven from equilibrium by a large electromagnetic field and emit sideband photons. These photons are produced from a phenomenon called High-order Sideband Generation (HSG), where a near-infrared laser (NIR) creates electron-hole pairs in bulk GaAs and a large Terahertz (THz) field accelerates the pair to higher energy, until the pair eventually collide and emit a higher energy HSG photon [1]. The polarization of the HSG photon is set by the interference between the wave functions of the two hole states as a result of different dynamical phases accumulated during the THz acceleration process [2]. At increasing sideband energies, the e-h pairs cover longer paths in the Brillouin Zone (BZ) to gain more energy from the THz field. Using Stokes polarimetry, we measure both the change in linear orientation and ellipticity of the sidebands as a function of BZ path length, resulting in a novel interference pattern and providing insight into the dynamical processes of the non-equilibrium states in driven quantum matter.

[1] B. Zaks et al. Nature 483 580-583 (2012)

[2] J.B Costello, S.D. O’Hara, Q. Wu et al. Nature 599 57-61 (2021)