"DIPC Colloquium: Quantum parallelism at room temperature by coherent excitonic dynamics of an ensemble CdSe quantum dot dimers"
Who: Francoise Remacle, Department of Chemistry, University of Liege, Belgium
Place: Donostia International Physics Center
Date: Thursday, 27 April 2023, 16:00
The ultrafast fs electronic coherences can be experimentally characterized in semi-conducting colloidal quantum dot (QD) assemblies at room temperature by two-dimensional electronic spectroscopy (2DES). These electronic coherences exhibit a wide range of beating periods and provide a versatile basis for parallel quantum information processing on a fs time scale at room temperature. An excitonic model Hamiltonian based on the effective mass approximation is used to compute the quantum dynamics. It includes the Coulomb, spin-orbit and crystal field interactions that give rise to the fine structure splittings. The interdot distance is sufficiently small to allow for efficient interdot coupling and delocalization of the excitons over the two QDs of the dimer. To account for the inherent few percent size dispersion of colloidal QDs, the optical response is modeled by averaging over an ensemble of 2000 dimers. The size dispersion is responsible for an inhomogeneous broadening that limits the lifetimes of the excitonic coherences that can be probed to about 150-200 fs.
We use the dynamics of the electronic coherences as they are probed in 2DES to design quantum emulators of non equilibrium vibrational dynamics of a linear triatomic molecule. The implementation relies on the underlying Lie algebraic structure of the hardware system: the N quantum levels of the QD dimers provide N2-1 observables, the N(N-1) electronic coherences and N-1 populations, which allows for processing N2-1 logic variables in parallel. Furthermore, the use of the classical ensemble allows a simultaneous reading of the observables.