Modelling the optical control of electron spin dynamics in a quantum dot near a two-dimensional semiconductor

Abstract

A quantum dot in the Voigt configuration is a basic system with important potential applications in quantum technologies. The spin states of this quantum dot can act as a prototype qubit. By applying laser pulses the dynamics of the quantum dot spin can be controlled and the necessary quantum gates can be achieved. An important problem is the initialization, i.e., the creation of one of the two electron spin states starting from the natural initial state of the system, which is an equal incoherent mixture of the two spin states. The initialization process can be achieved by proper interaction of the quantum dot with laser pulses. Also, it has been realized that the integration of the quantum dot with photonic structures that give preferential Purcell-enhanced decay rate towards the target spin state increases the fidelity of spin initialization. Here, we propose a new coupled quantum dot - nanophotonic structure that may give high initialization fidelity in short times by coupling the quantum dot with a tungsten disulfide (WS2) monolayer. For the modelling of the spin dynamics we combine quantum dynamics calculations with electromagnetic calculations. Specifically, we model the interaction of the quantum dot with the applied laser field with density matrix equations. Also, the spontaneous decay rates that enter in the density matrix equations are obtained by electromagnetic calculations based on the electromagnetic Green’s tensor, which is calculated with the scattering superposition method. We first show that the spontaneous decay rates for the quantum dot near a WS2 monolayer are enhanced by the Purcell effect and are anisotropic for quantum dot dipole moments parallel and perpendicular to the layer. We then use the most common method for initialization, optical pumping and show that a preferential Purcell-enhanced decay rate towards the target spin state increases the fidelity of spin initialization in short times, in comparison to the case that the quantum dot is placed in an isotropic photonic environment.