There is a lot of interest in quantum computing, as defined on qubits and making use of quantum superposition and entanglement of states, and optoelectronics, where information in circuits is transferred by electrons as well as fast-moving photons. Thus we need a theory that combines together quantum optics with quantum transport. On the other hand, to address a few important questions associated with time-dependent phenomena (ac response and transients, single-electron pumps and turnstiles, random telegraph signals, Rabi flopping, switching rates, interconnect delays, etc.), we need time-domain formulation of the transport theory that incorporates the memory effects, taking into consideration the non-Markovian character of the conduction process. The aim of this project is to analyze optically created signal on the singly occupied two-level system, i.e. Rabi oscillations related to populations of particular energy levels due to near-resonant interaction with monochromatic light, its transfer to the channel and electronic detection in the standard field-effect transistor (FET) configuration via current-time characteristics for fixed voltages. Schematic representation of the system under investigation as well as examplary results are shown in Figue 1. Our computational scheme is based on the fully time-dependent non-equilibrium Green's functions (TD-NEGF) formalism, while numerical results are obtained within the time-domain decomposition (TDD) technique. In particular, we recognized two different and coexisting mechanims for signal transfer between two subsystems: short-range quantum interference due to state blocking (dominant for stronger coupling case), and long-range Coulomb scattering due to charge redistribution (dominant for weak coupling case). Our results will be discussed in a few distinguished aspects: detuning, decoherence (relaxation and dephasing), chemical engineering related to orbital coupling, and gatability. Here we will also pay attention to the formal conditions under which adiabatic approximation can be justified.
Figure 1: Schematic visualization of the optoelectronic problem under investigation, where optically created signal on the dot is transferred to the channel by Coulomb scattering (CS) and quantum interference (QI) effects and detected electronically by measuring current-time oscillations for fixed bias voltage.
Smitha Vasudevan, Avik Ghosh