Ultimate control of electrons in nano- structures - Alan Gardin

In some systems, such as for the semiconductor quantum dots used in on-demand single-electron transport pumps [1-4] , fast time-dependent perturbation of the potentials confining the electrons allows one to observe time-dependent oscillations between two quantum states reminiscent of Rabi oscillations in qubit systems [5] . These oscillations are called non-adiabatic oscillations [5], where “non-adiabatic” refers to the fact that these phenomena are conditioned by a very fast operation of the single-electron pump, as opposed to the adiabatic operation (slow) of the pump. The adiabatic regime is characterized by the fact that the change is slow enough that the system can be considered at equilibrium at all time, and hence can be described as a succession of nonperturbed states. These non-adiabatic oscillations are not very well understood, and in our work, we shed some light on their characteristics. We demonstrate the simulation of the dynamics of the electron confined inside a spatially moving quantum dot. This tool allows to study the influence of the driving frequency of excitation and the trajectory of the quantum dot on the final state of the electron. We find that the dynamics is well described by considering the classical equation of motion. However, the final state of the system, a time-dependent superposition of the quantum states is not completely captured by this classical analogy. Since it may be possible to compute analytically the final state of the electron in the pump, this would hint at ways to operate the pump to damp non-adiabatic oscillations. Also, because our modelling does not capture the valley physics in silicon [6- 7], which is a material often used for the fabrication of single-electron pump devices, we then work on implementing these effects in the simulation to properly evaluate the potential of this system as an efficient single-electron pump. In more general terms, we believe that the modelling of the interaction between electromagnetic radiation and a confined quantum system is paramount to the most important quantum applications. The combination of the theory with the experiments that we are proposing could provide important advancements for these fields. As an example, theoretical and experimental studies of any kind of two-level quantum system coupled with a cavity are extremely useful and powerful for future developments also in Quantum Sensing and Quantum Metrology. References: [1] B. Kaestner and V. Kashcheyevs, Rep. Prog. Phys. 78 (2015) 103901 and J. P. Pekola et al, APS-RMP 85 (2013). [2] G. C. Tettamanzi et al, New Journal of Physics 16 (2014), 063036. [3] A. Rossi et al, G. C Tettamanzi, Nano-Letters 18 (2018) 4141. [4] J. van der Heijden, G. C. Tettamanzi et al, Nature Scientific Reports 7 (2017) Article number: 44371. [5] G. Yamahata et al, Nat. Nano 14 (2019) 1019. [6] F. A. Zwanenburg et al, Rev. Mod. Phys. 85 (2013) 961. [7] G. C. Tettamanzi, Entropy 21 (2019), 676.