Tuesday, January 24, 2012
12:30pm (JFB Library)
Title: Peculiarities of the Rabi Oscillations in a Quantum Dot Molecule
In a seminal paper of 1937 I. Rabi pointed out that the level population of an ac-driven two-level system oscillates with frequency, ΩR, proportional to the amplitude of the driving field. Rabi oscillations are well developed when ΩR exceeds the dephasing rate. In modern optical qubits, based on excitons in self-assembled quantum dots, experimental measurements of the Rabi oscillations are a test of the ability of these qubits to maintain a long-time coherence, and, thus, to their potential for the information processing. In the first part of the talk, experimental aspects of fabrication of self-assembled quantum dots and quantum dot molecules will be reviewed together with optical and electrical techniques of registration of the Rabi oscillations in these objects. In the bulk of the talk, the analytical theory of the Rabi oscillations in the quantum dot molecule will be developed. On the physical level, these Rabi oscillations involve creation and annihilation of both direct and indirect excitons in two tunnel-coupled dots. It will be demonstrated that interaction-induced difference in their binding energies leads to the strong correlation in the time evolution of both excitons. The difference between Rabi oscillations in a single quantum dot and molecule manifests itself, most prominently, when they are Fourier-transformed. Unlike conventional Rabi oscillations, where the Fourier transform contains a single peak at frequency, f = ΩR, the corresponding transform in a molecule contains three peaks at frequencies, f1, f2, and f3 = f1 + f2. The magnitudes and positions of these peaks evolve in a peculiar way with the driving field. In the end of the talk a possible connection between the results obtained and experimental results of Prof. C. Boehme's group on Rabi oscillations in two-spin pairs will be discussed.