Flux-dependent occupations and occupation difference in geometrically symmetric and energy degenerate double-dot Aharonov-Bohm interferometers

We study the steady-state characteristics and the transient behavior of the nonequilibrium double-dot Aharonov-Bohm interferometer using analytical tools and numerical simulations. Our simple setup includes noninteracting degenerate quantum dots that are coupled to two biased metallic leads at the same strength. A magnetic flux Phi pierces the interferometer perpendicularly. As we tune the degenerate dot energies away from the symmetric point, we observe four nontrivial magnetic flux-control effects: (i) flux dependency of the occupation of the dots, (ii) magnetic-flux-induced occupation difference between the dots, at degeneracy, (iii) the effect of phase localization of the dots' coherence holds only at the symmetric point, while in general both real and imaginary parts of the coherence are nonzero, and (iv) coherent evolution survives even when the dephasing strength, introduced via Buttiker probes, is large and comparable to the dot energies and the bias voltage. In fact, finite dephasing can actually introduce new types of coherent oscillations into the system dynamics. These four phenomena take place when the dot energies are gated, to be positioned away from the symmetric point, demonstrating that the combination of bias voltage, magnetic flux, and gating field can provide delicate control over the occupation of each of the quantum dots and their coherence. DOI: 10.1103/PhysRevB.87.045418