Coherent manipulation of electronic states in a double quantum dot

Zhan Shi, C. B. Simmons, Daniel R. Ward +9 more

Alexander Croy, Ulf Saalmann

The coherent time evolution of electrons in double quantum dots (DQDs) induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven DQDs are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation, we obtain the energy- and time-resolved electron transfer through the device that resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the initialization stage. By means of an analytical expression, obtained from a large-bias model, we can understand the prominent features of these oscillations seen in both the experimental data and the numerical results. These findings strengthen the common interpretation in terms of a coherent transfer of electrons between the dots.

N. H. Bonadeo, John Erland Østergaard, Dan Gammon +3 more

T. Hayashi, T. Fujisawa, Hai Du Cheong +2 more

We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed.

Louis Gaudreau, Ghislain Granger, A. Kam +6 more

Benoît Bertrand, Hanno Flentje, Shintaro Takada +6 more

We studied experimentally the dynamics of the exchange interaction between two antiparallel electron spins in an isolated double quantum dot where coupling to the electron reservoirs can be ignored. We demonstrate that the level of control of such a double dot is higher than in conventional double dots. In particular, it allows us to couple coherently two electron spins in an efficient manner following a scheme initially proposed by Loss and DiVincenzo [Phys. Rev. A 57, 120 (1998)]. The present study demonstrates that isolated quantum dots are a possible route to increase the number of coherently coupled quantum dots.