Electron spins in InGaAs quantum dots can interact strongly with the nuclear spins of the atoms in the host lattice via the contact hyperfine interaction. This project shows that as a result of this interaction, a feedback loop develops, yielding nonlinear dynamics of the electron spin. This effect could be useful, since it allows for indirect control of the nuclear bath. If the distribution of nuclear spin orientations can be narrowed through the use of an appropriate pulse sequence, then the dephasing time of the qubit should increase.
Figure 1. A set of Ramsey experiments. The delay between two pulses in increased, and decreased. If the spin was completely isolated, we would expect to see a pure sinusoidal signal in all cases. Instead, we see in (a) that a sinusoidal signal at short delays is spiky at longer delays, and its shape depends on whether the delay is being increased or decreased. In (b), this hysteresis is directly shown, as the delay is increased and then immediately decreased, in the same experiment.
Ladd et al. “Pulsed nuclear pumping and spin diffusion in a single charged quantum dot.” Physical Review Letters 105, 107401 (2010). [http://dx.doi.org/10.1103/PhysRevLett.105.107401]
Dr. David Press
Kristiaan De Greve
Dr. Thaddeus Ladd
Prof. Yoshihisa Yamamoto