Date/Time
Date(s) - 14/12/2005
3:30 pm - 4:30 pm

Title: Two-electron spin states in a Random Nuclear Field

Speaker: Dr. Josh Folk

Institute: University of British Columbia
Department of Physics & Astronomy

Location: ABB 102

Description:

We have formed a double-well potential in a GaAs heterostructure that is small enough to confine two single electrons. The two electrons interact via a tunnel coupling, leading to entanglement between the two electron spins in the form of singlet and triplet eigenstates. In addition, however, each electron also interacts with over one million Ga and As nuclei through a strong hyperfine interaction. This electron-nuclear interaction competes with the electron-electron interaction, and leads to a rapid collapse of the electron spin entanglement.

The statistical polarization of the nuclear spins gives rise to a random nuclear field, which creates a splitting between electron spin states of ~ 0.1 ueV. Because this field is different for the two electrons, it mixes singlet and triplet electron states and implies a time-averaged T2* ~ 10 ns for the electron spin. The 0.1 ueV energy scale also provides a sensitive probe of the two-electron spin levels as the double dot potential is tuned in situ using electrostatic gates. Electron transport involving transitions between triplets and singlets in turn polarizes the nuclei. This dynamic nuclear polarization results in striking bistabilities and hysteresis in the electron-nuclear system, but also suggests a strategy for controlling the nuclear field.

The electron-nuclear coupling in GaAs heterostructures implies significant challenges ahead in the effort to use electron spin for quantum information processing. But if the electron-nuclear interaction can be controlled, it provides exciting possibilities for long-lived quantum coherence in solid state systems.