Strong-arming electron spin dynamics – Jason Petta

Date: Mon. May 2nd, 2011, 12:30 pm-1:30 pm
Location: Rockefeller 221

A single electron spin in an external magnetic field forms a two-level system that can be used to create a spin qubit. However, achieving fast single spin rotations, as would be required to control a spin qubit, is a major challenge. It is difficult to drive spin rotations on timescales that are faster than the spin dephasing time and to individually address a single spin on the nanometer scale. I will describe a new method for quantum control of single spins that does not involve conventional electron spin resonance (ESR). In analogy with an optical beam splitter, we use an anti-crossing in the energy level spectrum of our quantum dot “artificial atom” as a beam splitter for an incoming quantum state. The anti-crossing is used to prepare a superposition of singlet and triplet spin states, which then evolve according to the time-dependent Schrodinger equation. A return sweep through the anti-crossing results in quantum interference of the spin states. By changing the effective path length of one arm of our interferometer, we are able to achieve coherent rotations between a singlet state and a T+ triplet state. The rotations are nearly a factor of 100 faster than spin rotations achieved using conventional ESR and allow spins to be locally controlled using simple gate voltage pulses.