Charge and spin manipulation in a few-electron double dot

TL;DR

This paper demonstrates fast charge and spin manipulation in a few-electron double quantum dot, including charge qubit control via microwaves and spin relaxation measurements, highlighting hyperfine interaction effects.

Contribution

It introduces high-speed control of charge and spin states in a double quantum dot, with new measurements of relaxation times and potential for spin qubit implementation.

Findings

Charge qubit transition measured with T1~16 ns

Lower bound for T2* estimated at 400 ps

Hyperfine interaction causes rapid spin relaxation at low magnetic fields

Abstract

We demonstrate high speed manipulation of a few-electron double quantum dot. In the one-electron regime, the double dot forms a charge qubit. Microwaves are used drive transitions between the (1,0) and (0,1) charge states of the double dot. A local quantum point contact charge detector measures the photon-induced change in occupancy of the charge states. Charge detection is used to measure T1~16 ns and also provides a lower bound estimate for T2* of 400 ps for the charge qubit. In the two-electron regime we use pulsed-gate techniques to measure the singlet-triplet relaxation time for nearly-degenerate spin states. These experiments demonstrate that the hyperfine interaction leads to fast spin relaxation at low magnetic fields. Finally, we discuss how two-electron spin states can be used to form a logical spin qubit.