Spin qubits

Electron spins are two-level quantum systems that provide robust quantum bits (qubits) since they are only weakly influenced by their environment. Furthermore, due to the electron’s charge, individual electrons can be isolated in semiconductor quantum dots. Taking advantage of these two properties, we have developed all-electrical techniques for the initialization, coherent control and read-out of single and coupled electron spins, and characterized the decoherence timescales and mechanisms. Our current focus is on scaling, integration and extending coherence times, for the realization of simple quantum protocols in this system.

Individual electrons are confined in quantum dot arrays defined by electrostatic gates in a two-dimensional electron gas (see images). The gate pattern is created by electron-beam lithography. Measurements are performed at 50 mK, in a dilution refrigerator. This approach is extremely powerful, as the number of electrons on each dot and the tunnel coupling between dots and from dots to leads can be controlled in-situ, using gate voltages. Microwave excitation can be used to drive single-spin rotations, and coherent exchange is achieved using nanosecond gate voltage pulses (Loss & DiVincenzo, PRA 1998).

AFM image (left) and schematic (right) of a double quantum dot.

Image gallery