Searching for entangled electron spin states with shot noise detection

Abstract

We report experimental research into the possibility of using shot noise measurements to detect the entangled states of electron spins. The study is part of the effort towards the demonstration of the use of electron spins as quantum bits (qubits) for quantum computing and quantum information processing. Electrons are electrically injected into two neighboring quantum dots and interact with each other through the exchange coupling, after which they tunnel out of the dots and are incident on a beam splitter, which introduces quantum interference between electron states. Depending on the state of the electrons exiting the dots, the outgoing states of electrons scattering off the beam splitter are different, corresponding to different shot noise in the electrical currents flowing into the channels after the beam splitter. Our experimental data is consistent with most theoretical predictions and provides initial evidence of electron spin ntanglement. A comprehensive study of the shot noise in mesoscopic semiconductor tunnel barriers is also reported. Besides the theoretically predicted full shot noise, suppressed and enhanced shot noise are also observed. Normal conductance measurements and numerical simulations are done to understand the shot noise deviation. Our study shows that shot noise in mesoscopic systems is extremely sensitive to the microscopic details, such as potential disorder and impurity configuration.