# Project A1

### Electrostatically Defined Quantum Dots as Qubits - Entangled States and Current Correlations

## PIs: Prof. J. Kotthaus, Dr. S. Ludwig, Prof. W. Wegscheider, Prof. C. Strunk

### Regensburg group:

Edge states in the integer quantum Hall are closest electronic analog of light beams in quantum optics. It is thus tempting to use edge states to realize the interference of electrons in the solid with a very high visibility. The electronic Mach-Zehnder interferometer is such a device and a promising test ground for the study of decoherence and orbital entanglement. Such interferometers have a very high interference contrast at temperatures around 20 mK. We found that the interference is controlled by filling factor and is restricted to one interval over magnetic field, which approximately ranges from filling factor 2.0 to 1.0, with maximum near 1.5. The temperature dependence of visibility taken at fixed magnetic field show exponential damping above ~ 45 mK. As a function of dc-voltage, the decay of visibility is oscillatory with a gaussian envelope. The energy scales extracted from both types of measurement depend in a very similar way on magnetic field, indicating that the local structure of edge states plays a central role for the interference contrast.

### LMU group:

Along the path towards quantum information processing we seek a fundamental understanding of semiconductor based nano devices. The electron's charge and spin degrees of freedom can be combined as building blocks of quantum bits (qubits) and quantum registers. We study the coherent dynamics and the entanglement of coupled qubits as well as the back-action of measurements. In detail, we plan to realize adiabatic quantum information transfer by moving electrons coherently between spin qubits. The figure shows a stability diagram of a few electrons triple quantum dot (the number of electrons charging each dot are indicated by triplets of integers).