Localized State in Quantum Point Contacts: Possible Qubit Implementation?

We discuss a possible implementation of a quantum bit as a localized state self-consistently formed in quantum point contacts (QPCs) near pinch-off conditions. Such formation has been connected to the so-called 0.7-anomaly, an additional feature observed in QPCs' conductance below the first quantized step. We report experimental data showing a clear peak in the conductance of another (detector) QPC in close proximity to a QPC driven to pinch-off. This peak is visible for temperatures up to 35 K. We attribute this peak to a Fano resonance when the direct path for electrons from the source to the drain through the detector QPC coherently interfere with the path via a localized state in the pinched-off (swept) QPC. To support such a conclusion, we perform a theoretical analysis based on the equations of motion for electron operators, reproducing all essential features of experiment. Also, we discuss possible advantages of a qubit based on that localized state in comparison to the standard quantum dot case.