Qubit Measurement and Backaction

Backaction in Qubit Readout by Quantum-Dot Detectors

Quantum dots, used as detectors of any kind of qubit susceptible to charge-readout provide a higher sensitivity thanquantum point contacts. However, the level and charge quantization of the detector requires an account of renormalizationeffects on the combined qubit-detector system due to fluctuations induced by the current-carrying electrodes, in particularin the limit of weak measurements. Besides relaxation and decoherence rates, the qubit is affected by coherent torquesacting on the qubit-isospin – reminiscent of spin-torques in quantum dot spin-valves.

(M. Hell, M. R. Wegewijs, D. DiVincenzo)