QDev Seminar: Michael Hell

Virtual fluctuations with real implications: spintronics, nanomagnetism and qubit readout with quantum dots

Abstract: In this talk, I show the possibilities of using interaction-induced renormalization effects for the manipulation, stabilization, and readout of few-level quantum-dot systems embedded in nanoscale transport setups. An example from spintronics is the dipolar exchange field that emerges in a quantum dot in proximity to ferromagnetic leads. This effective magnetic field induces a spin precession, which in the Coulomb blockade regime leads to a new type of resonance allowing for electric spin control. If the quantum dot has a high-spin ground state (S⩾1), an additional spin-anisotropy barrier arises that stabilizes the spin against reversal. I predict a ‘‘smoking-gun'' experiment that probes this anisotropy by inelastic transport spectroscopy. Transferring these insights to measurement setups for quantum-dot qubits, I identify a new, coherent backaction on a qubit when read out capacitively by a proximal sensor dot. The coherent backaction is shown to have significant impact on the stationary conductance signal and to mitigate the qubit decoherence.