Lecture by Dr. Sigmund Kohler

Landau-Zener-Stückelberg-Majorana interference, dispersive qubit readout, and Berry phases

The dynamics of a qubit that is swept repeatedly through an avoided crossing is known as Landau-Zener-Stückelberg-Majorana

(LZSM) interference.  Lately it is used for demonstrating quantum coherence as well as for determining qubit parameters such as the

T2 time.  One method for recording these interference patterns is dispersive readout performed by measuring the transmission of a cavity coupled to the qubit.  In this talk, I present a universal theory for dispersive readout of quantum systems in and out of equilibrium.  It is based on the backaction of the measured system to the cavity obtained with non-equilibrium linear response theory, which provides the signal in terms of a system susceptibility [1] as well as resonance conditions that relate the cavity transmission to spectral properties and Berry phases [2].  Examples are the readout of detuned qubits and thermally excited multi-level systems. For ac-driven quantum systems, we identify the relevant Fourier component of the susceptibility and introduce a computational scheme based on Floquet theory.  The theory is applied to LZSM interference in Si/SiGe double quantum dots, where the interference patterns exhibit a harp-like structure stemming from the valley degree of freedom [3].  The theoretical and experimental interference patterns show a striking agreement.

[1] S. Kohler, Phys. Rev. A 98, 023849 (2018).

[2] S. Kohler, Phys. Rev. Lett. 119, 196802 (2017).

[3] X. Mi, S. Kohler, J.R. Petta, Phys. Rev. B 98, 161404(R) (2018).


fre 18 jan 19
10:30 - 11:30


DTU Fotonik



Lyngby Campus

Building 344, room 125