Sigmund Kohler

Double Resonance Landau-Zener-Stückelburg-Majorana Interference in Circuit QED

  1. Ming-Bo Chen,
  2. Bao-Chuan Wang,
  3. Sigmund Kohler,
  4. Yuan Kang,
  5. Ting Lin,
  6. Si-Si Gu,
  7. Hai-Ou Li,
  8. Guang-Can Guo,
  9. Xuedong Hu,
  10. Hong-Wen Jiang,
  11. Gang Cao,
  12. and Guo-Ping Guo
We report on Floquet spectroscopy in a cavity-coupled double quantum dot system. By applying microwave induced consecutive passages, we observe Landau-Zener-Stückelberg-Majorana fringes
which are split by holes with the shape of crescents. We demonstrate that these crescents represent a universal feature that stems from a depletion of the predominantly occupied Floquet state at avoided crossings of the Floquet spectrum. The emergence of crescents can be controlled electrically via drive frequency and amplitude, which is perfectly consistent with the simulations based on our theoretical model. These results provide insight to the nonequilibrium population of Floquet states.
arxiv pdf

Employing Circuit QED to Measure Nonequilibrium Work Fluctuations

  1. Michele Campisi,
  2. Ralf Blattmann,
  3. Sigmund Kohler,
  4. David Zueco,
  5. and Peter Hänggi
We study an interferometric method for the measurement of the statistics of work performed on a driven quantum system, which has been put forward recently [Dorner et al., Phys. Rev.
Lett. 110 230601 (2013), Mazzola et al., Phys. Rev. Lett. 110 230602 (2013)]. The method allows replacing two projective measurements of the energy of the driven system with qubit tomography of an ancilla that is appropriately coupled to it. We highlight that this method could be employed to obtain the work statistics of closed as well as open driven system, even in the strongly dissipative regime. We then illustrate an implementation of the method in a circuit QED set-up, which allows one to experimentally obtain the work statistics of a parametrically driven harmonic oscillator. Our implementation is an extension of the original method, in which two ancilla-qubits are employed and the work statistics is retrieved through two-qubit state tomography. Our simulations demonstrate the experimental feasibility.
arxiv pdf

Non-Markovian qubit decoherence during dispersive readout

  1. Georg M. Reuther,
  2. Peter Hänggi,
  3. and Sigmund Kohler
We study qubit decoherence under generalized dispersive readout, i.e., we investigate a qubit coupled to a resonantly driven dissipative harmonic oscillator. We provide a complete picture
by allowing for arbitrarily large qubit-oscillator detuning and by considering also a coupling to the square of the oscillator coordinate, which is relevant for flux qubits. Analytical results for the decoherence time are obtained by a transformation of the qubit-oscillator Hamiltonian to the dispersive frame and a subsequent master equation treatment beyond the Markov limit. We predict a crossover from Markovian decay to a decay with Gaussian shape. Our results are corroborated by the numerical solution of the full qubit-oscillator master equation in the original frame.
arxiv pdf