Measurement of the topological Chern number by continuous probing of a qubit subject to a slowly varying Hamiltonian

  1. Peng Xu,
  2. Alexander Holm Kiilerich,
  3. Ralf Blattmann,
  4. Yang Yu,
  5. Shi-Liang Zhu,
  6. and Klaus Mølmer
We analyze a measurement scheme that allows determination of the Berry curvature and the topological Chern number of a Hamiltonian with parameters exploring a two-dimensional closed
manifold. Our method uses continuous monitoring of the gradient of the Hamiltonian with respect to one parameter during a single quasi-adiabatic quench of the other. Measurement back-action leads to disturbance of the system dynamics, but we show that this can be compensated by a feedback Hamiltonian. As an example, we analyze the implementation with a superconducting qubit subject to time varying, near resonant microwave fields; equivalent to a spin 1/2 particle in a magnetic field.

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.