Renato Portugal

Staggered quantum walks with superconducting microwave resonators

  1. Jalil Khatibi Moqadam,
  2. Marcos Cesar de Oliveira,
  3. and Renato Portugal
The staggered quantum walk model on a graph is defined by an evolution operator that is the product of local operators related to two or more independent graph tessellations. A graph
tessellation is a partition of the set of nodes that respects the neighborhood relation. Flip-flop coined quantum walks with the Hadamard or Grover coins can be expressed as staggered quantum walks by converting the coin degree of freedom into extra nodes in the graph. We propose an implementation of the staggered model with superconducting microwave resonators, where the required local operations are provided by the nearest neighbor interaction of the resonators coupled through superconducting quantum interference devices. The tunability of the interactions makes this system an excellent toolbox for this class of quantum walks. We focus on the one-dimensional case and discuss its generalization to a more general class known as triangle-free graphs.
arxiv pdf

Analyzing Toffoli Gate in Disordered Circuit QED

  1. J. Khatibi Moqadam,
  2. Renato Portugal,
  3. N. F. Svaiter,
  4. and G. O. Corrêa
We study the effects of imperfections on the fidelity of the Toffoli gate recently realized in a circuit QED setup. The noise is introduced to the interqubits interactions hence the
couplings no longer remain constant but belong to the interval [1-d,1+d]J, where J is the average coupling constant and parameter d quantifies the noise level. We consider both static and dynamical imperfections. We also obtain a more robust gate by solving the quantum optimization problem with a modified objective functional including an interval of coupling values rather than a single ideal value.
arxiv pdf