Some Publications by Frederico B. Brito

Guido Burkard and Frederico Brito Non-additivity of decoherence rates in superconducting qubits Physical Review B 72, 054528 (2005). We show that the relaxation and decoherence rates 1/T1 and 1/T2 of a superconducting flux qubit coupled to several noise sources are not in general the sum of the rates due to each individual noise source. Indeed, we present a case in which the total rates are lower than the simple sum of individual rates.

Frederico Brito, Harry Westfahl Jr., Amir O. Caldeira and Gilberto Medeiros-Ribeiro Driven dissipative dynamics of spins in quantum dots, preprint, cond-mat/0703009 March 2007. We have studied the dissipative dynamics of a driven electronic spin trapped in a quantum dot. Using an effective spectral function of the dissipative phonon bath, we evaluated the expectation values of the spin components through the Bloch-Redfield theory. We show that due to a sharp bath resonance present in the effective spectral function, with typical energy much smaller than the electronic confinement energy, the dissipative spin has a rich dynamical behavior that helps us to determine some features of the spin-bath coupling.

David P. DiVincenzo, Frederico Brito and Roger H. Koch Efficient evaluation of decoherence rates in complex Josephson circuits Physical Review B 74, 014514 (2006) We present a complete analysis of the decoherence properties of a Josephson junction qubit. We develop a general Born-Oppenheimer approximation to reduce the effective dimensionality of the system potential to one. The relaxation and decoherence times T1 and T2 are presented as a function of the control parameters.

Frederico Brito, David P. DiVincenzo, Roger H. Koch and Matthias Steffen Efficient one- and two-qubit pulsed gates for an oscillator stabilized Josephson qubit New Journal of Physics, September 2007. We present schemes for performing high-fidelity one- and two-qubit pulsed gates for a superconducting flux qubit. We introduce a simplified but accurate model to describe the dynamics of the lowest states of the qubit as a function of the external control parameters. This model provides a simpler way to analyze the physics of the problem, helping to make it easy to see what operations are necessary for performing the desired quantum gates. A complete characterization of the noise present during the gate implementation is presented and discussed. We show that the noise has a structure of a bias noise, and that the phase noise plays the major role.