%0 Journal Article
%J Physical Review B
%D 2008
%T Multilevel effects in the Rabi oscillations of a Josephson phase qubit
%A S. K. Dutta
%A Frederick W. Strauch
%A R. M. Lewis
%A Kaushik Mitra
%A Hanhee Paik
%A T. A. Palomaki
%A Eite Tiesinga
%A J. R. Anderson
%A Alex J. Dragt
%A C. J. Lobb
%A F. C. Wellstood
%X We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states.
%B Physical Review B
%V 78
%8 2008/9/15
%G eng
%U http://arxiv.org/abs/0806.4711v2
%N 10
%! Phys. Rev. B
%R 10.1103/PhysRevB.78.104510
%0 Journal Article
%J Physical Review B
%D 2008
%T Quantum behavior of the dc SQUID phase qubit
%A Kaushik Mitra
%A F. W. Strauch
%A C. J. Lobb
%A J. R. Anderson
%A F. C. Wellstood
%A Eite Tiesinga
%X We analyze the behavior of a dc Superconducting Quantum Interference Device (SQUID) phase qubit in which one junction acts as a phase qubit and the rest of the device provides isolation from dissipation and noise in the bias leads. Ignoring dissipation, we find the two-dimensional Hamiltonian of the system and use numerical methods and a cubic approximation to solve Schrodinger's equation for the eigenstates, energy levels, tunneling rates, and expectation value of the currents in the junctions. Using these results, we investigate how well this design provides isolation while preserving the characteristics of a phase qubit. In addition, we show that the expectation value of current flowing through the isolation junction depends on the state of the qubit and can be used for non-destructive read out of the qubit state.
%B Physical Review B
%V 77
%8 2008/6/13
%G eng
%U http://arxiv.org/abs/0805.3680v1
%N 21
%! Phys. Rev. B
%R 10.1103/PhysRevB.77.214512