Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2003-08-01
Phys. Rev. B 69, 064503 (2004)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
20 pages, 7 figures; v2: important simplification of results added, Appendix added, new figure, typos corrected; v3: published
Scientific paper
10.1103/PhysRevB.69.064503
We present a multi-level quantum theory of decoherence for a general circuit realization of a superconducting qubit. Using electrical network graph theory, we derive a Hamiltonian for the circuit. The dissipative circuit elements (external impedances, shunt resistors) are described using the Caldeira-Leggett model. The master equation for the superconducting phases in the Born-Markov approximation is derived and brought into the Bloch-Redfield form in order to describe multi-level dissipative quantum dynamics of the circuit. The model takes into account leakage effects, i.e. transitions from the allowed qubit states to higher excited states of the system. As a special case, we truncate the Hilbert space and derive a two-level (Bloch) theory with characteristic relaxation (T_1) and decoherence (T_2) times. We apply our theory to the class of superconducting flux qubits; however, the formalism can be applied for both superconducting flux and charge qubits.
Burkard Guido
DiVincenzo David P.
Koch Roger H.
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