Abstract
We compute the decoherence caused by fluctuations at low frequency in the critical current of Josephson junctions incorporated into flux, phase, charge, and hybrid flux-charge superconducting quantum bits (qubits). The dephasing time scales as , where is the energy-level splitting frequency, is the spectral density of the critical-current noise at , and is a parameter computed for given parameters for each type of qubit that specifies the sensitivity of the level splitting to critical-current fluctuations. Computer simulations show that the envelope of the coherent oscillations of any qubit after time scales as when the dephasing due to critical-current noise dominates the dephasing from all sources of dissipation. We compile published results for fluctuations in the critical current of Josephson tunnel junctions fabricated with different technologies and a wide range in and area , and show that their values of scale to within a factor of 3 of at . We empirically extrapolate to lower temperatures using a scaling . Using this result, we find that the predicted values of at range from , and are usually substantially longer than values measured experimentally at lower temperatures.
7 More- Received 16 January 2004
DOI:https://doi.org/10.1103/PhysRevB.70.064517
©2004 American Physical Society