Qubit decoherence under two-axis coupling to low-frequency noises

Low-decoherence flux qubit

J. Q. You,1,2 Xuedong Hu,3 S. Ashhab,2 and Franco Nori2,4 1Department of Physics and Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433, China 2Frontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi 351-0198, Japan 3Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260-1500, USA 4Center for Theoretic...

Decoherence of a Josephson qubit due to coupling to two-level systems

Noise and decoherence are major obstacles to the implementation of Josephson junction qubits in quantum computing. Recent experiments suggest that two-level systems TLS in the oxide tunnel barrier are a source of decoherence. We explore two decoherence mechanisms in which these two-level systems lead to the decay of Rabi oscillations that result when Josephson junction qubits are subjected to s...

One , Two , and n Qubit Decoherence

Non-Gaussian low-frequency noise as a source of qubit decoherence.

We study decoherence in a qubit with the distance between the two levels affected by random flips of bistable fluctuators. For the case of a single fluctuator we evaluate explicitly an exact expression for the phase-memory decay in the echo experiment with a resonant ac excitation. The echo signal as a function of time shows a sequence of plateaus. The position and the height of the plateaus ca...

Two-qubit decoherence mechanisms revealed via quantum process tomography

We analyze the quantum process tomography QPT in the presence of decoherence, focusing on distinguishing local and nonlocal decoherence mechanisms for a two-partite system from experimental QPT data. In particular, we consider the iSWAP gate realized with superconducting phase qubits and calculate the QPT matrix in the presence of several local and nonlocal decoherence processes. We determine s...