2004/10/06 by Jacek Dziarmaga
Computer Science · Physics and Astronomy · #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum and electron transport phenomena #cond-mat.other
paper · pdf · doi:10.1103/physrevb.71.054516
7 pages
arxiv created 2004/10/06 · openalex publication_date 2005/02/25 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The superconducting flux qubit has two quantum states with opposite currents which generate different magnetic fields. Environment of nuclear spins can find out the magnetic field after a decoherence time \ensuremathτ0 inversely proportional to the magnetic field and the square root of the number of spins. When the Hamiltonian of the qubit drives fast coherent Rabi oscillations between the states with opposite current, then the magnetic field is flipped at a constant rate \ensuremathω and the decoherence time \ensuremathτ=\ensuremathω\ensuremathτ02 is much longer than \ensuremathτ0. However, on closer inspection decoherence actually takes place on two time scales. The long time \ensuremathτ is a time of full decoherence but a part of quantum coherence is lost already after the much shorter time \ensuremathπ∕\ensuremathω. This fast partial decoherence biases coherent flux oscillations towards the initial flux direction and it can affect performance of the superconducting devices as qubits.