Accession Number ADA586764
Title Pure Dephasing in Flux Qubits due to Flux Noise with Spectral Density Scaling as 1/f(alpha).
Publication Date Jun 2012
Media Count 9p
Personal Author A. D. Fefferman C. Mueller J. S. Birenbaum S. M. Anton S. R. O'Kelley
Abstract For many types of superconducting qubits, magnetic flux noise is a source of pure dephasing. Measurements on a representative dc superconducting quantum interference device (SQUID) over a range of temperatures show that S(phi)(f) = A(2)/(f/1 Hz)(alpha), where S(phi) is the flux noise spectral density, A is of the order of 1 micron/phi(0) Hz(-1/2), 0.61 is less than or equal to alpha less than or equal to 0.95, and phi(0) is the flux quantum. For a qubit with an energy level splitting linearly coupled to the applied flux, calculations of the dependence of the pure dephasing time Tau(phi) of Ramsey and echo pulse sequences on alpha for fixed A show that Tau(phi) decreases rapidly as alpha is reduced. We find that Tau(phi) is relatively insensitive to the noise bandwidth, f(1) is less than or equal to f less than or equal to f2, for all alpha provided the ultraviolet cutoff frequency f2 greater than 1/Tau(phi). We calculate the ratio Tau(phi), Epsilon/Tau(phi), R of the echo (epsilon) and Ramsey (R) sequences and the dependence of the decay function on alpha and f2. We investigate the case in which S(phi) (f0) is fixed at the 'pivot frequency' f0 not equal to 1 Hz while alpha is varied and find that the choise of f0 can greatly influence the sensitivity of Tau(phi), Epsilon and Tau(phi), R to the value of alpha. Finally, we present calculated values Tau(phi) in a qubit corresponding to the values of A and alpha measured in our SQUID.
Keywords Dephasing
Energy levels
Flux density
Flux qubits
Magnetic properties
Noise
Pivots
Quantum theory
Scaling factor
Splitting
Squid(Superconducting quantum interference device)
Superconductivity


 
Source Agency Non Paid ADAS
NTIS Subject Category 72B - Algebra, Analysis, Geometry, & Mathematical Logic
72F - Statistical Analysis
46 - Physics
Corporate Author California Univ., Berkeley. Dept. of Physics.
Document Type Journal article
Title Note Journal article.
NTIS Issue Number 1405
Contract Number W911NF-09-1-0336

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