Lidar, Daniel A | Search NASA

DOE OSTI2011

Quadratic dynamical decoupling with nonuniform error suppression

We analyze numerically the performance of the near-optimal quadratic dynamical decoupling (QDD) single-qubit decoherence errors suppression method [J. West et al., Phys. Rev. Lett. 104, 130501 (2010)]. The QDD sequence is formed by nesting two optimal Uhrig dynamical decoupling sequences for two orthogonal axes, comprising N{sub 1} and N{sub 2} pulses, respectively. Varying these numbers, we study the decoherence suppression properties of QDD directly by isolating the errors associated with each system basis operator present in the system-bath interaction Hamiltonian. Each individual error scales with the lowest order of the Dyson series, therefore immediately yielding the order of decoherence suppression. We show that the error suppression properties of QDD are dependent upon the parities of N{sub 1} and N{sub 2}, and near-optimal performance is achieved for general single-qubit interactions when N{sub 1}=N{sub 2}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Quadratic dynamical decoupling: Universality proof and error analysis

We prove the universality of the generalized QDD{sub N{sub 1N{sub 2}}} (quadratic dynamical decoupling) pulse sequence for near-optimal suppression of general single-qubit decoherence. Earlier work showed numerically that this dynamical decoupling sequence, which consists of an inner Uhrig DD (UDD) and outer UDD sequence using N{sub 1} and N{sub 2} pulses, respectively, can eliminate decoherence to O(T{sup N}) using O(N{sup 2}) unequally spaced ''ideal'' (zero-width) pulses, where T is the total evolution time and N=N{sub 1}=N{sub 2}. A proof of the universality of QDD has been given for even N{sub 1}. Here we give a general universality proof of QDD for arbitrary N{sub 1} and N{sub 2}. As in earlier proofs, our result holds for arbitrary bounded environments. Furthermore, we explore the single-axis (polarization) error suppression abilities of the inner and outer UDD sequences. We analyze both the single-axis QDD performance and how the overall performance of QDD depends on the single-axis errors. We identify various performance effects related to the parities and relative magnitudes of N{sub 1} and N{sub 2}. We prove that using QDD{sub N{sub 1N{sub 2}}} decoherence can always be eliminated to O(T{sup min{l_brace}N{sub 1},N{sub 2}{r_brace}}).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗