11 research outputs found
Optimal Dynamical Decoupling Sequence for Ohmic Spectrum
We investigate the optimal dynamical decoupling sequence for a qubit coupled
to an ohmic environment. By analytically computing the derivatives of the
decoherence function, the optimal pulse locations are found to satisfy a set of
nonlinear equations which can be easily solved. These equations incorporates
the environment information such as high-energy (UV) cutoff frequency \omega_c,
giving a complete description of the decoupling process. The solutions explain
previous experimental and theoretical results of locally optimized dynamical
decoupling (LODD) sequence in high-frequency dominated environment, which were
obtained by purely numerical computation and experimental feedback. As shown in
numerical comparison, these solutions outperform the Uhrig dynamical decoupling
(UDD) sequence by one or more orders of magnitude in the ohmic case.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Optimized Dynamical Decoupling Sequences in Protecting Two-Qubit States
Aperiodic dynamical decoupling (DD) sequences of pulses are of great
interest to decoherence control and have been recently extended from
single-qubit to two-qubit systems. If the environmental noise power spectrum is
made available, then one may further optimize aperiodic DD sequences to reach
higher efficiency of decoherence suppression than known universal schemes. This
possibility is investigated in this work for the protection of two-qubit
states, using an exactly solvable pure dephasing model including both local and
nonlocal noise. The performance of optimized DD sequences in protecting
two-qubit states is compared with that achieved by nested Uhrig's DD
(nested-UDD) sequences, for several different types of noise spectrum. Except
for cases with noise spectrum decaying slowly in the high-frequency regime,
optimized DD sequences with tens of control pulses can perform orders of
magnitude better than that of nested-UDD. A two-qubit system with highly
unbalanced local noise is also examined to shed more light on a recent
experiment. Possible experiments that may be motivated by this work are
discussed.Comment: 9 pages, two figure