118 research outputs found
Soft-pulse dynamical decoupling in a cavity
Dynamical decoupling is a coherent control technique where the intrinsic and
extrinsic couplings of a quantum system are effectively averaged out by
application of specially designed driving fields (refocusing pulse sequences).
This entails pumping energy into the system, which can be especially dangerous
when it has sharp spectral features like a cavity mode close to resonance. In
this work we show that such an effect can be avoided with properly constructed
refocusing sequences. To this end we construct the average Hamiltonian
expansion for the system evolution operator associated with a single ``soft''
pi-pulse. To second order in the pulse duration, we characterize a symmetric
pulse shape by three parameters, two of which can be turned to zero by shaping.
We express the effective Hamiltonians for several pulse sequences in terms of
these parameters, and use the results to analyze the structure of error
operators for controlled Jaynes-Cummings Hamiltonian. When errors are cancelled
to second order, numerical simulations show excellent qubit fidelity with
strongly-suppressed oscillator heating.Comment: 9pages, 5eps figure
Quadratic Dynamical Decoupling with Non-Uniform 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 N1 and N2 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 N1 and N2, and near-optimal performance is
achieved for general single-qubit interactions when N1=N2.Comment: 17 pages, 22 figure
Soft-Pulse Dynamical Decoupling with Markovian Decoherence
We consider the effect of broadband decoherence on the performance of
refocusing sequences, having in mind applications of dynamical decoupling in
concatenation with quantum error correcting codes as the first stage of
coherence protection. Specifically, we construct cumulant expansions of
effective decoherence operators for a qubit driven by a pulse of a generic
symmetric shape, and for several sequences of - and -pulses. While,
in general, the performance of soft pulses in decoupling sequences in the
presence of Markovian decoherence is worse than that of the ideal
-pulses, it can be substantially improved by shaping.Comment: New version contains minor content clarification
High Fidelity Adiabatic Quantum Computation via Dynamical Decoupling
We introduce high-order dynamical decoupling strategies for open system
adiabatic quantum computation. Our numerical results demonstrate that a
judicious choice of high-order dynamical decoupling method, in conjunction with
an encoding which allows computation to proceed alongside decoupling, can
dramatically enhance the fidelity of adiabatic quantum computation in spite of
decoherence.Comment: 5 pages, 4 figure
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