Universal pulse sequence to minimize spin dephasing in the central spin decoherence problem

TL;DR

This paper demonstrates that Uhrig's pulse sequence, initially designed for a specific decoherence model, is actually universally effective for various dephasing Hamiltonians when pulses are applied with short delays, maximizing qubit fidelity.

Contribution

It reveals the model-independent universality of Uhrig's pulse sequence for arbitrary dephasing Hamiltonians under short delay conditions.

Findings

Uhrig's sequence maximizes qubit fidelity with increasing pulses.

Sequence cancels successive orders of fidelity decay.

Universality requires solving nonlinear equations for delay times.

Abstract

We present a remarkable finding that a recently discovered [G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)] series of pulse sequences, designed to optimally restore coherence to a qubit in the spin-boson model of decoherence, is in fact completely model-independent and generically valid for arbitrary dephasing Hamiltonians given sufficiently short delay times between pulses. The series maximizes qubit fidelity versus number of applied pulses for sufficiently short delay times because the series, with each additional pulse, cancels successive orders of a time expansion for the fidelity decay. The "magical" universality of this property, which was not appreciated earlier, requires that a linearly growing set of "unknowns" (the delay times) must simultaneously satisfy an exponentially growing set of nonlinear equations that involve arbitrary dephasing Hamiltonian operators.