Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dynamical decoupling noise spectroscopy at an optimal working point of a
  qubit   I present a theory of environmental noise spectroscopy via dynamical
decoupling of a qubit at an optimal working point. Considering a sequence of
$n$ pulses and pure dephasing due to quadratic coupling to Gaussian distributed
noise $\xi(t)$, I use the linked-cluster (cumulant) expansion to calculate the
coherence decay. Solutions allowing for reconstruction of spectral density of
noise are given. For noise with correlation time shorter than the timescale on
which coherence decays, the noise filtered by the dynamical decoupling
procedure can be treated as effectively Gaussian at large $n$, and
well-established methods of noise spectroscopy can be used to reconstruct the
spectrum of $\xi^{2}(t)$ noise. On the other hand, for noise of dominant
low-frequency character ($1/f^{\beta}$ noise with $\beta \! > \! 1$), an
infinite-order resummation of the cumulant expansion is necessary, and it leads
to an analytical formula for coherence decay having a power-law tail at long
times. In this case, the coherence at time $t$ depends both on spectral density
of $\xi(t)$ noise at $\omega \! = \! n\pi/t$, and on the effective
low-frequency cutoff of the noise spectrum, which is typically given by the
inverse of the data acquisition time. Simulations of decoherence due to purely
transverse noise show that the analytical formulas derived in this paper apply
in this often encountered case of an optimal working point, provided that the
number of pulses is not very large, and the longitudinal qubit splitting is
much larger than the transverse noise amplitude.

37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys