Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pure quantum dephasing of a solid state electron spin qubit in a large
  nuclear spin bath coupled by long-range hyperfine-mediated interactions   We investigate decoherence due to pure dephasing of a localized spin qubit
interacting with a nuclear spin bath. Although in the limit of a very large
magnetic field the only decoherence mechanism is spectral diffusion due to
dipolar flip-flops of nuclear spins, with decreasing field the
hyperfine-mediated interactions between the nuclear spins become important. We
take advantage of their long-range nature, and resum the leading terms in an
1/N expansion of the decoherence time-evolution function (N, being the number
of nuclear spins interacting appreciably with the electron spin, is large). For
the case of the thermal uncorrelated bath we show that our theory is applicable
down to low magnetic fields (~10 mT for a large dot with N=10^6) allowing for
comparison with recent experiments in GaAs quantum dot spin qubits. Within this
approach we calculate the free induction decay and spin echo decoherence in
GaAs and InGaAs as a function of the number of the nuclei in the bath (i.e. the
quantum dot size) and the magnetic field. Our theory for free induction decay
in a narrowed nuclear bath is shown to agree with the exact solution for
decoherence due to hyperfine-mediated interaction which can be obtained when
all the nuclei-electron coupling constants are identical. For the spin echo
evolution we show that the dominant decoherence process at low fields is due to
interactions between nuclei having significantly different Zeeman energies
(i.e. nuclei of As and two isotopes of Ga in GaAs), and we compare our results
with recent measurements of spin echo signal of a single spin confined in a
GaAs quantum dot. For the same set of parameters we perform calculations of
decoherence under various dynamical decoupling pulse sequences, and predict the
effect of these sequences in low B regime in GaAs.

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The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph