Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Staying positive: going beyond Lindblad with perturbative master
  equations   The perturbative master equation (Bloch-Redfield) is extensively used to
study dissipative quantum mechanics - particularly for qubits - despite the 25
year old criticism that it violates positivity (generating negative
probabilities). We take an arbitrary system coupled to an environment
containing many degrees-of-freedom, and cast its perturbative master equation
(derived from a perturbative treatment of Nakajima-Zwanzig or Schoeller-Schon
equations) in the form of a Lindblad master equation. We find that the
equation's parameters are time-dependent. This time-dependence is rarely
accounted for, and invalidates Lindblad's dynamical semigroup analysis. We
analyze one such Bloch-Redfield master equation (for a two-level system coupled
to an environment with a short but non-vanishing memory time), which apparently
violates positivity. We show analytically that, once the time-dependence of the
parameters is accounted for, positivity is preserved.

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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
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The categories of this paper are: astro-ph
3
The categories of this paper are: physics
16
The categories of this paper are: stat
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc