Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum non-demolition measurements of a qubit coupled to a harmonic
  oscillator   We theoretically describe the weak measurement of a two-level system (qubit)
and quantify the degree to which such a qubit measurement has a quantum
non-demolition (QND) character. The qubit is coupled to a harmonic oscillator
which undergoes a projective measurement. Information on the qubit state is
extracted from the oscillator measurement outcomes, and the QND character of
the measurement is inferred by the result of subsequent measurements of the
oscillator. We use the positive operator valued measure (POVM) formalism to
describe the qubit measurement. Two mechanisms lead to deviations from a
perfect QND measurement: (i) the quantum fluctuations of the oscillator, and
(ii) quantum tunneling between the qubit states $|0>$ and $|1>$ during
measurements. Our theory can be applied to QND measurements performed on
superconducting qubits coupled to a circuit oscillator.

20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex