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False qubits?: Polarization of light and Josephson junction
Robert Alicki
abstract: We compare two physical systems: polarization degrees of freedom of a
macroscopic light beam and the Josephson junction (JJ) in the "charge qubit
regime". The first system obviously cannot carry genuine quantum information
and we show that the maximal entanglement which could be encoded into
polarization of two light beams scales like 1/(photon number). Two theories of
JJ, one leading to the picture of "JJ-qubit" and the other based on the
mean-field approach are discussed. The later, which seems to be more
appropriate, implies that the JJ system is, essentially, mathematically
equivalent to the polarization of a light beam with the number of photons
replaced by the number of Cooper pairs. The existing experiments consistent
with the "JJ-qubit" picture and the theoretical arguments supporting, on the
contrary, the classical model are briefly discussed. The Franck-Hertz-type
experiment is suggested as an ultimate test of the JJ nature.
- oai_identifier:
- oai:arXiv.org:quant-ph/0606242
- categories:
- quant-ph
- comments:
- 4 pages, essentially altered text, added references
- arxiv_id:
- quant-ph/0606242
- created:
- 2006-06-29
- updated:
- 2006-11-29
Full article ▸
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