5,041 research outputs found
Reply to Norsen's paper "Are there really two different Bell's theorems?"
Yes. That is my polemical reply to the titular question in Travis Norsen's
self-styled "polemical response to Howard Wiseman's recent paper." Less
polemically, I am pleased to see that on two of my positions --- that Bell's
1964 theorem is different from Bell's 1976 theorem, and that the former does
not include Bell's one-paragraph heuristic presentation of the EPR argument ---
Norsen has made significant concessions. In his response, Norsen admits that
"Bell's recapitulation of the EPR argument in [the relevant] paragraph leaves
something to be desired," that it "disappoints" and is "problematic". Moreover,
Norsen makes other statements that imply, on the face of it, that he should
have no objections to the title of my recent paper ("The Two Bell's Theorems of
John Bell"). My principle aim in writing that paper was to try to bridge the
gap between two interpretational camps, whom I call 'operationalists' and
'realists', by pointing out that they use the phrase "Bell's theorem" to mean
different things: his 1964 theorem (assuming locality and determinism) and his
1976 theorem (assuming local causality), respectively. Thus, it is heartening
that at least one person from one side has taken one step on my bridge. That
said, there are several issues of contention with Norsen, which we (the two
authors) address after discussing the extent of our agreement with Norsen. The
most significant issues are: the indefiniteness of the word 'locality' prior to
1964; and the assumptions Einstein made in the paper quoted by Bell in 1964 and
their relation to Bell's theorem.Comment: 13 pages (arXiv version) in http://www.ijqf.org/archives/209
Investigation of electrocaloric effects in ferroelectric substances Status report no. 4, Sep. 1, 1965 - Feb. 28, 1966
Electrocaloric measurements on triglycine sulfate crystal
Investigation of electrocaloric effects in ferroelectric substances Final report, 1 Mar. 1964 - 1 Jul. 1967
Dielectric temperature change effects observed in ferroelectric and pyroelectric substance
A matched expansion approach to practical self-force calculations
We discuss a practical method to compute the self-force on a particle moving
through a curved spacetime. This method involves two expansions to calculate
the self-force, one arising from the particle's immediate past and the other
from the more distant past. The expansion in the immediate past is a covariant
Taylor series and can be carried out for all geometries. The more distant
expansion is a mode sum, and may be carried out in those cases where the wave
equation for the field mediating the self-force admits a mode expansion of the
solution. In particular, this method can be used to calculate the gravitational
self-force for a particle of mass mu orbiting a black hole of mass M to order
mu^2, provided mu/M << 1. We discuss how to use these two expansions to
construct a full self-force, and in particular investigate criteria for
matching the two expansions. As with all methods of computing self-forces for
particles moving in black hole spacetimes, one encounters considerable
technical difficulty in applying this method; nevertheless, it appears that the
convergence of each series is good enough that a practical implementation may
be plausible.Comment: IOP style, 8 eps figures, accepted for publication in a special issue
of Classical and Quantum Gravit
Quantum error correction for continuously detected errors
We show that quantum feedback control can be used as a quantum error
correction process for errors induced by weak continuous measurement. In
particular, when the error model is restricted to one, perfectly measured,
error channel per physical qubit, quantum feedback can act to perfectly protect
a stabilizer codespace. Using the stabilizer formalism we derive an explicit
scheme, involving feedback and an additional constant Hamiltonian, to protect
an ()-qubit logical state encoded in physical qubits. This works for
both Poisson (jump) and white-noise (diffusion) measurement processes. In
addition, universal quantum computation is possible in this scheme. As an
example, we show that detected-spontaneous emission error correction with a
driving Hamiltonian can greatly reduce the amount of redundancy required to
protect a state from that which has been previously postulated [e.g., Alber
\emph{et al.}, Phys. Rev. Lett. 86, 4402 (2001)].Comment: 11 pages, 1 figure; minor correction
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