36,211 research outputs found
Weak Values and Consistent Histories in Quantum Theory
A relation is obtained between weak values of quantum observables and the
consistency criterion for histories of quantum events. It is shown that
``strange'' weak values for projection operators (such as values less than
zero) always correspond to inconsistent families of histories. It is argued
that using the ABL rule to obtain probabilities for counterfactual measurements
corresponding to those strange weak values gives inconsistent results. This
problem is shown to be remedied by using the conditional weight, or
pseudo-probability, obtained from the multiple-time application of Luders'
Rule. It is argued that an assumption of reverse causality (a form of time
symmetry) implies that weak values obtain, in a restricted sense, at the time
of the weak measurement as well as at the time of post-selection. Finally, it
is argued that weak values are more appropriately characterised as
multiple-time amplitudes than expectation values, and as such can have little
to say about counterfactual questions.Comment: Final version, to appear in Studies in History and Philosophy of
Modern Physic
CLS 2+1 flavor simulations at physical light- and strange-quark masses
We report recent efforts by CLS to generate an ensemble with physical light-
and strange-quark masses in a lattice volume of 192x96^3 at
corresponding to a lattice spacing of 0.064 fm. This ensemble is being
generated as part of the CLS 2+1 flavor effort with improved Wilson fermions.
Our simulations currently cover 5 lattice spacings ranging from 0.039 fm to
0.086 fm at various pion masses along chiral trajectories with either the sum
of the quark masses kept fixed, or with the strange-quark mass at the physical
value. The current status of simulations is briefly reviewed, including a short
discussion of measured autocorrelation times and of the main features of the
simulations. We then proceed to discuss the thermalization strategy employed
for the generation of the physical quark-mass ensemble and present first
results for some simple observables. Challenges encountered in the simulation
are highlighted.Comment: 7 pages, 8 figures; Proceedings, 35th International Symposium on
Lattice Field Theory (Lattice2017): Granada, Spai
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