77,233 research outputs found
Comment on "Separability of quantum states and the violation of Bell-type inequalities"
The statement of E.R. Loubenets, Phys. Rev. A 69, 042102 (2004), that
separable states can violate classical probabilistic constraints is based on a
misleading definition of classicality, which is much narrower than Bell's
concept of local hidden variables. In a Bell type setting the notion of
classicality used by Loubenets corresponds to the assumption of perfect
correlations if the same observable is measured on both sides. While it is
obvious that most separable states do not satisfy this assumption, this does
not constitute "non-classical" behaviour in any usual sense of the word.Comment: 1 page, accepted by Phys. Rev.
Monogamy of Bell's inequality violations in non-signaling theories
We derive monogamy relations (tradeoffs) between strengths of violations of
Bell's inequalities from the non-signaling condition. Our result applies to
general Bell inequalities with an arbitrary large number of partners, outcomes
and measurement settings. The method is simple, efficient and does not require
linear programming. The results are used to derive optimal fidelity for
asymmetric cloning in nonsignaling theories.Comment: 4 pages, 2 figures, published versio
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Evidence for heat losses via party wall cavities in masonry construction
This paper presents empirical evidence and analysis that supports the existence of a significant heat loss mechanism resulting from air movement through cavities in party walls in masonry construction. A range of heat loss experiments were undertaken as part of the Stamford Brook housing field trial in Altrincham in the United Kingdom. Co-heating tests showed a large discrepancy between the predicted and measured whole house heat loss coefficients. Analysis of the co-heating results, along with internal temperature data, thermal imaging and a theoretical analysis indicated that the most likely explanation for the discrepancy was bypassing of the thermal insulation via the uninsulated party wall cavities. The data show that such a bypass mechanism is potentially the largest single contributor to heat loss in terraced dwellings built to the 2006 revision of the Building Regulations. A comparable convective heat bypass associated with masonry party walls was identified in the late 1970s during the course of the Twin Rivers Project in the United States, albeit in a somewhat different construction from that used at Stamford Brook. A similar effect was also reported in the United Kingdom in the mid 1990s. However, it appears that no action was taken at that time either to confirm the results, to develop any technical solutions, or to amend standards for calculating heat losses from buildings. Current conventions for heat loss calculations in the United Kingdom do not take account of heat losses associated with party walls and it is suggested by the authors that such conventions may need to be updated to take account of the effect described in this paper. In the final part of the paper, the authors propose straightforward solutions to prevent bypassing of roof insulation via party walls by for example filling the cavity of the party wall with mineral fibre insulation, or by inserting a cavity closer across the cavity in the plane of the roof insulation.Practical application: The heat bypass mechanism described in this paper is believed by the authors to contribute to a significant proportion of heat loss from buildings in the UK constructed with clear cavities such as those found in separating walls between cavity masonry dwellings. It is proposed that relatively simple design changes could be undertaken to eliminate such heat loss pathways from new buildings. In addition, simple and cost effective measures are envisaged that could be used to minimise or eliminate the bypass from existing buildings. Such an approach could give rise to a significant reduction in carbon emissions from UK housing
Loophole-free test of quantum non-locality using high-efficiency homodyne detectors
We provide a detailed analysis of the recently proposed setup for a
loophole-free test of Bell inequality using conditionally generated
non-Gaussian states of light and balanced homodyning. In the proposed scheme, a
two-mode squeezed vacuum state is de-gaussified by subtracting a single photon
from each mode with the use of an unbalanced beam splitter and a standard
low-efficiency single-photon detector. We thoroughly discuss the dependence of
the achievable Bell violation on the various relevant experimental parameters
such as the detector efficiencies, the electronic noise and the mixedness of
the initial Gaussian state. We also consider several alternative schemes
involving squeezed states, linear optical elements, conditional photon
subtraction and homodyne detection.Comment: 13 pages, 14 figures, RevTeX
Maximal violation of Bell inequality for any given two-qubit pure state
In the case of bipartite two qubits systems, we derive the analytical
expression of bound of Bell operator for any given pure state. Our result not
only manifest some properties of Bell inequality, for example which may be
violated by any pure entangled state and only be maximally violated for a
maximally entangled state, but also give the explicit values of maximal
violation for any pure state. Finally we point out that for two qubits systems
there is no mixed state which can produce maximal violation of Bell inequality.Comment: 3 pages, 1 figure
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