551 research outputs found
Contextuality under weak assumptions
The presence of contextuality in quantum theory was first highlighted by Bell, Kochen and Specker, who discovered that for quantum systems of three or more dimensions, measurements could not be viewed as deterministically revealing pre-existing properties of the system. More precisely, no model can assign deterministic outcomes to the projectors of a quantum measurement in a way that depends only on the projector and not the context (the full set of projectors) in which it appeared, despite the fact that the Born rule probabilities associated with projectors are independent of the context. A more general, operational definition of contextuality introduced by Spekkens, which we will term "probabilistic contextuality", drops the assumption of determinism and allows for operations other than measurements to be considered contextual. Even two-dimensional quantum mechanics can be shown to be contextual under this generalised notion. Probabilistic noncontextuality represents the postulate that elements of an operational theory that cannot be distinguished from each other based on the statistics of arbitrarily many repeated experiments (they give rise to the same operational probabilities) are ontologically identical. In this paper, we introduce a framework that enables us to distinguish between different noncontextuality assumptions in terms of the relationships between the ontological representations of objects in the theory given a certain relation between their operational representations. This framework can be used to motivate and define a "possibilistic" analogue, encapsulating the idea that elements of an operational theory that cannot be unambiguously distinguished operationally can also not be unambiguously distinguished ontologically. We then prove that possibilistic noncontextuality is equivalent to an alternative notion of noncontextuality proposed by Hardy. Finally, we demonstrate that these weaker noncontextuality assumptions are sufficient to prove alternative versions of known "no-go" theorems that constrain ψ-epistemic models for quantum mechanics
Species identification of Middle Eastern blowflies (Diptera: Calliphoridae) of forensic importance.
The lack of reliable tools for species identification of necrophagous blowflies of the Middle East is a serious obstacle to the development of forensic entomology in the majority of countries of this region. Adding to the complexity of diagnosing the regional fauna is that species representing three different zoogeographical elements exist in sympatry. In response to this situation, a high-quality key to the adults of all species of forensically relevant blowflies of the Middle East has been prepared. Thanks to the modern technique of image-stack stereomicroscopy and high-quality entomological materials, this new key can be easily applied by investigators inexperienced in the taxonomy of blowflies. The major technical problems relating to the species identification of necrophagous blowflies of the Middle East are also discussed
Revisiting consistency conditions for quantum states of systems on closed timelike curves: an epistemic perspective
There has been considerable recent interest in the consequences of closed
timelike curves (CTCs) for the dynamics of quantum mechanical systems. A vast
majority of research into this area makes use of the dynamical equations
developed by Deutsch, which were developed from a consistency condition that
assumes that mixed quantum states uniquely describe the physical state of a
system. We criticise this choice of consistency condition from an epistemic
perspective, i.e., a perspective in which the quantum state represents a state
of knowledge about a system. We demonstrate that directly applying Deutsch's
condition when mixed states are treated as representing an observer's knowledge
of a system can conceal time travel paradoxes from the observer, rather than
resolving them. To shed further light on the appropriate dynamics for quantum
systems traversing CTCs, we make use of a toy epistemic theory with a strictly
classical ontology due to Spekkens and show that, in contrast to the results of
Deutsch, many of the traditional paradoxical effects of time travel are
present.Comment: 10 pages, 6 figures, comments welcome; v2 added references and
clarified some points; v3 published versio
Recommended from our members
Mild coal gasification: Product separation, pilot-unit support, twin screw heat transfer, and H sub 2 S evolution
Our general objective is to further the development of efficient continuous mild coal gasification processes. Our efforts this year have been in four main areas. A new thrust has been to identify and develop efficient processes to separate the vapor product stream into particulate-free liquid and mist-free gas. We continued work aimed at predicting heat transfer rates (hence throughput) in externally-heated twin-screw pyrolyzers. We sought to provide technical support for the design, installation, startup, and operation of the DOE-sponsored 500 kg/hr twin-screw mild gasification unit at Coal Technology Corporation (CTC). A smaller laboratory effort had the objective of identifying and testing the reaction mechanisms of sulfur species during coal pyrolysis. Detailed subproject objectives are given in their respective sections. 20 refs., 4 figs., 1 tab
Guaranteed violation of a Bell inequality without aligned reference frames or calibrated devices
Bell tests---the experimental demonstration of a Bell inequality
violation---are central to understanding the foundations of quantum mechanics,
underpin quantum technologies, and are a powerful diagnostic tool for
technological developments in these areas. To date, Bell tests have relied on
careful calibration of the measurement devices and alignment of a shared
reference frame between the two parties---both technically demanding tasks in
general. Surprisingly, we show that neither of these operations are necessary,
violating Bell inequalities with near certainty with (i) unaligned, but
calibrated, measurement devices, and (ii) uncalibrated and unaligned devices.
We demonstrate generic quantum nonlocality with randomly chosen local
measurements on a singlet state of two photons implemented with reconfigurable
integrated optical waveguide circuits based on voltage-controlled phase
shifters. The observed results demonstrate the robustness of our schemes to
imperfections and statistical noise. This new approach is likely to have
important applications in both fundamental science and in quantum technologies,
including device independent quantum key distribution.Comment: 7 pages, 7 figure
Recommended from our members
Nonthermal aftertreatment of diesel engine exhaust
The ultimate objective of this work has been to develop a nonthermal plasma process to reduce NO{sub x} in diesel exhaust gas. A secondary objective has been to study the possibility of particulate matter (soot) reduction by the same technique. The early work revealed a fundamental difficulty with this NO{sub x} reduction approach in the gas environment of the diesel engine exhaust. These observations necessitated a thorough study of the unfavorable chemistry in the hope that knowledge of the chemical mechanism would offer an opportunity to make the approach useful for NO{sub x} reduction. Whereas fundamental understanding of the mechanism has been obtained, the authors have not found any measure that would make the approach meet its original objective
- …