36,216 research outputs found
Quantum Stopwatch: How To Store Time in a Quantum Memory
Quantum mechanics imposes a fundamental tradeoff between the accuracy of time
measurements and the size of the systems used as clocks. When the measurements
of different time intervals are combined, the errors due to the finite clock
size accumulate, resulting in an overall inaccuracy that grows with the
complexity of the setup. Here we introduce a method that in principle eludes
the accumulation of errors by coherently transferring information from a
quantum clock to a quantum memory of the smallest possible size. Our method
could be used to measure the total duration of a sequence of events with
enhanced accuracy, and to reduce the amount of quantum communication needed to
stabilize clocks in a quantum network.Comment: 10 + 5 pages, 3 figure
Quantum correlations require multipartite information principles
Identifying which correlations among distant observers are possible within
our current description of Nature, based on quantum mechanics, is a fundamental
problem in Physics. Recently, information concepts have been proposed as the
key ingredient to characterize the set of quantum correlations. Novel
information principles, such as, information causality or non-trivial
communication complexity, have been introduced in this context and successfully
applied to some concrete scenarios. We show in this work a fundamental
limitation of this approach: no principle based on bipartite information
concepts is able to single out the set of quantum correlations for an arbitrary
number of parties. Our results reflect the intricate structure of quantum
correlations and imply that new and intrinsically multipartite information
concepts are needed for their full understanding.Comment: Appendix adde
Information Causality, the Tsirelson Bound, and the 'Being-Thus' of Things
The principle of `information causality' can be used to derive an upper
bound---known as the `Tsirelson bound'---on the strength of quantum mechanical
correlations, and has been conjectured to be a foundational principle of
nature. To date, however, it has not been sufficiently motivated to play such a
foundational role. The motivations that have so far been given are, as I argue,
either unsatisfactorily vague or appeal to little if anything more than
intuition. Thus in this paper I consider whether some way might be found to
successfully motivate the principle. And I propose that a compelling way of so
doing is to understand it as a generalisation of Einstein's principle of the
mutually independent existence---the `being-thus'---of spatially distant
things. In particular I first describe an argument, due to Demopoulos, to the
effect that the so-called `no-signalling' condition can be viewed as a
generalisation of Einstein's principle that is appropriate for an irreducibly
statistical theory such as quantum mechanics. I then argue that a compelling
way to motivate information causality is to in turn consider it as a further
generalisation of the Einsteinian principle that is appropriate for a theory of
communication. I describe, however, some important conceptual obstacles that
must yet be overcome if the project of establishing information causality as a
foundational principle of nature is to succeed.Comment: '*' footnote added to page 1; 24 pages, 1 figure; Forthcoming in
Studies in History and Philosophy of Modern Physic
Information and the reconstruction of quantum physics
The reconstruction of quantum physics has been connected with the interpretation of the quantum formalism, and has continued to be so with the recent deeper consideration of the relation of information to quantum states and processes. This recent form of reconstruction has mainly involved conceiving quantum theory on the basis of informational principles, providing new perspectives on physical correlations and entanglement that can be used to encode information. By contrast to the traditional, interpretational approach to the foundations of quantum mechanics, which attempts directly to establish the meaning of the elements of the theory and often touches on metaphysical issues, the newer, more purely reconstructive approach sometimes defers this task, focusing instead on the mathematical derivation of the theoretical apparatus from simple principles or axioms. In its most pure form, this sort of theory reconstruction is fundamentally the mathematical derivation of the elements of theory from explicitly presented, often operational principles involving a minimum of extraâmathematical content. Here, a representative series of specifically informationâbased treatmentsâfrom partial reconstructions that make connections with information to rigorous axiomatizations, including those involving the theories of generalized probability and abstract systemsâis reviewed.Accepted manuscrip
Quantum Correlations and Quantum Non-Locality: A Review and a Few New Ideas
In this paper we make an extensive description of quantum non-locality, one
of the most intriguing and fascinating facets of quantum mechanics. After a
general presentation of several studies on this subject, we consider if quantum
non-locality, and the friction it carries with special relativity, can
eventually find a "solution" by considering higher dimensional spaces.Comment: 1
No-signaling, dynamical independence, and the local observability principle
Within a general operational framework I show that a-causality at a distance
of "local actions" (the so-called "no-signaling") is a direct consequence of
commutativity of local transformations, i.e. of dynamical independence. On the
other hand, the tensor product of Quantum Mechanics is not just a consequence
of such dynamical independence, but needs in addition the Local Observability
Principle.Comment: Presented at the conference "Theory and Technology in Quantum
Information, Communication, Computation and Cryptography", Trieste SISSA,
June 2006. Submitted to J. Phys. A. Math. Ge
- âŠ