We investigate possible explanations of quantum correlations that satisfy the principle of continuity, which states that everything propagates gradually and continuously through space and time. In particular, following [J.D. Bancal et al, Nature Physics 2012], we show that any combination of local common causes and direct causes satisfying this principle, i.e. propagating at any finite speed, leads to signalling. This is true even if the common and direct causes are allowed to propagate at a supraluminal-but-finite speed defined in a Newtonian-like privileged universal reference frame. Consequently, either there is supraluminal communication or the conclusion that Nature is nonlocal (i.e. discontinuous) is unavoidable.
Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text N. Gisin, I. Marcikic, H. de Riedmatten, W. Tittel, and H. Zbinden, "Quantum Information: Long Distance Quantum Teleportation," Optics & Photonics News 14(12), 39-39 (2003) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
The impossibility of perfectly copying (or cloning) an unknown quantum state is one of the basic rules governing the physics of quantum systems. The processes that perform the optimal approximate cloning have been found in many cases. These ``quantum cloning machines'' are important tools for studying a wide variety of tasks, e.g., state estimation and eavesdropping on quantum cryptography. This paper provides a comprehensive review of quantum cloning machines both for discrete-dimensional and for continuous-variable quantum systems. In addition, it presents the role of cloning in quantum cryptography, the link between optimal cloning and light amplification via stimulated emission, and the experimental demonstrations of optimal quantum cloning.
The polarization coupling length, an important parameter of the PMD probability distribution, is obtained from measurements and modeling of the nonlinear polarization rotation in optical fibers. Results for different types of fibers are presented.
A systematic first-order correction to the standard Markov master equation for open quantum systems interacting with a bosonic bath is presented. It extends the Markov Lindblad master equation to the more general case of non-Markovian evolution. The meaning and applications of our `post'-Markov master equation are illustrated with several examples, including a damped two-level atom, the spin-boson model and the quantum Brownian motion model. Limitations of the Markov approximation, the problem of positivity violation and initial slips are also discussed.
We show with an example that Weinberg's general framework for introducing non-linear corrections into quantum mechanics allows for arbitrarily fast communications.
We consider a quantum system composed of two subsystems. Among the properties of this system we study the set of those that can be tested when the subsystems are spatially separated. We show that not all properties satisfy this criterion, but that there are enough such properties to characterize any pure state of the composed system.
We investigate possible explanations of quantum correlations that satisfy the principle of continuity, which states that everything propagates gradually and continuously through space and time. In particular, following (Bancal et al. in Nat. Phys., 2012) we show that any combination of local common causes and direct causes satisfying this principle, i.e. propagating at any finite speed, leads to sig- nalling. This is true even if the common and direct causes are allowed to propagate at a supraluminal-but-finite speed defined in a Newtonian-like privileged univer- sal reference frame. Consequently, either there is supraluminal communication or the conclusion that Nature is nonlocal (i.e. discontinuous) is unavoidable. (Editor's note: for a video of the talk given by Prof. Gisin at the Aharonov-80 conference in 2012 at Chapman University, see quantum.chapman.edu/talk-28.)
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Pressure effects in polarization maintaining fibers are investigated both experimentally and theoretically. Interferometric measurements of the propagation times and polarization mode dispersion as a function of hydrostatic pressure over the range 0 to 40 MPa are presented. The finite-element method is used to calculate the pressure-induced variations of the asymmetrical stress in the core. It is observed and comprehensively explained that the birefringence increases with external applied hydrostatic pressure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An alternative to the electrical microphone for photoacoustic detection of trace gases is presented. This new microphone is made of standard monomode optical fibers wound and glued on a thin plate and is one of the arms of a Michelson interferometer. A detection scheme with a Sagnac interferometer has also been used and has given better results. Three cells working with different resonance modes and different microphone configurations have been tested.
