In search of superluminal quantum communications: recent experiments and possible improvements

As shown in the famous EPR paper (Einstein, Podolsky e Rosen, 1935), Quantum Mechanics is non-local. The Bell theorem and the experiments by Aspect and many others, ruled out the possibility of explaining quantum correlations between entangled particles using local hidden variables models (except for implausible combinations of loopholes). Some authors (Bell, Eberhard, Bohm and Hiley) suggested that quantum correlations could be due to superluminal communications (tachyons) that propagate isotropically with velocity vt > c in a preferred reference frame. For finite values of vt, Quantum Mechanics and superluminal models lead to different predictions. Some years ago a Geneva group and our group did experiments on entangled photons to evidence possible discrepancies between experimental results and quantum predictions. Since no discrepancy was found, these experiments established only lower bounds for the possible tachyon velocities vt. Here we propose an improved experiment that should lead us to explore a much larger range of possible tachyon velocities Vt for any possible direction of velocity vec V of the tachyons preferred frame

Quantum correlations in Newtonian space and time: arbitrarily fast communication or nonlocality

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.Comment: It is an honor to dedicate this article to Yakir Aharonov, the master of quantum paradoxes. Version 2 contains some more references and a clarified conclusio

Are There Quantum Effects Coming from Outside Space-time? Nonlocality, free will and "no many-worlds"

Observing the violation of Bell's inequality tells us something about all possible future theories: they must all predict nonlocal correlations. Hence Nature is nonlocal. After an elementary introduction to nonlocality and a brief review of some recent experiments, I argue that Nature's nonlocality together with the existence of free will is incompatible with the many-worlds view of quantum physics.Comment: Talk presented at the meeting "Is Science Compatible with Our Desire for Freedom?" organised by the Social Trends Institute at the IESE Business School in Barcelona, Octobre 201

Quantum nonlocality based on finite-speed causal influences leads to superluminal signaling

The experimental violation of Bell inequalities using spacelike separated measurements precludes the explanation of quantum correlations through causal influences propagating at subluminal speed. Yet, any such experimental violation could always be explained in principle through models based on hidden influences propagating at a finite speed v>c, provided v is large enough. Here, we show that for any finite speed v with c<v<infinity, such models predict correlations that can be exploited for faster-than-light communication. This superluminal communication does not require access to any hidden physical quantities, but only the manipulation of measurement devices at the level of our present-day description of quantum experiments. Hence, assuming the impossibility of using nonlocal correlations for superluminal communication, we exclude any possible explanation of quantum correlations in terms of influences propagating at any finite speed. Our result uncovers a new aspect of the complex relationship between multipartite quantum nonlocality and the impossibility of signalling.Comment: 5+8 pages, 4 figures, version similar to the published on

Shut yourself up below decks ...

The principle of relativity, as originally expressed by Galileo, points out that the area of competence of the principle itself is that of isolated systems as well as inertial reference frames. The principle does not claim that it is always possible to isolate any physical system; indeed it leaves it open to the possibility of the existence of phenomena concerning nonisolable physical systems, e.g., phenomena regulated by some nondraggable ether. After the Aspect experiment realist and local models have been proposed specifically based on the hypothesis that entangled systems are not isolated. It is hypothesized that the correlations which allow the violation of Bell's inequality are due to exchanges of superluminal signals between the various parts of the system, and those signals do not generate causal paradoxes because their propagation is regulated by a nondraggable ether. In the present paper the perfect compatibility of such models with the relativity theory is strongly advocated. A criterion is finally proposed to determine the causal ordering between events since, when there are superluminal signals, that ordering can no longer be associated to the time ordering induced by the standard synchronization

Elastic, dielectric and optical constants of the nematic mixture E49

The Merck nematic mixture E49 exhibits a large nematic interval (0-100 C) and a large dielectric anisotropy. Both of these features make E49 interesting for applications and basic physics. Unfortunately, no systematic measurements of the material constants of this mixture and their temperature dependence have been reported in the literature. In this paper we report experimental measurements of the splay and bend elastic constants (K11 and K33) of the ordinary and the extraordinary refractive indices (nort and npar) at the wavelength = 632.8 nm and of the two elastic constants parallel and orthogonal to the director (par and ort) at the frequency = 5 kHz. The temperature dependence of all of these parameters is found in the temperature range 25-99 C. The measurements of the elastic constants are performed using both a dielectric and an optical method simultaneously on the same nematic sample. The results obtained using the two methods are in a satisfactory agreement between them within the estimated experimental uncertainty. The ordinary and the extraordinary indices are measured using the prism method

EXPERIMENTAL INVESTIGATION OF CAPILLARITY EFFECTS ON SURFACE GRAVITY-WAVES - NONWETTING BOUNDARY-CONDITIONS

Damping and eigenfrequencies of surface capillary-gravity waves greatly depend on the boundary conditions. To the best of our knowledge. so far no direct measurement has been made of the dynamic behaviour of the contact angle at the three-phase interface (fluid-vapour-solid walls) in the presence of surface oscillation. Therefore, theoretical models of surface gravity-capillary waves involve ad hoc phenomenological assumptions as far as the behaviour of the contact angle is concerned. In this paper we report a systematic experimental investigation of the static and dynamic properties of surface waves in a cylindrical container where the free surface makes a static contact angle theta(c) = 62-degrees with the vertical walls. The actual boundary condition relating the contact angle to the velocity of the contact line is obtained using a new stroboscopic optical method. The experimental results are compared with the theoretical expressions to be found in the literature. Two different regimes are observed: (i) a low-amplitude regime, where the contact line always remains at rest and the contact angle oscillates during the oscillation of the free surface; (ii) a higher-amplitude regime, where the contact line slides on the vertical walls. The profile, the eigenfrequency and the damping rate of the first non-axisymmetric mode of the surface gravity waves are investigated, The eigenfrequency and damping rate in regime (i) are in satisfactory agreement with the predictions of the Graham-Eagle theory (1983) of pinned-end edge conditions. The eigenfrequency and damping rate in regime (ii) show a strongly nonlinear dependence on the oscillation amplitude of the free surface. All the experimental results concerning regime (ii) can be explained in terms of the Hocking (1987 a) and Miles (1967, 1991) models of capillary damping by introducing an 'effective' capillary coefficient lambda(eff). This coefficient is directly obtained for the first time in our experiment from dynamic measurements on the contact line. A satisfactory agreement is found to exist between theory and experiment

CAPILLARITY EFFECTS ON SURFACE GRAVITY-WAVES IN A CYLINDRICAL CONTAINER - WETTING BOUNDARY-CONDITIONS

Surface capillary-gravity waves are experimentally investigated in a cylindrical basin subjected to a horizontal oscillation by using a high-sensitivity optical method. We study the low-oscillation-amplitude regimes for a fluid which wets the vertical walls and we show that the presence of the capillary meniscus can effect greatly the main properties of the system. Both the free decay and the forced oscillations of surface oscillations are investigated. The amplitude, the phase and the damping of gravity waves are investigated in detail. The damping of the fundamental surface mode is found to exhibit nonlinear behaviour which is in qualitative agreement with the predictions of the Miles (1967) theory of capillary damping. The amplitude and the phase of gravity waves with respect to the oscillation of the container exhibit unusual behaviour which is strictly connected with the presence of the wetting boundary condition for the fluid at the vertical walls

A lower bound for the velocity of quantum communications in the preferred frame

An EPR experiment with polarized entangled photons is performed to test the Eberhard model. According to the Eberhard model, quantum correlations between space-like separated events are due to a superluminal communication signal propagating in a preferred frame. The coincidences between entangled photons passing through two polarizers aligned along a East-West axis are measured as a function of time during 21 sidereal days. No deviation from the predictions of the Quantum Theory is observed. Tacking into account for the experimental uncertainties, we infer that, if a preferred frame for superluminal signals exists which moves at velocity (v) over right arrow with respect to the Earth, the modulus of the velocity of quantum communications in this frame has to be greater than v(t) similar or equal to 0.6 x 10(4)c for v . (C) 2010 Elsevier B.V. All rights reserved