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Daniele Tommasini

Publications and source records attributed to Daniele Tommasini.

27 records · Page 2Linked to original sources

Photons uncertainty solves Einstein-Podolsky-Rosen paradox

Einstein, Podolsky and Rosen (EPR) pointed out that the quantum-mechanical description of "physical reality" implied an unphysical, instantaneous action between distant measurements. To avoid such an action at a distance, EPR concluded that Quantum Mechanics had to be incomplete. However, its extensions involving additional "hidden variables", allowing for the recovery of determinism and locality, have been disproved experimentally (Bell's theorem). Here, I present an opposite solution of the paradox based on the greater indeterminism of the modern Quantum Field Theory (QFT) description of Particle Physics, that prevents the preparation of any state having a definite number of particles. The resulting uncertainty in photons radiation has interesting consequences in Quantum Information Theory (e.g. cryptography and teleportation). Moreover, since it allows for less elements of EPR physical reality than the old non-relativistic Quantum Mechanics, QFT satisfies the EPR condition of completeness without the need of hidden variables. The residual physical reality does never violate locality, thus the unique objective proof of "quantum nonlocality" is removed in an interpretation-independent way. On the other hand, the supposed nonlocality of the EPR correlations turns out to be a problem of the interpretation of the theory. If we do not rely on hidden variables or new physics beyond QFT, the unique viable interpretation is a minimal statistical one, that preserves locality and Lorentz symmetry.

quant-ph↗

A single quantum cannot be teleported

Due to the Heisemberg uncertainty principle, it is impossible to design a procedure which permits perfect cloning of an arbitrary, unknown "qubit" (the spin or polarization state of a single quantum system)1,2. However, it is believed that a perfect copying protocol can be achieved, at least in principle, if the qubit to be copied is destroyed in the original system. Quantum teleportation3,4 is supposed to allow for such a result. Here, this belief is shown to be invalidated by a fundamental uncertainty about the number of particles involved in any process, as predicted by Quantum Field Theory. As a result, teleportation cannot provide an infallible copying procedure for the single qubits, not even in the limit of perfect experimental sensitivities. The no-cloning theorem1,2 can then be generalized to the case of destroying the original. Teleportation remains an interesting statistical procedure, having an unavoidable theoretical error at the percent level or few orders of magnitude smaller, depending on the physical process that is used. Although it cannot be made arbitrarily small, such an error is small enough to remain hidden in present experiments.

quant-ph↗

Reality, measurement and locality in Quantum Field Theory

It is currently believed that the local causality of Quantum Field Theory (QFT) is destroyed by the measurement process. This belief is also based on the Einstein-Podolsky-Rosen (EPR) paradox and on the so-called Bell's theorem, that are thought to prove the existence of a mysterious, instantaneous action between distant measurements. However, I have shown recently that the EPR argument is removed, in an interpretation-independent way, by taking into account the fact that the Standard Model of Particle Physics prevents the production of entangled states with a definite number of particles. This result is used here to argue in favor of a statistical interpretation of QFT and to show that it allows for a full reconciliation with locality and causality. Within such an interpretation, as Ballentine and Jarret pointed out long ago, Bell's theorem does not demonstrate any nonlocality.

hep-th↗

Photons uncertainty removes Einstein-Podolsky-Rosen paradox

Einstein, Podolsky and Rosen (EPR) argued that the quantum-mechanical probabilistic description of physical reality had to be incomplete, in order to avoid an instantaneous action between distant measurements. This suggested the need for additional "hidden variables", allowing for the recovery of determinism and locality, but such a solution has been disproved experimentally. Here, I present an opposite solution, based on the greater indeterminism of the modern quantum theory of Particle Physics, predicting that the number of photons is always uncertain. No violation of locality is allowed for the physical reality, and the theory can fulfill the EPR criterion of completeness.

quant-ph↗

Quantum Electrodynamics is free from the Einstein-Podolsky-Rosen paradox

I show that Quantum Electrodynamics (QED) predicts a sort of uncertainty principle on the number of the "soft photons" that can be produced in coincidence with the particles that are observed in any EPR experiment. This result is argued to be sufficient to remove the original EPR paradox. A signature of this soft-photons solution of the EPR paradox would be the observation of apparent symmetry violation in single events. On the other hand, in the case of the EPR experiments that have actually been realized, the QED correlations are argued to be very close to those calculated by the previous, incomplete treatment, which showed a good agreement with the data. Finally, the usual interpretation of the correlations themselves as a real sign of nonlocality is also criticized.

quant-ph↗

Quantum Theory finally reconciled with Special Relativity

In 1935 Einstein, Podolsky and Rosen (EPR) pointed out that Quantum Mechanics apparently implied some mysterious, instantaneous action at a distance. This paradox is supposed to be related to the probabilistic nature of the theory, but since deterministic alternatives involving "Hidden Variables" hardly agree with the experiments, the scientific community is now accepting this ``quantum nonlocality" as if it were a reality. However, I have argued recently that Quantum Electrodynamics is free from the EPR paradox, due to an indetermination on the number of the unobserved "soft photons" that can be present in any step of any experiment. Here, I will provide a more general proof, based on an approach to the "problem of measurement" that implies the full reconciliation of Quantum Field Theory with Special Relativity. I will then conclude with some considerations on the interpretation of the Quantum Theory itself.

quant-ph↗

Horizontal Symmetries for the Supersymmetric Flavor Problem

The heaviness of the third family fermions and the experimental absence of large flavor violating processes suggest, in supersymmetric theories, that the three families belong to a $2+1$ representation of a horizontal symmetry $G_H$. In this framework, we discuss a class of models based on the group U(2) that describe the fermion flavor structure and are compatible with an underlying GUT. We study the phenomenology of these models and focus on two interesting scenarios: In the first one, the first and second family scalars are assumed to be heavier than the weak scale allowing for complex soft supersymmetry breaking terms. In the second one, all the CP-violating phases are assumed to be small. Both scenarios present a rich phenomenology in agreement with constraints from flavor violating processes and electric dipole moments.

hep-ph↗

New Neutral Gauge Bosons and New Heavy Fermions in the Light of the New LEP Data

We derive limits on a class of new physics effects that are naturally present in grand unified theories based on extended gauge groups, and in particular in $E_6$ and $SO(10)$ models. We concentrate on $i$) the effects of the mixing of new neutral gauge bosons with the standard $Z_0$; $ii$) the effects of a mixing of the known fermions with new heavy states. We perform a global analysis including all the LEP data on the $Z$ decay widths and asymmetries collected until 1993, the SLC measurement of the left--right asymmetry, the measurement of the $W$ boson mass, various charged current constraints, and the low energy neutral current experiments. We use a top mass value in the range announced by CDF. We derive limits on the $Z_0$--$Z_1$ mixing, which are always $\lsim 0.01$ and are at the level of a few {\it per mille} if some specific model is assumed. Model-dependent theoretical relations between the mixing and the mass of the new gauge boson in most cases require $M_{Z'} > 1\,$TeV. Limits on light--heavy fermion mixings are also largely improved with respect to previous analyses, and are particularly relevant for a class of models that we discuss.

hep-ph↗