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VIP-2 Experiment

The VIP experiment

 

The VIP experiment is performing high sensitivity tests of fundamental pillars of Quantum Mechanics, in the extremely low cosmic background environment of the underground Gran Sasso National Laboratory (LNGS) of INFN (Italy). The experiment is presently studying the Pauli Exclusion Principle (PEP) for electrons and the collapse of the wave-function.

 

 

Test of the PEP for electrons

 

The Pauli Exclusion Principle (PEP) represents one of the fundamental principles of the modern physics on which relies our comprehension of plenty of phenomena such as the stability of matter, the conductivity in metals and the neutron stars structure.

 

Wolfgang Pauli introduced the PEP in order to explain the periodic table of the elements [1] and originally postulated that two identical fermions can not simultaneously occupy the same quantum state (see also Ref. [2]). In Quantum Mechanics, the Symmetrization Postulate (SP) generalizes the principle, asserting that the total wave function of a system of identical bosons/fermions is symmetric/antisymmetric with respect to their permutation [3,4]. Later on, the SP was demonstrated in the context of relativistic quantum field theory (RQFT) by Pauli himself, who gave a negative proof based on a series of group-theoretic and relativistic arguments [5]. Another proof was formulated by Lüders and Zumino [6] who showed that the Spin Statistics Theorem (SST) can be derived from few, very general assumptions (i.e., Lorentz/Poncaré and CPT symmetries, locality, unitarity, and causality) which are deeply embedded in the same structure of space and time. Theories beyond the standard model, trying to unveil the fundamental connection between spin and statistics, or looking for an effective generalization which can accommodate tiny PEP violations, strongly need experimental verification. VIP could shed new light on the fermionic/bosonic nature of the elementary particles, and on the very foundations of QFT.

 

Possible reasons for PEP violation are related to: extra-dimensions, non-commutativity of the space-time coordinates, Lorentz symmetry or micro-causality violations or (certain types of) non-locality.

 

Aimed to constraint different classes of models, which foresee spin-statistics violation on the basis of the abovementioned motivations, the VIP-2 experiment consists of two, intertwined and complementary research branches, each of them characterized by a set of dedicated experiments, which investigate possible PEP violations in opened or closed systems.

 

 

Investigating models of dynamical wave function collapse

 

Dynamical models of Collapse are phenomenological theories introduced to solve the problem of measurement in Quantum Mechanics and explain the quantum-to-classical transition [7-12]. According to these models, the linear and unitary evolution given by the Schrödinger equation is modified by adding non-linear and stochastic terms. These modifications have two very important consequences: (i) they lead to the collapse of the wave function of the system in space (localization mechanism) and (ii) the collapse effects get amplified with the mass of the system (amplification mechanism). The combination of these two properties guarantees that macroscopic objects always have well defined positions, explaining why we do not observe quantum behaviour at the macroscopic level. On the other hand, for microscopic systems, the effect of the non-linear interaction with the stochastic noise field is very small and their dynamics is dominated by the Schrödinger evolution. Due to the presence of the non-linear interaction with the noise field, collapse models predict slight deviations from the standard Quantum Mechanics predictions [13], which the VIP experiment aims to unveil with high precision spectroscopic measurements.

 

 

 

References

 

  • [1]. Pauli,W. On the connexion between the completion of electron groups in an atom with the complex structure of spectra. Z. Für Phys. 1925, 31, 765.
  • [2]. Kaplan, I.G. The Pauli Exclusion Principle and the Problems of Its Experimental Verification. Symmetry 2020, 12, 320.
  • [3]. Hilborn, R.; Tino, G. Spin-Statistics Connection and Commutation Relations: Experimental Tests and Theoretical Implications, Anacapri, Capri Island, Italy, 31 May–3 June 2000; AIP Conference Proceedings; American Institute of Physics: Melville, NY, USA, 2000.
  • [4]. Curceanu, C.; Gillaspy, J.; Hilborn, R.C. Resource letter SS–1: The spin-statistics connection. Am. J. Phys. 2012, 80, 561–577.
  • [5]. Pauli, W. The Connection Between Spin and Statistics. Phys. Rev. 1940, 58, 716–722.
  • [6]. Lüders, G.; Zumino, B. Connection between spin and statistics. Phys. Rev. 1958, 110, 145.
  • [7]. Bassi, A.; Ghirardi, G.C. Dynamical reduction models. Phys. Rep. 2003, 379, 257–426.
  • [8]. Pearle, P. Collapse Models Open Systems and Measurements in Relativistic Quantum Field Theory; Lecture Notes in Physics; Breuer, H.-P., Petruccione, F., Eds.; Springer: Berlin/Heidelberg, Germany, 1999; Volume 526.
  • [9]. Diósi, L. Models for Universal Reduction of Macroscopic Quantum Fluctuations. Phys. Rev. A 1989, 40, 1165.
  • [10]. Bassi, A. Collapse Models: Analysis of the Free Particle Dynamics. Available online: https://arxiv.org/abs/quant-ph/0410222.pdf (accessed on 25 March 2009).
  • [11]. Adler, S.L. Quantum Theory as an Emergent Phenomenon; Cambridge University Press: Cambridge, UK, 2004; Charpter 6.
  • [12]. Weber, T. Quantum mechanics with spontaneous localization revisited. Il Nuovo Cimento B 1991, 106, 1111–1124.
  • [13]. Fu, Q. Spontaneous radiation of free electrons in a nonrelativistic collapse model. Phys. Rev. A 1997, 56, 1806.