Identical Quantum Particles, Entanglement, and Individuality

Abstract

Particles in classical physics are distinguishable objects, which can be picked out individually on the basis of their unique physical properties. By contrast, in the philosophy of physics, the standard view is that particles of the same kind (“identical particles”) are completely indistinguishable from each other and lack identity. This standard view is problematic: Particle indistinguishability is irreconcilable not only with the very meaning of “particle” in ordinary language and in classical physical theory, but also with how this term is actually used in the practice of present-day physics. Moreover, the indistinguishability doctrine prevents a smooth transition from quantum particles to what we normally understand by “particles” in the classical limit of quantum mechanics. Elaborating on earlier work, we here analyze the premises of the standard view and discuss an alternative that avoids these and similar problems. As it turns out, this alternative approach connects to recent discussions in quantum information theory.

Identical Particles in Quantum Mechanics: Against the Received View

“…may prove to be not possible at all. This signals a basic feature of quantum mechanics in the interpretation that we are discussing: the concept of a particle is not basic and has no claim to general applicability in the quantum realm, but rather is emergent (Dieks and Lubberdink 2011;Dieks 2020;Dieks and Lubberdink 2020). Only if certain conditions are fulfilled (e.g.…”

“…Details of an encompassing interpretation, rival to the Received View, in which this result is incorporated were discussed in (Dieks and Lubberdink 2011;Dieks 2020;Dieks and Lubberdink 2020), to which we refer. In the following we will summarize a number of key points.…”

“…This is so because both of the two initial particles contribute to all detection results at L ′ and R ′ , which leads to interference. A calculation shows (Tichy et al 2013;Dieks 2020) that correlations between spin values obtained at L ′ and R ′ will be found that suggest the presence of an entangled state (i.e., not a symmetrized product state) of the Einstein-Podolsky-Rosen type; this is a "holistic" state that does not represent two independently existing particles each possessing its own set of distinctive physical properties (Dieks and Lubberdink 2011;Dieks 2020;Dieks and Lubberdink 2020).…”

Identical Quantum Particles as Distinguishable Objects

“…Sophisticated experiments will be able to reveal the restricted validity of the emergent concepts and laws. This is true even when dealing with "particle states" like (5): this state remains a quantum state, and it is possible to design measurements that are able to bring out typical non-classical effects like interference even in this state (Dieks 2020). It is only when we refrain from "quantum probing" and stay within the realm of the standard measurement repertoire of classical physics that the classical particle description can be relied upon.…”

“…14 Whether such general particle pictures, defined by arbitrary orthogonal one-particle states, are relevant for the explanation of experimental results depends on the kind of measurements that are performed. In measurements that do not probe the "particle basis" of orthogonal one-particle states, the particulate character of the system will not be manifest(Dieks 2020). In practice, measurement interactions will have a local character, and therefore situations in which the one-particle states are-more or less-spatially localized are most relevant for a particle interpretation, also in connection with the classical limit.…”