The Wave-Particle Duality: Its History and Current Status

The historical vicissitudes of wave–corpuscle duality (Olivier Darrigol)

At the turn of the twentieth century, there was a broad consensus that matter was corpuscular and light was wavelike. Early attempts to challenge this fundamental asymmetry were met with justifiable skepticism. We will examine the arguments that ultimately convinced the majority of physicists that both matter and light possessed both corpuscular and wave properties. In doing so, we will encounter a variety of interpretations of this duality, shaped by the philosophical predispositions of the actors involved. Special attention will be devoted to Niels Bohr’s position and to its compatibility with recent experimental manifestations of wave–corpuscle duality.

Raising Schrödinger ‘s kittens: On the Universality of the Wave-Particle Duality (Markus Arndt)

While Louis de Broglie postulated in 1923 that all matter is accompanied by an « oscillatory phenomenon in phase with a wave » and believed this to “solve almost all the problems brought up by quanta”, Erwin Schrödinger speculated in 1926 that “material points…are nothing but wave systems” and conceded that « this extreme conception may be wrong » but that treating “motion of material points, has led to such grave difficulties”. Both pioneers of quantum physics were bold in their claims, without any backup by experimental observation.

A century later, the wave nature of matter has been observed from electrons over atoms to fullerenes, vitamins and polypeptides, massive macromolecules, and most recently metal nanoparticles beyond 175,000 atomic mass units, covering more than eight orders of magnitude in particle mass. The de Broglie wavelength can be femtometers small, 100,000 times smaller than the particle itself, or micrometers wide in ultra-cold atoms.

I will discuss key developments and applications with electrons, neutrons and atoms and focus on experiments at the University of Vienna, where we use in particular near-field Talbot–Lau interferometry on atoms, molecules, clusters of atoms and clusters of molecules.

Heisenberg’s uncertainty relation is key in the preparation of coherence and delocalization, and the act of projective measurement has become a useful beam splitting mechanism for matter-waves. Decoherence by collisions or radiation is measured quantitatively and is interpreted, quantitatively equivalently, from three different philosophical perspectives: from Heisenberg’s microscope and Bohr’s complementarity to decoherence theory that builds on entanglement with an ignored environment.

The appearance of nanoscale interference fringes is not only proof for one of the most unusual properties in physic but also at the heart of many modern applications in precision metrology: Quantum interference turns atoms in outstanding inertial sensors and molecule interferometers into devices that can measure electric, magnetic, optical and structural properties of clusters and molecules with high sensitivity