Virtual levels of n-particle systems

Simon Barth, Andreas Bitter, Semjon A. Vugalter

We study virtual levels of N-particle Schrödinger operators and prove that if the particles are one-dimensional and N ≥ 3, then virtual levels at the bottom of the essential spectrum correspond to eigenvalues. The same is true for two-dimensional particles if N ≥ 4. These results are applied to prove the non-existence of the Efimov effect in systems of N ≥ 4 one-dimensional or N ≥ 5 two-dimensional particles.

Jan-Markus Schwindt

Omar Di Stefano, Roberto Stassi, Luigi Garziano +3 more

In quantum field theory, bare particles are dressed by a cloud of virtual particles to form physical particles. The virtual particles affect properties such as the mass and charge of the physical particles, and it is only these modified properties that can be measured in experiments, not the properties of the bare particles. The influence of virtual particles is prominent in the ultrastrong-coupling regime of cavity quantum electrodynamics (QED), which has recently been realised in several condensed-matter systems. In some of these systems, the effective interaction between atom-like transitions and the cavity photons can be switched on or off by external control pulses. This offers unprecedented possibilities for exploring quantum vacuum fluctuations and the relation between physical and bare particles. We consider a single three-level quantum system coupled to an optical resonator. Here we show that, by applying external electromagnetic pulses of suitable amplitude and frequency, each virtual photon dressing a physical excitation in cavity-QED systems can be converted into a physical observable photon, and back again. In this way, the hidden relationship between the bare and the physical excitations can be unravelled and becomes experimentally testable. The conversion between virtual and physical photons can be clearly pictured using Feynman diagrams with cut loops.

Andreas Bitter

Wolfgang Nolting