New type of quantum excitation behaves like a solitary particle

A soliton, a relative of the leviton.

JPL

In solids, the interactions between electrons and atoms conspire to produce the material's properties: how well it conducts electricity, how magnetic it is, and so forth. When an external voltage is applied, the result is a number of particle-like quantum excitations. The problem is that these excitations come in groups, the result of complex interactions in the material. However, just as it is sometimes useful to have access to single electrons or photons, researchers would like to make and manipulate single excitations.

A new experiment has managed to do so, using an idea from earlier theoretical calculations. By crafting the variation in strength of the voltage they sent through the material, J. Dubois and colleagues produced single quantum excitations. They named these particle-like objects "levitons" for physicist Leonid S. Levitov, who predicted their existence in a set of papers with various collaborators. The discovery opens up an entirely new subfield of experiments involving quantum excitations.

When you pluck a guitar string, both the string and the guitar body vibrate at many different frequencies simultaneously, creating the fundamental tone and its overtones. The combination of frequencies is what makes a guitar distinct from another instrument. That idea is analogous to quantum excitations in most materials: if you apply an external voltage (pluck the string), it produces fluctuations that behave like particles (the vibrating string) but also affect the bulk of the material (the guitar body). The particular excitations depend on the material's properties and the temperature; lower temperatures reduce the possibility of random fluctuations dominating the excitations.