Repulsive Casimir forces at quantum criticality (Vol. 47 No. 3)

Casimir forces act between macroscopic objects immersed in a fluctuating entity, which may be the quantum vacuum or material medium in a state hosting sizable fluctuations. These forces were first discussed in 1948 as an observable manifestation of the quantum nature of the vacuum, lying at the heart of quantum electrodynamics. At a somewhat later stage it was realized that a material medium brought to the vicinity of a critical state induces analogous interactions once some macroscopic bodies become immersed therein.

In most of the known cases the Casimir force is attractive in situations where the bodies in question are identical. This however turns out not to be a general rule.

In our theoretical work we addressed a system of bosonic particles in the vicinity of a quantum critical state, where both thermal and quantum fluctuations are strong. As our exact analysis indicates, the sign of the Casimir force between two bodies immersed in such a medium may be changed by varying the ratio between their separation D and the thermal de Broglie length λ. In the thermal regime D>>λ the force in question is attractive, however, by varying the system setup so that D<<λ one crosses over to a regime admitting repulsive Casimir interactions.

P. Jakubczyk, M. Napiórkowski and T. Sęk, Repulsive Casimir forces at quantum criticality, EPL 113, 30006 (2016)
[Abstract]