Escape from potential traps assisted by the Casimir-Polder force fluctuations*

Continuous progress in nanotechnology leads to technologies with ever smaller features, with size down to a few nanometers. In this regime, quantum effects that used to be the subjects of theoretical physics become technologically important and can add functionalities or induce failures to nanodevices.  Such is the Casimir force that has recently attracted attention because of its effects on nanoelectromechanical systems. However, much less studied are the fluctuations of the Casimir force, which can be strong enough to influence systems in which the mean value of the Casimir force is negligible.

 

Here, we study the effects of the fluctuations of the Casimir-Polder force induced by a surface on a classical particle in a confining potential. Specifically, we study the motion of the particle in a harmonic potential using the Langevin equation that results from the coupling of the particle to the zero-point fluctuation of the electromagnetic field of the surface. We show that, even at absolute zero temperature, the classical particle has a non-zero average kinetic energy that can be used to escape a finite potential barrier.

We study both charged and neutral, but polarizable, particles. In the case of the polarizable particles we identify a term in the formula for the kinetic energy that has been ignored in previous studies. This term is linear in the polarizability of the particle, which is counter intuitive because the Casimir-Polder force itself is linear in polarizability and we expect its fluctuation squared to be quadratic in polarizability. However, this argument only holds for the average value of the Casimir-Polder force and not its fluctuations.

In conclusion, we find that both charged and neutral particles next to a surface will obtain a non-zero kinetic energy due to the fluctuations of the electromagnetic field. The kinetic energy might then be enough to allow the particle to escape over a potential barrier.

Our findings have important implications for future technologies. For example, they suggest that quantum dots that are a few nanometers close to a surface will experience a high non-radiative decay rate and that, since a particle can have non-zero kinetic energy at zero temperature, chemical reactions at absolute zero might be possible using a surface as a catalyst.