Controlling the Casimir Torque

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Our understanding of electrical charges and forces can break down when quantum effects play a role. For example, when two conductive plates or surfaces are brought together they either repel or attract each other depending on whether they have the same or opposite electric charges. If they are uncharged, there is no electrical force between them. However, this classical picture breaks down when the surfaces are brought very close together with a gap of a few nanometers. At that small distance the electric field between the surfaces exhibits quantum effects and there is a small but measureable force between them. This is called the Casimir effect, named after the scientist who explained how the quantized electromagnetic field results in a force between uncharged surfaces. Understanding various types of Casimir forces is important for our fundamental knowledge of quantum physics and for applications to materials used in micro- and nano-technologies. This project will study a phenomenon referred to as the Casimir torque in which the two surfaces are caused to rotate. The research team will demonstrate and quantify how materials with different optical properties experience the Casimir torque. Despite the pervasive nature of quantum fluctuations of the electromagnetic field and their influence on nanoscale science and engineering, control of fluctuation-induced phenomena is difficult. Here it is proposed to test several hypotheses and predictions related to the Casimir torque, which will lead to the generation of new knowledge about controlling these interactions. The first test will be of the hypothesis that the measured torque can be strengthened by increasing the optical anisotropy of the two materials. The second test will be of the hypothesis that the direction of rotation depends on whether the optical axis of a birefringent material has an index of refraction that is higher or lower than that of its extraordinary axis. The third will be to explore the idea of using the Casimir force to translate lateral motion into rotational motion. These experiments will not only advance the science related to quantum phenomena but will also lead to new experimental techniques.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.