Casimir Forces and Geometry in Nanosystems

Fluctuations of the Casimir-like force between two membrane inclusions

Although Casimir forces are inseparable from their fluctuations, little is known about these fluctuations in soft matter systems. We use the membrane stress tensor to study the fluctuations of the membrane-mediated Casimir-like force. This method enables us to recover the Casimir force between two inclusions and to calculate its variance. We show that the Casimir force is dominated by its fluctuations. Furthermore, when the distance d between the inclusions is decreased from infinity, the variance of the Casimir force decreases as -1/d^2. This distance dependence shares a common physical origi…

Casimir force on interacting Bose-Einstein condensate

We have presented an analytic theory for the Casimir force on a Bose-Einstein condensate (BEC) which is confined between two parallel plates. We have considered Dirichlet boundary conditions for the condensate wave function as well as for the phonon field. We have shown that, the condensate wave function (which obeys the Gross-Pitaevskii equation) is responsible for the mean field part of Casimir force, which usually dominates over the quantum (fluctuations) part of the Casimir force.

Casimir force for geometrically confined ideal Bose gas in a harmonic-optical potential

In this study, we have derived close form of the Casimir force for the non-interacting ideal Bose gas between two slabs in harmonic-optical lattice potential by using Ketterle and van Druten approximation. We find that Bose-Einstein condensation temperature $T_{c}$ is a critical point for different physical behavior of the Casimir force. We have shown that Casimir force of confined Bose gas in the presence of the harmonic-optical potential decays with inversely proportional to $d^{5}$ when $T\leq T_{c}$. However, in the case of $T>T_{c}$, it decays exponentially depends on separation $d$ of th…

Repulsive Casimir forces

We discuss repulsive Casimir forces between dielectric materials with non trivial magnetic susceptibility. It is shown that considerations based on naive pair-wise summation of Van der Waals and Casimir Polder forces may not only give an incorrect estimate of the magnitude of the total Casimir force, but even the wrong sign of the force when materials with high dielectric and magnetic response are involved. Indeed repulsive Casimir forces may be found in a large range of parameters, and we suggest that the effect may be realized in known materials. The phenomenon of repulsive Casimir forces ma…

Direct calculation of the critical Casimir force in a binary fluid

We show that critical Casimir effects can be accessed through direct simulation of a model binary fluid passing through the demixing transition. We work in the semi grand canonical ensemble, in slab geometry, in which the Casimir force appears as the excess of the generalized pressure, $P_{\bot}-nμ$. The excesses of the perpendicular pressure, $P_{\bot}$, and of $nμ$, are individually of much larger amplitude. A critical pressure anisotropy is observed between forces parallel and perpendicular to the confinement direction, which collapses onto a universal scaling function closely related to th…

Pseudo-Casimir force in confined nematic polymers

We investigate the pseudo-Casimir force in a slab of material composed of nematically ordered long polymers. We write the total mesoscopic energy together with the constraint connecting the local density and director fluctuations and evaluate the corresponding fluctuation free energy by standard methods. It leads to a pseudo-Casimir force of a different type than in the case of standard, short molecule nematic. We investigate its separation dependence and its magnitude and explicitly derive the relevant limiting cases.

利用激光诱导加热开展光镊捕获下临界卡西米尔力的实验研究

Laser-induced heating for the experimental study of critical Casimir forces with optical trapping

本研究利用激光诱导加热调控二元混合溶液中光镊捕获胶体微球的临界卡西米尔力，借助系统临界行为实现自测温，结合涨落定理分析非平衡驱动下临界胶体系统的能量学特性，为浴诱导力非平衡研究与临界驱动纳米系统设计提供新途径。

Transient Casimir forces from quenches in thermal and active matter

We compute fluctuation-induced (Casimir) forces for classical systems after a temperature quench. Using a generic coarse-grained model for fluctuations of a conserved density, we find that transient forces arise even if the initial and final states are force-free. In setups reminiscent of Casimir (planar walls) and van der Waals (small inclusions) interactions, we find comparable exact universal expressions for the force. Dynamical details only scale the time axis of transient force curves. We propose that such quenches can be achieved, for instance, in experiments on active matter, employing …

Casimir Forces: An Exact Approach for Periodically Deformed Objects

A novel approach for calculating Casimir forces between periodically deformed objects is developed. This approach allows, for the first time, a rigorous non-perturbative treatment of the Casimir effect for disconnected objects beyond Casimir's original two-plate configuration. The approach takes into account the collective nature of fluctuation induced forces, going beyond the commonly used pairwise summation of two-body van der Waals forces. As an application of the method, we exactly calculate the Casimir force due to scalar field fluctuations between a flat and a rectangular corrugated plat…

Comment on ``Lateral Casimir force beyond the proximity-force approximation''

We demonstrate that the approach by Rodrigues et al. (PRL, v.96, 100402, 2006) to the description of the lateral Casimir force between corrugated surfaces is in disagreement with a path-integral theory by Emig et al. (PRA, v.67, 022114, 2003), and the approximations used are not appropriate for comparison to experiment.

Repulsive Casimir force in Bose-Einstein Condensate

We study the Casimir effect for a three dimensional system of ideal free massive Bose gas in a slab geometry with Zaremba and anti-periodic boundary conditions. It is found that for these type of boundary conditions the resulting Casimir force is repulsive in nature, in contrast with usual periodic, Dirichlet or Neumann boundary condition where the Casimir force is attractive (Martin P. A. and Zagrebnov V. A., Europhys. Lett., 73 (2006) 15.). Casimir forces in these boundary conditions also maintain a power law decay function below condensation temperature and exponential decay function above …

Attractive Casimir Forces in a Closed Geometry

We study the Casimir force acting on a conducting piston with arbitrary cross section. We find the exact solution for a rectangular cross section and the first three terms in the asymptotic expansion for small height to width ratio when the cross section is arbitrary. Though weakened by the presence of the walls, the Casimir force turns out to be always attractive. Claims of repulsive Casimir forces for related configurations, like the cube, are invalidated by cutoff dependence.

On the calculation of the Casimir forces

Casimir forces are a manifestation of the change in the zero-point energy of the vacuum caused by the insertion of boundaries. We show how the Casimir force can be computed by consideration of the vacuum fluctuations that are suppressed by the boundaries, and rederive the scalar Casimir effects for a series of geometries. For the planar case a finite universal force is automatically found. For curved geometries formally divergent expressions are encountered which we argue are largely due to the divergent self-energy of the boundary contributing to the force. This idea is supported by computing…

Control of the Casimir Force Using Semiconductor Test Bodies

We describe experimental and related theoretical work on the measurement of the Casimir force using semiconductor test bodies. This field of research started in 2005 and several important and interesting results have already been obtained. Specifically, the Casimir force or its gradient were measured in the configuration of an Au-coated sphere and different semiconductor surfaces. It was found that the force magnitude depends significantly on the replacement of the metal with a semiconductor and on the concentration of charge carriers in the semiconductor material. Special attention is paid to…

Casimir forces in a T operator approach

We explore the scattering approach to Casimir forces. Our main tool is the description of Casimir energy in terms of transition operators, as presented in Kenneth and Klich, Phys. Rev. Lett. 97, 160401 (2006). We study the convergence properties of the formula and how to utilize it, together with scattering data to compute the force. We illustrate the approach by describing the force between scatterers in 1d and 3d,, and in particular show how it may be applied in order to study the interaction between two spherical bodies at all distances.

Opposites Attract - A Theorem About The Casimir Force

We consider the Casimir interaction between (non-magnetic) dielectric bodies or conductors. Our main result is a proof that the Casimir force between two bodies related by reflection is always attractive, independent of the exact form of the bodies or dielectric properties. Apart from being a fundamental property of fields, the theorem and its corollaries also rule out a class of suggestions to obtain repulsive forces, such as the two hemisphere repulsion suggestion and its relatives.