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Register a new userOptical pulling using topologically protected one-way-transport surface-arc waves
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This paper proposes a new method to achieve robust optical pulling of particles by using an air waveguide sandwiched between two chiral hyperbolic metamaterials. The pulling force is induced by mode conversion between a pair of one-way-transport surface-arc waves supported on the two metamaterial surfaces of the waveguide. The surface arcs bridge the momentum gaps between isolated bulk equifrequency surfaces (EFSs) and are topologically protected by the nontrivial Chern numbers of the EFSs. When an incident surface-arc wave with a relatively small wavenumber $k_{x1}$ is scattered by the particle, a part of its energy is transferred to the other surface-arc mode with $k_{x2}(>k_{x1}). Because the electromagnetic wave acquires an additional forward momentum from the particle proportional to $k_{x2}-k_{x1}$ during this process, the particle will always be subjected to an optical pulling force irrespective of its material, shape and size. Since the chiral surface-arc waves are immune to backscattering from local disorders and the metamaterials are isotropic in the xy plane, robust optical pulling can be achieved in a curved air waveguide and can go beyond standard optical pulling mechanisms which are limited to pull in a straight-line.
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We show that long-range and robust acoustic pulling can be achieved by using a pair of one-way chiral surface waves supported on the interface between two phononic crystals composed of spinning cylinders with equal but opposite spinning velocities embedded in water. When the chiral surface mode with a relative small Bloch wave vector is excited, the particle located in the interface waveguide will scatter the excited surface mode to another chiral surface mode with a greater Bloch wave vector, resulting in an acoustic pulling force, irrespective of the size and material of the particle. Thanks to the backscattering immunity of the chiral surface waves against local disorders, the particle can be pulled following a flexible trajectory as determined by the shape of the interface. As such, this new acoustic pulling scheme overcomes some of the limitations of the traditional acoustic pulling using structured beams, such as short pulling distances, straight-line type pulling and strong dependence on the scattering properties of the particle. Our work may also inspire the application of topological acoustics to acoustic manipulations.
We demonstrate both analytically and numerically the existence of optical pulling forces acting on particles located near plasmonic interfaces. Two main factors contribute to the appearance of this negative reaction force. The interference between the incident and reflected waves induces a rotating dipole with an asymmetric scattering pattern while the directional excitation of surface plasmon polaritons (SPP) enhances the linear momentum of scattered light. The strongly asymmetric SPP excitation is determined by spin-orbit coupling of the rotating dipole and surface plasmon polariton. As a result of the total momentum conservation, the force acting on the particle points in a direction opposite to the incident wave propagation. We derive analytical expressions for the force acting on a dipolar particles placed in the proximity of plasmonic surfaces. Analytical expressions for this pulling force are derived within the dipole approximation and are in excellent agreement with results of electromagnetic numerical calculations. The forces acting on larger particles are analyzed numerically, beyond the dipole approximation.
Entangled multiphoton states lie at the heart of quantum information, computing, and communications. In recent years, topology has risen as a new avenue to robustly transport quantum states in the presence of fabrication defects, disorder and other noise sources. Whereas topological protection of single photons and correlated photons has been recently demonstrated experimentally, the observation of topologically protected entangled states has thus far remained elusive. Here, we experimentally demonstrate the topological protection of spatially-entangled biphoton states. We observe robustness in crucial features of the topological biphoton correlation map in the presence of deliberately introduced disorder in the silicon nanophotonic structure, in contrast with the lack of robustness in nontopological structures. The topological protection is shown to ensure the coherent propagation of the entangled topological modes, which may lead to robust propagation of quantum information in disordered systems.
The tremendous progress in light scattering engineering made it feasible to develop optical tweezers allowing capture, hold, and controllable displacement of submicronsize particles and biological structures. However, the momentum conservation law imposes a fundamental restriction on the optical pressure to be repulsive in paraxial fields. Although different approaches to get around this restriction have been proposed, they are rather sophisticated and rely on either wavefront engineering or utilize active media. Herein, we revisit the issue of optical forces by their analytic continuation to the complex frequency plane and considering their behavior in transient. We show that the exponential excitation at the complex frequency offers an intriguing ability to achieve a pulling force for a passive resonator of any shape and composition even in the paraxial approximation, the remarkable effect which is not reduced to the Fourier transform. The approach is linked to the virtual gain effect when an appropriate transient decay of the excitation signal makes it weaker than the outgoing signal that carries away greater energy and momentum flux density. The approach is implemented for the Fabry-Perot cavity and a high refractive index dielectric nanoparticle, a fruitful platform for intracellular spectroscopy and lab-on-a-chip technologies where the proposed technique may found unprecedented capabilities.
It is shown that quantum walks on one-dimensional arrays of special linear-optical units allow the simulation of discrete-time Hamiltonian systems with distinct topological phases. In particular, a slightly modified version of the Su-Schrieffer-Heeger (SSH) system can be simulated, which exhibits states of nonzero winding number and has topologically protected boundary states. In the large-system limit this approach uses quadratically fewer resources to carry out quantum simulations than previous linear-optical approaches and can be readily generalized to higher-dimensional systems. The basic optical units that implement this simulation consist of combinations of optical multiports that allow photons to reverse direction.
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