RUI, OP: Space-Variant Polarization States of Light

Colgate University, Hamilton NY

Investigators

Abstract

The use of beams of light, like laser beams, has been transformative in the development of modern technologies, from telephone communications where information is encoded in the light traveling through fibers, to laser surgery where high light intensity is delivered to small areas of tissue. These technologies exploit light's color or energy. Yet another property of light is its polarization, which is invisible to the unaided eye, but seen indirectly, for example, through the visual effects of some types of 3D movies or in polarizing sunglasses. This research will involve preparing light beams with polarization that varies from point to point across the beam, like in an image. This polarization will be encoded onto individual photons (the "particles" of light). Photons can carry a lot of information while at the same time being quantum, or whole. Technologies that harness the quantum aspects of light and matter have the potential to upgrade current communication technologies to ones with substantially increased speed and capacity. Polarization also holds promise as a tool to manipulate molecules that are chiral, or corkscrew-like. This encompasses most organic molecules, including DNA (the double helix). This research will test recent theories which predict that the polarization of light can be used to segregate chiral molecules into those that spiral clockwise or counterclockwise when viewed from a particular end (DNA always spirals one way but not the other, for example). This is an important step in the synthesis of medicines because molecules that spiral one way could cure while those that spiral the other way could cause harm. This research will involve undergraduates, introducing them to the scientific process while training them in modern photonic technologies. States of light that have spatially variable polarization are similar to entangled quantum states in that both are non-separable. Thus, space-variant-polarization states are well suited for use in quantum information. They add higher dimensions to the quantum states of photons in the following ways: they entail non-separable superpositions of polarization (in two dimensions) and transverse spatial modes of light (in principle, adding an infinite number of additional dimensions). Thus, spatial modes add a higher dimensionality to the space in which to encode quantum information onto single photons. We have developed techniques that encode and decode these states, which due to their space-variant polarization can be diagnosed by imaging techniques. This research will investigate the space of photon pairs entangled in polarization and spatial modes and the nonlocal space-variant polarization images that those states will encode. In parallel, intense beams carrying space-variant polarization will be used to investigate a predicted but yet unconfirmed new light force, which affects chiral molecules in such a way that it segregates the molecules by their handedness. That is, the light creates a field gradient that applies a force that is of opposite sign for right and left handed chiralities. This new force, fundamentally related to optical activity, could be of importance in the chemical synthesis of complex organic molecules, where it is desirable to separate one chirality from the other.