http://www.sciencemag.org/content/348/6242/1448.short Quantum spin Hall effect of light: ABSTRACT: Maxwell’s equations, formulated 150 years ago, ultimately describe properties of light, from classical electromagnetism to quantum and relativistic aspects. The latter ones result in remarkable geometric and topological phenomena related to the spin-1 massless nature of photons. By analyzing fundamental spin properties of Maxwell waves, we show that free-space light exhibits an intrinsic quantum spin Hall effect—surface modes with strong spin-momentum locking. These modes are evanescent waves that form, for example, surface plasmon-polaritons at vacuum-metal interfaces. Our findings illuminate the unusual transverse spin in evanescent waves and explain recent experiments that have demonstrated the transverse spin-direction locking in the excitation of surface optical modes. This deepens our understanding of Maxwell’s theory, reveals analogies with topological insulators for electrons, and offers applications for robust spin-directional optical interfaces.
http://theconversation.com/scientis...operty-of-light-150-years-after-maxwell-43928 extract: Beginning to see the light Now, the new study suggests that the seeds of this seemingly exotic quantum spin Hall effect are actually all around us. And it is not to electrons that we should look to find them, but rather to light itself. In modern physics, matter can be described either as a wave or a particle. In Maxwell’s theory, light is an electromagnetic wave. This means it travels as a synchronised oscillation of electric and magnetic fields. By considering the way in which these fields rotate as the wave propagates, the researchers were able to define a property of the wave, the “transverse spin”, that plays the role of the electron spin in the quantum spin Hall effect. In a homogeneous medium, like air, this spin is exactly zero. However, at the interface between two media (air and gold, for example), the character of the waves change dramatically and a transverse spin develops. Furthermore, the direction of this spin is precisely locked to the direction of travel of the light wave at the interface. Thus, when viewed in the correct way, we see that the basic topological ingredients of the quantum spin Hall effect that we know for electrons are shared by light waves.
The following link attempts to explain things in a simpler fashion. http://www.spacedaily.com/reports/T...t_is_a_fundamental_property_of_light_999.html
I am not the least bit surprised at this result I also believe it will get more interesting than this.
Ahem. Photon spin is polarisation. Photons are spin-1 quanta, so there are 2 x 1 + 1 = 3 polarisation states. We can measure horizontal or vertical polarisation or some linear combination of both, we can measure circular or elliptic polarisation, where the latter is a combination of linear and circular polarisation, and finally there is this "unusual" transverse polarisation, which I think is polarisation along the axis of propagation. The first kind of polarisation can be considered as (some linear combination of) spin up/down and spin left/right, but also as some combination of circular polarisation (rotating clockwise and anticlockwise in superposition). Damn, it is confusing, unless you've studied say QED or QFT, and you really understand what a (choice of) quantum gauge is. P.S. I'm not saying I do, but I do know it's something you inevitably have to learn (if you want to graduate, say).
And as if that isn't confusing enough, W and Z bosons exhibit one more axis of polarization that photons cannot, evidently because they have mass and must therefore propagate slower than c. The Berkeley physics text 'Waves' (vol 3 or 4) used to provide a little polarization experimenter's kit including linear polarizers, circular polarizers, quarter and half wave birefringent plates so that you could experiment and play with them. One of my all time favorite toys, when I wore a younger man's clothes. Linear polarizers like those are made by chemically bonding iodine to long chains of polymer molecules and then stretching the sheets so that the polymers make a grid of parallel fibers. The axis of polarization is actually at 90 degrees with respect to these elongated polymer chains. You can also make a nice linear polarizer with a chunk of glass inside of a collimated opaque block, tilted at Brewster's angle. This device isn't in the kit, but it makes a cool demonstration. Not quite as lossy as a polymer type polarizer either. Get some strips of cheap cellophane tape and criss cross layers of it to make a polarized rotating color stained glass window display sandwiched between two linear polarizers. Monochromatic LP light of different colors decode to different orientation of the objective (decoder) LP sheet. Rotating them allows you to view different colors in the same way they are obtained from the flatscreen monitor you are probably viewing right now.
Some of the old experiments are still fun. Thanks for the reminder of my youth. I guess.. Please Register or Log in to view the hidden image!
