Earlier in this QM-101 series I posted about quantum spin. That post looked at spin 1/2 particles, such as electrons (and silver atoms). This post looks at spin in photons, which are spin 1 particles. (Bell tests have used both spin types.) In photons, spin manifests as polarization.
Photon spin connects the Bloch sphere to the Poincaré sphere — an optics version designed to represent different polarization states. Both involve a two-state system (a qubit) where system state is a superposition of two basis states.
Incidentally, photon polarization reflects light’s wave-particle duality.
Lately I’ve been playing a little game of What’s the Wavelength? The question is certainly a bit evocative. Wavelength could refer to many things: a favorite radio station or, metaphorically extended, a favorite anything. It might even evoke an old news meme, although the supposed question posed that time was about frequency (which is just the inverse of wavelength).
Wavelength might even apply to one’s political, social, sexual, musical, or whatever, alignment, but in this case I mean it literally and physically. Under quantum mechanics — our best description of small-scale physical reality — everything manifests as a wave. That means everything has a wavelength — the de Broglie wavelength.
I’ve been curious about it for a couple of reasons.