A Modern Approach to Quantum Mechanics · Problem 2.18

Angular Momentum — John S. Townsend

Physics — Quantum Mechanics · projection-operators-photon-polarization

Problem

Construct projection operators out of bras and kets for xx-polarized and yy-polarized photons. Give physical examples of devices that can serve as these projection operators. Use (a) the properties of bras and kets and (b) the properties of the physical devices to show that the projection operators satisfy P^x2=P^x\hat{P}_x^2 = \hat{P}_x, P^y2=P^y\hat{P}_y^2 = \hat{P}_y, and P^xP^y=P^yP^x=0\hat{P}_x\hat{P}_y = \hat{P}_y\hat{P}_x = 0.

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