Refractive index of glass for the VIS light is about 1.5, meaning that light will be reflected with some ratio (say 0.04, if we have normal incidence and semi infinite media). It is obvious for many photons, but how does it look for only 1 photon? How will the ratio of the reflected to incident intensity look like? Will it be 0 or 1? Or is there a flaw somewhere in my reasoning? How does the polarization comes into picture here?
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$\begingroup$ Thanks for the help. Now to be clear: probability means that one photon reflects while other one will pass, and ration will be 4 to 96 in average. What in the Universe defines the path of the photon? If all photons are same, and material is the same, what chages from event to event? $\endgroup$– VitalyCommented Jan 18, 2017 at 16:45
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2 Answers
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Reflection is probabilistic. Meaning that each photon has a probability of 4% of being reflected.
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For the purposes of calculation of the unitary evolution of the one-photon electromagnetic field state, the refractive index is exactly the same as for a classical field. As a quantum state, such an EM field propagating in matter is simply a quantum superposition of a one photon free EM field state and excited matter states. The EM field is coupled to the excited states of all the matter atoms / molecules at once in superposition. See my answer here or here for more details on these issues.
As BoyFarrell's Answer says, the actual reflexion, as measured by a light detector, is probabilistic, with each launched photon having a probability of being reflected and detected (assuming the detection aperture is big enough) of a value given by the Fresnel-equation caclculated reflexion to incident intensity ratio.
answered Jan 17, 2017 at 7:11
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$\begingroup$ Thanks for the help. Now to be clear: probability means that one photon reflects while other one will pass, and ration will be 4 to 96 in average. What in the Universe defines the path of the photon? If all photons are same, and material is the same, what chages from event to event? $\endgroup$– VitalyCommented Jan 20, 2017 at 10:10
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$\begingroup$ @user142244 The path of the photon is not well defined: the quantum field in a one-photon number state propagates in a manner described by Maxwell's equations - very similar to classical electromagnetic fields (i.e. at the speed of light, with the same diffraction, focussing, etc effects, so that the field as the same "shape" and region of influence as a propagating classical EM field). The quantum EM field then interacts with the detector to drop to the ground (vacuum) state. What gives rise to the probabilistic effect? ..... $\endgroup$ Commented Jan 20, 2017 at 12:32
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$\begingroup$ @user142244 .... That's the basic measurement problem. Your calculation of ratios is correct, BTW, for normal incidence on an interface between air and glass with $n=1.5$. $\endgroup$ Commented Jan 20, 2017 at 12:33