Is my understanding of EM field quantization correct?

[HomogenousCow]

Essentially how I understand it is, (this is for the quantization of an EM field in vaccum)
-Fields become operators, a specific E operator will contain the number and multiple of rising and lowering operators needed to raise a vacuum state into the desired quantum state
-The electromagnetic field is a superposition of monochromatic states, corresponding to a superposition of monochromatic waves in the classical theory

However my question is, where do the uncertainties and probabilities come in? If I have a photon state in two frequencies, does that mean the field has a fifty-fifty chance of being in either frequency? I think this must be wrong because if it were true, then all fields would be monochromatic when measured.

 

[mfb]

However my question is, where do the uncertainties and probabilities come in? If I have a photon state in two frequencies, does that mean the field has a fifty-fifty chance of being in either frequency? I think this must be wrong because if it were true, then all fields would be monochromatic when measured.

If you measure photon frequencies with arbitrary precision, you will always get a single value for each measured photon. Real radiation is always a superposition within some frequency range, and a measurement will give some single value. Note that this depends a bit on your favorite interpretation of quantum mechanics.