I Can an electron in a magnetic field radiate a virtual photon?

[docnet]

TL;DR

Does a spin in a magnetic field radiate a virtual photon?

In Theoretical Minimum: Quantum mechanics, Leonard Susskind describes an electron in the higher energy spin state in a magnetic field radiates a photon of energy $\hbarγ|B_0|$ and flips into the lower energy spin state. I am wondering if this photon is related to the "virutal photon" that mediates the electromagnetic field. I am wondering whether a large number of such a photon relates the Zeeman transition of the spin 1/2 particles to a classically observable magnetic field, such as MRI? I am sorry if my question is not clear, I do not have a strong background in physics yet. A thoughtful explanation including equations would be greatly appreciated. Thank you.

 

[hutchphd]

The quantum description of absorbing energy by atoms (or electrons) for magnetic resonance involves actual (not virtual) photons of low energy (i.e. radio frequencies). The MRI uses the transitions of protons in the hydrogen nucleus and so while similar to the electron Zeeman splitting, it is not usually called that.
Most of the details of magnetic resonance are completely understandable in terms of Classical physics although the Quantum explanation is sometimes easier to understand.

There are many articles extant without me reproducing them here.

 

[weirdoguy]

Virtual photons are internal lines in Feynman diagrams, hence they can't be radiated as real photons which correspond to external lines. And, as always with virtual particles, I recommend reading these Insights articles:

https://www.physicsforums.com/insights/what-are-virtual-particles-intro/
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/

 

[vanhees71]

The photon emitted due to a spin flip of an electron within an atom with the energy difference between the two possible spin orientations due to the magnetic field of nucleus, i.e., the hyperfine structure of the atomic energy levels, is of course a real photon. It can be observed as em. waves. The most important example for astrophysicists is the 21 cm (wavelength) line of the hydrogen atom:

https://en.wikipedia.org/wiki/Hydrogen_line