# Why is the Gupta-Bleuler gauge unfashionable?

In the early days of quantum electrodynamics, the most popular gauge chosen was the Gupta-Bleuler gauge stating that for physical states, $$\langle \chi | \partial^\mu A_\mu | \psi \rangle = 0.$$

However, this gauge is practically never used now. Why? Is there anything wrong or inappropriate with the Gupta-Bleuler gauge?

How is the Gupta-Bleuler gauge related to the $R_\xi$ gauge?

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I think that you've got to emphasize that the gauge is not the same as $\partial^\mu A_\mu=0$. Link to wikipedia will do. –  Kostya Feb 10 '11 at 9:27