= Momentum representation in quantum mechanics
{title2=$\phi(k)=(2\pi)^{-1/2}\int\psi(x)e^{-ikx}\,dx$}
The <Fourier transform> in the title represents a one-dimensional state in the <wavevector> basis. Its <probability density> is $|\phi(k)|^2$, normalized by $\int|\phi(k)|^2dk=1$ when $\int|\psi(x)|^2dx=1$. For physical <momentum> $p=\hbar k$, the density per unit momentum is $|\phi(p/\hbar)|^2/\hbar$. A confined stationary <energy eigenstate> need not be a <momentum eigenstate>.
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