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Any known way to diagonalize the Hamiltonian of a charge particle in a EM field?

Physics Asked on February 15, 2021

Consider the Hamiltonian of a free (charged) particle, i.e.,
$$
H = frac{p^2}{2m}.
$$

This is easily "diagonalized" by wave functions $e^{ikx}$ (where I’m speaking loosely of diagonalization since $e^{ikx}$ are not eigenstates in the Hilbert space $L^2$. Of course, we could regularize the problem by considering the Hamiltonian on a finite lattice with periodic boundary condition so that wave functions are indeed eigenstate.)

If we were to add a EM field, then by minimal coupling, the Hamiltonian becomes
$$
H = frac{1}{2m}(p-eA)^2 +evarphi
$$

Question. Is there an analytic or operator-based solution (e.g., latter operators) of diagonalizing this minimally-coupled Hamiltonian (we can ignore $varphi$ if that helps)? If this problem is not regularized, we could also think of Peierls substitution of a second-quantized hopping Hamiltonian on a finite lattice with periodic boundary conditions, i..e,
$$
H= sum_{i,j} t_{ij} c_i^* exp{(-iA_{ij})} c_j
$$

One Answer

For a uniform/constant magnetic field, this is problem of Landau quantization. It is essentially harmonic oscillator, with a momentum-dependant shift in its energy eigenvalues, and therefore can be understood in terms of ladder operators.

For a generic $A$ and $varphi$ I don't know if this is possible, but somehow I would doubt it would be doable generally (apart from special cases of interest for $A$ and $varphi$).

Answered by QuantumEyedea on February 15, 2021

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