Consider a quantum mechanical system described by the Hamiltonian operator \(\hat H\), with eigenfunctions \(\psi_n\) and corresponding eigenvalues \(E_n\) such that: \(H^{ψ_n}​=E_n​ψ_n\)

where  n = 0, 1, 2, \dots" id="MathJax-Element-75-Frame" role="presentation" style="position: relative;" tabindex="0"> n = 0, 1, 2, \dots , and the eigenvalues are ordered as " id="MathJax-Element-76-Frame" role="presentation" style="position: relative;" tabindex="0"> \(E_0​≤E_1​≤E_2​≤….\)

An arbitrary wavefunction \(\psi\) is expanded in terms of these eigenfunctions as: \(Ψ=n∑​c_n​ψ_n\)

where  are complex coefficients.

The expectation value of the Hamiltonian \(\hat H\) for this wavefunction  \Psi" id="MathJax-Element-78-Frame" role="presentation" style="position: relative;" tabindex="0"> \Psi is given by:\(⟨\hat H⟩=\frac{∑_n​∣c_n​∣^2E_n}{∑_n​∣c_n​∣^2}\)

Which of the following statements about the expectation value \(<\hat H>\) is correct?

1

2
\(⟨\hat H⟩≥E_0\)
3
\(⟨\hat H⟩=E_0​ for\, any\, choice\, of \, coefficients \, c_n\)
4
\(⟨\hat H⟩≤E_1\,​ only\, if\, c_0​=0\)

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