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Multiple choice
A Hamiltonian has eigenvalues {−1,0,2}\{-1, 0, 2\}. By the variational principle, the expectation ⟨ψ∣H∣ψ⟩\langle\psi|H|\psi\rangle for any normalized trial state ∣ψ⟩|\psi\rangle is bounded below by the ground-state energy. What is that lower bound?