Quantum Phase Estimation (QPE) | Eigenvalue Evaluation Primitive
Quick Technical Answer:
Quantum Phase Estimation (QPE) calculates the unknown phase θ of a unitary operator's eigenvalue U|u⟩ = e^{2πiθ}|u⟩ to n bits of precision using ancilla qubits, controlled-U^{2^j} powers, and the Inverse Quantum Fourier Transform (IQFT).
Formula / Unitary:
U|u\rangle = e^{2\pi i \theta} |u\rangle, \quad |0\rangle^{\otimes t} |u\rangle \xrightarrow{\text{QPE}} |\tilde{\theta}\rangle |u\rangle
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Frequently Asked Questions
What is the primary application of QPE in chemistry?
In quantum chemistry, QPE is applied to the molecular Hamiltonian propagator U = e^{-iHt} to measure exact molecular ground state energies with exponential precision.