Optimal Coherent Quantum Phase Estimation via Tapering

Understand

Due to its significance as a subroutine, in this work, we consider the coherent version of the quantum phase estimation problem, where given an arbitrary input state and black-box access to unitaries $U$ and controlled-$U$, the goal is to estimate the phases of $U$ in superposition.

• Most existing phase estimation algorithms involve intermediary measurements that disrupt coherence.
• Only a couple of algorithms, including the standard quantum phase estimation algorithm, consider this coherent setting.
• However, the standard algorithm only succeeds with a constant probability.