Quantum Algorithms Database
Iterative Quantum Phase Estimation
A resource-efficient variant of standard quantum phase estimation that uses a single ancilla qubit repeatedly, instead of many qubits at once — better suited to near-term hardware.
Year
2007 (Dobšíček et al.)
Inventor(s)
Dobšíček, Johansson, Shimoni & Nori
Speedup Type
Exponential Speedup
Difficulty
★★★★☆
The Problem
Estimating the phase associated with a quantum operation's eigenstate (as in standard phase estimation), but using significantly fewer physical qubits.
How It Works
Repeats a single-qubit measurement-and-feedback procedure multiple times, extracting one bit of phase information per round instead of using a large register of qubits simultaneously.
Real-World Impact
Makes phase estimation — a key subroutine in Shor's Algorithm and quantum chemistry simulation — more practical on today's qubit-limited NISQ hardware.