Joint approach improves accuracy of quantum expectation calculations
New directions in dynamical expectation estimation
Emerging Technologies
Summary
Calculating certain values in quantum systems usually involves approximations made separately for parts of the problem, which can lead to errors adding up. The authors propose a new method that considers both the parts together when making approximations, which helps reduce mistakes. They use a special algorithm that updates the estimates forward and backward to improve accuracy. Tests on simulated quantum circuits show their method can be much more precise than older techniques.
What this means in practice
- •For quantum algorithm developers: Increase precision of expectation value calculations in quantum simulation algorithms to improve overall result accuracy.
- •For quantum hardware designers: Enhance benchmarking processes by obtaining more accurate estimated measurements from quantum circuits using joint state-observable approximations.
Authors
Panjin Kim, Kyung Chul Jeong, Yun-Tak Oh
Abstract
Computing dynamical expectation values typically relies on approximations optimized for the state or observable separately, without accounting for how their errors combine in the final expression.This work explores an alternative approach in which each approximation is guided by both the state and the observable, accounting for how they jointly determine the target expectation value. This idea is implemented through a sweep algorithm with coupled loss functions for forward state and backward observable updates. Exact error relations provide an analytical rationale for how the proposed losses can improve the accuracy. Numerical tests on 30-qubit random circuits show errors two to three orders of magnitude smaller than those of variational state compression at equal bond dimensions. These results motivate further exploration of joint state and observable approximation for dynamical expectation value estimation.