Variational quantum state preparation within an entangle-rotate circuit framework for quantum-enhanced metrology in noisy systems

TL;DR

This paper presents a variational quantum circuit framework for generating quantum states optimized for enhanced metrology in noisy two-level systems, demonstrating improved quantum Fisher information with increased circuit depth.

Contribution

It introduces an entangle-rotate circuit architecture that enhances state preparation for quantum metrology under realistic noise, applicable to various interaction types and system sizes.

Findings

QFI improves with increased circuit layers even under noise

The architecture expands the accessible state space in noisy conditions

Effective for systems with more than 8 qubits

Abstract

We investigate the generation of quantum states for precision metrology in noisy two-level systems. These states are obtained by optimizing a variational quantum circuit to maximize the quantum Fisher information (QFI) of the output state for a given decoherence rate and interaction Hamiltonian. The circuit architecture, inspired by twist-and-turn schemes, features a sequence of $n$ entangling layers, each consisting of entangling gates followed by a global rotation. We observe notable improvements in the QFI as the circuit layer depth increases, even for appreciable noise rates, demonstrating that our entangle-rotate architecture expands the accessible state space under realistic noise conditions. Our approach thus provides a general and efficient framework for generating quantum-enhanced sensing states. Our analysis extends to systems of power-law interactions spanning from all-to-all to nearest-neighbor interactions. We also analyze the capabilities of our circuit to prepare states for system sizes greater than $8$ qubits.