Free-Fermionic Topological Quantum Sensors

TL;DR

This paper demonstrates that topological edge states in free-fermionic systems enable quantum-enhanced sensing near phase boundaries, independent of symmetry-breaking or long-range entanglement, highlighting gap closing as a key factor.

Contribution

It shows quantum sensing enhancement in topological systems without symmetry-breaking or long-range entanglement, emphasizing the role of gap closing and providing a simple measurement strategy.

Findings

Quantum enhancement occurs near topological phase boundaries.

Edge states enable near-optimal sensing precision.

Enhancement persists in experimentally accessible models.

Abstract

Second order quantum phase transitions, with well-known features such as long-range entanglement, symmetry breaking, and gap closing, exhibit quantum enhancement for sensing at criticality. However, it is unclear which of these features are responsible for this enhancement. To address this issue, we investigate phase transitions in free-fermionic topological systems that exhibit neither symmetry-breaking nor long-range entanglement. We analytically demonstrate that quantum enhanced sensing is possible using topological edge states near the phase boundary. Remarkably, such enhancement also endures for ground states of such models that are accessible in solid state experiments. We illustrate the results with 1D Su-Schrieffer-Heeger chain and a 2D Chern insulator which are both experimentally accessible. While neither symmetry-breaking nor long-range entanglement are essential, gap closing remains as the major candidate for the ultimate source of quantum enhanced sensing. In addition, we also provide a fixed and simple measurement strategy that achieves near-optimal precision for sensing using generic edge states irrespective of the parameter value. This paves the way for development of topological quantum sensors which are expected to also be robust against local perturbations.