Sarkar Saubhik, Mukhopadhyay Chiranjib, Alase Abhijeet, Bayat Abolfazl
Institute for Quantum Science and Technology and Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
RCQI, Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, 84511 Bratislava, Slovakia.
Phys Rev Lett. 2022 Aug 26;129(9):090503. doi: 10.1103/PhysRevLett.129.090503.
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.
二阶量子相变具有诸如长程纠缠、对称性破缺和能隙关闭等众所周知的特征，在临界状态下展现出用于传感的量子增强效应。然而，尚不清楚这些特征中哪些是造成这种增强效应的原因。为解决这一问题，我们研究了自由费米子拓扑系统中的相变，这类系统既不表现出对称性破缺，也不具有长程纠缠。我们通过分析证明，利用相边界附近的拓扑边缘态可以实现量子增强传感。值得注意的是，这种增强效应在固态实验可实现的此类模型的基态中同样存在。我们用一维Su-Schrieffer-Heeger链和二维陈绝缘体来说明结果，这两者在实验中均可实现。虽然对称性破缺和长程纠缠都不是必需的，但能隙关闭仍是量子增强传感最终来源的主要候选因素。此外，我们还提供了一种固定且简单的测量策略，该策略使用通用边缘态实现近乎最优的传感精度，而与参数值无关。这为拓扑量子传感器的发展铺平了道路，预计这类传感器对局部扰动也具有鲁棒性。
