Recently, the research team led by Prof. Xiao Lei from the School of Physics, 91抖淫, in collaboration with partners, achieved a significant breakthrough in quantum sensing. They observed criticality-enhanced quantum sensing on an experimental platform of non-unitary optical quantum walks. For the first time, this study directly observed that near the closure of point and line gaps in non-Hermitian systems, the estimation precision of parameters exhibits super-linear scaling with system size. This opens a new pathway for utilizing quantum criticality to achieve high-performance sensing in open quantum systems. The findings were published in Phys. Rev. Lett. 136, 060802 (2026) under the title of “Observation of Criticality-Enhanced Quantum Sensing in Nonunitary Quantum Walks.”
Quantum sensing leverages quantum physics to achieve parameter measurement precision beyond classical limits. Quantum criticality, which typically renders asystem's physical attributes extremely sensitive to specific parameter changes, is considered a key resource for enhancing quantum sensing. However, traditional sensing schemes based on quantum criticality face severe experimental challenges: they require preparing the system in its critical ground state or steady state, a process that is usually extremely time-consuming, thus limiting practical applications.
To overcome the time-consuming challenge of preparing steady states in traditional schemes, Xiao's team designed and constructed a discrete-time quantum-walk experimental platform based on single-photon interference. By introducing controllable photon losses, they precisely simulated the dynamics of a one-dimensional non-Hermitian topological Hamiltonian and successfully observed critical phenomena associated with the closure of point gaps and line gaps (Fig. 1). Simultaneously, they proposed a novel sensing scheme that operates during the non-steady-state evolution process. This scheme prepares the probe in a quantum state after a specific number of evolution stepsproportional to the system size,thereby cleverly avoiding the lengthy process of waiting for the system to reach a steady state.
Based on this platform, Xiao's team systematically investigated the sensing performance near both types of topological phase transitions: point-gapand line-gap closure. First, they theoretically confirmed that when the probe is in a steady state, the peak value of the Quantum Fisher Information near the critical point scales quadratically with system size, approaching or reaching the Heisenberg limit. More importantly, they discovered that even when the probe is in a transient evolutionary state, its Quantum Fisher Information near the critical point is significantly higher than in non-critical situations and exhibits a rapidly increasing trend, indicating that the criticality-enhanced effect can be manifested within experimentally accessible timescales (Fig. 2).
This work achieves the first experimental demonstration of criticality-enhanced quantum sensing in non-Hermitian topological systems. It overcomes the limitation of traditional quantum critical sensing, which requires a long time to reach a steady state, and demonstrates the possibility of achieving super-linear precision enhancement within transient times. The results not only reveal the crucial role of point-gap and line-gap closuresfor quantum sensing but also provide new insights for the high-precision measurement of physical quantities such as electric fields, magnetic fields, and gravitational gradients using non-Hermitian topological systems.
This research was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Open Project Fund of the Beijing National Laboratory for Condensed Matter Physics.
Paperlink: DOI: https://doi.org/10.1103/6gql-zgkb
Source: School of Physics, 91抖淫
Translated by: Melody Zhang
Proofread by: Gao Min
Edited by: Leah Li
