Non-Hermitian Topological Quantum Sensors

• Applicant: Professor Dr. Jan Budich
• Subject Area: Theoretical Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459864239

This project is devoted to exploring the promising potential of non-Hermitian (NH) topological phases for applications in quantum sensing. The extreme sensitivity of the the complex energy-spectra of NH matrices, which would be mathematically impossible in closed Hermitian systems, serves as the main starting point of this endeavor. In the context of the aforementioned NH topological phases, this anomalous sensitivity is generically encountered upon small changes of the system's boundary conditions. To harness this intriguing phenomenology for novel quantum sensing devices, coined non-Hermitian topological quantum sensors (NTOQS), the following major steps will be taken.(i) First, using an effective description of open quantum systems in terms of NH Hamiltonians, concrete topological lattice models of minimal complexity that exhibit the aforementioned boundary sensitivity, and thus serve as NTOQS candidate models, will be identified and analyzed. The coupling to the measurand observed by the sensor generically happens via a tunnel coupling (weak link in the lattice model) that effectively tunes the boundary conditions of the NTOQS system.(ii) Building up on the intuition from NH Hamiltonians, the NTOQS candidate models will be translated to a fully microscopic open quantum system description in the framework of quantum master equations and quantum Langevin equations, respectively. This allows for the analysis and assessment of the fundamental quantum noise limited precision of NTOQS in the framework of quantum noise theory.(iii) In parallel to the above theoretical aspects, a major objective of this project is to devise experimentally feasible blueprints for the realization of NTOQS in both quantum optical systems and ultracold atomic gases. In addition to the practical implementation of the relevant NTOQS lattice models, a main focus will be to identify suitable observables to be detected by the proposed sensing devices, and to microscopically model their coupling to the boundary conditions of the NH topological lattice model representing the NTOQS. Finally, the goal is to numerically simulate the dynamical operation of the NTOQS devices, taking into account the most relevant imperfections expected for the proposed individual experimental platforms, thus reaching clear predictions for future experiments.

• DFG Programme: Research Grants