Beyond Conventional Quantum Limits: From Sensing Interaction with Symmetries to Non-CP Energy Extraction
Seminar author:Aparajita Bhattacharyya
Event date and time:10/14/2025 11:00:am
Event location:Online
Event contact:
Quantum advantages often emerge when one ventures beyond conventional physical or information-theoretic constraints. In this talk, I will present two instances of such advantages in distinct quantum tasks, i.e. precision sensing and energy extraction. In the first part, we investigate how the scaling of quantum Fisher information with system size depends on the number of particles interacting in a k-body Hamiltonian. We uncover a super-Heisenberg scaling that strengthens with increasing interaction order and reveal a fundamental dichotomy: optimal estimation of odd-body interactions necessarily requires genuine multipartite entanglement, whereas for even-body interactions, asymmetry among local subsystems – rather than full multipartite entanglement – serves as the essential resource. In the second part, we explore energy extraction from quantum batteries. While completely positive trace-preserving (CPTP) maps set the conventional limits of local passivity, we show that physically realizable non-completely positive (non-CP) maps can surpass these bounds, allowing efficient local energy extraction from CPTP-passive states even in the asymptotic limit. We provide a necessary and sufficient condition for an arbitrary bipartite state to be unable to supply any energy using NCP operations on one party with respect to an arbitrary but fixed Hamiltonian. The surpassing of the maximum energy extractable by NCP maps for CPTP-passive as well as for CPTP-nonpassive battery states can act as detectors of non-CPness of quantum maps. Together, these studies highlight how relaxing standard structural constraints – whether in probe states or in quantum dynamics – can unlock enhanced quantum capabilities.