Topological eigenvalues braiding and quantum state transfer near a third-order exceptional point

TL;DR

This paper experimentally explores the topological eigenvalue braiding and quantum state transfer near third-order exceptional points in a non-Hermitian quantum system using superconducting circuits, revealing new insights into non-Hermitian topological structures.

Contribution

It demonstrates the first experimental investigation of eigenvalue braiding and state transfer near third-order EPs in a quantum system, including topological characterization and dynamic state manipulation.

Findings

Eigenvalues braiding described by braid group $B_3$

Chiral state transfer observed under fast driving when no EP is enclosed

Time-symmetric behavior occurs when at least one EP is encircled

Abstract

Non-Hermitian systems exhibit a variety of unique features rooted in the presence of exceptional points (EP). The distinct topological structure in the proximity of an EP gives rise to counterintuitive behaviors absent in Hermitian systems, which emerge after encircling the EP either quasistatically or dynamically. However, experimental exploration of EP encirclement in quantum systems, particularly those involving high-order EPs, remains challenging due to the difficulty of coherently controlling more degrees of freedom. In this work, we experimentally investigate the eigenvalues braiding and state transfer arising from the encirclement of EP in a three-dimensional non-Hermitian quantum system using superconducting circuits. We characterize the second- and third-order EPs through the coalescence of eigenvalues. Then we reveal the topological structure near the EP3 by quasistatically encircling it along various paths with three independent parameters, which yields the eigenvalues braiding described by the braid group $B_3$. Additionally, we observe chiral state transfer between three eigenstates under a fast driving scheme when no EPs are enclosed, while time-symmetric behavior occurs when at least one EP is encircled. Our findings offer insights into understanding non-Hermitian topological structures and the manipulation of quantum states through dynamic operations.