# Experimental witness of quantum jump induced high-order Liouvillian exceptional points

## TL;DR

The paper experimentally confirms third-order Liouvillian exceptional points in a trapped-ion system, revealing new dynamics in open quantum systems.

## Contribution

First experimental observation of third-order LEPs induced by quantum jumps and their movement due to decay-dephasing competition.

## Key findings

- Third-order Liouvillian exceptional points were observed in an ultracold trapped-ion system.
- LEPs movement was demonstrated through the interplay of decay and dephasing processes.
- Non-commutativity of Lindblad superoperators influences LEP dynamics in open quantum systems.

## Abstract

The exceptional point has presented considerably interesting and counterintuitive phenomena associated with nonreciprocity, precision measurement, and topological dynamics. The Liouvillian exceptional point (LEP), involving the interplay of energy loss and decoherence inherently relevant to quantum jumps, has recently drawn much attention due to capability to fully capture quantum system dynamics and naturally facilitate non-Hermitian quantum investigations. It was also predicted that quantum jumps could give rise to third-order LEPs in two-level quantum systems for its high dimensional Liouvillian superoperator, which, however, has never been experimentally confirmed until now. Here we report the observation of the third-order LEPs emerging from quantum jumps in an ultracold two-level trapped-ion system. Moreover, by combining decay with dephasing processes, we present the experimental exploration of LEPs involving combinatorial effect of decay and dephasing. In particular, due to non-commutativity between the Lindblad superoperators governing LEPs for decay and dephasing, we witness the movement of LEPs driven by the competition between decay and dephasing occurring in an open quantum system. This unique feature of non-Hermitian quantum systems paves a new avenue for modifying nonreciprocity, enhancing precision measurement, and manipulating topological dynamics by tuning the LEPs.

Recent studies have shown the potential of higher-order exceptional points originating from the Liouvillian dynamics as opposed to their Hamiltonian counterparts. Here, the authors explore different classes of third-order Liouvillian exceptional points in a two-level system realised in a single trapped ion.