Observation of Entangled States of a Fully Controlled 20-Qubit System

TL;DR

This paper reports the creation and characterization of entangled states in a 20-qubit system of trapped ions, demonstrating complex multipartite entanglement during dynamical evolution.

Contribution

It is the first to generate and analyze genuine multipartite entanglement in a fully controlled 20-qubit ion trap system during out-of-equilibrium dynamics.

Findings

All neighboring qubit pairs develop genuine multipartite entanglement.

Most triplets, quadruplets, and some quintuplets show multipartite entanglement.

Entanglement is mainly generated between neighboring groups during early evolution.

Abstract

We generate and characterise entangled states of a register of 20 individually controlled qubits, where each qubit is encoded into the electronic state of a trapped atomic ion. Entanglement is generated amongst the qubits during the out-of-equilibrium dynamics of an Ising-type Hamiltonian, engineered via laser fields. Since the qubit-qubit interactions decay with distance, entanglement is generated at early times predominantly between neighbouring groups of qubits. We characterise entanglement between these groups by designing and applying witnesses for genuine multipartite entanglement. Our results show that, during the dynamical evolution, all neighbouring qubit pairs, triplets, most quadruplets, and some quintuplets simultaneously develop genuine multipartite entanglement. Witnessing genuine multipartite entanglement in larger groups of qubits in our system remains an open challenge.