• Open Access

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

Nicolai Friis, Oliver Marty, Christine Maier, Cornelius Hempel, Milan Holzäpfel, Petar Jurcevic, Martin B. Plenio, Marcus Huber, Christian Roos, Rainer Blatt, and Ben Lanyon
Phys. Rev. X 8, 021012 – Published 10 April 2018

Abstract

We generate and characterize 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 neighboring groups of qubits. We characterize entanglement between these groups by designing and applying witnesses for genuine multipartite entanglement. Our results show that, during the dynamical evolution, all neighboring 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.

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  • Received 11 December 2017
  • Revised 13 February 2018

DOI:https://doi.org/10.1103/PhysRevX.8.021012

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Nicolai Friis1,‡, Oliver Marty2,‡, Christine Maier3,4, Cornelius Hempel3,4,†, Milan Holzäpfel2, Petar Jurcevic3,4, Martin B. Plenio2, Marcus Huber1, Christian Roos3, Rainer Blatt3,4, and Ben Lanyon3,*

  • 1Institute for Quantum Optics and Quantum Information-IQOQI Vienna, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
  • 2Institut für Theoretische Physik and IQST, Albert-Einstein-Allee 11, Universität Ulm, 89069 Ulm, Germany
  • 3Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Technikerstraße 21a, 6020 Innsbruck, Austria
  • 4Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria

  • *ben.lanyon@uibk.ac.at
  • Present address: ARC Centre for Engineered Quantum Systems, School of Physics, The University of Sydney, 2006 New South Wales, Australia.
  • These authors contributed equally to this work.

Popular Summary

At the heart of useful quantum technologies such as simulators or computers lies the ability to create quantum entanglement, a type of correlation among atomic particles that has no analog in everyday experience. One challenge is to establish and maintain this fragile property for large numbers of particles such as qubits, the quantum equivalent of digital bits. Another challenge is to develop methods to detect entanglement. Here, we report progress on both of these tasks. We present two methods for entanglement detection and use them to detect entanglement in a system of 20 qubits, the largest fully controllable entangled quantum system to date.

We experimentally study the dynamical evolution of the multipartite entanglement structure of 20 qubits encoded in a quantum simulator built from trapped ions. We track the buildup of entanglement between neighboring qubit pairs and triples, and we even verify genuine quantum correlations for up to 5 neighbors. Most importantly, our evaluation only requires a number of measurement settings proportional to the number of qubits—just 27 out of the more than 3 billion possible measurements. This is in contrast to full state reconstruction, where this number grows exponentially with the system size, which is not viable for scalable entanglement detection. Our two methods trade off computational effort and noise robustness. One method is easy to use at any system size, whereas the other performs better at the cost of a more involved numerical optimization.

Our work opens a path to further increase the size and complexity of entangled systems, allowing researchers to go beyond the realm of classical simulation.

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Vol. 8, Iss. 2 — April - June 2018

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