Relaxation times do not capture logical qubit dynamics

Quantum, vol. 6, pp. 632

Abstract

Quantum error correction procedures have the potential to enable faithful operation of large-scale quantum computers. They protect information from environmental decoherence by storing it in logical qubits, built from ensembles of entangled physical qubits according to suitably tailored quantum error correcting encodings. To date, no generally accepted framework to characterise the behaviour of logical qubits as quantum memories has been developed. In this work, we show that generalisations of well-established figures of merit of physical qubits, such as relaxation times, to logical qubits fail and do not capture dynamics of logical qubits. We experimentally illustrate that, in particular, spatial noise correlations can give rise to rich and counter-intuitive dynamical behavior of logical qubits. We show that a suitable set of observables, formed by code space population and logical operators within the code space, allows one to track and characterize the dynamical behaviour of logical qubits. Awareness of these effects and the efficient characterisation tools used in this work will help to guide and benchmark experimental implementations of logical qubits.

Authors 8

1. Amit Kumar Pal

   Swansea University · Indian Institute of Technology Palakkad · University of Warsaw

   Affiliation as printed

   Department of Physics, College of Science, Swansea University, Singleton Park, Swansea - SA2 8PP, United Kingdom

   Department of Physics, Indian Institute of Technology Palakkad, Palakkad 678557, India

   Faculty of Physics, University of Warsaw, ul. Pasteura 5, PL-02-093 Warszawa, Poland

2. Philipp Schindler

   Universität Innsbruck

   Affiliation as printed

   Institut für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

3. Alexander Erhard

   Universität Innsbruck

   Affiliation as printed

   Institut für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

4. ́Angel Rivas

   Universidad Complutense de Madrid · Universidad Politécnica de Madrid

   Affiliation as printed

   CCS -Center for Computational Simulation, Campus de Montegancedo UPM, 28660 Boadilla del Monte, Madrid, Spain

   Departamento de Física Teórica, Facultad de Ciencias Físicas, Universidad Complutense, 28040 Madrid, Spain

5. Miguel-Angel Martin-Delgado

   Universidad Complutense de Madrid · Universidad Politécnica de Madrid

   Affiliation as printed

   CCS -Center for Computational Simulation, Campus de Montegancedo UPM, 28660 Boadilla del Monte, Madrid, Spain

   Departamento de Física Teórica, Facultad de Ciencias Físicas, Universidad Complutense, 28040 Madrid, Spain

6. R. Blatt

   Austrian Academy of Sciences · Universität Innsbruck · Institute for Quantum Optics and Quantum Information Innsbruck

   Affiliation as printed

   Institut für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

   Institut für Quantenoptik und Quanteninformation, Österreichische Akademie der Wissenschaften, Otto-Hittmair-Platz 1, A-6020 Innsbruck, Austria

7. Thomas Monz

   Universität Innsbruck · Alpine Quantum Technologies (Austria)

   Affiliation as printed

   Alpine Quantum Technologies GmbH, 6020 Innsbruck, Austria

   Institut für Experimentalphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria

8. Markus Michael Müller Aachen Institute for Quantum Information

   Forschungszentrum Jülich · Swansea University · RWTH Aachen University

   Affiliation as printed

   Department of Physics, College of Science, Swansea University, Singleton Park, Swansea - SA2 8PP, United Kingdom

   Institute for Quantum Information, RWTH Aachen University, D-52056 Aachen, Germany

   Peter Grünberg Institute, Theoretical Nanoelectronics, Forschungszentrum Jülich, D-52425 Jülich, Germany