RETRACTED ARTICLE: Quantized Majorana conductance
Authors: Leo P Kouwenhoven
S Das Sarma
Erik P A M Bakkers
Sasa Gazibegovic
Jouri D S Bommer
Daniel J Pennachio
Sebastian Koelling
Joon Sue Lee
Chris J Palmstrøm
Di Xu
Petrus J van Veldhoven
Diana Car
Roy L M Op Het Veld
Hao Zhang
Michiel W A de Moor
Chun-Xiao Liu
Marcel A Verheijen
Borzoyeh Shojaei
John A Logan
Nick van Loo
Guanzhong Wang
Mihir Pendharkar
Journal: Nature (2018)
Discipline: Multidisciplinary
Keywords: Majorana zero-modes; topological quantum computing; tunnelling spectroscopy; zero-bias peak; differential conductance
Affiliations: QuTech and Kavli Institute of NanoScience, Delft University of Technology, 2600 GA Delft, The Netherlands., Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742, USA., Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands., Materials Engineering, University of California Santa Barbara, Santa Barbara, California 93106, USA., Philips Innovation Services Eindhoven, High Tech Campus 11, 5656AE Eindhoven, The Netherlands., Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California 93106, USA., California NanoSystems Institute, University of California Santa Barbara, Santa Barbara, California 93106, USA., Microsoft Station Q Delft, 2600 GA Delft, The Netherlands.

Abstract:  Majorana zero-modes-a type of localized quasiparticle-hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The height of the Majorana zero-bias peak is predicted to be quantized at the universal conductance value of 2e2/h at zero temperature (where e is the charge of an electron and h is the Planck constant), as a direct consequence of the famous Majorana symmetry in which a particle is its own antiparticle. The Majorana symmetry protects the quantization against disorder, interactions and variations in the tunnel coupling. Previous experiments, however, have mostly shown zero-bias peaks much smaller than 2e2/h, with a recent observation of a peak height close to 2e2/h. Here we report a quantized conductance plateau at 2e2/h in the zero-bias conductance measured in indium antimonide semiconductor nanowires covered with an aluminium superconducting shell. The height of our zero-bias peak remains constant despite changing parameters such as the magnetic field and tunnel coupling, indicating that it is a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins by investigating its robustness to electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of Majorana zero-modes in the system, consequently paving the way for future braiding experiments that could lead to topological quantum computing. 

Retracted: No

PubPeer comments:
 An Editorial Expression of Concern was published today:  The authors have alerted the editors of Nature to potential problems in the manner in which the raw data in this Letter have been processed, and these will have an impact on the conclusions that can be reliably drawn. Nature is working with the authors to resolve the matter, but in the meantime, readers are cautioned against using results from this Letter. https: www.nature.com articles s41586-020-2252-6 , 
 https: twitter.com spinespresso status 1357111565242220545 , 
 https: www.wired.com story microsoft-win-quantum-computing-error , 
 Retracted. Copy pasted from https: www.nature.com articles s41586-021-03373-x :  In this Letter, we reported electrical measurements and numerical simulations of hybrid superconductingu2013semiconducting nanowires in a magnetic field. We reported plateaus in the conductance at 2e2 h, which we interpreted as evidence for the presence of Majorana zero-modes. However, several inconsistencies were pointed out by Sergey Frolov and Vincent Mourik between the raw measurement data that was made available to them and the figures that were published in the paper. We therefore re-analysed all the existing raw data for our original measurements and rebuilt the original experimental set-up for a re-calibration of the conductance values. We established that the data in two of the figures (Fig. 2a and Extended Data Fig. 4b) had been unnecessarily corrected for charge jumps (corrections that were not mentioned explicitly in the paper), and that one of the figure axes was mislabelled (Fig. 4b). The new conductance calibration shifted the plateau values by 8 per cent, above 2e2 h, which affects all the figures1. When the data are replotted over the full parameter range, including ranges that were not made available earlier, points are outside the 2-sigma error bars. We can therefore no longer claim the observation of a quantized Majorana conductance, and wish to retract this Letter. After informing Nature of this decision, Nature issued an Editorial Expression of Concern2 and initiated the retraction process. In ref. 1 we provide all the raw data underlying the published figures as well as the unpublished datasets. Ref. 1 also contains the analysis methods and a side-by-side comparison between the original and the corrected figures. In ref. 3 we provide a new manuscript with corrected and extended datasets, discussed in the context of new insights on zero-energy states in systems with inhomogeneous potentials and disorder. We thank Piet Brouwer, Klaus Ensslin, David Goldhaber-Gordon and Patrick Lee for the expert evaluation report available via ref. 1. We also thank Michael Wimmer and Bernard van Heck for their help with the analyses. We apologize to the community for insufficient scientific rigour in our original manuscript. References 1. Zhang, H. et al. Data repository accompanying retraction of u201cQuantized Majorana conductanceu201d. https: doi.org 10.5281 zenodo.4545577 (2021). 2. Zhang, H. et al. Editorial Expression of Concern: Quantized Majorana conductance. Nature 581, E4 (2020). 3. Zhang, H. et al. Large zero-bias peaks in InSb-Al hybrid semiconductor-superconductor nanowire devices. Preprint at https: arxiv.org abs 2101.11456 (2021). Published 08 March 2021 , 
 https: retractionwatch.com 2021 03 08 authors-retract-nature-majorana-paper-apologize-for-insufficient-scientific-rigour The reaction from the critics (reproduced below) is very illuminating, as it shows that the authors were somewhat less cooperative and proactive than the retraction note suggests. There also seems to be a promise of more to come:  The retraction note published today in Nature misrepresents the sequence of events. It omits that the two of us have contacted Nature, not the authors. We took this step after our communication with the authors exhausted itself. Only after Nature asked the authors for explanation have they made their decision to retract.  We are pleased that our findings are supported by the experts recruited by Delft University of Technology. The expert report puts u201cplateauu201d in quotes. The original claim of a u201crobustu201d conductance plateau is a result of selecting a dataset with irreproducible artefacts. The retraction note does not directly acknowledge data selection issues. We praise the authors for making additional data public on Zenodo. This allows us to share what we found a year ago in early 2020. We will be explaining our findings to the public in the coming days.  We praise the authors for making additional data public on Zenodo. This allows us to share what we found a year ago in early 2020. We will be explaining our findings to the public in the coming days.  We request that Delft University of Technology provides access to data from other related experiments. We wish to independently re-analyze those results and verify conclusions. Access to data is guaranteed by the Netherlands Code of Conduct for Research Integrity. , 
 In the dutch newspaper NRC the current situation regarding this subject is given, have a look at: https: www.nrc.nl nieuws 2022 03 16 quantumonderzoeker-leo-kouwenhoven-weg-bij-microsoft-a4102446 , 
 A full investigation of this case can be found at https: lowi.nl advies-2022-03-en-04 (unforfunately in dutch) ,