Second article by Delft quantum researchers withdrawn

For the second time, a scientific publication of the research group of Delft quantum researcher Leo Kouwenhoven withdrawn from the magazine Nature† Research data has been incorrectly omitted in key figures. Researchers from Eindhoven University of Technology were also involved in the study.

At the beginning of last year, the journal Nature already deleted a publication from 2018. The authors also indicated that there were problems with the data processing. TU Delft then started two integrity investigations into the working method within the research group. Those studies are still ongoing now that Nature has withdrawn the second study.

Kouwenhoven is an acclaimed quantum researcher. He is a professor at TU Delft. In 2007 Kouwenhoven received a Spinoza Prize for his research. In 2016 he became director of a new lab on the TU Delft campus, where the quantum computer of the tech company Microsoft was being developed. Kouwenhoven left Microsoft last month. According to Kouwenhoven, his departure has nothing to do with the withdrawn study from 2018, the professor said earlier.

Search for majoranas

Kouwenhoven has been looking for stable majorana particles since 2010. In theory, these can be used as qubits (bits that a quantum computer uses for calculations). Theorists say they exist, but experimental evidence is still lacking.

Kouwenhoven and his colleagues are trying to find majorana particles with nanowires, wires fifty times thinner than a hair. In the research from 2017, which has now been deleted, Kouwenhoven’s research group described a material for generating majorana particles that he developed together with Professor Erik Bakkers of Eindhoven University of Technology. Bakkers’ group in Eindhoven specializes in nanofabrication. For the majorana research, the group in Eindhoven made a network of nanowires. Kouwenhoven’s group in Delft investigated how suitable the nanowire network was for generating majorana particles. In the publication, the researchers claimed that this is indeed a perfect material with which to generate majorana particles for quantum computers in the future.

Cut and paste

But that claim is now in question. Last week, the study authors drew the publication back from Nature due to data processing problems. Cut and pasted a number of charts and data contradicting the claim have been omitted from the publication. All 25 co-authors agreed with the decision to withdraw the article as a result.

“It is very disappointing that the study has been withdrawn,” Bakkers responds. “But I still stand behind the work we have done here in Eindhoven. I am still proud of that.” Kouwenhoven did not respond to a request for comment. A press officer from TU Delft says that she cannot comment on the subject because of absences due to the May holidays.

In the retracted 2018 study, Kouwenhoven and his colleagues claimed to have found the majorana particle. That was world news at the time. But Kouwenhoven’s former employees Vincent Mourik and Sergey Frolov saw that, also in the 2018 study, the data had been pasted and cut. External experts who were asked for advice by TU Delft concluded in a report that there was no intent, “but the authors’ enthusiasm blinded them to data that didn’t show what they were hoping for.”

Second investigation

Last February, TU Delft launched a second integrity investigation into the group when they received reports that even more studies by the group may contain errors. That investigation is still ongoing.

Are findings from one of the two integrity studies the reason that the researchers withdrew a study from Nature for the second time? Bakkers thinks not. “When the first study was scrapped last year, the authors on their own initiative scanned dozens of studies for errors. Including our study from 2017. As long as the integrity investigation is ongoing, we are not allowed to say anything more about it.”

Former employees Mourik and Frolov say they have found problems in at least two other studies from Kouwenhoven’s research group. What will happen with that is still unclear.

Kouwenhoven will remain professor of physics at TU Delft for the time being without an appointment. That means he is not paid by the university. That is still the case, confirms QuTech, the quantum institute of TU Delft and TNO. Kouwenhoven now supervises twelve PhD students at QuTech.