The Dutch team that developed topological quantum computers for Microsoft was retracted again

On April 25, 2022, a scientific paper by Leo Kouwenhoven's research team at Delft University of Technology (TU Delft) was retracted from Nature again for the same reasons as the first retraction, omitting key data.
 
Back in 2018, Dutch physicist Leo Kouwenhoven, then a Microsoft employee at the time, and colleagues published a Nature paper demonstrating that he had observed an elusive particle, the Majorana fermion.
 
However, by early 2021, Leo Kouwenhoven and his 21 co-authors posted that they had not discovered Majorana fermions three years ago, and an accompanying note from the authors states that the study, published in the journal Nature The original paper will be retracted for "technical error".

Original paper:
https://arxiv.org/abs/2101.11456 (Nature manuscript retracted)
Withdrawal statement:
https://www.nature.com/articles/s41586-021-03373-x
 
TU Delft then started two completeness surveys of the research team's working methods. These investigations are still ongoing, and the second study (2017) has been retracted by Nature.
 
Original paper:
https://www.nature.com/articles/nature23468
Withdrawal statement:
https://www.nature.com/articles/s41586-022-04704-2
 
Kouwenhoven is an acclaimed quantum researcher and professor at Delft University of Technology. In 2007, Kouwenhoven received the Spinoza Prize (the highest honor in the Dutch scientific community) for his research; in 2016, he became director of a new laboratory at Delft University of Technology, where he was involved in the development of Microsoft's quantum computer; Kouwenhoven left Microsoft in March 2022, and according to Kouwenhoven earlier, his departure was unrelated to the retraction of the 2018 paper.
 
It is worth mentioning that Kouwenhoven is currently on leave and therefore did not respond to a request for comment on the second retraction.

 

Leo Kouwenhoven (1st from left)
 

Looking for Majorana fermions 
 

As early as 2005, Microsoft began to study topological quantum computers, which are characterized by stability.

In architectures such as superconductivity, the error rate rises sharply as the number of qubits increases. The error comes from Local Noise: In the microscopic world, even extremely small electromagnetic fields can interfere with particles, resulting in so-called local noise.

Topological qubits, on the other hand, process information through the topological positions and topological motions of elementary particles. Just like in ancient times, human beings knotted a rope and recorded different information. The different (topological) structures woven by different nodes and ropes represent different information. No matter how the rope is shaken (perturbation), the storage of information is stable.

Schematic diagram of topological quantum computing

The key to topological qubits is the Majorana fermion. Since 2010, Kouwenhoven and his colleagues have been trying to find Majorana fermions using nanowires.
 
Why are Majorana fermions needed? Because the quantum state of particles currently used in quantum computing is not stable, and the antiparticle of Majorana fermions is itself, its state is very stable.
 
Majorana fermions were proposed in 1937 by Italian physicist Ettore Majorana. However, more than 80 years later, capturing Majorana fermions is still a world problem. But Microsoft is convinced of the existence of Majorana fermions, and hopes to use Majorana fermions to create truly stable qubits.
 
Kouwenhoven has been working on topological quantum computers for Microsoft since 2016. In 2018, a research team led by him announced the discovery of Majorana particles (which can act as topological qubits). Early last year, they retracted the paper due to data processing issues.
 
But just recently, another team at Microsoft, the Microsoft Quantum Materials Laboratory in Copenhagen, took a major step toward a topological quantum computer, using a different approach than Kouwenhoven's team. The Copenhagen team's ability to create and maintain quantum phases through Majorana zero-mode and measurable topological gaps removes the biggest obstacle to generating topological qubits.
 
Perhaps Microsoft is blazing a new path with other researchers, physicist Carlo Bennacker of Leiden University said in an interview.
 
Data processing issues

The retracted paper was published in the journal Nature in 2017. In a 2017 study, the Kouwenhoven research team, together with Professor Erik Bakkers of the Eindhoven University of Technology in the Netherlands, announced the development of a material for the production of Majorana fermions. Bakkers' team in Eindhoven specializes in nanofabrication and built a nanowire network; Kouwenhoven's research team in Delft investigated the suitability of the nanowire network for generating Majorana fermions.

Nanowire mesh developed at Eindhoven University of Technology
 

In the paper, the researchers claim that this is indeed the perfect material for future generation of Majorana fermions for quantum computers.
 
But that claim is now being questioned. On April 19, the study authors retracted their paper from Nature due to data processing issues. The reason for the retraction is that some figures and figures that contradict the statement were cut and pasted and that figures and figures have been removed from the publication. Therefore, all 25 co-authors agreed with the decision to retract the paper.
 
"It's very disappointing that this study was withdrawn," Bakkers responded, "but I still support the work we're doing at Eindhoven University. I'm still proud of it." Kouwenhoven was absent due to the May holiday , which did not respond to a request for comment.
 
Integrity investigation continues

In February 2021, TU Delft conducted a second integrity survey of the Kouwenhoven research team, when they received reports that more of the team's research may contain errors. Today, the investigation is still ongoing.
 
Could the findings of one of the two integrity studies be the reason the researchers withdrew the study from Nature for the second time? When the first study was retracted last year, the authors proactively checked dozens of studies for errors, including this 2017 study.
 
Mourik and Frolov, former members of the Kouwenhoven research team, said they found problems in at least two other studies by the team, but it was unclear what would happen afterward.
 
Link:
[1] https://pledgetimes.com/second-article-by-delft-quantum-researchers-withdrawn/
[2] https://www.nrc.nl/nieuws/2022/04/25/tweede-artikel-van-delftse-quantumonderzoekers-teruggetrokken-a4118477