Microsoft announces a new quantum processor and is met with skepticism

The news sounds spectacular. On Wednesday, Microsoft presented a new type of quantum chip called Majorana 1, which is based on topological quantum bits. These quantum bits are much less prone to errors than those used by companies such as Google, IBM or IonQ. With topological quantum bits, it will therefore be possible to build quantum computers that can solve meaningful problems in just a few years, rather than decades, Microsoft promises.

The company speaks of a decisive step forward and refers to a publication that appeared on the same day in the journal Nature . However, there is no mention of a topological quantum bit, let alone a chip with several such bits. Instead, it says that the results are a significant step forward on the way to realizing a topological quantum bit. So where does Microsoft stand with its research?

It is undisputed that topological quantum bits would greatly accelerate the construction of a powerful quantum computer. Today's quantum computers use neutral atoms, ions or tiny superconducting circuits to store information. These quantum bits can be put into states that allow calculations to be made much more efficiently than the states of a conventional bit. The hope is that one day this will make it possible to solve problems that even today's supercomputers cannot handle.

However, the quantum bits used today are very error-prone. Even the smallest disturbance causes the sensitive quantum states to decay, and the entire advantage over a classical computer is gone. The trend is therefore towards combining many quantum bits into a logical quantum bit, which is less error-prone than the individual bits. Google recently showed that this approach is promising. However, it requires a huge superstructure of quantum bits that do nothing other than correct errors.

Microsoft has long been pursuing a different path. The company is trying to develop quantum bits that are inherently robust and therefore need to be corrected less often. To do this, the quantum information must be stored in a way that is immune to isolated disturbances. The quantum information is then said to be topologically protected.

Research into such topological quantum bits has been going on for years. The basic idea is to bring a semiconducting nanowire into contact with a superconductor. If a magnetic field is applied parallel to the wire, two excited states should form at its ends. These spatially separated but interconnected states are called Majorana states. Theoretically, they are suitable for storing quantum information.

In the Nature publication, the Microsoft researchers demonstrate how the two states 0 and 1 of a quantum bit can be distinguished. However, they cannot rule out that the measured differences are simulated by other effects in the nanowire, and therefore have nothing to do with the robust Majorana states. The Microsoft experiment cannot therefore yet be described as a topological quantum bit, says solid-state physicist Klaus Ensslin from ETH Zurich.

However, that hasn't stopped Microsoft from going public and claiming that it has overcome a crucial hurdle on the way to a fault-tolerant quantum computer. It literally says: "Today we demonstrated the world's first topological qubit."

The publication was submitted to Nature a year ago, explains Chetan Nayak, who is responsible for the development of the topological quantum computer at Microsoft. Since then, considerable progress has been made. A chip with eight topological quantum bits has been developed. It has also been shown how such a bit can be put into a state that simultaneously represents the values ​​0 and 1. Such superposition states distinguish a quantum bit from an ordinary bit, which can only represent one of these two values.

These additional findings were shared this week at a meeting with more than a hundred scientists, says Nayak. Darpa is also convinced by the concept. The agency of the US Department of Defense recently decided to support the construction of a topological quantum computer.

If Microsoft's new results are correct, this would indeed be a major step forward. However, as long as there is no publication, this cannot be assessed seriously.

Microsoft could have guessed that its approach would be met with skepticism. It would not be the first time that too much has been promised in this field. In 2018, a working group at the TU Delft funded by Microsoft published a paper in Nature that provided strong evidence for the existence of Majorana states. Two years later, it had to be retracted . A group of experts concluded that the authors had only presented data that supported their hypothesis. Data that cast doubt on the success story had been omitted.

Microsoft has now stopped its collaboration with TU Delft. Since then, research into topological quantum computers has mainly taken place in the company's laboratories.

In recent years, however, Microsoft itself seems to have doubted its success. In parallel to researching topological quantum bits, the company has invested in two start-ups that rely on conventional quantum bits: Quantinum's quantum computers calculate with ionized atoms, while Atom Computing's calculate with neutral atoms. With both partners, Microsoft has shown in recent months how quantum bit errors can be successfully reduced. Whether a topological quantum computer will achieve the goal more quickly will only be able to be assessed once Microsoft publishes all the data.

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