Microsoft And Copenhagen University Develop New Quantum Computing Material
Semiconductor/superconductor/ferromagnetic insulator hybrid can hold delicate quantum information and protect it from decoherence
Researchers at the Microsoft Quantum Materials Lab and the University of Copenhagen have developed a promising material for use in a future quantum computer. The material - a semiconductor, superconductor, and ferromagnetic insulator hybrid - can hold the delicate quantum information and protect it from decoherence. The research is published in Nature Physics.
The graphic above show the three materials combined to form the new material. Aluminium is the superconductor, EuS is the ferromagnet, and InAs is the compound semiconductor.
Topological states have held a great deal of promise for quantum computing but one of the challenges has been that a large magnetic field had to be applied. With the new material, it has become possible to realise topological states without the magnetic field.
"The result is one of many new developments needed before an actual quantum computer is realised, but along the way better understanding of how quantum systems work, and might be applied to medicine, catalysts or materials, will be some of the positive side effects to this research", says researcher Charles Marcus from the Niels Bohr Institute.
Topological states in condensed-matter systems have generated immense excitement and activity in the last decade, including the 2016 Nobel Prize in Physics. There is a natural fault-tolerance of the so called Majorana zero modes, which makes topological states ideally suited for quantum computing. But progress in realising topological Majorana zero modes has been hampered by the requirement of large magnetic fields to induce the topological phase, which comes at a cost: the system must be operated in the bore of a large magnet, and every topological segment must be precisely aligned along the direction of field.
The new results report a key signature of topological superconductivity, but now in the absence of an applied magnetic field. A thin layer of the material europium sulphide (EuS), whose internal magnetism naturally aligns with the axis of the nanowire and induces an effective magnetic field (more than ten thousand times stronger than the Earth's magnetic field) in the superconductor and semiconductor components, appears sufficient to induce the topological superconducting phase.
Triple hybrid of semiconductor, superconductor, and ferromagnetic insulator
Marcus explains the progress this way: "The combination of three components into a single crystal - semiconductor, superconductor, ferromagnetic insulator - a triple hybrid - is new. It's great news that it forms a topological superconductor at low temperature. This gives us a new path to making components for topological quantum computing, and gives physicists a new physical system to explore".
New results will soon be applied to engineering the qubit
The next step will be to apply these results in order to get closer to realising the actual working qubit. So far the researchers have worked on the physics and now they are about to embark on engineering an actual device. This device, the qubit, is essentially to a quantum computer what the transistor is to the ordinary computer we know today. It is the unit performing the calculations, but this is where the comparison ends. The potential for the performance of a quantum computer is so large that today we are not even really able to imagine the possibilities.
Peter Krogstrup, scientific director at the Microsoft Materials Lab and Yu Liu, postdoc at the Niels Bohr Institute grew the materials, Saulius Vaitiekenas, lead experimentalist at the Microsoft Quantum Materials Lab carried out the measurements and built the devices, and Charles Marcus at the Niels Bohr Institute, along with everyone else, interpreted the ensuing data. Marcus says: "There may be different roles and competences involved, but the process of collaborating on science is most times a very fluid and open ended process".
'Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires' by S. Vaitiekėnas et al; Nature Physics (2020)