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Quantum Bit from High Temperature Superconductor

Researchers propose material for powerful, compact quantum computers

Jülich, 13 February 2020 - Although they were actually pursuing a different goal, scientists from Jülich, Münster and Moscow discovered a method that could one day pave the way for quantum computers to leave specialized laboratories behind and enter into much wider usage. The key to this is a material for qubits that does not need to be cooled to near absolute zero.

Quantum computers should in future be able to perform certain calculations much faster than the fastest supercomputers in the world. This can be useful in a wide range of issues, from optimized traffic control, or the design of more efficient materials, right through to pharmaceutical research and the development of new medicines. However, quantum computers currently exist only as prototypes in the laboratory or in specialist applications.

In attempting to develop more efficient quantum computers, various technological strategies are being pursued in parallel. Qubits, the bits of quantum computers, can for example consist of trapped ions or superconducting circuits. In both cases, complex cooling systems are necessary to bring the qubits to temperatures of approximately -273 °C, which corresponds to slightly more than 0 Kelvin. These systems are as expensive as a single-family house and require more space than a large refrigerator.

Researchers from Jülich, Münster and Moscow have now discovered that superconducting qubits could perhaps be produced not only from the usual low-temperature superconductors, but also from high-temperature superconductors, which means that much cheaper cooling technology, involving cooling systems the size of a small suitcase, would be sufficient. It should also be possible to accommodate a larger number of such qubits on a chip than is currently possible, and the computing speed achievable should increase by orders of magnitude. The latter is due, among other things, to the extended lifetime of the excited state of at least 20 milliseconds at 5 Kelvin.

Das Jülicher Team (ohne Prof. Rafal Dunin-Borkowski), von links: Dr. Matvey Lyatti, Dr. Irina Gundareva, Maximilian Kruth.The Jülich team (without Prof. Rafal Dunin Borkowski), from left: Dr. Matvey Lyatti, Dr. Irina Gundareva, Maximilian Kruth. In the background is the Helios Nanolab DualBeam 400S (FEI ) which the researchers used to cut the nanowires.
Copyright: Forschungszentrum Jülich / Dmitry Bratanov

Technically speaking, the researchers working together with Prof. Rafal Dunin-Borkowski, Director at the Ernst Ruska-Centre and Peter Grünberg Institute in Jülich, along with Jun. Prof. Carsten Schuck from the University of Münster were actually researching components for single-photon detectors, for which reduced cooling would be sufficient. Such detectors are needed, for example, in the encryption of data using quantum cryptography. Schuck’s group has extensive experience in developing single-photon detectors based on low-temperature superconductors.

The basis of the new detector was to be nanowire made of yttrium-barium-copper oxide (YBCO), a material that is already superconducting below a comparatively warm -181.15 °C. Jülich has many years of experience in the production of high-quality thin films from this high-temperature superconductor and moreover has unique equipment and methods at its disposal, some of which were developed in-house. The Jülich researchers used a focused ion beam to cut the wires they needed from thin films into the desired shape.

Zur Herstellung der dünnen YBCO-Schichten nutzten Dr. Matvey Lyatti, Dr. Irina Gundareva und ihre Kollegen ein am Jülicher Institut entwickeltes Sputtersystem.To produce the thin YBCO layers, Dr. Matvey Lyatti, Dr. Irina Gundareva and their colleagues used a sputtering system developed at the Jülich institute. Target atoms are sputtered by high-pressure oxygen plasma and deposited in thin layers onto a selected substrate heated up to high temperature.
Copyright: Forschungszentrum Jülich / Dmitry Bratanov

"We experimented with nanowires of different widths, hit them with photons and measured the resistance that this creates in the superconductor”, explains physicist Dr. Matvey Lyatti, who first conducted research on the project in Münster and later in Jülich. The detection of the photons is based on this principle. “But the results at widths under 100 nanometres did not meet our expectations."

As it turned out, quantum effects become apparent at 12-13 Kelvin: the superconducting nanowire only accepts selected energy states. This discovery could be used to encode information. Conventional quantum bits would require temperatures several hundred times lower, which are much more difficult to achieve.

"Our results were so surprising that we could hardly believe them ourselves," recalls Jülich physicist Dr. Irina Gundareva. But the measurements ultimately convinced even the initially skeptical reviewers of the results now published in Nature Communications.

Rasterelektronenmikroskopische Aufnahme eines YBCO-Nanodrahts, geformt durch zwei horizontale Schnitte (schwarz) in einem YBCO-Film (grau). Der Maßstabsbalken (weiß) entspricht 5 Tausendstel Millimeter.Scanning electron microscope image of a YBCO nanowire formed by two horizontal cuts (black) in a YBCO film (grey). The scale bar (white) corresponds to 5 thousandths of a millimeter.
Copyright: M. Lyatti et al./Nature Communications, unaltered. This image is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit

The researchers will continue their work on YBCO nanowires and plan to develop nanowire-based superconducting quantum circuits in the coming years, with the final goal of making a compact desktop quantum computer possible. They are also pursuing their objective of developing novel superconducting single-photon detectors that can be cooled by compact cryocooler. Here too, the YBCO nanowires being investigated proved suitable for this purpose and demonstrated significant advantages over existing technology with respect to necessary cooling temperatures as well as temporal signal resolution.

Original publication: M. Lyatti et al. (2019): Energy-level quantization and single-photon control of phase slips in YBa2Cu3O7–x nanowires. Nature Communications (07 February 2020); DOI: 10.1038/s41467-020-14548-x

Further Information:

Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C) - Physics of Nanoscale Systems (ER-C-1)/Microstructure Research (PGI-5)

University of Münster, AG Schuck "Integrated Quantum Technology"

Press release University of Münster from February 2020 "Quantum technologies: New insights into superconducting processes"


Dr. Matvey Lyatti
Peter Grünberg Institute – Semiconductor Nanoelectronics (PGI-9)
Tel: +49 2461 61-6482

Dr. Irina Gundareva
Ernst Ruska-Centrum for Microscopy and Spectroscopy with Electrons (ER-C) – Physics of Nanoscale Systems (ER-C-1) / Peter Grünberg Institute (PGI) - Microstructure Research (PGI-5)
Tel: +49 2461 61-6642

Press contact:

Angela Wenzik, Science journalist
Forschungszentrum Jülich
Tel: +49 2461 61-6048