Sweden’s Chalmers University of Technology has achieved an extraordinary breakthrough in quantum computing. It has developed a new thermometer that can easily and quickly measure temperatures during quantum calculations. From this discovery stems a very sophisticated measuring tool, whose interest above all is to accelerate the work of the university in order to develop a functional quantum computer.
Chalmers University is leading the OpenSuperQ project under the auspices of the research institute The Wallenberg Center for Quantum Technology (WACQT), its main technology partner. WACQT has set itself the goal of building a quantum computer capable of performing accurate calculations by 2030.
But on the technical side, this ambitious project requires superconducting circuits and at least 100 perfectly functional qubits. To realize this idea, the OpenSuperQ project must have a processor with an operating temperature close to absolute zero or -273.14 ° C (less than 10 millikelines). Working at the lowest possible temperature actually minimizes the risk of introducing errors in qubits. It was still necessary to ensure that this temperature was maintained.
Make the signals arriving at the quantum processor more reliable
For researchers, it is about ensuring that the waveguides – coaxial cables that bring the waves to the quantum processor – do not carry noise due to the thermal stirring of electrons over the pulses they send. For this, the microwave pulses propagated by the waveguides to the quantum processor are cooled at extremely low temperatures during their journey.
The researchers then had to accurately measure the temperature of the electromagnetic fields at the cold end of the waveguides, the point where the control pulses are delivered to the qubits of the computer. Until recently, however, researchers could only measure this temperature indirectly with a relatively long delay. Now the Chalmers researchers’ new thermometer can measure very low temperatures directly at the receiving end of the waveguide with very high accuracy and very high temporal resolution.
Simone GasparinettiAssociate Professor, Quantum Technology Laboratory, Chalmers University
“Our thermometer is a superconducting circuit directly connected to the end of the measured waveguide,” explains Simone Gasparinetti, associate professor at Chalmers Quantum Technology Laboratory. “It is relatively simple and is probably the fastest and most sensitive thermometer for this particular use, on the millikelvin scale.”
“The new thermometer developed by the university provides researchers with an invaluable tool for measuring system efficiency,” adds Per Delsing, professor at the Department of Microtechnology and Nanoscience at Chalmers and director of WACQT.
“A certain temperature corresponds to a given number of thermal photons, knowing that this number decreases exponentially with temperature,” he continues. “If we can successfully lower the temperature to 10 millikelvin at the end where the waveguide meets the qubit, the chance of failure of our qubits is greatly reduced.”
Within the framework of the OpenSuperQ project, the university has an important role to play. She is responsible for developing application algorithms to run on the OpenSuperQ quantum computer. It will also support the development of algorithms for quantum chemistry, optimization and machine learning.
Chalmers will strive to improve the quantum coherence of chips by coupling a host of qubits in hardware design, process development, manufacturing, packaging and testing. She will also conduct research to evaluate the performance of 2-qubit gates, to develop advanced methods for managing qubits, to avoid systematic and inconsistent errors, and to ensure that the expected reliability of logical gates is achieved.
The challenge of putting Sweden at the forefront of quantum technologies
Hosted by the Chalmers University Research Hub, located in Gothenburg, the OpenSuperQ project was launched in 2018 and will be completed in 2027. In addition to Chalmers University, WACQT also collaborates on this topic with the Institute Stockholm University of Technology (Kungliga) Tekniska Högskolan) and with other partner universities in Lund, Stockholm, Linköping and Gothenburg.
Funding for the OpenSuperQ project, which is managed by WACQT, is provided by the Knut and Alice Wallenberg Foundation together with twenty other Swedish private companies. It is currently at 1.3 billion Swedish kroner, or 128 million euros. In March, the fund doubled its financial commitment by investing SEK 80 million a year over the next four years.
This new boost from the foundation will allow the WACQT research team to evolve. The organization aims to recruit 40 other researchers for the OpenSuperQ project by 2022. A new team will be responsible for studying nanophotonic devices that can connect several small quantum processors to a larger quantum computer.
The Wallenberg Group brings together sixteen public and private funds. Each year, these foundations allocate around SEK 2.5 billion to research projects in various fields, such as technology, science and medicine, in Sweden.
The OpenSuperQ project aims to put Sweden at the forefront of quantum technologies (data processing, sensing, communication and simulation), says Peter Wallenberg, chairman of the Knut and Alice Wallenberg Foundation.
“Quantum technology has enormous potential, so it is essential that Sweden has the necessary expertise in this area. WACQT provides a highly competent research environment and collaborates with big names in Swedish industry. He managed to develop qubits whose ability to solve problems is well established. We can move forward with full confidence in the results of the WACQT. »