Sweden’s Chalmers University of Technology has achieved a quantum computing efficiency breakthrough through a novel type of thermometer that is capable of simplifying and rapidly measuring temperatures during quantum calculations.
The discovery adds a more advanced benchmarking tool that will accelerate Chalmers’ work in quantum computing development.
The novel thermometer is the latest innovation to emerge from the university’s research to develop an advanced quantum computer. The so-called OpenSuperQ project at Chalmers is coordinated with technology research organisation the Wallenberg Centre for Quantum Technology (WACQT), which is the OpenSuperQ project’s main technology partner.
WACQT has set the goal of building a quantum computer capable of performing precise calculations by 2030. The technical requirements behind this ambitious target are based on superconducting circuits and developing a quantum computer with at least 100 well-functioning qubits. To realise this ambition, the OpenSuperQ project will require a processor working temperature close to absolute zero, ideally as low as 10 millikelvin (-273.14° C).
Headquartered at Chalmers University’s research hub in Gothenburg, the OpenSuperQ project, launched in 2018, is intended to run until 2027. Working alongside the university in Gothenburg, WACQT is also operating support projects being run at the Royal Institute of Technology (Kungliga Tekniska Högskolan) in Stockholm and collaborating universities in Lund, Stockholm, Linköping and Gothenburg.
Pledged capital funding for the WACQT-managed OpenSuperQ project which has been committed by the Knut and Alice Wallenberg Foundation together with 20 other private corporations in Sweden, currently amounts to SEK1.3bn (€128m). In March, the foundation scaled up its funding commitment to WACQT, doubling its annual budget to SEK80m over the next four years.
The increased funding by the foundation will lead to the expansion of WACQT’s QC research team, and the organisation is looking to recruit a further 40 researchers for the OpenSuperQ project in 2021-2022. A new team is to be established to study nanophotonic devices, which can enable the interconnection of several smaller quantum processors into a large quantum computer.
The Wallenberg sphere incorporates 16 public and private foundations operated by various family members. Each year, these foundations allocate about SEK2.5bn to research projects in the fields of technology, natural sciences and medicine in Sweden.
The OpenSuperQ project aims to take Sweden to the forefront of quantum technologies, including computing, sensing, communications and simulation, said Peter Wallenberg, chairman of the Knut and Alice Wallenberg Foundation.
“Quantum technology has enormous potential, so it is vital that Sweden has the necessary expertise in this area. WACQT has built up a qualified research environment and established collaborations with Swedish industry. It has succeeded in developing qubits with proven problem-solving ability. We can move ahead with great confidence in what WACQT will go on to achieve.”
The novel thermometer breakthrough opens the door to experiments in the dynamic field of quantum thermodynamics, said Simone Gasparinetti, assistant professor at Chalmers’ quantum technology laboratory.
“Our thermometer is a superconducting circuit and directly connected to the end of the waveguide being measured,” said Gasparinetti. “It is relatively simple – and probably the world’s fastest and most sensitive thermometer for this particular purpose at the millikelvin scale.”
Coaxial cables and waveguides – the structures that guide waveforms and serve as the critical connection to the quantum processor – remain key components in quantum computers. The microwave pulses that travel down the waveguides to the quantum processor are cooled to extremely low temperatures along the way.
For researchers, a fundamental goal is to ensure that these waveguides are not carrying noise due to the thermal motion of electrons on top of the pulses that they send. Precise temperature measurement readings of the electromagnetic fields are needed at the cold end of the microwave waveguides, the point where the controlling pulses are delivered to the computer’s qubits.
Working at the lowest possible temperature minimises the risk of introducing errors in the qubits. Until now, researchers have only been able to measure this temperature indirectly, and with relatively long delays. Chalmers University’s novel thermometer enables very low temperatures to be measured directly at the receiving end of the waveguide – with elevated accuracy and with extremely high time resolution.
The novel thermometer developed at the university provides researchers with a value-added tool to measure the efficiency of systems while identifying possible shortcomings, said Per Delsing, a 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, and that number decreases exponentially with temperature,” he said. “If we succeed in lowering the temperature at the end where the waveguide meets the qubit to 10 millikelvin, the risk of errors in our qubits is reduced drastically.”
The university’s primary role in the OpenSuperQ project is to lead the work on developing the application algorithms that will be executed on the OpenSuperQ quantum computer. It will also support the development of algorithms for quantum chemistry, optimisation and machine learning.
Also, Chalmers will head up efforts to improve quantum coherence in chips with multiple coupled qubits, including device design, process development, fabrication, packaging and testing. It will also conduct research to evaluate the performance of 2-qubit gates and develop advanced qubit control methods to mitigate systematic and incoherent errors to achieve targeted gate fidelities.
