Researchers develop new thermometer to speed up quantum computer development

In a new study, researchers at Chalmers University of Technology in Gothenburg, Sweden recently developed a new type of thermometer that can simply and quickly measure temperatures during quantum calculations with extremely high accuracy. .

This breakthrough provides a valuable benchmarking tool for quantum computing – and paves the way for experiments in the exciting field of quantum thermodynamics.

A key component of quantum computers are coaxial cables and waveguides – structures that guide waveforms and act as the vital connection between the quantum processor and the classical electronics that control it. The microwave pulses travel along the waveguides to the quantum processor and are cooled to extremely low temperatures along the way. The waveguide also attenuates and filters the pulses, allowing the extremely sensitive quantum computer to work with stable quantum states.

In order to have maximum control over this mechanism, researchers must ensure that these waveguides do not carry noise due to the thermal movement of electrons above the pulses they send out. In other words, they must measure the temperature of the electromagnetic fields at the cold end of the microwave waveguides, the point where the control pulses are delivered to the computer’s qubits. Working at the lowest possible temperature minimizes the risk of introducing errors into the qubits.

So far, researchers have only been able to measure this temperature indirectly, with a relatively large delay. Now, with the new thermometer from the Chalmers researchers, very low temperatures can be measured directly at the receiving end of the waveguide – very precisely and with extremely high temporal resolution.

“Our thermometer is a superconducting circuit, directly connected to the end of the waveguide being measured. It is relatively simple – and probably the world’s fastest and most sensitive thermometer for this purpose at the millikelvin scale,” says Simone Gasparinetti, assistant professor in the Quantum Technology Laboratory, Chalmers University of Technology.

Important for measuring the performance of quantum computers

Researchers at the Wallenberg Center for Quantum Technology, WACQT, aim to build a quantum computer – based on superconducting circuits – with at least 100 qubits running well, performing correct calculations by 2030. This requires an operating temperature of the processor close to the absolute. zero, ideally up to 10 millikelvin. The new thermometer gives researchers an important tool to measure the quality of their systems and existing shortcomings – a necessary step in order to be able to refine the technology and achieve their goal.

“A certain temperature corresponds to a given number of thermal photons, and that number decreases exponentially with temperature. If we succeed in lowering the temperature at the end where the waveguide meets the qubit at 10 millikelvin, the risk of errors in our qubits is drastically reduced, says Per Delsing, professor in the Department of Microengineering and Nanosciences at Chalmers University of Technology and head of WACQT.

Accurate temperature measurement is also necessary for suppliers who need to be able to guarantee the quality of their components, for example cables used to process signals up to quantum states.

New opportunities in the field of quantum thermodynamics

The phenomena of quantum mechanics such as superposition, entanglement and decoherence signify a revolution not only for future computation but potentially also for thermodynamics. It may be that the laws of thermodynamics change one way or another when working at the nanoscale, in a way that could one day be exploited to produce more powerful motors, more charged batteries. fast, etc.

“For 15-20 years, people have been studying how the laws of thermodynamics could be changed by quantum phenomena, but the search for a real quantum advantage in thermodynamics is still open,” says Simone Gasparinetti, who recently launched her own research group and plans to contribute to this research with a new range of experiments.

The new thermometer can, for example, measure the diffusion of thermal microwaves from a circuit acting as a quantum heat engine or refrigerator.

Standard thermometers were fundamental to the development of classical thermodynamics. We hope that in the future our thermometer may be considered essential for the development of quantum thermodynamics, says Marco Scigliuzzo, a doctoral student in the Department of Microtechnology and Nanosciences at Chalmers University of Technology.