The development offers a quantum computing measurement tool of great value – and opens up experiments in the exciting field of quantum thermodynamics.
A key component of quantum computers is coaxial cables and waveguides – structures that regulate waveforms and create vital connections between the quantum processor, and classical electronics controls. Microwave pulses travel through waveguides to the quantum processor and cool down to extremely low temperatures along the way. The waveguide also reduces and filters pulses, enabling the most sensitive quantum computer to work with stable quantum regions.
In order to have more control over this process, researchers need to make sure that these waveguides do not carry noise due to the hot movement of electrons above the pulses they send. In other words, they have to measure the temperature of the electromagnetic fields at the cold end of the microwave wavelengths, the point at which the control particles are delivered to the computer qubits. Working at very low temperatures reduces the risk of bringing errors to the qubits.
To date, researchers have only been able to measure this temperature indirectly, with the greatest delay. Now, with the novel thermometer of the Chalmers researchers, very low temperatures can be measured directly at the end of the waveguide discovery – with great accuracy and precision over time.
“Our thermometer is a hard-working circuit, directly connected to the end of the measured wave. It is very simple – and probably the fastest and most sensitive thermometer in the world for this purpose in the millikelvin scale,” said Simone Gasparinetti, Deputy Professor Quantum Technology Laboratory, Chalmers University of Technology.
It is important to measure the performance of quantum computers
Researchers at the Wallenberg Center for Quantum Technology, WACQT, aim to build a quantum computer – based on larger circuits – at least 100 efficient qubits, making the necessary calculations by 2030. It requires a temperature processor that works close to zero, actually down to 10 millikelvins. The new thermometer provides researchers with an important tool for measuring the effectiveness of their programs and their shortcomings – a necessary step for them to immerse themselves in technology and achieve their goal.
“A certain temperature is equivalent to a given number of hot photons, and that number is greatly reduced by heat. If we succeed in lowering the temperature at the end when the waveguide meets qubit to 10 millikelvins, the risk of errors in our qubits is greatly reduced,” said Per. Delsing, Professor in the Department of Microtechnology and Nanoscience, Chalmers University of Technology, and WCQT leader.
Accurate temperature measurement is also required for suppliers who need to be able to ensure the quality of their products, for example, the cables used to handle signals have moved to quantum regions.
New opportunities in the field of quantum thermodynamics
Quantum mechanical conditions such as superposition, traction and decoherence mean the transformation not only of the future computer but also of thermodynamics. It is possible that thermodynamic rules somehow change as they operate down to the nanoscale, in a way that could one day be used to produce more powerful engines, faster-charging batteries, and more.
“For 15 to 20 years, people have learned how the rules of thermodynamics can be changed by quantum conditions, but the real quest for thermodynamics is still open,” said Simone Gasparinetti, who recently started her own research and program team to contribute to this wide range of experiments…
A new thermometer, for example, can measure the distribution of hot microwaves from a region that acts as a quantum heat engine or refrigerator.
“Ordinary thermometers are important in the development of classical thermodynamics. We hope that perhaps, in the future, our thermometer will be regarded as a milestone in the development of quantum thermodynamics,” said Marco Scigliuzzo, a doctoral student in the Department of Microtechnology and Nanoscience at Chalmers University.