The development of quantum computers could be sped up thanks to a newly designed highly sensitive superconducting thermometer

Researchers at Chalmers University of Technology in Gothenburg, Sweden, have created a new form of thermometer that can rapidly and accurately calculate temperature during quantum calculations. This achievement establishes an important benchmark for quantum computing and paves the way for exciting quantum thermodynamics experiments.

The quantum thermometer on the new chip is on the front. According to Chalmers University researchers, this may be the world’s fastest and most accurate thermometer for calculating the temperature of a waveguide’s cold end on the milliKelvin scale.

A coaxial cable and a waveguide—the structure that directs the waveform and acts as a vital communication channel between the quantum processor and the classic electronic products that power it—are essential components of a quantum computer. The microwave pulse travels through the waveguide to the quantum processor, where it is cooled to a very low temperature. The waveguide often attenuates and filters the pulses, allowing highly sensitive quantum computers to operate in a quantum state that is stable.

Researchers must ensure that these waveguides do not bear noise due to the thermal movement of electrons on top of the pulses they send in order to maximize control of this mechanism. To put it another way, they need to calculate the temperature of the electromagnetic field at the microwave waveguide’s cold end, which is where the control pulse is transmitted to the device qubit. Working at the lowest temperature possible reduces the chance of introducing errors into the qubit.

The superconducting circuit used in Scigliuzzo et alexperiment .’s (left) and its ability to quantify thermal microwaves at a single excitation quantum level (artistic impression).

Researchers can only calculate this temperature indirectly and with a significant delay so far. With a new thermometer invented by Chalmers University researchers, it is now possible to directly measure very low temperatures at the waveguide’s receiving end—exactly and with extremely high time resolution. This is critical for determining the efficiency of quantum computers.

By 2030, researchers at the Wallenberg Center for Quantum Technology (WACQT) hope to have built a quantum computer with at least 100 well-functioning qubits that can perform accurate calculations, based on superconducting circuits. It necessitates a processor operating temperature near absolute zero, ideally less than 10 millikelvin. The new thermometer gives researchers a valuable tool for determining how effective their device is and what flaws it has—an important step toward perfecting the technology and achieving the target.

The qubit will be destroyed by any photon that occurs. At a normal operating frequency, a temperature increase of 20mK to 30mK results in 50 times the number of thermal photons, resulting in a 50-fold increase in the probability of error. A specific temperature is associated with a specific number of thermal photons, which decreases exponentially as the temperature rises. The probability of errors in our qubit would be significantly reduced if the temperature of the end where the waveguide reaches the qubit is successfully reduced to 10 milliKelvin.

Suppliers that need to guarantee the quality of their materials, such as cables used to process signals down to the quantum state, need accurate temperature measurement as well.

Quantum mechanical phenomena including superposition, entanglement, and decoherence foreshadow not just a potential revolution in computation, but also a future revolution in thermodynamics. When operating at the nanometer scale, it’s likely that the law of thermodynamics has changed, and this approach will one day be used to create more efficient motors, better rechargeable batteries, and so on.