Finnish scientists develop nanodevice that can measure microwave power down to femtowatt level

Scientists in Finland have made a remarkable breakthrough in microwave power measurement for quantum technology. A team of researchers from Aalto University, VTT Technical Research Center of Finland, Bluefors, and IQM collaborated to enhance the accuracy of a special thermometer known as a bolometer. While the previous bolometer developed by the team allowed for the observation of relative power levels, it fell short in determining the absolute energy amount with high precision.

To address this limitation, the researchers added a heater to the bolometer. By applying a known heater current and measuring the voltage, they could calibrate the power of the input radiation against the heater power. This innovative approach enabled the creation of a self-calibrating bolometer that operates at low temperatures, thereby facilitating accurate measurements of absolute powers at cryogenic levels.

The significance of this advancement lies in the unprecedented capability of the new bolometer to measure microwave power at a scale one trillion times lower than that of commercial power sensors. While conventional sensors typically measure power in the range of one milliwatt, the developed bolometer can accurately and reliably measure power at or below one femtowatt. This breakthrough opens up new possibilities for precise power measurements in quantum experiments and quantum technology applications.

Covering both deep and wide scales

The newly developed bolometer holds great potential for enhancing the performance of quantum computers, according to Möttönen. By accurately measuring the radiation temperature without interference from the qubit circuitry, the bolometer ensures that the measurement lines controlling qubits are maintained at ultra-low temperatures, free from thermal photons and excess radiation. This capability is crucial for obtaining precise results in quantum computations.

Another notable feature of the bolometer is its broadband nature, allowing it to measure the power absorbed across a wide range of frequencies. Unlike conventional sensors limited to narrow bands, the bolometer provides the flexibility to assess power absorption at different frequencies, making it highly valuable in various quantum technology applications.

The significance of this advancement extends beyond quantum computing. While accurate microwave power measurements are commonplace in fields like wireless communications and radar technology, the ability to measure extremely weak microwave signals for quantum technology was previously lacking. The bolometer fills this gap as an advanced diagnostic instrument, contributing to the toolbox of quantum technology.

The collaboration between Aalto University and Bluefors exemplifies the fruitful partnership between academia and industry. The device was developed at Aalto’s Quantum Computing and Devices (QCD) group, a part of the Academy of Finland Center of Excellence in Quantum Technology (QTF). The team utilized Micronova clean rooms, which are part of the national research infrastructure OtaNano. The successful testing of the device in both academic and industrial facilities demonstrates its applicability and relevance for professionals working in the field of quantum technology.

Source: Aalto University

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