Ultraprecise Calorimeters for Discoveries in Quantum Science and Technology

by Prof. Mikko Möttönen (Aalto University)

Tuesday 11 Feb 2025, 15:00 → 17:00 Europe/Berlin

A.1.01/03 - Alps (New)

Superconducting qubits have made significant strides in recent years, with two-qubit gate fidelities reaching up to 99.9% and qubit number to hundreds. The pursuit of these and future advances have catalyzed the development of multi-purpose devices such as quantum-limited parametric amplifiers, which present promising opportunities to enhance low-temperature detection.

Simultaneously, ultrasensitive bolometers and calorimeters, long-standing tools in low-temperature detection [1], have undergone transformative evolution. Recent findings demonstrate that calorimeters can operate at speeds and energy levels required for superconducting qubits [2]. This breakthrough represents a culmination of years of dedicated research and development. 

After an introduction to our ultrasensitive low-temperature detectors and quntum computers, I present the calorimetric readout of superconducting qubits. Leveraging an ultrasensitive bolometer in place of a parametric amplifier, we achieved a single-shot qubit readout fidelity of 0.618, primarily limited by the qubit energy relaxation time [3]. Without these energy relaxation time errors, the fidelity is 0.927, underscoring the potential of this novel approach [3]. 

Looking ahead, the future of low-temperature detectors in the realm of new scientific discoveries appears promising. Our recently demonstrated single-zeptojoule energy resolution [4] can be greatly further improved by using graphene as the absorber and thermometer material [2] in addition to improvements in the design of these elements. Thus for axion detection where the energy to be detected exceeds several time the calorimetric energy resolution seems appealing.

References:

[1] R. Kokkoniemi et al., Nanobolometer with ultralow noise equivalent power, Commun. Phys. 2, 124 (2019).
[2] R. Kokkoniemi, Bolometer operating at the threshold for circuit quantum electrodynamics, Nature 586, 47 (2020).
[3] A. M. Gunyho et al., Bolometric readout of a superconducting qubit, Nature Electronics 7, 288 (2024).
[4] A. M. Gunyho et al., Zeptojoule calorimetry, https://arxiv.org/abs/2412.14079 (2024)