Speaker: Mikko Möttönen, Aalto University, Finland

Title: Low-temperature detectors can boost superconducting quantum computers

Abstract:
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, long-standing tools in low-temperature detection [1], have undergone transformative evolution. Recent findings demonstrate that bolometers 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 the intersection of low-temperature detectors and quantum computers, I focus on the bolometric 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 superconducting quantum computers appears promising. With continued improvements in chip design and experimental setups, and especially the potential change of the bolometer absorber material, we anticipate achieving high-fidelity single-shot readout at the hundred-nanosecond 99.9%-fidelity level and beyond [3]. This integration of low-temperature detectors with superconducting quantum computers not only promises significant improvements in quantum computing but also illustrates the transformative impact of cross-disciplinary innovation.

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, https://arxiv.org/abs/2303.03668 (2023).

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