911±¬ÁÏÍø

Imaging the wavefunction of propagating microwave photons

Chen Qiming (911±¬ÁÏÍø)

Abstract Propagating photons are essential carriers of quantum information in future quantum networks. While optical quantum networks thrive, detecting microwave photons at the quantum level remains a significant challenge. The superconductor-normal metal-superconductor (SNS) bolometer is a highly sensitive thermal detector that holds the current record of sensitivity for detecting the weakest signals down to the single-photon level. In this talk, I will first introduce the QCD efforts in pushing the power resolution of the SNS bolometer to 10^-18 W [1] and its energy resolution to 10^-21 J [2]. Then, I will show how this extreme sensitivity enables novel applications in quantum technology, including single-shot readout of superconducting qubits [3] and quantum correlation measurement of microwave photons [4]. Here, I will focus on our recent breakthrough in quantum state tomography [5]: By adapting the principles of computed tomography (CT) in medical imaging, we directly image the wavefunctions of propagating microwave photons using the SNS bolometer operating at millikelvin temperatures.

[1] R. Kokkoniemi, et al. Bolometer operating at the threshold for circuit quantum electrodynamics. Nature 586, 47–51 (2020)

[2] A. Gunyho, et al. Zeptojoule Calorimetry. arXiv:2412.14079 (2024)

[3] A. Gunyho, et al. Single-shot readout of a superconducting qubit using a thermal detector. Nat. Electron. 7, 288–298 (2024)

[4] A. Keranen and Q. Chen, et al. Measurement of microwave photon correlations at millikelvin with a thermal detector. Nat. Commun. 16, 3875 (2025)

[5] Q. Chen, et al. Computed tomography of propagating microwave photons, In preparation (2025)