One of the most promising approaches towards large-scale quantum computation uses devices based on many Josephson junctions. Yet, even today, open questions regarding the single junction remain unsolved, such as the detailed understanding of the quantum phase transitions, the coupling of the Josephson junction to the environment or how to improve the coherence of a superconducting qubit. Here we design and build an engineered on-chip reservoir connected to a Josephson junction that acts as an efficient bolometer for detecting the Josephson radiation under non-equilibrium, that is, biased conditions. The bolometer converts the a.c. Josephson current at microwave frequencies up to about 100 GHz into a temperature rise measured by d.c. thermometry. A circuit model based on realistic parameter values captures both the current–voltage characteristics and the measured power quantitatively. The present experiment demonstrates an efficient, wide-band, thermal detection scheme of microwave photons and provides a sensitive detector of Josephson dynamics beyond the standard conductance measurements.

大规模量子计算最有前途的方法之一是使用基于许多约瑟夫森结点的设备。然而，即使在今天，关于单结的悬而未决的问题仍未解决，例如对量子相变的详细理解、约瑟夫森结与环境的耦合或如何提高超导量子比特的相干性。在这里，我们设计并构建了一个连接到约瑟夫森结的工程片上储液器，该储液器充当在非平衡（即偏置条件下）检测约瑟夫森辐射的有效辐射热计。辐射热计将交流电转换微波频率高达约 100 GHz 的约瑟夫森电流转化为通过直流测温法测量的温升。基于实际参数值的电路模型可以定量捕获电流-电压特性和测得的功率。本实验展示了一种高效的、宽带的微波光子热探测方案，并提供了超出标准电导测量的灵敏约瑟夫森动力学探测器。