Broadband, energy-efficient signal transfer between a cryogenic and room-temperature environment has been a major bottleneck for superconducting quantum and classical logic circuits. Photonic links promise to overcome this challenge by offering simultaneous high bandwidth and low thermal load. However, the development of cryogenic electro-optic modulators—a key component for the photonic readout of electrical signals—has been stifled by the stringent requirements of superconducting circuits. Rapid single-flux-quantum circuits, for example, operate with a tiny signal amplitude of only a few millivolts, far below the volt-level signal used in conventional circuits. Here we demonstrate one of the first direct optical readouts of a rapid single-flux-quantum circuit without additional electrical amplification enabled by a novel superconducting electro-optic modulator featuring a record-low half-wave voltage V_π of 42 mV on a 1-m-long superconducting electro-optic modulator. Leveraging the low ohmic loss of superconductors, we break the fundamental V_π–bandwidth trade-off and demonstrate an electro-optic bandwidth up to 17 GHz on a 0.2-m-long superconducting electro-optic modulator at cryogenic temperatures. Our work presents a viable solution towards high-bandwidth signal transfer between future large-scale superconducting circuits and room-temperature electronics.

低温和室温环境之间的宽带、节能信号传输一直是超导量子和经典逻辑电路的主要瓶颈。光子链路有望通过同时提供高带宽和低热负载来克服这一挑战。然而，低温电光调制器（电信号光子读出的关键部件）的发展受到超导电路严格要求的阻碍。例如，快速单通量量子电路以仅几毫伏的微小信号幅度运行，远低于传统电路中使用的伏级信号。在这里，我们展示了快速单通量量子电路的第一个直接光学读数，无需额外的电放大，由新型超导电光调制器实现，该调制器在 1- 上具有42 mV 的创纪录低半波电压V _π m长超导电光调制器。利用超导体的低欧姆损耗，我们打破了基本的V _π带宽权衡，并在低温下在 0.2 米长的超导电光调制器上展示了高达 17 GHz 的电光带宽。我们的工作为未来大规模超导电路和室温电子设备之间的高带宽信号传输提供了可行的解决方案。