Highly sensitive phase- and frequency-resolved detection of microwave electric fields is of central importance in a wide range of fields, including cosmology^1,2, meteorology³, communication⁴ and microwave quantum technology⁵. Atom-based electrometers^6,7 promise traceable standards for microwave electrometry, but their best sensitivity is currently limited to a few μV cm⁻¹ Hz^−1/2 (refs. ^8,9) and they only yield information about the field amplitude and polarization¹⁰. Here, we demonstrate a conceptually new microwave electric field sensor—the Rydberg-atom superheterodyne receiver (superhet). The sensitivity of this technique scales favourably, achieving even 55 nV cm⁻¹ Hz^−1/2 with a modest set-up. The minimum detectable field of 780 pV cm⁻¹ is three orders of magnitude smaller than what can be reached by existing atomic electrometers. The Rydberg-atom superhet allows SI-traceable measurements, reaching uncertainty levels of 10⁻⁸ V cm⁻¹ when measuring a sub-μV cm⁻¹ field, which has been inaccessible so far with atomic sensors. Our method also enables phase and frequency detection. In sensing Doppler frequencies, sub-μHz precision is reached for fields of a few hundred nV cm⁻¹. This work is a first step towards realizing electromagnetic-wave quantum sensors with quantum projection noise-limited sensitivity. Such a device will impact diverse areas like radio astronomy, radar technology and metrology.

微波电场的高灵敏度相位和频率分辨检测在包括宇宙学^1,2，气象³，通信⁴和微波量子技术⁵在内的广泛领域中至关重要。基于原子的静电计^6,7有望成为微波静电测定的可追溯标准，但目前其最佳灵敏度仅限于几个μVcm ^-1  Hz ^-1/2（参考^8.9），并且它们仅产生有关场振幅和极化¹⁰。在这里，我们演示了一种概念上新颖的微波电场传感器-Rydberg原子超外差接收器（superhet）。该技术的灵敏度具有良好的缩放比例，通过适当的设置即可达到55 nV cm ^-1  Hz ^-1。780 pV cm ^-1的最小可检测场比现有原子静电计所能达到的场小三个数量级。里德伯原子超外差允许SI可追踪测量，达到10不确定性水平^-8  V CM ^-1测量时子μV厘米^-1领域，到目前为止，原子传感器尚无法实现。我们的方法还可以检测相位和频率。在感测多普勒频率时，对于几百nV cm ^-1的场达到亚μHz的精度。这项工作是实现具有量子投影噪声限制灵敏度的电磁波量子传感器的第一步。这种设备将影响射电天文学，雷达技术和计量学等各个领域。