Gordon Joshua A, Simons Matthew T, Haddab Abdulaziz H, Holloway Christopher L
National Institute of Standards and Technology (NIST), RF Technology Division, U.S. Department of Commerce, Boulder Laboratories, Boulder, Colorado 80305, USA.
Department of Physics, University of Colorado, Boulder, Colorado 80302, USA.
Appl Phys Lett. 2019;9. doi: 10.1063/1.5095633.
Rydberg atoms have been used for measuring radio-frequency (RF) electric (E)-fields due to their strong dipole moments over the frequency range of 500 MHz-1 THz. For this, electromagnetically induced transparency (EIT) within the Autler-Townes (AT) regime is used such that the detected E-field is proportional to AT splitting. However, for weak E-fields AT peak separation becomes unresolvable thus limiting the minimum detectable E-field. Here, we demonstrate using the Rydberg atoms as an RF mixer for weak E-field detection well below the AT regime with frequency discrimination better than 1 Hz resolution. A heterodyne detection scenario with two E-fields incident on a vapor cell filled with cesium atoms is used. One E-field at 19.626000 GHz drives the Rydberg transition and acts as a local oscillator (LO) and a second signal E-field (Sig) of interest is at 19.626090 GHz. In the presence of the LO, the Rydberg atoms naturally down convert the Sig field to a 90 kHz intermediate frequency (IF) signal. This IF signal manifests as an oscillation in the probe laser intensity through the Rydberg vapor and is easily detected with a photodiode and lock-in amplifier. In the configuration used here, E-field strength down to were detected with a sensitivity of . Furthermore, neighboring fields 0.1 Hz away and equal in strength to Sig could be discriminated without any leakage into the lock-in signal. For signals 1 Hz away and as high as +60 dB above Sig, leakage into the lock-in signal could be kept below -3 dB.
里德堡原子由于其在500兆赫兹至1太赫兹频率范围内具有很强的偶极矩，已被用于测量射频（RF）电场。为此，在奥特勒-汤斯（AT）机制内使用电磁感应透明（EIT），使得检测到的电场与AT分裂成正比。然而，对于弱电场，AT峰间距变得无法分辨，从而限制了最小可检测电场。在此，我们展示了使用里德堡原子作为射频混频器来检测远低于AT机制的弱电场，频率分辨率优于1赫兹。采用了一种外差检测方案，其中两个电场入射到充满铯原子的蒸汽池中。一个频率为19.626000吉赫兹的电场驱动里德堡跃迁并充当本地振荡器（LO），另一个感兴趣的信号电场（Sig）频率为19.626090吉赫兹。在LO存在的情况下，里德堡原子自然地将Sig场下变频为90千赫兹的中频（IF）信号。该IF信号通过里德堡蒸汽表现为探测激光强度的振荡，并且很容易用光电二极管和锁相放大器检测到。在这里使用的配置中，检测到的电场强度低至 ，灵敏度为 。此外，可以区分相邻的、强度与Sig相等且频率相差0.1赫兹的电场，而不会有任何泄漏到锁相信号中。对于频率相差1赫兹且比Sig高60分贝的信号，泄漏到锁相信号中的部分可以保持在-3分贝以下。
