Weak electric-field detection with sub-1 Hz resolution at radio frequencies using a Rydberg atom-based mixer

Abstract

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. Two E-fields incident on a vapor cell filled with cesium atoms are used. One E-field at 19.626000 GHz drives the 34D 5/2 → 35P 3/2 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 ≈ 46 µV/m ± 2 µV/m were detected. 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.

Embedding a Rydberg Atom-Based Sensor Into an Antenna for Phase and Amplitude Detection of Radio-Frequency Fields and Modulated Signals

“…3]. The solid curves correspond to the results using the beat note amplitude obtained using the atom mixer, as discussed in [28]. The amplitude of the beat note signal decreases as the horn antenna is rotated from the x-axis to the y-axis.…”

“…The beat note amplitude is a non-linear function of the E-field for both the LO and SIG, where the E-field strength seen by the atoms is given by [28] |E…”

“…In effect, the atoms are acting as a down-conversion mixer. The Rydberg atom-based mixer can also be used to detect weak fields with sub-Hz frequency resolution [28]. While the configuration in Fig.…”

Phase-Sensitive Vector Terahertz Electrometry from Precision Spectroscopy of Molecular Ions

“…The uncertainty of the polarization orientation may be conservatively estimated by assuming that the total electric field uncertainty is perpendicular to the electric field direction. Summing quadratically the uncertainties of the amplitudes of the Cartesian components from Equation (22) and dividing to the amplitude yields an angular uncertainty of 2.1 × 10 −4 rad. The sensitivity of this method is estimated with the lowest amplitude of the THz wave for which the amplitudes and phases of the Cartesian components of the THz electric field can be determined with uncertainties smaller than the corresponding nominal values.…”

“…The surpassing of the photon shot noise limitation is nontrivial [19]. The measurements with Rydberg atomic transitions were extended to vector microwave electrometry with 0.5 • angular resolution [20] and to a Rydberg-atom-based mixer for microwave phase shift measurement with an uncertainty better than 0.5 rad [21], offering also the opportunity to detect weak microwave signals [22].…”