In this work, we demonstrate the use of a Rydberg atom-based sensor for determining the angle of arrival of an incident radio frequency (RF) wave or signal. The technique uses electromagnetically induced transparency in Rydberg atomic vapor in conjunction with a heterodyne Rydberg atom-based mixer. The Rydberg atom mixer measures the phase of the incident RF wave at two different locations inside an atomic vapor cell. The phase difference at these two locations is related to the direction of arrival of the incident RF wave. To demonstrate this approach, we measure phase differences of an incident 19.18 GHz wave at two locations inside a vapor cell filled with cesium atoms for various incident angles. Comparisons of these measurements with both the full-wave simulation and the plane wave theoretical model show that these atom-based sub-wavelength phase measurements can be used to determine the angle of arrival of an RF field.

We investigate the use of a split-ring resonator (SRR) incorporated with an atomic-vapor cell to improve the sensitivity and the minimal detectable electric (E) field of Rydberg atom-based sensors. In this approach, a sub-wavelength SRR is placed around an atomic vapor-cell filled with cesium atoms for E-field measurements at 1.3 GHz. The SRR provides a factor of 100 in the enhancement of the E-field measurement sensitivity. Using electromagnetically induced transparency (EIT) with Aulter–Townes splitting, E-field measurements down to 5 mV/m are demonstrated with the SRR, while in the absence of the SRR, the minimal detectable field is 500 mV/m. We demonstrate that by combining EIT with a heterodyne Rydberg atom-based mixer approach, the SRR allows for a sensitivity of 5.5  μV/m[Formula: see text], which is two-orders of magnitude improvement in sensitivity than when the SRR is not used.

We demonstrate improved sensitivity of Rydberg electrometry based on electromagnetically induced transparency (EIT) with a ground state repumping laser. Though there are many factors that limit the sensitivity of radio frequency field measurements, we show that repumping can enhance the interaction strength while avoiding additional Doppler or power broadening. Through this method, we nearly double the EIT amplitude without an increase in the width of the peak. A similar increase in amplitude without the repumping field is not possible through simple optimization. We also establish that one of the key limits to detection is the photon shot noise of the probe laser. We show an improvement on the sensitivity of the device by a factor of nearly 2 in the presence of the repump field.

We propose and demonstrate a polarization-based truncated SU(1,1) interferometer that outputs the desired optical joint-quadrature of a two-mode squeezed vacuum field and allows its measurements using a single balanced homodyne detector. Using such setup we demonstrated up to ≈ 2 dB of quantum noise suppression below the shot-noise limit in intensity-difference and phase-sum joint quadratures, and confirmed entanglement between the two quantum fields. Our proposed technique results in a better balance between the two ports of the detector and, consequently, in better common noise suppression for differential measurements. As a result, we were able to observe flat jointquadrature squeezing and entanglement at wide range of detection frequencies: from several MHz (limited by the photodiode gain bandwidth) down to a few hundred Hz (limited by electronic noises).