Atom-based measurements of length, time, gravity, inertial forces and electromagnetic fields are receiving increasing attention. Atoms possess properties that suggest clear advantages as self calibrating platforms for measurements of these quantities. In this review, we describe work on a new method for measuring radio frequency (RF) electric fields based on quantum interference using either Cs or Rb atoms contained in a dielectric vapor cell. Using a bright resonance prepared within an electromagnetically induced transparency window it is possible to achieve high sensitivities, <1 μV cm−1 Hz−1/2, and detect small RF electric fields μV cm−1 with a modest setup. Some of the limitations of the sensitivity are addressed in the review. The method can be used to image RF electric fields and can be adapted to measure the vector electric field amplitude. Extensions of Rydberg atom-based electrometry for frequencies up to the terahertz regime are described.
Rydberg atom-based electrometry enables traceable electric field measurements with high sensitivity over a large frequency range, from gigahertz to terahertz. Such measurements are particularly useful for the calibration of radio frequency and terahertz devices, as well as other applications like near field imaging of electric fields. We utilize frequency modulated spectroscopy with active control of residual amplitude modulation to improve the signal to noise ratio of the optical readout of Rydberg atom-based radio frequency electrometry.Matched filtering of the signal is also implemented. Although we have reached similarly, high sensitivity with other read-out methods, frequency modulated spectroscopy is advantageous because it is well-suited for building a compact, portable sensor. In the current experiment, ∼3 µV cm −1 Hz −1/2 sensitivity is achieved and is found to be photon shot noise limited.
We utilize a homodyne detection technique to achieve a new sensitivity limit for atom-based, absolute radio-frequency electric field sensing of 5 μV cm−1 Hz−1/2. A Mach-Zehnder interferometer is used for the homodyne detection. With the increased sensitivity, we investigate the dominant dephasing mechanisms that affect the performance of the sensor. In particular, we present data on power broadening, collisional broadening and transit time broadening. Our results are compared to density matrix calculations. We show that photon shot noise in the signal readout is currently a limiting factor. We suggest that new approaches with superior readout with respect to photon shot noise are needed to increase the sensitivity further.
We have recently shown that Alkali atoms contained in a vapor cell can serve as a highly accurate standard for microwave electric field strength as well as polarization using the principles of Rydberg atom electromagnetically induced transparency. Here, we show, for the first time, that Rydberg atom electromagnetically induced transparency can be used to image microwave electric fields with unprecedented precision. The spatial resolution of the method is far into the sub-wavelength regime. The electric field resolutions are similar to those we have demonstrated in our prior experiments. Our experimental results agree with finite element calculations of test electric field patterns.Atomic standards are important because they enable stable and uniform measurements and often link physical quantities to each other via universal constants [1]. We have demonstrated in our prior work that atoms contained in a vapor cell can be used for a practical and, in principle, portable microwave (MW) electric field standard using Rydberg atom electromagnetically induced transparency (EIT) [2, 3]. The accurate measurement of MW electric field strength and polarization can lead to advances in applications such as antenna design, device development, characterization of electro-magnetic interference, advanced radar applications and materials characterization [4-9], including metamaterials [10][11][12].To our knowledge, no other work exists on imaging MW electric fields with atoms in vapor cells. Even in the field of magnetometry, where vapor cell magnetometers have played a central part [13], absorption imaging for vapor cell MW magnetometry has only been recently reported [14, 15]. Many of the technical issues of imaging a MW magnetic field as opposed to an electric field with a vapor cell are different. Knowledge of both fields is important. Despite the rather straightforward connection between the electric and magnetic fields in free space, there is not always a simple relation between them in the near field. The absolute measurement of MW electric fields at sub-wavelength resolutions and in the near field is necessary for many MW applications.To meet the need for sub-wavelength imaging of MW electric fields, we demonstrate a scheme for subwavelength MW electrometry using Rydberg atom EIT [16, 17] in Cesium (Cs) atomic vapor cells at room temperature. In contrast to scanning probe technology [18, 19], our approach avoids cryogenics and eliminates the presence of conducting materials near the sample, therefore minimizing field disturbances. We achieve a 2-dimensional spatial resolution of ∼ λ MW /650, ∼ 66 µm at ∼ 6.9 GHz, using a test MW electric field in the form of a standing wave and image the MW electric field di- * Corresponding author: shaffer@nhn.ou.edu rectly above a co-planar waveguide (CPW) to demonstrate near field imaging. The electric field resolution is ∼ 50 µV cm −1 limited by our detection setup. The measurements are compatible with our prior work where we attained a minimum detectable electric field amplitude of ...
A new approach to detect absolute radio-frequency (RF) electric fields (E-fields) that uses Rydberg atoms at room temperature in vapor cells has recently been demonstrated. The large transition dipole moments between energetically adjacent Rydberg states enable this technique to make traceable E-field measurements with high sensitivity over a large frequency range, from 1 GHz to 1 THz. In this paper, we experimentally investigate how the vapor cell geometry affects the accuracy of the measurements. We find that the effects of the vapor cell on the measured RF E-field can be minimized by making the vapor cell size small compared to the wavelength of the RF E-field.
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