Up to now, the measurement of radio-frequency (RF) electric field achieved using the electromagnetically-induced transparency (EIT) of Rydberg atoms has proved to be of high-sensitivity and shows a potential to produce a promising atomic RF receiver at resonance between two chosen Rydberg states. In this paper, we study the extension of the feasibility of digital communication via this quantum-based antenna over a continuously tunable RF-carrier at off-resonance. Our experiment shows that the digital communication at a rate of 500 kbps can be performed reliably within a tunable bandwidth of 200 MHz near a 10.22 GHz carrier. Outside of this range, the bit error rate (BER) increases, rising to, for example, 15% at an RF-detuning of $\pm 150$ MHz. In the measurement, the time-varying RF field is retrieved by detecting the optical power of the probe laser at the center frequency of RF-induced symmetric or asymmetric Autler-Townes splitting in EIT. Prior to the digital test, we studied the RF-reception quality as a function of various parameters including the RF detuning and found that a choice of linear gain response to the RF-amplitude can suppress the signal distortion. The modulating signal can be decoded at speeds up to 500 kHz in the tunable bandwidth. Our test consolidates the physical basis for reliable communication and spectral sensing over a wider broadband RF-carrier, which paves a way for the concurrent multi-channel communications founded on the same pair of Rydberg states.

The Rydberg atom-based microwave electric field sensor has high sensitivity for weak RF-field detection. Selection of Rydberg states with larger electric dipole moment is beneficial to enhance the sensitivity, and we choose Rydberg states with its principal quantum number up to n ∼ 80. We study the probe laser transmission response to a microwave field for these chosen high Rydberg states at room temperature. It agrees well with theoretical simulation based on an optical Bloch equation with considered microwave-atom interaction and Doppler broadening effect. In our experiment, the microwave sensing sensitivity based on 85 Rb transition | 78 S 1 / 2 ⟩ → | 78 P 3 / 2 ⟩ arrives at 5.102(49) nV cm − 1 Hz − 1 / 2 at 1 kHz.

We have studied the phenomenon of electromagnetically induced transparency (EIT) of ⁸⁷ Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D ₂ line of ⁸⁷ Rb in a Λ -type configuration. With a 5 Torr N ₂ buffer gas in the thermal 2 cm vapor cell, the state 5 2 P 3 / 2 has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of ⁸⁷ Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.

A microwave electric field sensing has been set up based on a three-color electromagnetically induced absorption in rubidium vapor cell via cascading transitions. All transitions are irradiated by infrared lasers: a 780 nm laser servers as probe to monitor the optical transmittancy via transition 5S_1/2→P_3/2;, a 776 nm laser and a 1260 nm laser are used to couple the states 5P_3/2 and 5D_5/2 and states 5D_5/2 and 44F_7/2, respectively. We find that a frequency detuning ∼2π × ( − 40) MHz of the 776 nm dressing beam prefers to a better signal-to-noise ratio for the probe beam. The off-resonance greatly depresses the double resonance pumping effect. A demonstration measurement for the electric field of microwave 1.18988 GHz, corresponding to the coupling resonance between two adjacent Rydberg states 44F_7/2 and 44F_9/2, gives a sensitivity of 55.79 ( 23 ) nVcm − 1 / Hz and a smallest discernible electric field of 78.9(33) nVcm⁻¹ in time scale of 500 ms.

We report the observation of a controlled Landau-Zener transition (LZT) in Rydberg atoms by breaking the symmetry of the underlying Hamiltonian. For a nonhydrogenic Rydberg atom inside a changing electric ($F$) field, a LZT occurs between the avoided crossing energy levels of neighboring Rydberg states only for a sufficiently high changing rate. If a transverse magnetic ($B$) field is applied as we implement, the atomic level symmetry is broken, which causes the Stark manifolds denoted by a different $|m|$ ($m$ is the magnetic quantum number) to interact with each other. The mixed state levels end up pushing the adiabatically repelled target states closer and additionally they serve as stepping stones for the sequential LZTs between the neighboring sublevels. Such a feature significantly decreases the changing rate required for an efficient LZT inside a pure electric field. We report experimental observations that support the above scenario. It opens a versatile approach for engineering a controlled LZT in more general systems.

We have studied the high resolution spectroscopy of Rydberg state ⁸⁷Rb in a ladder-type electromagnetically induced transparency (EIT) configuration at room temperature. A highly excited Rydberg atom is nearly degenerate for its hyperfine states but this degeneracy will be broken by an applied magnetic field, resulting in a spectral splitting in a coupled basis. In our ladder-type EIT experiment, we observed the high resolution spectral splitting of Rydberg atoms in an external magnetic field with two different optical polarization combinations of σ⁺ − σ⁺ and σ⁺ − σ⁻ for probe and coupling laser beams. A strict theory has been set up to explain the observed spectral line position and intensity accurately considering the Zeeman effects of three EIT-concerned states all in the coupled basis. Specially for the Rydberg state, we can transform its wavefunction back into the decoupled basis for the spectral line assignment.