Radiation and polarization characteristics of Rydberg atomic states. Part 2

S. Feneuille, P. Jacquinot

Igor L. Glukhov, Aleksandr A. Kamenski, A. S. Kornev +3 more

Once created, an ensemble of atoms in their identical Rydberg states immediately experiences significant variations of its structure and corresponding properties. The variation is caused by the inevitable radiation transitions of highly excited states into different states of higher or lower energies. In particular, the change of a uniform definite-state population for another kind of population of different states will change the long-range interaction between atoms, even transforming the van der Waals interaction, Δ E vdW =− C 6 / R 6 , into dipole–dipole interaction with a different dependence on the interatomic distance, Δ E d−d =− C 3 / R 3 . In this paper, the most important—dipole radiation transitions from Rydberg states to higher- or lower-energy | n ′ 1 P 1 ⟩ states—are considered, both spontaneous and induced by the blackbody radiation (BBR) of the environment. The total transition probability rate, which is usually determined as the natural width, equals the imaginary part of the Rydberg-state energy Γ n S /2=−Im E n S . The probabilities of the | n ′ 1 P 1 ⟩-state populations W n S ( n ′ P, T ), which depend on the BBR temperature T , on the lifetime scale are also rather important optical characteristics of the ensemble of the Rydberg-state atoms. The value of W n S ( n ′ P, T ) is determined as the ratio of a particular transition probability rate Γ n S→ n ′ P sp +Γ n S→ n ′ P BBR ( T ) to the sum of all possible radiative transition rates, which include spontaneous and BBR-induced rates, where the latter depend on the temperature T of the environment. Numerical values of W n S ( n ′ P, T ) are calculated and presented in wide regions of the principal quantum numbers n , n ′ , and BBR temperatures T .

FRANK B. ROSMEJ, Valery Alexandrovich Astapenko, Valery S. Lisitsa

P. Goy, L. Moi, M. Groß +3 more

The "triggering" of transient maser systems using excited Rydberg atoms as active medium is investigated theoretically and experimentally. We show how the maser pulse characteristics are modified by the interaction of the active medium with small amounts of resonant mm-wave radiation. The phase, polarization, and emission delay of the radiated field are modified by this triggering: this can be used to detect very small powers of mm-or sub-mm-wave radiation. A complete discussion of the quantum and thermal noise of these detectors is presented. A demonstration of the feasibility of this technique is reported. Triggering signals corresponding to a detectivity of ${3\ifmmode\times\else\texttimes\fi{}10}^{\ensuremath{-}17}$ ${\mathrm{W}/\mathrm{H}\mathrm{z}}^{1/2}$ at 108 GHz ($\ensuremath{\lambda}=2.8$ mm) have been measured at room temperature. The quantum-noise limit---corresponding to ${6\ifmmode\times\else\texttimes\fi{}10}^{\ensuremath{-}19}$ ${\mathrm{W}/\mathrm{H}\mathrm{z}}^{1/2}$---should be reached with liquid-helium-temperature-cooled detectors.

HERBERT WALTHER

Shuai Yuan, Xinyi Y. I. Xu, Jinpeng Yuan +5 more

Rydberg atom-based antennas exploit the quantum properties of highly excited Rydberg atoms, providing unique advantages over classical antennas, such as high sensitivity, broad frequency range, and low intrinsic noise. Despite the increasing interests in their applications in antenna and communication engineering, some key properties, involving the lack of polarization multiplexing and isotropic reception without mutual coupling, remain unexplored in the analysis of Rydberg atom-based multiple-input–multiple-output (MIMO) communications. Generally, the design considerations for any antenna, even for atomic ones, can be extracted to factors, such as radiation pattern, efficiency, and polarization, allowing them to be seamlessly integrated into existing system models. In this letter, we extract the antenna properties from relevant quantum characteristics, enabling electromagnetic modeling and capacity analysis of Rydberg MIMO systems in both far-field and near-field scenarios. Focusing on spatial multiplexing performance under the same signal-to-noise level, our results indicate that Rydberg atom-based antenna arrays offer certain advantages over classical dipole-type arrays in single-polarization MIMO communications.