Rydberg atoms are very excited atomic states prepared close to the ionization limit. They have huge dimensions at atomic scale, very long lifetimes and very large electric dipole matrix elements for transitions connecting nearby levels and falling in the millimeter range. Moreover, they are very easy to detect. These features make these species very attractive for new developments in microwave and far-infrared technology.
Rydberg atoms are very excited atomic states prepared close to the ionization limit. They have huge dimensions at atomic scale, very long lifetimes and very large electric dipole matrix elements for transitions connecting nearby levels and falling in the millimeter range. Moreover, they are very easy to detect. These features make these species very attractive for new developments in microwave and far-infrared technology.
A small number N (105≥N≥1) of sodium atoms in an atomic beam are prepared by pulsed laser excitation in a nS Rydberg level (n≂30) while transversing a millimeter wave Fabry–Perot cavity tuned to a transition connecting the nS state to a nearby n′P level. The atoms absorb the radiation in the cavity (nS→nP upward transition), or amplify it in a maser process [nS→(n−1)P, nS→(n−2)P... downward transition]. Due to the huge size of the electric dipole matrix element between nearby Rydberg levels, the system is extremely sensitive to the millimeter wave radiation field (enhanced by the tuned cavity) in both absorption and emission processes. Simple numerical expressions are given. The experiments demonstrate that the system can be used as an absolute power meter, an ultrasensitive millimeter photon counter, an absolute quantum thermometer, and a transient millimeter-wave amplifier.
This topical review addresses how Rydberg atoms can serve as building blocks for emerging quantum technologies. Whereas the fabrication of large numbers of artificial quantum systems with the uniformity required for the most attractive applications is difficult if not impossible, atoms provide stable quantum systems which, for the same species and isotope, are all identical. Whilst atomic ground-states provide scalable quantum objects, their applications are limited by the range over which their properties can be varied. In contrast, Rydberg atoms offer strong and controllable atomic interactions that can be tuned by selecting states with different principal quantum number or orbital angular momentum. In addition Rydberg atoms are comparatively long-lived, and the large number of available energy levels and their separations allow coupling to electromagnetic fields spanning over 6 orders of magnitude in frequency. These features make Rydberg atoms highly desirable for developing new quantum technologies. After giving a brief introduction to how the properties of Rydberg atoms can be tuned, we give several examples of current areas where the unique advantages of Rydberg atom systems are being exploited to enable new applications in quantum computing, electromagnetic field sensing, and quantum optics.
Introduction Series of atomic spectral lines had been studied by emission from excited vapors even before Balmer described the regularity of the visible lines of hydrogen in 1884. However, direct excitation had been restricted to the few lowest-lying levels, particularly those accessible by electric dipole transitions from the ground state using classical light sources. The advent of tunable lasers in the 1970s changed such spectroscopic limitations enormonsly, allowing excitation to a very much larger number of states. Atoms in highly excited states, typically with principal quantum numbers n ≥ 10, are called Rydberg atoms. They are oversize, fragile states of significant intrinsic interest. They are very rare in nature because of their size and fragility, but they are found in interstellar space (H I regions). One of the best sources for comprehensive descriptions of Rydberg atoms and references to the literature describing their exploration is Ref. [120]. It describes their characteristic properties and behavior both classically and quantum mechanically, and especially their strongly enhanced interactions with external fields. The first thing to note is that Rydberg atoms are usually characterized by a single, highly excited electron while all the other electrons remain in their original states. Thus their properties are very nearly classical, and the atoms are much closer to the ideal hydrogen-like model of Chap. 7, along with appropriate quantum defects (see Chap. 10). The spectroscopy of such states is especially interesting because the active electron is much less perturbed by the other electrons in the atom than when it is in lower states. Moreover, there are some special circumstances in which the energy of a Rydberg state is degenerate with an atomic state having two electrons excited to lower levels, and such configurations yield further new information. Second, Rydberg atoms do not usually decay back to the ground state by emission of characteristic radiation, so their study is mediated by other techniques that reveal new and interesting properties. Such properties arise because Rydberg atoms have a huge dipole moment and very low binding energy resulting from the large average distance between the excited electron and the nucleus-plus-core of the rest of the atom with net charge e . Third, transitions between Rydberg states are quite different from those connecting to the ground state for at least three reasons.
Abstract This topical review addresses how Rydberg atoms can serve as building blocks for emerging quantum technologies. Whereas the fabrication of large numbers of artificial quantum systems with the uniformity required for the most attractive applications is difficult if not impossible, atoms provide stable quantum systems which, for the same species and isotope, are all identical. Whilst atomic ground states provide scalable quantum objects, their applications are limited by the range over which their properties can be varied. In contrast, Rydberg atoms offer strong and controllable atomic interactions that can be tuned by selecting states with different principal quantum number or orbital angular momentum. In addition Rydberg atoms are comparatively long-lived, and the large number of available energy levels and their separations allow coupling to electromagnetic fields spanning over 6 orders of magnitude in frequency. These features make Rydberg atoms highly desirable for developing new quantum technologies. After giving a brief introduction to how the properties of Rydberg atoms can be tuned, we give several examples of current areas where the unique advantages of Rydberg atom systems are being exploited to enable new applications in quantum computing, electromagnetic field sensing, and quantum optics.
Because of their unusual properties, Rydberg atoms, i.e., atoms with one electron occupying a highly excited orbit, have attracted the interest of many physicists. For example, due to their large size, such atoms are particularly sensitive to external fields. Fifty years ago, Segre and co-workers1 investigated the Stark effect and atomic diamagnetism of Rydberg states of alkalis with principal quantum numbers up to n = 30. During the last decade, Rydberg states have been studied extensively2 due to the availability of tunable laser radiation.
Rydberg atoms are highly promising for microwave electric field sensing owing to their large dipole matrix elements. While most experimental developments have focused on room-temperature vapors so far, utilizing cold atoms in this context could open new possibilities for applications where accuracy, long term stability and highresolution at large integration times are required, such as calibrating blackbody shifts in state-of-the-art optical clocks or measuring the cosmic MW background. Here, we report a novel approach [1] for the metrology of microwave fields with cold 87 Rubidium Rydberg atoms based on trap-loss-spectroscopy in a magneto-optical trap (MOT).