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.
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.
This introductory chapter presents the scope of this book: namely that the book is devoted to Rydberg (i.e., highly-excited) atoms and molecules They have striking distinctions to atoms and molecules in the ground or low-excited states. For Rydberg atoms, with the increase of the principal quantum number n, their characteristic size and the electric dipole moment scales as n 2 (which is why they are extremely sensitive to even weak electric fields and electromagnetic radiation) and their radiative lifetime scales as n 3. They strongly interact not only with an electric field, but also with each other: their dipole–dipole interaction scales as n 4/R 3 and their van der Waals interaction scales as n 11/R 6, where R is their separation from each other. In laboratory conditions experimentalists deal with Rydberg atoms having the quantum number of several tens. In the Universe, in H II regions, the principal quantum number of Rydberg atoms can reach n ~ 1000. In the latter case, the Rydberg atoms cannot be considered anymore as microscopic objects: the diameter of their electron orbit is ~ 0.1 mm, i.e., twice the diameter of human hair. Studies of Rydberg atoms and molecules have numerous applications. Examples are highly-responsive sensing, quantum optics (where the light is manipulated at the level of a single photon), quantum computing, quantum chaos, ultracold Rydberg gases and plasmas, anti-hydrogen formation, and plasma diagnostics.
The past few years has seen an upsurge of interest in the Rydberg atom, described by H J Metcalf of the State University of New York in his review article in Nature (1980 280 127) as ‘an ion core and an isolated electron very far away, floating lazily around in a slow orbit, much like a distant planet of the solar system’. A single active electron is in a highly excited state where it is much less perturbed by the presence of the other electrons than it was in the lower states, bringing its behaviour closer to that in the ideal hydrogen-like model and making it a valuable subject for study.
Since the discovery of the Rydberg atom in 1885, research on the Rydberg atom has presented numerous discoveries about the Rydberg atom. As the atoms has valence electron in a high principal quantum number state, Rydberg atoms can interact with each other in a unique way, such as dipole-dipole interactions, Rydberg blockade and anti-blockade. To reach the Rydberg state, it is usually necessary to use a laser to excite the atoms from their ground state. Due to the special characteristics about Rydberg atoms as well as their interactions, it has demonstrated promising of application in different fields, for example, quantum computing and quantum information, as well as nonlinear optics and photonics. However, due to the technical limitations, the demand of deterministic atoms sources and the effect of blackbody radiation are still hindering the research relative to Rydberg atoms. For future study relative to Rydberg atoms, the additions with laser-trapping could be beneficial for fields like quantum electro dynamics and localized electromagnetic field probing.
Rydberg physics is the land of gentle giants—highly-excited electronic states where an electron is, on average, far from the nucleus. They are created with a lot of energy, have unusually large size and live relatively long. They are useful because they are extremely sensitive to their environment; so much so that a single photon of light can change the behaviour of not only one, but dozens or hundreds of them, over distances we can easily see under an optical microscope. Wherever Rydberg states are created—in atoms, molecules or solids—they all share common features that are exemplified by the physical description of highly-excited hydrogen atoms, with energy levels described by the Rydberg formula. In this ebook, we outline the universal properties of Rydberg systems and then present a selection of ideas that demonstrate their increasing relevance to applications, including sensing, the manipulation of light on the single photon level (quantum optics) and in engineering the interactions between individual quanta (quantum simulation).
Rydberg molecule, formed by one or more Rydberg atoms, exhibits remarkable properties, including an exceptionally large spatial extent, rich rovibrational level structures, permanent electric dipole moments, and a pronounced sensitivity to external fields. Based on the underlying binding mechanisms, Rydberg molecules can be divided into three categories, the ground-Rydberg molecule that is bound via a low-energy electron-atom scattering interaction between ground atom and Rydberg electron, the Rydberg-Rydberg molecule that is bound via a long-range electrostatic interaction between Rydberg atoms, and the ion-Rydberg molecule that is bound via single- or multi-polar interactions between Rydberg atom and ion. This review focuses on recent theoretical and experimental advances in diatomic Rydberg molecules, covering their formation and binding mechanisms, potential energy curves, experimental observations, and spectroscopic properties, with the aim of providing a comprehensive overview of the current state and future prospects of this rapidly developing field.
Rydberg physics is the land of gentle giants—highly-excited electronic states where an electron is, on average, far from the nucleus. They are created with a lot of energy, have unusually large size and live relatively long. They are useful because they are extremely sensitive to their environment; so much so that a single photon of light can change the behaviour of not only one, but dozens or hundreds of them, over distances we can easily see under an optical microscope. Wherever Rydberg states are created—in atoms, molecules or solids—they all share common features that are exemplified by the physical description of highly-excited hydrogen atoms, with energy levels described by the Rydberg formula. In this ebook, we outline the universal properties of Rydberg systems and then present a selection of ideas that demonstrate their increasing relevance to applications, including sensing, the manipulation of light on the single photon level (quantum optics) and in engineering the interactions between individual quanta (quantum simulation).