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Experimental Considerations of 2D Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
The electron behavior in graphene monolayer defies the conventional notion of a donor or acceptor impurity when an ionized impurity becomes a scattering center55. For understanding of this behavior the notion of the Rydberg states is introduced. The Rydberg states are the states that are electronically excited with energies that correspond to the Rydberg formula. The Rydberg formula was designed to describe atomic energy levels. It may be used to describe other electronic systems. The threshold ionization energy is the energy necessary to detach the electron from the ionic core of an atom. A Rydberg wavepacket is created by a laser pulse that is aimed at an atom populating a superposition of Rydberg states. The energy of Rydberg states is determined using a correction, the so-called quantum defect. An anticipated behavior of massless particles in 2D-space precludes the establishment of bound states at a charge center and an infinite number of quasibound states are brought about when the Coulomb potential strength surpasses a crystal magnitude β = ½. () β=Ze2/κhυF;
Laser Ionization Techniques
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Beyer and Merkt (2016a, 2016b) studied the quasi-bound levels of H2+ by PFI-ZEKE PES. The spectra were recorded by monitoring the electron signal produced by field ionization of very high Rydberg states (n > 100) as a function of the laser excitation energy hνVUV + hν1 + hν2 (the last tunable). Since the bound and quasi-bound rotational levels of the highest vibrational states of the electronic ground state of the anion H2+ exhibit a large average internuclear separation and are therefore not directly accessible from the electronic ground state of the neutral H2, a resonant stepwise three-photon excitation sequence via the B- and H-states as intermediates was employed to gradually enlarge the internuclear separation; the scheme is noted in the left-hand side of Figure 16.21. The associated, level-annotated PFI-ZEKE photoelectron spectra of ortho- and para-H2, in the region of the dissociation limit to H2+X2Σg+ are depicted in the lower and upper data panels, respectively (note that the para-H2 spectrum is flipped vertically for clarity).
Theoretical approaches for doubly-excited Rydberg states in quasi-two-electron systems: two-electron dynamics far away from the nucleus
Published in Molecular Physics, 2021
Rydberg states are associated with electrons promoted to atomic orbitals that are much larger in size than the residual ion ‘core’. Rydberg electrons are labelled by their principal quantum number n, orbital-angular-momentum quantum number l and total-angular-momentum quantum number j. In the following, we distinguish three different types of Rydberg states: (i) singly-excited Rydberg states, in which one electron is in a Rydberg orbital and the ion core is in its electronic ground state; (ii) core-excited Rydberg states, in which one electron is in a Rydberg orbital and the ion core is in a low-lying excited electronic state; (iii) doubly-excited Rydberg states, where two electrons are in Rydberg orbitals. These three types of Rydberg states possess distinctive physical properties that are detailed below for the case of quasi-two-electron atoms.
Fluorescence-lifetime-limited trapping of Rydberg helium atoms on a chip
Published in Molecular Physics, 2019
V. Zhelyazkova, M. Žeško*, H. Schmutz, J. A. Agner, F. Merkt
Atomic and molecular Rydberg states of high principal quantum number n have large electric dipole moments, which in first approximation scale as for the outermost members of the Stark manifolds of states [1, 2]. Breeden and Metcalf [3] and Wing [4] proposed to use these large electric dipole moments to accelerate and trap Rydberg atoms using inhomogeneous electric fields in the early 1980s.
Tightly trapped highly excited Rydberg atom in dipole–quadrupole potential landscape
Published in Journal of Modern Optics, 2019
Atomic ground state is ideal for preserving quantum coherence (17), while the implementation of fast and deterministic quantum operations needs a quantum superposition of a ground and a Rydberg state to achieve coherent state transfer between Rydberg and long-living ground states (18). The electric dipole strength of highly excited Rydberg atoms results in the Rydberg excitation blockade (19), which can be used in combination with electromagnetically induced transparency (20) to generate quantum states of light and photonic quantum logic gates (21–24). In order to perform high-fidelity quantum logic gates, it is important to cancel imperfections in the Rydberg excitation process. One of the most significant challenges in improving quantum information processing based on the excitation of single atom into a highly excited Rydberg state is increasing the coherent time of the trapped single Rydberg atom to store and measure quantum information at the single-qubit or –qudit level. The highly excited Rydberg states are sensitive to the stray lights, which makes it difficult to achieve precision control over the trapping system to keep the stored information unchanged. Moreover, due to the different trapping potential of the ground and the Rydberg state, the Rydberg state moves in different optical potential than that experienced by the ground state. Consequently, the vibrational state of the atom in the trap may change after the gate operation is completed, leading to decoherence due to motional heating. In addition, since the distance of Rydberg electron from the core is large (about 1 µm) and comparable to the scale of spatial variations of laser intensity, it is necessary to consider the local trapping potential averaged over the Rydberg electron wave function. These are problematic for implementing quantum gates and other quantum information protocols with Rydberg atoms and therefore, it is interesting to find a trapping system that keeps the Rydberg atom localized in a region decoupled from sources of decoherence during the excitation process. Diverse avenues have been pursued for trapping Rydberg state, discussing traps for Rydberg atoms based on electric (25), or magnetic fields (26,27). By particular choice of trapping laser wavelength (magic wavelength) (28), it is possible to match the frequency-dependent polarizabilities of the atom in its ground and Rydberg states. Equalization of the optical potential, seen by the atom at the ground state and Rydberg state, and suppression of decoherence, due to atomic motion during the Rydberg excitation, provide the optimal scheme for the Rydberg gate operation (28). However, the residual AC Stark shifts due to the stray lights would cause decoherence. By switching the trap off during the time of the gate action, it is possible to eliminate the disrupting effects of trapping system on the gate operation. This procedure also heats the atom up and results in the atomic centre-of-mass motion. The blue detuned structured laser beams with spatial transverse intensity distribution can provide the atomic trap with lower atomic level shifts (11).