More Like this

1. Long-Range Interactions for Hydrogen Atoms in Excited D States

   https://doi.org/10.3390/atoms10010006  

   Adhikari, Chandra M.; Jentschura, Ulrich D. (March 2022, Atoms)

   Pressure shifts inside an atomic beam are among the more theoretically challenging effects in high-precision measurements of atomic transitions. A crucial element in their theoretical analysis is the understanding of long-range interatomic interactions inside the beam. For excited reference states, the presence of quasi-degenerate states leads to additional challenges, due to the necessity to diagonalize large matrices in the quasi-degenerate hyperfine manifolds. Here, we focus on the interactions of hydrogen atoms in reference states composed of an excited nD state (atom A), and in the metastable 2S state (atom B). We devote special attention to the cases n=3 and n=8. For n=3, the main effect is generated by quasi-degenerate virtual P states from both atoms A and B and leads to experimentally relevant second-order long-range (van-der-Waals) interactions proportional to the sixth inverse power of the interatomic distance. For n=8, in addition to virtual states with two states of P symmetry, one needs to take into account combined virtual P and F states from atoms A and B. The numerical value of the so-called C6 coefficients multiplying the interaction energy was found to grow with the principal quantum number of the reference D state; it was found to be of the order of 1011 in atomic units. The result allows for the calculation of the pressure shift inside atomic beams while driving transitions to nD states. 

   more » « less
2. Hydrodynamic superradiance in wave-mediated cooperative tunneling

   https://doi.org/10.1038/s42005-022-00918-y  

   Papatryfonos, Konstantinos; Ruelle, Mélanie; Bourdiol, Corentin; Nachbin, André; Bush, John W.; Labousse, Matthieu (December 2022, Communications Physics)

   Abstract Superradiance occurs in quantum optics when the emission rate of photons from multiple atoms is enhanced by inter-atom interactions. When the distance between two atoms is comparable to the emission wavelength, the atoms become entangled and their emission rate varies sinusoidally with their separation distance due to quantum interference. We here explore a theoretical model of pilot-wave hydrodynamics, wherein droplets self-propel on the surface of a vibrating bath. When a droplet is confined to a pair of hydrodynamic cavities between which it may transition unpredictably, in certain instances the system constitutes a two-level system with well-defined ground and excited states. When two such two-level systems are coupled through an intervening cavity, the probability of transition between states may be enhanced or diminished owing to the wave-mediated influence of its neighbour. Moreover, the tunneling probability varies sinusoidally with the coupling-cavity length. We thus establish a classical analog of quantum superradiance. 

   more » « less
3. Valence-, Dipole- and Quadropole-Bound Electronically Excited States of Closed-Shell Anions Formed by Deprotonation of Cyano- and Ethynyl-Disubstituted Polycyclic Aromatic Hydrocarbons

   https://doi.org/10.3390/chemistry4010004  

   Strauss, Marie E.; Santaloci, Taylor J.; Fortenberry, Ryan C. (March 2022, Chemistry)

   Dicyano-functionalized benzene and naphthalene anion derivatives exhibit a relatively rich population of electronically excited states in stark contrast to many assumptions regarding the photophysics of anions in general. The present work has quantum chemically analyzed the potential electronically excited states of closed-shell anions created by replacing hydrogen atoms with valence-bound lone pairs in benzene and naphthalene difunctionalized with combinations of -CN and -C2H. Dicyanobenzene anion derivatives can exhibit dipole-bound excited states as long as the cyano groups are not in para position to one another. This also extends to cyanoethynylbenzene anions as well as deprotonated dicyano- and cyanoethynylnaphthalene anion derivatives. Diethynyl functionalization is less consistent. While large dipole moments are created in some cases for deprotonation on the -C2H group itself, the presence of electronically excited states beyond those that are dipole-bound is less consistent. Beyond these general trends, 2-dicyanonaphthalene-34 gives strong indication for exhibiting a quadrupole-bound excited state, and the 1-cyanoethynylnaphthalene-29 and -36 anion derivatives are shown to possess as many as two valence-bound excited states and one dipole-bound excited state. These photophysical properties may have an influence on regions where polycyclic aromatic hydrocarbons are known to exist such as in various astrochemical environments or even in combustion flames. 

   more » « less
4. Two-photon spectroscopy of the NaLi triplet ground state

   https://doi.org/10.1039/C7CP08481A  

   Rvachov, Timur M.; Son, Hyungmok; Park, Juliana J.; Ebadi, Sepehr; Zwierlein, Martin W.; Ketterle, Wolfgang; Jamison, Alan O. (January 2018, Physical Chemistry Chemical Physics)

   We employ two-photon spectroscopy to study the vibrational states of the triplet ground state potential (a 3 Σ + ) of the 23 Na 6 Li molecule. Pairs of Na and Li atoms in an ultracold mixture are photoassociated into an excited triplet molecular state, which in turn is coupled to vibrational states of the triplet ground potential. Vibrational state binding energies, line strengths, and potential fitting parameters for the triplet ground a 3 Σ + potential are reported. We also observe rotational splitting in the lowest vibrational state. 

   more » « less
5. Delay-induced spontaneous dark-state generation from two distant excited atoms

   https://doi.org/10.1103/PhysRevResearch.6.023213  

   Alvarez-Giron, W; Solano, P; Sinha, K; Barberis-Blostein, P (May 2024, Physical Review Research)

   We investigate the collective non-Markovian dynamics of two fully excited two-level atoms coupled to a one-dimensional waveguide in the presence of delay. We demonstrate that analogous to the well-known superfluorescence phenomena, where an inverted atomic ensemble synchronizes to enhance its emission, there is a “subfluorescence” effect that synchronizes the atoms into an entangled dark state depending on the interatomic separation. The phenomenon can lead to a two-photon bound state in the continuum. Our results are pertinent to long-distance quantum networks, presenting a mechanism for spontaneous entanglement generation between distant quantum emitters. Published by the American Physical Society2024 

   more » « less