Search

Virtual photons can mediate interaction between atoms, resulting in an energy shift known as a collective Lamb shift. Observing the collective Lamb shift is challenging, since it can be obscured by radiative decay and direct atom-atom interactions. Here, we place two superconducting qubits in a transmission line terminated by a mirror, which suppresses decay. We measure a collective Lamb shift reaching 0.8% of the qubit transition frequency and exceeding the transition linewidth. We also show that the qubits can interact via the transmission line even if one of them does not decay into it., Comment: 7+5 pages, 4+2 figures

Quantum-state-selective thermal desorption of ${\mathrm{H}}_{2}$ weakly physisorbed on Ag(111) demonstrates significantly different desorption features between the nuclear-spin modifications. An energy shift due to the rotational-symmetry breaking induced by an anisotropic interaction affects not only the enthalpy but also the entropy of adsorption. The preexponential factor for desorption of the ortho-${\mathrm{H}}_{2}$ is about three times as large as that of the para-${\mathrm{H}}_{2}$. The entropy difference indicates a perpendicular orientation preference of anisotropic physisorption potential, which also suggests the importance of partial hybridization interaction for weak physisorption.

DD-produced protons are used to measure the imploded fuel-shell areal density $\ensuremath{\rho}\ensuremath{\Delta}R$. Twelve green beams of the GEKKO XII laser directly imploded a cryogenic foam-shell target containing a liquid or solid ${\mathrm{D}}_{2}$ fuel. The proton emission is detected through a dipole magnet on a CR-39 plate, whose energy shift from 3.02 MeV yielded the maximum $\ensuremath{\rho}\ensuremath{\Delta}R$ of 10 mg/c${\mathrm{m}}^{2}$ or the density of 6 g/c${\mathrm{m}}^{3}$, in agreement with that from the secondary neutron method within a factor of 2. The proton energy spread is sensitive to the laser energy imbalance.

We use scanning tunneling microscopy and spectroscopy to measure the energy shift of empty quantum-well (QW) states in Pb islands on the Cu(111) surface. It is found that, with an increase of the electric field, the behavior of the energy shift can be grouped into two different modes for most QW states. In the first mode, the state energy moves toward high energy monotonically. In the second mode, the state energy shifts to a lower energy initially and then turns around to a higher energy. Moreover, we have observed that the QW states of higher energy behave in preference to the first mode, but they gradually change to the second mode as the Pb island becomes thicker. This thickness-dependent behavior reflects the existence of local expansion in the Pb islands, due to the electric field, and that the expansion is larger for a thicker island. QW states can thus be used for studying the localized lattice deformation in the nanometer scale.

Low-temperature scanning tunneling spectroscopy over Co nanoislands on Cu(111) showed that the surface states of the islands vary with their size. Occupied states exhibit a sizeable downward energy shift as the island size decreases. The position of the occupied states also significantly changes across the islands. Atomic-scale simulations and ab inito calculations demonstrate that the driving force for the observed shift is related to size-dependent mesoscopic relaxations in the nanoislands., Comment: 4 pages, 4 figures

We have measured the shift and width of the kaonic hydrogen $1s$ state due to the $\overline{K}N$ strong interaction. We have observed, for the first time, distinct $K$-series kaonic hydrogen x rays with good signal-to-noise ratio in the energy spectrum. The measured energy shift and width were determined to be $\ensuremath{\Delta}E(1s)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}323\ifmmode\pm\else\textpm\fi{}63(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}11(\mathrm{syst})\mathrm{eV}$ (repulsive) and $\ensuremath{\gamma}(1s)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}407\ifmmode\pm\else\textpm\fi{}208(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}100(\mathrm{syst})\mathrm{eV}$, respectively.

A novel finite basis set method is used to calculate the Bethe logarithm for the ground $2\text{ }^{2}S_{1/2}$ and excited $3\text{ }^{2}S_{1/2}$ states of lithium. The basis sets are constructed to span a huge range of distance scales within a single calculation, leading to well-converged values for the Bethe logarithm. The results are used to calculate an accurate value for the complete quantum electrodynamic energy shift up to order ${\ensuremath{\alpha}}^{3}$ Ry. The calculated $3\text{ }^{2}S_{1/2}--2\text{ }^{2}S_{1/2}$ transition frequency for $^{7}\mathrm{L}\mathrm{i}$ is $27\text{ }206.092\text{ }6(9)\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}1}$, and the ionization potential for the $2\text{ }^{2}S_{1/2}$ state is $43\text{ }487.158\text{ }3(6)\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}1}$. The $^{7}\mathrm{L}\mathrm{i}$--$^{6}\mathrm{L}\mathrm{i}$ isotope shift is also considered, and all the results compared with experiment.

The asymmetry of the natural line profile for transitions in hydrogen-like atoms is evaluated within a QED framework. For the Lyman-alpha $1s-2p$ absorption transition in neutral hydrogen this asymmetry results in an additional energy shift of 2.929856 Hz. For the $2s_{1/2}-2p_{3/2}$ transition it amounts to -1.512674 Hz. As a new feature this correction turns out to be process dependent. The quoted numbers refer to the Compton-scattering process., Comment: RevTex, 7 Latex pages, 1 figure

We have performed x-ray two-photon photoelectron spectroscopy using the Linac Coherent Light Source x-ray free-electron laser in order to study double core-hole (DCH) states of CO2, N2O, and N-2. The experiment verifies the theory behind the chemical sensitivity of two-site DCH states by comparing a set of small molecules with respect to the energy shift of the two-site DCH state and by extracting the relevant parameters from this shift.

It is shown that the energy shift of $K$ x rays emitted by an atom doubly ionized in the $K$ shell comprises a 16% Breit-interaction contribution for $Z=81$ and thus constitutes a sensitive test of these corrections. The calculated shift of the $K{\ensuremath{\alpha}}_{1}$ line agrees with the present experiment (1160 \ifmmode\pm\else\textpm\fi{} 70 e V). This invalidates the much larger 2100-e V shift, reported by another group, which appears to be due to spurious effects.

The excitation functions for the reactions $^{12}\mathrm{C}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}, \ensuremath{\pi}N)^{11}\mathrm{C}$ have been measured by activation over the energy ranges 50 to 470 MeV for ${\ensuremath{\pi}}^{+}$ and 40 to 550 MeV for ${\ensuremath{\pi}}^{\ensuremath{-}}$. These excitation functions, clearly reflecting the (3,3) pion-nucleon resonance, show an upward energy shift in the resonance peak for ${\ensuremath{\pi}}^{\ensuremath{-}}$ and a downward shift for ${\ensuremath{\pi}}^{+}$. The $\frac{{\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{\ensuremath{-}}}}{{\ensuremath{\sigma}}_{{\ensuremath{\pi}}^{+}}}$ ratio at 180 MeV is 1.55 \ifmmode\pm\else\textpm\fi{} 0.10.

Data on spontaneous and stimulated emission, in the photon-energy range ${E}_{g}+5\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{LO}}\ensuremath{\gtrsim}\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\gtrsim}{E}_{g}$, are presented on ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$-GaAs quantum-well heterostructures with ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ ($x\ensuremath{\sim}0.4\ensuremath{-}0.5$) coupling barriers of size ${L}_{B}\ensuremath{\sim}40\ensuremath{-}70$ \AA{} and GaAs wells of size ${L}_{z}\ensuremath{\sim}30\ensuremath{-}40$ \AA{}. For ${L}_{z}$,${L}_{B}\ensuremath{\lesssim}50$ \AA{}, Al-Ga disorder (clustering) in the alloy barriers is consistent with the observed spectral broadening and downward energy shift of the confined-particle transitions. A simple substitution of binary (AlAs) for ternary (AlGaAs) barriers eliminates alloy clustering and its effects, and makes unambiguous the identification of clustering in alloy barriers.

We develop a two-potential approach to the decay of a quasistationary state. The method enables us to obtain a simple algebraic formula for the decay width and the energy shift of a metastable state. The quasiclassical limit of the width found leads to the well-known Gamow formula, this time with a well-defiend preexponential factor. The energy shift together with its quasiclassical limit is obtained in closed form.