Atomic Physics
Time reversal invariance violation in neutron-nucleus scattering (1903.08937v1)
Pavel Fadeev, Victor V. Flambaum
2019-03-21
Planning and interpretation of the experiments searching for the time reversal (T) and parity (P) violation in neutron reactions require values of the matrix elements of the T,P-violating nuclear forces between nuclear compound states. We calculate the root mean square values and the ratio of the matrix elements of the T,P-violating and P-violating interactions using statistical theory based on the properties of chaotic compound states and present the results in terms of the fundamental parameters in four different forms: in terms of the constants of the contact nuclear interaction, meson exchange constants, QCD theta-term and quark chromo-EDMs. Using current limits on these parameters, we obtain the upper bounds on the ratio of the matrix elements.
Search for Anderson localization of light by cold atoms in a static electric field (1901.04853v2)
S. E. Skipetrov, I. M. Sokolov
2019-01-15
We explore the potential of a static electric field to induce Anderson localization of light in a large three-dimensional (3D) cloud of randomly distributed, immobile atoms with a degenerate ground state (total angular momentum
) and a three-fold degenerate excited state (
). We study both the spatial structure of quasimodes of the atomic cloud and the scaling of the Thouless number with the size of the cloud. Our results indicate that unlike the static magnetic field, the electric field does not induce Anderson localization of light by atoms. We explain this conclusion by the incomplete removal of degeneracy of the excited atomic state by the field and the relatively strong residual dipole-dipole coupling between atoms which is weaker than in the absence of external fields but stronger than in the presence of a static magnetic field. A joint analysis of these results together with our previous results concerning Anderson localization of scalar waves and light suggests the existence of a critical strength of dipole-dipole interactions that should not be surpassed for Anderson localization to be possible in 3D.
Calculations of Bethe logarithms for Hydrogen and Helium atoms using B-splines in different gauges (1903.08802v1)
Yong-Hui Zhang, Lu-Jun Shen, Chang-Ming Xiao, Jun-Yi Zhang, Ting-Yun Shi
2019-03-21
The efficient and simple B-splines variational method of calculating the hydrogen atom Bethe logarithms in the acceleration gauge [Y-B Tang et.al., Phys. Rev. A
, 022510 (2013)] is successfully applied to other gauges. The ground state Bethe logarithm of H with fourteen accurate figures is obtained in the velocity gauge, and in the length gauge the ground state value has eleven accurate figures. Present velocity- and length-gauge results for the
,
,
, and
states up to
of H are at the 10
level of accuracy. This represents the successful variational attempt to calculate Bethe logarithms of the hydrogen atom in the velocity and length gauges. Furthermore, the B-splines variational method is successfully extended to the helium atom by the aid of configuration interaction. Bethe logarithms for
states are calculated in three different gauges. The acceleration-gauge value of 4.364 036 7(2) a.u. and the velocity-acceleration gauge value of 4.364 036 4(2) a.u. for the
state are achieved, which are both at the 10
level of accuracy. For other triplet states, present results in three different gauges all have five to seven accurate figures. While for the singlet states, the best convergent values are obtained in the pa-gauge, of which the numerical precision is also at the
to
level of accuracy.
Electric-field induced helium-helium resonances (1903.08698v1)
Qingze Guan, Doerte Blume
2019-03-20
The tunability of the helium-helium interaction through an external electric field is investigated. For a static external field, electric-field induced resonances and associated electric-field induced bound states are calculated for the
He-
He-
How to observe the vacuum decay in low-energy heavy-ion collisions (1903.08546v1)
I. A. Maltsev, V. M. Shabaev, R. V. Popov, Y. S. Kozhedub, G. Plunien, X. Ma, Th. Stöhlker
2019-03-20
In slow collisions of two bare nuclei with the total charge larger than the critical value
, the initially neutral vacuum can spontaneously decay into the charged vacuum and two positrons. Detection of the spontaneous emission of positrons would be the direct evidence of this fundamental phenomenon. However, the spontaneously produced particles are indistinguishable from the dynamical background in the positron spectra. We show that the vacuum decay can nevertheless be observed via impact-sensitive measurements of pair-production probabilities. Possibility of such observation is demonstrated using numerical calculations of pair production in low-energy collisions of heavy nuclei.
-Symmetry in Hartree-Fock Theory (1903.08489v1)
Hugh G. A. Burton, Alex J. W. Thom, Pierre-François Loos
2019-03-20
and time reversal
--- provides a weaker condition than (Dirac) Hermiticity for ensuring a real energy spectrum of a general non-Hermitian Hamiltonian.
Compact bulk-machined electromagnets for quantum gas experiments (1901.08791v3)
K. Roux, B. Cilenti, V. Helson, H. Konishi, J. P. Brantut
2019-01-25
We present an electromagnet combining a large number of windings in a constrained volume with efficient cooling. It is based on bulk copper where a small pitch spiral is cut out and impregnated with epoxy, forming an ensemble which is then machined at will to maximize the use of the available volume. Water cooling is achieved in parallel by direct contact between coolant and the copper windings. A pair of such coils produces magnetic fields suitable for exploiting the broad Feshbach resonance of
Li at 832.2 G. It offers a compact and cost-effective solution for quantum gas experiments.
Tuning nonthermal distributions to thermal ones in time-dependent Paul traps (1809.10519v2)
H. Landa
2018-09-27
We study the probability distribution of an atomic ion being laser-cooled in a periodically-driven Paul trap using a Floquet approach to the semiclassical photon scattering dynamics. We show that despite the microscopic nonequilibrium forces, a stationary thermal-like exponential distribution can be obtained in the Hamiltonian action, or equivalently in the number of quanta (phonons) of the motion linearized about the zero of the potential. At the presence of additional stray electric fields, the ion is pushed from the origin of the potential and set into a large-amplitude driven oscillation, and above a threshold amplitude of such "excess micromotion", the action distribution of excitations about the driven oscillation broadens and becomes distinctly nonthermal. We find that by a proper choice of the laser detuning the distribution can be made exponential again, with a mean phonon number close to that of the Doppler cooling limit. We derive a relation allowing to deduce just from the experimentally observable photon scattering rate both the required detuning for optimal cooling and the final mean phonon number. These results are important for quantum information processing and other applications, and in particular the derived approach can be applied to crystals of trapped ions in planar configurations, where the driven motion of ions is unavoidable.
Partial-wave analysis of multiphoton ionization of sodium by femtosecond laser pulses of 800 nm wavelength in over-the-barrier ionization regime (1903.08422v1)
Andrej Bunac, Duška B. Popović, Nenad S. Simonović
2019-03-20
Multiphoton ionization of sodium by laser pulses of 800 nm wavelength and 57 fs duration is studied in the range of laser peak intensities belonging to over-the-barrier ionization regime. Photoelectron momentum distributions (PMD) and the energy spectra are determined numerically by solving the time dependent Schr"odinger equation. The calculated spectra agree well with the spectra obtained experimentally by Hart et al. [Phys. Rev. A 93, 063426 (2016)]. The contributions of photoelectrons with different values of the orbital quantum number in the PMD are determined by expanding the photoelectron wave function in terms of partial waves. Partial wave analysis of the spectral peaks related to Freeman resonances has shown that each peak has photoelectron contributions from different ionization channels which are characterized by different photoelectron energies and different symmetries of released photoelectron wave-packets. These findings are justified by calculating the populations of excited states during the pulse. Our analysis indicates that the contribution of specific ionization channels in the total photoelectron yield might be selectively increased by varying to some extent the values of pulse parameters used here.
Linear-response range-separated density-functional theory for atomic photoexcitation and photoionization spectra (1903.08369v1)
Felipe Zapata, Eleonora Luppi, Julien Toulouse
2019-03-20
We investigate the performance of the range-separated hybrid (RSH) scheme, which combines long-range Hartree-Fock (HF) and a short-range density-functional approximation (DFA), for calculating photoexcitation/photoionization spectra of the H and He atoms, using a B-spline basis set in order to correctly describe the continuum part of the spectra. The study of these simple systems allows us to quantify the influence on the spectra of the errors coming from the short-range exchange-correlation DFA and from the missing long-range correlation in the RSH scheme. We study the differences between using the long-range HF exchange (nonlocal) potential and the long-range exact exchange (local) potential. Contrary to the former, the latter supports a series of Rydberg states and gives reasonable photoexcitation/photoionization spectra, even without applying linear-response theory. The most accurate spectra are obtained with the linear-response time-dependent range-separated hybrid (TDRSH) scheme. In particular, for the He atom at the optimal value of the range-separation parameter, TDRSH gives slightly more accurate photoexcitation and photoioniza-tion spectra than standard linear-response time-dependent HF. More generally, the present work shows the potential of range-separated density-functional theory for calculating linear and nonlinear optical properties involving continuum states.
