The n=60, L z =0 angular momentum manifold in helium is studied in the presence of an electric field parallel to a fixed magnetic field (B=0.1539 T). Results obtained from a CW laser-atomic beam experiment are compared with diagonalization calculations and with a WKB approximation including core effects. Core-induced anticrossings have been analysed in detail. The supersymmetry, including quasi-crossings in hydrogen to occur at the same value of the electric field strength, does not apply for L z =0 manifolds in non-hydrogenic Rydberg atoms.
A spectroscopic study of Rydberg states of helium (n = 30 and 45) in magnetic, electric and combined magnetic and electric fields with arbitrary relative orientations of the field vectors is presented. The emphasis is on two special cases where (i) the diamagnetic term is negligible and both paramagnetic Zeeman and Stark effects are linear (n = 30, B ≤ 120 mT and F = 0-78 V cm⁻¹), and (ii) the diamagnetic term is dominant and the Stark effect is linear (n = 45, B = 277 mT and F = 0-8 V cm⁻¹). Both cases correspond to regimes where the interactions induced by the electric and magnetic fields are much weaker than the Coulomb interaction, but much stronger than the spin-orbit interaction. The experimental spectra are compared to spectra calculated by determining the eigenvalues of the Hamiltonian matrix describing helium Rydberg states in the external fields. The spectra and the calculated energy-level diagrams in external fields reveal avoided crossings between levels of different m ₗ values and pronounced m ₁-mixing effects at all angles between the electric- and magnetic-field vectors other than 0. These observations are discussed in the context of the development of a method to generate dense samples of cold atoms and molecules in a magnetic trap following Rydberg-Stark deceleration.
Abstract A spectroscopic study of Rydberg states of helium ( n = 30 and 45) in magnetic, electric and combined magnetic and electric fields with arbitrary relative orientations of the field vectors is presented. The emphasis is on two special cases where (i) the diamagnetic term is negligible and both paramagnetic Zeeman and Stark effects are linear ( n = 30, B ≤ 120 mT and F = 0–78 V cm −1 ), and (ii) the diamagnetic term is dominant and the Stark effect is linear ( n = 45, B = 277 mT and F = 0–8 V cm −1 ). Both cases correspond to regimes where the interactions induced by the electric and magnetic fields are much weaker than the Coulomb interaction, but much stronger than the spin–orbit interaction. The experimental spectra are compared to spectra calculated by determining the eigenvalues of the Hamiltonian matrix describing helium Rydberg states in the external fields. The spectra and the calculated energy-level diagrams in external fields reveal avoided crossings between levels of different m l values and pronounced m l -mixing effects at all angles between the electric- and magnetic-field vectors other than 0. These observations are discussed in the context of the development of a method to generate dense samples of cold atoms and molecules in a magnetic trap following Rydberg–Stark deceleration.
A quasihydrogenic complete diamagnetic manifold is investigated experimentally. The spectra are obtained in a uniform magnetic field by exciting in a one-step process, using polarised laser light, the lithium atoms of an atomic beam. The whole structure of the M=0 odd diamagnetic multiplet has been recorded for the first time. This experiment provides a confirmation for the existence of the two classes of states predicted for the diamagnetic Hamiltonian of atomic hydrogen in the weak-field limit. The fundamental features of diamagnetism still subsist for such high field strengths so that the diamagnetic interaction cannot be regarded as a perturbation with respect to the Coulomb problem. The intermanifold coupling and the influence of effects due to the ionic core in the lithium atom are evaluated quantitatively.
Circular Rydberg states with
n=70 have been prepared in helium using a modified version of the crossed-fields method. This approach to the preparation of high-
n circular Rydberg states overcomes limitations of the standard crossed-fields method which arise at this, and higher, values of
n. The experiments were performed with atoms traveling in pulsed supersonic beams that were initially laser photoexcited from the metastable
1s2s3S1 level to the
1s73s3S1 level by resonance-enhanced two-color two-photon excitation in a magnetic field of 16.154 G. These excited atoms were then polarized using a perpendicular electric field of 0.844 V/cm, and transferred by a pulse of microwave radiation to the state that, when adiabatically depolarized, evolves into the
n=70 circular state in zero electric field. The excited atoms were detected by state-selective electric field ionization. Each step of the circular state preparation process was validated by comparison with the calculated atomic energy-level structure in the perpendicular electric and magnetic fields used. Of the atoms initially excited to the
1s73s3S1 level, $\ensuremath{\sim}80%$ were transferred to the
n=70 circular state. At these high values of $n, \mathrm{\ensuremath{\Delta}}n=1$ circular-to-circular Rydberg state transitions occur at frequencies below 20 GHz. Consequently, atoms in these states, and the circular state preparation process presented here, are well suited to hybrid cavity QED experiments with Rydberg atoms and superconducting microwave circuits.
Helium atoms travelling in pulsed supersonic beams have been photoexcited from the metastable 1s2s 3 S 1 level to Rydberg states with principal quantum numbers exceeding 400 by resonance-enhanced two-colour two-photon excitation using narrow-bandwidth CW laser radiation. To achieve this, the photoexcitation region was shielded and stray electric fields cancelled using a cubic arrangement of 80 mm × 80 mm copper plates. The excited Rydberg atoms were detected by pulsed electric field ionisation downstream from this photoexcitation region. Comparison of the experimental spectra with the results of calculations indicate that the stray electric fields at the position of Rydberg state photoexcitation were reduced to as low as 160 μ V cm –1 . Using helium in these experiments minimises temporal changes in the stray fields resulting from surface adsorption. Measurements performed 70 h apart indicate that the rate of change of these fields was on the order of 2 μ V cm –1 per h, making beams of metastable helium atoms ideally suited as probes for high precision electrometry in spectroscopy experiments involving less readily available species such as positronium or antihydrogen.