Rydberg–Stark states in oscillating electric fields (original) (raw)
Related papers
Dipole-dipole interactions between helium atoms excited to Rydberg-Stark states with principal quantum number n = 52 and approximately linear Stark shifts corresponding to induced electric dipole moments of approximately 7900 D, have been investigated experimentally. The experiments described were performed in pulsed supersonic beams with particle number densities of ∼ 10^9 cm−3. These high densities enabled us to probe the dipole-dipole interactions within the ensembles of atoms upon photoexcitation, building on previous work on (i) the observation of resonant dipole-dipole interactions between Rydberg atoms arising from their large transition moments, and (ii) the second order van der Waals interactions exploited in Rydberg excitation blockade experiments and studies of many- body effects in ensembles of cold atoms. The large electric dipole moments exploited in our experiment are very sensitive to the presence of non-resonant low frequency electric fields. These fields modify the energy level structure of the Rydberg-Stark states which can be described theoretically using Floquet methods. These shifts can therefore be used as sensitive probes of broadband electrical noise. We also show that the modified spectral intensity distributions of the Rydberg-Stark states in the presence of applied low electric field can be exploited as a new spectroscopic technique for directly probing coherent many-body interactions without the need to count atoms. The experimental results are in excellent agreement with calculations of the Rydberg energy level structure carried out using Floquet methods, and indicate that the coherent excitations observed are shared by up to 4 atoms.
Effects of electric fields on ultracold Rydberg atom interactions
Journal of Physics B: Atomic, Molecular and Optical Physics, 2011
The behaviour of interacting ultracold Rydberg atoms in both constant electric fields and laser fields is important for designing experiments and constructing realistic models of them. In this paper, we briefly review our prior work and present new results on how electric fields affect interacting ultracold Rydberg atoms. Specifically, we address the topics of constant background electric fields on Rydberg atom pair excitation and laser-induced Stark shifts on pair excitation.
We discuss the spectrum of very high Rydberg states as detected via ionization in weak external electric fields. For the conditions of interest, namely, states just below the ionization continuum and weak fields, the classical barrier to dissociation is extremely far out from the core. About the saddle point the potential is very shallow. It is concluded that ionization by tunneling is far too slow. Only electrons whose energy is above the classical barrier can be detected via ionization. However, not all electrons which energetically can ionize will necessarily do so. Electrons may fail to ionize if the fraction of their energy which is in the direction perpendicular to the field is high. The computed fraction of electrons which fails to ionize does depend, in a sensitive way, on the diabatic vs adiabatic switching on of the external field. More experiments and theoretical work is needed on this point. A classical procedure based on the adiabatic invariance of the volume in phase space is developed for the computation of the fraction of electrons that can surmount the classical barrier for a given field. Analytically exact results are obtained for adiabatic switching and for the sudden limit where the rise time of the field is shorter than the period of the orbit. For the case of diabatic switching (which is appropriate for very high n values), the exact classical computations on the yield of ionization show that the onset of ionization is at an energy of 4.25 F1I2 cm-I below the ionization potential and the 50% point it as 3.7 F1I2 cm-I for a field F in V/cm.
A quantum-field theory approach to the calculation of energy levels in helium-like Rydberg atoms
Annals of Physics, 1987
We discuss the tine structure splitting of the energy levels in Rydberg states of helium or helium-like ions on the basis of quantum electrodynamics, using time-independent perturbation theory and the radiation gauge. For the zero-order description of the states we use products of Dirac-type wavefunctions. with shielding for the outer electron. The perturbing interaction includes the residual electrostatic potential, the interaction coming from the exchange of virtual photons, and the creation of virtual electron-positron pairs. It is shown that the level shifts for low-Z ions are given to high accuracy by a procedure followed previously.
High Rydberg states of an atom in parallel electric and magnetic fields
Physical Review A, 1987
We have calculated the energy spectrum of a highly excited atom in parallel electric and magnetic fields. The eigenvalues were obtained by semiclassical quantization of action variables calculated from first-order classical perturbation theory. For the field strengths studied, the electron moves on a Kepler ellipse whose orbital parameters evolve slowly in time, and first-order perturbation theory reduces the problem to just one degree of freedom. Action variables were calculated from perturbation theory and the eigenvalues were obtained by semiclassical quantization of the action. The semiclassical analysis leads directly to a correlation diagram which connects the eigenstates of the Stark effect to those of the diamagnetic effect. A classification scheme for the eigenstates is proposed. Comparison with first-order degenerate quantum perturbation theory verifies the accuracy of the semiclassical treatment.
Electric-Field Induced Dipole Blockade with Rydberg Atoms
Physical Review Letters, 2007
High resolution laser Stark excitation of np (60 < n < 85) Rydberg states of ultra-cold cesium atoms shows an efficient blockade of the excitation attributed to long-range dipole-dipole interaction. The dipole blockade effect is observed as a quenching of the Rydberg excitation depending on the value of the dipole moment induced by the external electric field. Effects of eventual ions which could match the dipole blockade effect are discussed in detail but are ruled out for our experimental conditions. Analytic and Monte-Carlo simulations of the excitation of an ensemble of interacting Rydberg atoms agree with the experiments indicates a major role of the nearest neighboring Rydberg atom.
Coherent excitation of ultracold atoms between ground and Rydberg states
2011
This thesis describes the development of an experiment to study coherent population transfer between ground states, and between ground and Rydberg states, in ultracold atoms. In order to study coherent transfer between hyperfine ground states a pair of phase stable Raman beams is required. Both beams are derived from a single master laser before being spatially separated into individual components using a novel Faraday filtering technique. The frequency dependent Faraday effect in an isotopically pure thermal vapour is exploited to rotate the plane of polarisation of each Raman component such that they may be separated using a polarising beam splitter. The Raman beams are applied to a sample of ultracold atoms and evidence of coherent population transfer is observed. Rydberg states offer an ideal tool for electrometry; the electric field induced Rydberg energy level shift scales with the seventh power of the principle quantum number. Electromagnetically induced transparency (EIT) is used to map Rydberg energy level shifts onto a ground state transition. EIT in a thermal vapour cell also provides a novel method of stabilising the Rydberg coupling laser. The Rydberg energy level shift is highly sensitive to the electric field produced by adsorbates bonded to a nearby dielectric surface. These effects are found to be time dependent and can be eliminated if the electric field is applied transiently. The measured electric field is compared to that calculated by numerical solution of Laplace's equation; the bulk dielectric is found to have a strong effect on the local electric field experienced by the atoms. The exaggerated properties of Rydberg states make these systems ideal for quantum information processing and precision electrometry.
Observation of the Stark effect in autoionising Rydberg states of molecular hydrogen
Chemical Physics Letters, 1991
The dc Stark effect is studied for autoionising Rydberg states of H 2 converging on the ν +=2 ionisation limit. The levels ( n = 13-22) are excited from the ground state using a coherent XUV source (bandwidth ≈ 1 cm -1) and are strongly perturbed by the field (15-2000 V/cm). Many new states are observed, including the high-/hydrogenic manifolds. A detailed Stark map is obtained for the first time, and a matrix diagonalisation calculation of field-induced state mixing is carried out to explain some of the observed features.
IONIZATION OF RYDBERG ATOMS BY SUBPICOSECOND ELECTROMAGNETIC PULSES
1993
Theoretical analysis of the recently observed ionization of Rydberg atoms by ultra-short half-cycle single-polarity electromagnetic pulses is presented. It is shown that the observations are consistent with the general classical scaling for the hydrogen atom in a microwave field, but the quantitative explanation of the results is possible only within the framework of quantum mechanics. In other words, the photonic basis approach for quantum dynamics and the multiphoton ionization theory yield the measured threshold fields. This is an example of classical scaling of a non-classical effect.