2pi Omega Research Articles

Strong Light-Matter Coupling in Subwavelength Metal-Dielectric Microcavities at Terahertz Frequencies

We have demonstrated that a metal-dielectric-metal microcavity combined with quantum well intersubband transitions is an ideal system for the generation of cavity polariton states in the terahertz region. The metallic cavity has highly confined radiation modes that can be tuned in resonance with the intersubband transition. In this system we were able to measure a very strong light-matter splitting (the Rabi splitting 2 variant Planck's over 2pi Omega R), corresponding to 22% of the transition energy. We believe this result to be the first demonstration of intersubband polaritons in the terahertz frequency range.

Rapidly rotating Bose-Einstein condensates in and near the lowest Landau level.

We create rapidly rotating Bose-Einstein condensates in the lowest Landau level by spinning up the condensates to rotation rates Omega > 99% of the centrifugal limit for a harmonically trapped gas, while reducing the number of atoms. As a consequence, the chemical potential drops below the cyclotron energy 2 variant Planck's over 2pi Omega. While in this mean-field quantum-Hall regime we still observe an ordered vortex lattice, its elastic shear strength is strongly reduced, as evidenced by the observed very low frequency of Tkachenko modes. Furthermore, the gas approaches the quasi-two-dimensional limit. The associated crossover from interacting- to ideal-gas behavior along the rotation axis results in a shift of the axial breathing mode frequency.

Temporal structure of attosecond pulses from intense laser-atom interactions.

We find that the high harmonics have a power-law spectrum I(omega) approximately omega(-3.3+/-0.25) in a wide frequency domain starting at the ionization potential I(p) and down to the plateau beginning. Our spectrotemporal analysis of the emitted radiation displays clear bowlike structures in the (t,omega) plane. These "bows" correspond to Corkum's reencounters of the freed electron with the atom. We find that the bows are not filled and thus cannot be due to any bremsstrahlung. Rather, it is a resonant process that we call stimulated recombination (SR). It occurs when an electron with momentum p reencounters the incompletely ionized atom, and interferes with itself still remaining in the ground state. The SR leads to a highly efficient resonant emission at Planck's over 2pi omega=p(2)/2m+I(p) in the form of attosecond pulses. The SR relies on a low level of ionization and strongly benefits from the use of few-cycle laser pulses.

Neutrino-12C scattering in the Ab initio shell model with a realistic three-body interaction.

We investigate cross sections for neutrino-12C exclusive scattering and for muon capture on 12C using wave functions obtained in the ab initio no-core shell model. In our parameter-free calculations with basis spaces up to the 6 variant Planck's over 2pi Omega we show that realistic nucleon-nucleon interactions, like, e.g., the CD-Bonn, underpredict the experimental cross sections by more than a factor of 2. By including a realistic three-body interaction, Tucson-Melbourne TM'(99), the cross sections are enhanced significantly and a much better agreement with experiment is achieved. At the same time, the TM'(99) interaction improves the calculated level ordering in 12C. The comparison between the CD-Bonn and the three-body calculations provides strong confirmation for the need to include a realistic three-body interaction to account for the spin-orbit strength in p-shell nuclei.

Charge-Ordering Signatures in the Optical Properties ofβ−Na0.33V2O5

Temperature dependent optical spectra are reported for beta-Na0.33V2O5. The sodium ordering transition at T(Na)=240 K and, in particular, the charge ordering transition at T(MI)=136 K strongly influence the optical spectra. The metal-insulator transition at T(MI) leads to the opening of a pseudogap ( variant Planck's over 2pi omega=1700 cm(-1)) and to the appearance of a large number of optical phonons. These observations and the presence of a midinfrared band (typical for low dimensional metals) strongly suggest that the charge carriers in beta-Na0.33V2O5 are small polarons.

Electrodynamics of a Coulomb glass in n-type silicon.

Measurements of the complex frequency dependent conductivity of uncompensated n-type silicon are reported. The experiments are done in the quantum limit, variant Planck's over 2pi omega>k(B)T, across a broad doping range on the insulating side of the metal-insulator transition. The low energy linear frequency dependence is consistent with theories of a Coulomb glass, but discrepancies exist in the relative magnitudes of the complex components. At higher energies we observe a crossover to a quadratic frequency dependence that is sharper than expected. The concentration dependence gives evidence that the Coulomb interaction energy is the energy scale that determines this crossover.

Perturbative effective theory in an oscillator basis?

The effective interaction problem in nuclear physics is believed to be highly nonperturbative, requiring extended high-momentum spaces for accurate solution. We trace this to difficulties that arise at both short and long distances when the included space is defined in terms of a basis of harmonic oscillator Slater determinants. We show, in the simplest case of the deuteron, that both difficulties can be circumvented, yielding highly perturbative results in the potential even for modest (approximately 4 variant Planck's over 2pi omega) included spaces.