לוח שנה משולב

A hundred years ago Arnold Sommerfeld (1868-1951) extended Bohr's atomic model. The Bohr-Sommerfeld atom paved the way for quantum mechanics. Sommerfeld's institute at Munich University became a center of modern theoretical physics where quantum pioneers like Wolfgang Pauli, Werner Heisenberg, Hans Bethe and others began their career.

In my presentation I sketch Sommerfeld's own career with the focus on his quantum contributions. The extension of Bohr's model resulted in a theory of the fine structure (Sommerfeld's fine-structure constant) and turned the analysis of spectral lines into a new science. Sommerfeld's textbook Atomic Structure and Spectral Lines was regarded as the "bible“ from which the first generation of quantum physicists learned their craft.

I hope to provide insight into the mechanisms at work in the decade between the extension of Bohr's theory and the birth of quantum mechanics

Polaritons in 2D semiconductor microcavities have been a unique manybody system that demonstrates non-equilibrium quantum orders. To go beyond 2D condensation physics, it becomes important to control the fundamental properties of polaritons without destroying the quantum orders. I will discuss a unconventional microcavity system we make. It incorporates a slab photonic crystal as one of the cavity mirrors to confine, control and coupling polaritons in a non-destructive and scalable manner. We showed that strong-coupling can be established in the new cavity system, fundamental properties of the polaritons can be controlled by design, including the polarization, energy-momentum dispersion, and dimensionality. Coupled polariton systems are readily created. We also showed single-mode polariton lasing in a 0D cavity, which, unlike (quasi) 2D polariton lasers demonstrated in the past, featured Poisson intensity noise expected of a coherent state and strong condensate interactions manifested in Gaussian line-broadening of the polariton laser. Such a 0D polariton lasers provides a building block for coupled polariton lattices with designable fundamental properties. It may open a door to experimental implementation of coupled cavity quantum electrodynamics systems and quantum technologies based on manybody quantum fluids.

In the last few years, remarkable experimental progress has been made on a type of high- plasma device known as the field-reversed configuration (FRC). Confinement times have been increased to near-classical values and the stability times attained are 105 times longer than predicted by MHD theory. Based on these advances, a number of groups have proposed upgrading their devices to achieve reactor-relevant parameters to produce net fusion power. In this talk, I will present recent experimental findings, numerical simulations, and analytic results on a single type of FRC, one heated by a radio-frequency technique having a particular symmetry, one predicted to improve energy confinement, drive current, and heat both ions and electrons. The benefits and limitations arising from the use of the aneutronic fuel mixture D-3He will be discussed. One unique application for this type of reactor is as a rocket engine for critical missions within and outside the solar system.