Chad Orzel

Creation of an Ultracold Neutral Plasma

The study of ionized gases in neutral plasma physics spans temperatures ranging from 10 16 K in the magnetosphere of a pulsar to 300 K in the earth’s ionosphere [1]. At lower temperatures, the properties of plasmas are expected to differ significantly. For instance, three-body recombination, which is prevalent in high temperature plasmas, should be suppressed [2]. If the thermal energy of the particles is less than the Coulomb interaction energy, the plasma becomes strongly coupled, and the usual hydrodynamic equations of motion and collective mode dispersion relations are no longer valid [3]. Strongly coupled plasmas are difficult to produce in the laboratory and only a handful of examples exist [4], but such plasmas do occur naturally in astrophysical systems. In this work, we create an ultracold neutral plasma with an electron temperature as low as Te 100 mK, an ion temperature as low as Ti 10 mK, and densities as high as n 2 3 10 9 cm 23 . We obtain this novel plasma by photoionization of laser-cooled xenon atoms. Within the experimentally accessible ranges of temperatures and densities, both components can be simultaneously strongly coupled. A simple model describes the evolution of the plasma in terms of the competition between the kinetic energy of the electrons and the Coulomb attraction between electrons and ions. A numerical calculation accurately reproduces the data. Photoionization and laser cooling have been used before in plasma experiments. Photoionization in a 600 K Cs vapor cell produced a plasma with Te

Nonequilibrium coherence dynamics of a soft boson lattice

2000 K [5], and a strongly coupled non-neutral plasma was created by laser cooling magnetically trapped Be 1 ions [6]. A plasma is often defined as an ionized gas in which the charged particles exhibit collective effects [7]. The length scale which divides individual particle behavior and collective behavior is the Debye screening length lD. It is the distance over which an electric field is screened by redistribution of electrons in the plasma, and is given by lD p

Radioactive krypton background evaluation using atom counting

We study the nonequilibrium evolution of the phase coherence of a Bose-Einstein condensate in a one-dimensional optical lattice as the lattice array is suddenly quenched from a highly-number-squeezed to a superfluid state. We observe slowly damped phase coherence oscillations in the regime of large filling factor (

The brave new-media world

\ensuremath{\sim}100

Dreiste Lügen und Statistiken

bosons per site) at a frequency proportional to the generalized Josephson frequency.

Wie Schach ohne Würfel

Abstract The beta-decay of 85 Kr is a significant radioactive background for experiments that use liquified noble gases to search for dark matter and measure the low-energy solar neutrino flux. While there are several proposed methods for reducing Kr levels in these experiments, an independent technique is needed for measuring very low Kr levels. By selectively exciting Kr atoms to a metastable state, capturing them in a magneto-optical trap (MOT), and detecting fluorescence from the trapped atoms, individual Kr atoms can be counted with a high signal-to-noise ratio. This approach could be used to ascertain Kr impurity levels in other noble gases, with an estimated sensitivity of 3 × 10 - 14 .

Die Entstehung der Arten wird gesammelt

When physicists in Italy claimed to have seen hints of faster-than-light neutrinos, it initiated a media frenzy as well as criticism of publicity-seeking.

Nadeln in Heuhaufen

Zwar suchen viele Menschen gezielt nach statistischen Analysen von Sportereignissen und lesen sie, die meisten anderen Formen von Statistiken werden aber mit Abscheu betrachtet. Dennoch ist es fast unmoglich, ihnen aus dem Weg zu gehen: Praktisch jede offentlich bekannte politische Entscheidung kann man nur mit statistischen Methoden verstehen. Die Effekte einer Entscheidung auf den Einzelnen zu prophezeien, ist so gut wie unmoglich, aber welche Gesamtwirkung sie auf die ganze Bevolkerung einer Stadt, eines Staates oder Landes hat, lasst sich oft mithilfe der Statistik prazise voraussagen.

Die Alleinherrschaft der Wissenschaftsküche

Zu den beliebtesten volkstumlichen Klischeevorstellungen uber Wissenschaftler gehort die von einer unuberbruckbaren Kluft zwischen Fachidioten und Sportskanonen. Aber wie die meisten Klischees, so wird auch dieses beiden Seiten nicht gerecht. Entgegen einem allgemeinen Vorurteil haben Fachidioten nicht von ihrem Wesen her etwas gegen sportliche Betatigungen – viele Physiker aus meinem Bekanntenkreis sind begeisterte Wanderer oder Fahrradfahrer, und jahrelang fanden im Rahmen der internationalen Fachtagung auf meinem Gebiet der Physik uberraschend hochklassige Softballpartien zwischen den Belegschaften des MIT und des National Institute of Standards and Technology in Boulder statt.

Walter im Zoo der Galaxien

Zu den beliebtesten Hobbys gehort das Sammeln verschiedenster Dinge. Man denke nur an ein beliebiges Objekt, das es in mehreren Varianten gibt, so findet man mit ziemlicher Sicherheit jemanden, der diese Varianten sammelt, und vermutlich wird die Sammlertatigkeit in mindestens einem Internetforum in allen Einzelheiten erortert, ganz gleich, um was fur Gegenstande es geht.