Bose-Einstein condensation - Preface

Abstract

and Technology was established in 1988 by Congress to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . . . and to facilitate rapid commercialization . . . of products based on new scientific discoveries."NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government.As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering, and develops measurement techniques, test methods, standards, and related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80303. For more information contact the Public Inquiries Desk, 301-975-3058. T Cover:The figure on the cover depicts a time sequence of images showing one cycle of the ringing of a Bose-Einstein condensate (BEC) in the JILA TOP (time-averaged orbiting potential) trap after being driven by strong oscillations of trap potential. The top left image shows the earliest time, with time increasing from left to right. To create each image, a BEC was formed and then strongly driven and finally allowed to expand ballistically, after which a picture was taken. BEC excitations have recently been observed in both the JILA [D. S. Jin et al., Phys. Rev. Lett. 77, 420 (1996)] and MIT [M.-O. Mewes et al., Phys. Rev. Lett. 77, 988 (1996)] traps. The ringing frequencies of a BEC for weak driving agree well with zero-temperature mean-field theory. Cover photographs courtesy Eric Cornell, JILA, Boulder, CO 80309. Bose-Einstein Condensation PrefaceAmong the most remarkable effects that quantum mechanics adds to the catalog of the thermal properties of matter is the "condensation" of an ideal gas of identical particles into a single quantum state, the principle of which was discovered in the theory of statistical mechanics by Bose and Einstein in the 1920s.Bose-Einstein condensation (BEC) is thus a mechanism for producing a macroscopic quantum system, and is exemplary of the macroscopic quantum phenomena of superconductivity and superfluidity. However, it has proven most difficult to attain BEC in the laboratory vs in the theory of the ideal gas. As discussed in the first article of this Special Issue, the basic criterion for BEC is that the typical distance between particles be comparable to or less than their deBroglie wavelengths; and in virtually every real material system, the effects of...

Atom lasers, coherent states, and coherence II. Maximally robust ensembles of pure states

“…A robustness analysis for a Bose-Einstein condensate has been done by one of us with Barnett and Burnett [7]. This produced similar results to that of Gea-Banacloche [6], although it was based on the fidelity [8] which measures the overlap of the initial state with the state at a later time.…”

Nature of magnetic excitations in the iron pnictides and its pertinence to superconductivity as studied by inelastic neutron scattering

“…This bosonic nature allows the Cooper-pairs to form a Bose-Einstein-condensate whereby all Cooper-pairs can occupy the same highly-degenerate ground state [15]; it is important to note that, since some fraction of the Cooper-pairs will be broken at any finite temperature below c and since there are no Cooper-pairs above c , the total number of bosons is not conserved and the Cooper-pair quasiparticles are not a pure Bose-Einstein-condensate. Furthermore, there is no excited state above the Bose-Einstein-condensate ground state within an energy gap of magnitude ∈ ( B c ).…”

Interference of Bose-Einstein Condensates in Momentum Space

“…This opens new interesting perspectives in the field of quantum measurement in macroscopic systems. However, measuring fringe patterns in the density profiles requires overlapping of the condensates in coordinate space and one cannot exclude the possibility that interactions among atoms block the relative phase before measurement [10,14].In this paper we propose an alternative way to investigate interference and coherence effects, by exploring the behaviour of the condensate in momentum rather than in coordinate space. Our proposal is stimulated by the recent experiment of [15] where, by measuring the dynamic structure factor at high momentum transfer via stimulated two-photon Bragg scattering, it was possible to prove that a single condensate does not exhibit phase fluctuations, i.e "it does not consist of smaller quasicondensates with random relative phase" [15].…”

“…This opens new interesting perspectives in the field of quantum measurement in macroscopic systems. However, measuring fringe patterns in the density profiles requires overlapping of the condensates in coordinate space and one cannot exclude the possibility that interactions among atoms block the relative phase before measurement [10,14].…”

“…In a similar context Anderson [6] raised the intriguing question "do two superfluids which have never "seen" one another possess a definitive phase?". This question has been the object of theoretical speculations [7] and has been more recently reconsidered [8][9][10][11][12] after the experimental realization of BEC in trapped atomic gases [13]. The point of view shared by most authors is that the relative phase between two condensates is "created" during the measurement.…”