Polarization-controlled single photons

Vacuum-stimulated Raman transitions are driven between two magnetic substates of a rubidium-87 atom strongly coupled to an optical cavity. A magnetic field lifts the degeneracy of these states, and the atom is alternately exposed to laser pulses of two different frequencies. This produces a stream of single photons with alternating circular polarization in a predetermined spatio-temporal mode. MHz repetition rates are possible as no recycling of the atom between photon generations is required. Photon indistinguishability is tested by time-resolved two-photon interference.Comment: 4 pages, 3 figure

A nonlinear model dynamics for closed-system, constrained, maximal-entropy-generation relaxation by energy redistribution

We discuss a nonlinear model for the relaxation by energy redistribution within an isolated, closed system composed of non-interacting identical particles with energy levels e_i with i=1,2,...,N. The time-dependent occupation probabilities p_i(t) are assumed to obey the nonlinear rate equations tau dp_i/dt=-p_i ln p_i+ alpha(t)p_i-beta(t)e_ip_i where alpha(t) and beta(t) are functionals of the p_i(t)'s that maintain invariant the mean energy E=sum_i e_ip_i(t) and the normalization condition 1=sum_i p_i(t). The entropy S(t)=-k sum_i p_i(t) ln p_i(t) is a non-decreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions p_i(t) of the rate equations are unique and well-defined for arbitrary initial conditions p_i(0) and for all times. Existence and uniqueness both forward and backward in time allows the reconstruction of the primordial lowest entropy state. The time evolution is at all times along the local direction of steepest entropy ascent or, equivalently, of maximal entropy generation. These rate equations have the same mathematical structure and basic features of the nonlinear dynamical equation proposed in a series of papers ended with G.P.Beretta, Found.Phys., 17, 365 (1987) and recently rediscovered in S. Gheorghiu-Svirschevski, Phys.Rev.A, 63, 022105 and 054102 (2001). Numerical results illustrate the features of the dynamics and the differences with the rate equations recently considered for the same problem in M.Lemanska and Z.Jaeger, Physica D, 170, 72 (2002).Comment: 11 pages, 7 eps figures (psfrag use removed), uses subeqn, minor revisions, accepted for Physical Review

Ordovician conodonts from the Mithaka Formation (Georgina Basin, Australia). Regional and paleobiogeographical implications

The systematic analysis of conodonts from the previously unstudied Mithaka Formation (Georgina Basin) yielded 1366 identifiable elements, representing 25 species and 21 genera. One new species was recovered and identified, Triangulodus mithakensis n. sp. Four other new species are described in open nomenclature as Bergstroemognathus? n. sp. A, ?Periodon n. sp. A, Phragmodus n. sp. A and Taoqupognathus n. sp. A. The Mithaka Fm fauna shows similarity with conodonts from several previous Australian studies and lesser similarity with conodonts from North China and North America. Some species of North American Midcontinent (Laurentian Province) affinity include Erismodus quadridactylus (STAUFFER) and Staufferella divisa SWEET, whereas some species of North Chinese affinity include Aurilobodus leptosomatus AN, Panderodus nogamii (LEE) and ?Serratognathus sp. However, many species are distinctly Australian: Bergstroemognathus? n. sp. A, ?Periodon n. sp. A, Phragmodus n. sp. A, Drucognathus yiranus ZHANG, BARNES and COOPER, Erismodus nicolli ZHANG, BARNES and COOPER, Yaoxianognathus? neonychodonta ZHANG, BARNES and COOPER, Triangulodus mithakensis n. sp. and Taoqupognathus n. sp. A. These Australian species support the placement of the Mithaka Fm fauna within the proposed Australian Province. This new conodont fauna is correlated to the early Late Ordovician upper Drucognathus yiranus Zone of the Amadeus Basin, Central Australia and the late Gisbornian Stage. The conodont fauna indicates a shallow open lagoon depositional environment