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Electron cooling of trapped antiprotons allows their storage at energies more than 6x 10 7 times lower than is available in any antiproton storage ring. More than 60000 antiprotons with energies from 0 to 3000 eV are stored in an ion trap from a single pulse of 5.9-MeV antiprotons from LEAR. Trapped antiprotons maintain their initial energy distribution over days unless allowed to collide with a cold buffer gas of trapped electrons, whereupon they slow and cool below 100 meV in 10 s. The antiprotons are cooled in a harmonic potential well suited for precision measurements and have remained more than 2 days without detectable particle loss. Energy widths as narrow as 9 meV are directly observed. PACS numbers: 36.10.-k, 14.20.Dh, 29.25.FbInteresting experiments await the availability of verylow-energy antiprotons. For example, a much more accurate measurement of the inertial mass of the antiproton becomes feasible with antiproton energies below 1 meV. l This would be one of only a few precise tests of CPT invariance, the only such test with baryons. 2 Measuring the gravitational force on sub-meV antiprotons has also been proposed. 3 It may even become possible to produce and study cold antihydrogen, 4 perhaps allowing a measurement of the gravitational force without the severe competition of electrical forces. 5 Although initial slowing and cooling from the GeV energies at which antiprotons are produced and collected is now routinely done in a series of storage rings at CERN, the lowestenergy antiprotons generally available for experiments still have a kinetic energy of 5.9 MeV. These antiprotons are stochastically cooled, stored, and then ejected from the Low Energy Antiproton Ring (LEAR) which was built for this purpose. Lower storage energies ( < 3 keV) have been achieved in only one experiment, when several hundred antiprotons were briefly stored in an ion trap. 6 In this Letter, we report the first observation of electron cooling within a particle trap, whereby antiprotons cool via repeated collisions with a buffer gas of cold-trapped electrons. 7 (A neutral buffer gas as used for cooling many trapped ions species would cause the antiprotons to annihilate.) As anticipated, 8 electron cooling is extremely effective compared to adiabatic or resistive cooling, even when the cooling rate for the latter is enhanced using electronic feedback techniques. 910 The observed cooling is similar in some respects to the cooling of the hotter species in a two-component plasma, to the cooling of energetic particle beams using a collinear electron beam matched in velocity, 12 and to the sympathetic cooling of one ion species by another in an ion trap. 13 Pulses of 5.9-MeV antiprotons, typically 250 ns in duration and containing up to 3xl0 8 antiprotons, leave our LEAR beam line directed upwards through a Ti window. They pass through another Ti window into a completely sealed vacuum enclosure which is cooled to 4.2 K and located in a 6-T magnetic field. The ion trap inside [ Fig. 1 (a)] consists of an aluminum plate at the bo...

We measure the quantum speed of the state evolution of the field in a weakly-driven optical cavity QED system. To this end, the mode of the electromagnetic field is considered as a quantum system of interest with a preferential coupling to a tunable environment: the atoms. By controlling the environment, i.e., changing the number of atoms coupled to the optical cavity mode, an environment assisted speed-up is realized: the quantum speed of the state re-population in the optical cavity increases with the coupling strength between the optical cavity mode and this non-Markovian environment (the number of atoms). PACS numbers: 42.50.Pq, 42.50.Lc,32.50.+d Identifying time-optimized processes is a ubiquitous goal in virtually all areas of quantum physics, such as quantum communication [1], quantum computation [2], quantum thermodynamics [3], quantum control and feedback [4], and quantum metrology [5]. To this end, the notion of a quantum speed limit (QSL) has proven to be useful and important. The QSL determines the theoretical upper bound on the speed of evolution of a quantum system. It can be understood as a generalization of the Heisenberg uncertainty relation for energy and time. It has been derived for isolated, uncontrolled systems [6-8], time-dependent Hamiltonians [9-13], and more recently for more general open system dynamics [14][15][16][17][18][19][20][21]. Although fundamental in nature, practical consequences or even experimental applications of the QSL are still lacking. Nevertheless, achieving the maximal quantum speed is of high practical relevance, especially in the development of quantum information processing devices.On the theoretical side, a recent study [14] hinted at the possibility of observing speed-ups of the quantum evolution if an open quantum system is subject to environmental changes. Ref. [14] analyzes the dynamics of the damped Jaynes-Cummings model, which describes many cavity QED systems. These systems in both the intermediate and strong coupling regime can exhibit environmentassisted evolution [22] -such as non-exponential decay.This letter reports an experimental realization of the theoretically proposed environment assisted speed-up [14]. To this end, we look at the system in an unusual way -as just consisting of the cavity field. This allows us to treat the atomic number that generates the atomic polarization (the off diagonal elements of the atomic master equation) as a tunable environment with a range of coupling constants. We demonstrate that increasing the interaction of the optical cavity field with the environment by tuning the number of atoms, modifies the time dependent non-classical intensity correlation function, enhancing -speeds-up-the rate of evolution of the cavity field in a range with no clear oscillations present.Our cavity QED system operates in the intermediate coupling regime, where the cavity-atom parameters are of the same order: (g, κ, γ) /2π = (3.2, 4.5, 6.0) MHz. Here g denotes the electric dipole interaction strength of an atom maximally coupled to th...

We measure the hyperfine splitting of the 9S_{1/2} level of 210Fr, and find a magnetic dipole hyperfine constant A=622.25(36) MHz. The theoretical value, obtained using the relativistic all-order method from the electronic wave function at the nucleus, allows us to extract a nuclear magnetic moment of 4.38(5)micro_{N} for this isotope, which represents a factor of 2 improvement in precision over previous measurements. The same method can be applied to other rare isotopes and elements.