944 research outputs found
Steady-state magneto-optical trap of fermionic strontium on a narrow-line transition
A steady-state magneto-optical trap (MOT) of fermionic strontium atoms
operating on the 7.5 kHz-wide transition
is demonstrated. This MOT features atoms, a loading rate of
atoms/s, and an average temperature of 12 K. These
parameters make it well suited to serve as a source of atoms for
continuous-wave superradiant lasers operating on strontium's mHz-wide clock
transition. Such lasers have only been demonstrated using pulsed Sr sources,
limiting their range of applications. Our MOT makes an important step toward
continuous operation of these devices, paving the way for continuous-wave
active optical clocks.Comment: 11 pages, 7 figure
Bose Einstein Condensate in a Box
Bose-Einstein condensates have been produced in an optical box trap. This
novel optical trap type has strong confinement in two directions comparable to
that which is possible in an optical lattice, yet produces individual
condensates rather than the thousands typical of a lattice. The box trap is
integrated with single atom detection capability, paving the way for studies of
quantum atom statistics.Comment: 4 pages, 5 figure
Continuous Bose-Einstein condensation
Bose-Einstein condensates (BECs) are macroscopic coherent matter waves that
have revolutionized quantum science and atomic physics. They are essential to
quantum simulation and sensing, for example underlying atom interferometers in
space and ambitious tests of Einstein's equivalence principle. The key to
dramatically increasing the bandwidth and precision of such matter-wave sensors
lies in sustaining a coherent matter wave indefinitely. Here we demonstrate
continuous Bose-Einstein condensation by creating a continuous-wave (CW)
condensate of strontium atoms that lasts indefinitely. The coherent matter wave
is sustained by amplification through Bose-stimulated gain of atoms from a
thermal bath. By steadily replenishing this bath while achieving 1000x higher
phase-space densities than previous works, we maintain the conditions for
condensation. This advance overcomes a fundamental limitation of all atomic
quantum gas experiments to date: the need to execute several cooling stages
time-sequentially. Continuous matter-wave amplification will make possible CW
atom lasers, atomic counterparts of CW optical lasers that have become
ubiquitous in technology and society. The coherence of such atom lasers will no
longer be fundamentally limited by the atom number in a BEC and can ultimately
reach the standard quantum limit. Our development provides a new, hitherto
missing piece of atom optics, enabling the construction of continuous coherent
matter-wave devices. From infrasound gravitational wave detectors to optical
clocks, the dramatic improvement in coherence, bandwidth and precision now
within reach will be decisive in the creation of a new class of quantum
sensors.Comment: 17 pages, 10 figure
Differential p38-dependent signalling in response to cellular stress and mitogenic stimulation in fibroblasts
p38 MAP kinase is known to be activated by cellular stress finally leading to cell cycle arrest or apoptosis. Furthermore, a tumour suppressor role of p38 MAPK has been proposed. In contrast, a requirement of p38 for proliferation has also been described. To clarify this paradox, we investigated stress- and mitogen-induced p38 signalling in the same cell type using fibroblasts. We demonstrate that - in the same cell line - p38 is activated by mitogens or cellular stress, but p38-dependent signalling is different. Exposure to cellular stress, such as anisomycin, leads to a strong and persistent p38 activation independent of GTPases. As a result, MK2 and downstream the transcription factor CREB are phosphorylated. In contrast, mitogenic stimulation results in a weaker and transient p38 activation, which upstream involves small GTPases and is required for cyclin D1 induction. Consequently, the retinoblastoma protein is phosphorylated and allows G1/S transition. Our data suggest a dual role of p38 and indicate that the level and/or duration of p38 activation determines the cellular response, i.e either proliferation or cell cycle arrest
Two-species magneto-optical trap with 40K and 87Rb
We trap and cool a gas composed of 40K and 87Rb, using a two-species
magneto-optical trap (MOT). This trap represents the first step towards cooling
the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is
derived from laser diodes and amplified with a single high power semiconductor
amplifier chip. The four-color laser system is described, and the
single-species and two-species MOTs are characterized. Atom numbers of 1x10^7
40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap
loss due to collisions between species is presented and future prospects for
the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review
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