High-precision spectroscopy of the forbidden 2 3S1 - 2 1P1 transition in quantum degenerate metastable helium

We have measured the forbidden 2 3S1 - 2 1P1 transition at 887 nm in a quantum degenerate gas of metastable He-4 atoms confined in an optical dipole trap. The determined transition frequency is 338 133 594.4 (0.5) MHz, from which we obtain an ionization energy of the 2 1P1 state of 814 709 148.6 (0.5) MHz. This ionization energy is in disagreement by > 3 sigma with the most accurate quantum electrodynamics (QED) calculations available. Our measurements also provide a new determination of the lifetime of the 2 1P1 state of 0.551 (0.004)stat (+ 0.013,- 0.000)syst ns, which is the most accurate determination to date and in excellent agreement with theory.Comment: 10 pages, 13 figures, paper includes supplemental information. Paper submitted for revie

Quantum-State Controlled Penning Ionization Reactions between Ultracold Alkali and Metastable Helium Atoms

In an ultracold, optically trapped mixture of $^{87}$Rb and metastable triplet $^4$He atoms we have studied trap loss for different spin-state combinations, for which interspecies Penning ionization is the main two-body loss process. We observe long trapping lifetimes for the purely quartet spin-state combination, indicating strong suppression of Penning ionization loss by at least two orders of magnitude. For the other spin-mixtures we observe short lifetimes that depend linearly on the doublet character of the entrance channel. We compare the extracted loss rate coefficient with recent predictions of multichannel quantum-defect theory for reactive collisions involving a strong exothermic loss channel and find near-universal loss for doublet scattering. Our work demonstrates control of reactive collisions by internal atomic state preparation.Comment: 5 pages, 5 figures + Supplemental Material

LIFE-Nature along European coasts

Since 1992, LIFE-Nature has been funding nature conservation projects across the European territory of the EC Member states. The current article briefly explains the rationale of the LIFE-Nature programme, its relationship to the implementation of the Birds and Habitats Directives and provides an overview of the types of actions funded. Given that LIFE-Nature is a limited fund compared to the needs of the Natura 2000 network, funding is only available for the most relevant actions at the European level

Nanolithography with metastable helium atoms in a high-power standing-wave light field

We have created periodic nanoscale structures in a gold substrate with a lithography process using metastable triplet helium atoms that damage a hydrofobic resist layer on top of the substrate. A beam of metastable helium atoms is transversely cooled and guided through an intense standing-wave light field. Compared to commonly used low-power optical masks, a high-power light field (saturation parameter of 10E7) increases the confinement of the atoms in the standing-wave considerably, and makes the alignment of the experimental setup less critical. Due to the high internal energy of the metastable helium atoms (20 eV), a dose of only one atom per resist molecule is required. With an exposure time of only eight minutes, parallel lines with a separation of 542 nm and a width of 100 nm (1/11th of the wavelength used for the optical mask) are created.Comment: 5 pages, 5 figure

Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate in a hybrid trap

We have realized Bose-Einstein condensation (BEC) of 87Rb in the F=2, m_F=2 hyperfine substate in a hybrid trap, consisting of a quadrupole magnetic field and a single optical dipole beam. The symmetry axis of the quadrupole magnetic trap coincides with the optical beam axis, which gives stronger axial confinement than previous hybrid traps. After loading 2x10^6 atoms at 14 muK from a quadrupole magnetic trap into the hybrid trap, we perform efficient forced evaporation and reach the onset of BEC at a temperature of 0.5 muK and with 4x10^5 atoms. We also obtain thermal clouds of 1x10^6 atoms below 1 muK in a pure single beam optical dipole trap, by ramping down the magnetic field gradient after evaporative cooling in the hybrid trap.Comment: 8 pages, 8 figures, improved on basis of referee comment

Non-exponential one-body loss in a Bose-Einstein condensate

We have studied the decay of a Bose-Einstein condensate of metastable helium atoms in an optical dipole trap. In the regime where two- and three-body losses can be neglected we show that the Bose-Einstein condensate and the thermal cloud show fundamentally different decay characteristics. The total number of atoms decays exponentially with time constant tau; however, the thermal cloud decays exponentially with time constant (4/3)tau and the condensate decays much faster, and non-exponentially. We show that this behaviour, which should be present for all BECs in thermal equilibrium with a considerable thermal fraction, is due to a transfer of atoms from the condensate to the thermal cloud during its decay.Comment: The intuitive explanation of the atomic transfer effect has been correcte

High temperature oxidation and burner rig testing of different TBCs in the frame of the European Project TOPPCOAT: A summary of results

The major S&T objective of the project is the development of improved TBC systems using advanced bonding concepts in combination with additional protective functional coatings. The first specific objective will be to use these developments to provide a significant improvement to state-of-the-art APS coatings and hence provide a cost-effective alternative to EB-PVD. The second objective will be to combine these new concepts with new coating technologies to provide new, advance materials for thermal barrier systems with a capability exceeding the performance of EB-PVD coatings