Multimode quantum limits to the linewidth of an atom laser

The linewidth of an atom laser can be limited by excitation of higher energy modes in the source Bose-Einstein condensate, energy shifts in that condensate due to the atomic interactions, or phase diffusion of the lasing mode due to those interactions. The first two are effects that can be described with a semiclassical model, and have been studied in detail for both pumped and unpumped atom lasers. The third is a purely quantum statistical effect, and has been studied only in zero dimensional models. We examine an unpumped atom laser in one dimension using a quantum field theory using stochastic methods based on the truncated Wigner approach. This allows spatial and statistical effects to be examined simultaneously, and the linewidth limit for unpumped atom lasers is quantified in various limits.Comment: 8 Figure

Approaching the Heisenberg limit in an atom laser

We present experimental and theoretical results showing the improved beam quality and reduced divergence of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces them, typically a factor of 1.3 above the Heisenberg limit

Observation of transverse interference fringes on an atom laser beam

Using the unique detection properties offered by metastable helium atoms we have produced high resolution images of the transverse spatial profiles of an atom laser beam. We observe fringes on the beam, resulting from quantum mechanical interference between atoms that start from rest at different transverse locations within the outcoupling surface and end up at a later time with different velocities at the same transverse position. Numerical simulations in the low output-coupling limit give good quantitative agreement with our experimental data

Building in vitro tools for livestock genomics:chromosomal variation within the PK15 cell line

BACKGROUND: Cultured porcine cell lines are powerful tools for functional genomics and in vitro phenotypic testing of candidate causal variants. However, to be utilised for genomic or variant interrogation assays, the genome sequence and structure of cultured cell lines must be realised. In this work, we called variants and used read coverage in combination with within-sample allele frequency to detect potential aneuploidy in two immortalised porcine kidney epithelial (PK15) cell lines and in a pig embryonic fibroblast line.RESULTS: We compared two PK15 cultured cells samples: a new American Type Culture Collection (ATCC) sample and one that has been utilised and passaged within the laboratory for an extended period (&gt; 10 years). Read coverage and within-sample allele frequencies showed that several chromosomes are fully or partially aneuploid in both PK15 lines, including potential trisomy of chromosome 4 and tetrasomy of chromosome 17. The older PK15 line showed evidence of additional structural variation and potentially clonal variation. By comparison, the pig embryonic fibroblast line was free from the gross aneuploidies seen in the PK15s.CONCLUSIONS: Our results show that the PK15 cell lines examined have aneuploidies and complex structural variants in their genomes. We propose that screening for aneuploidy should be considered for cell lines, and discuss implications for livestock genomics.</p

A multibeam atom laser: coherent atom beam splitting from a single far detuned laser

We report the experimental realisation of a multibeam atom laser. A single continuous atom laser is outcoupled from a Bose-Einstein condensate (BEC) via an optical Raman transition. The atom laser is subsequently split into up to five atomic beams with slightly different momenta, resulting in multiple, nearly co-propagating, coherent beams which could be of use in interferometric experiments. The splitting process itself is a novel realization of Bragg diffraction, driven by each of the optical Raman laser beams independently. This presents a significantly simpler implementation of an atomic beam splitter, one of the main elements of coherent atom optics

Probing single-photon ionization on the attosecond time scale

We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the $3s^2$ and from the $3p^6$ shell, at different excitation energies ranging from 32 to 42 eV. The determination of single photoemission time delays requires to take into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using an universal formula and is found to account for a substantial fraction of the measured delay.Comment: 4 pages, 4 figures, under consideratio