Two-photon spectroscopy of the 6S_(1/2) → 6D_(5/2) transition of trapped atomic cesium

Two-photon spectroscopy of atomic cesium confined and cooled in a magneto-optical trap is reported. The hyperfine structure of the 6D_(5/2) state is determined with 1% accuracy. New capabilities for studying ac Stark shifts and kinetic transport for cold atoms are suggested

Atoms as nonlinear mixers for detection of quantum correlations at ultrahigh frequencies

Measurements of quantum correlations are reported for a frequency difference of 25 THz between the signal and idler output fields generated by a subthreshold nondegenerate optical parametric oscillator. By simultaneously exciting a two-photon transition in atomic Cs by a combination of signal, idler, and "references oscillator" fields, we record modulation of the excited-state population due to quantum interference between two alternative excitation pathways. The observed phase-sensitive modulation is proportional to the correlation function〈EsEi〉for the quantized signal and idler fields

Frequency metrology by use of quantum interference

Quantum interference in the rate of two-photon excitation of the 6S1/2 → 6P3/2 → 6D5/2 transition in atomic cesium is exploited to demonstrate phase-sensitive frequency demodulation for an optical interval of 612.5 THz. By thus using atoms as ultrafast nonlinear mixing elements, we suggest and analyze a new avenue for absolute comparisons of a dense set of frequencies over the range of 200–2000 nm

Quantum interference in two-photon excitation with squeezed and coherent fields

Two-photon excitation of a three-level atom in a ladder configuration (1-->2-->3) by simultaneous illumination with fields in squeezed vacuum and coherent states results in quantum interference for the excitation process. The particular configuration considered here is one for which the signal and idler output fields of a subthreshold nondegenerate optical parametric oscillator are in resonance with the two-stepwise dipole atomic transitions (1-->2,2-->3), while a "reference oscillator" field is in two-photon resonance with the quadrupole transition (1-->3). In an extension of the work of Ficek and Drummond [Phys. Rev. A 43, 6247 (1991)], a theoretical formulation based on the full quantum master equation for the problem is presented. The combined effects of quantum interference and the nonclassical character of the squeezed state are investigated, and offer the potential for a new detection strategy for quantum fluctuations of the electromagnetic field with ultrahigh frequencies (10's-100's THz). Based on the theory developed, we analyze quantum interference in excitation in several special cases relevant to experimental realizations, including the effects of a small focusing angle of the squeezing onto the atoms, and unusual population inversions. Special emphasis is given to identifying intrinsically quantum optical field effects versus classical field effects. Procedures that could distinguish between the two (i.e., classical and nonclassical) are suggested

Delta-like and gtl2 are reciprocally expressed, differentially methylated linked imprinted genes on mouse chromosome 12

AbstractThe distal portion of mouse chromosome 12 is imprinted. To date, however, Gtl2 is the only imprinted gene identified on chromosome 12. Gtl2 encodes multiple alternatively spliced transcripts with no apparent open reading frame. Using conceptuses with maternal or paternal uniparental disomy for chromosome 12 (UPD12), we found that Gtl2 is expressed from the maternal allele and methylated at the 5′ end of the silent paternal allele. A reciprocally imprinted gene, Delta-like (Dlk), with homology to genes involved in the Notch signalling pathway was identified 80kb upstream of Gtl2. Dlk was expressed exclusively from the paternal allele in both the embryo and placenta, but the CpG-island promoter of Dlk was completely unmethylated on both parental alleles. Rather, a paternally methylated region was identified in the last exon of the active Dlk allele. The proximity, reciprocal imprinting and methylation in this domain are reminiscent of the co-ordinately regulated Igf2–H19 imprinted domain on mouse chromosome 7. Like H19 and Igf2, Gtl2 and Dlk were found to be co-expressed in the same tissues throughout development, though not after birth. These results have implications for the regulation, function and evolution of imprinted domains

Optimisation and validation of a PCR to detect viable Tenacibaculum maritimum in salmon skin tissue samples

A PCR protocol was optimised and validated for the detection of viable Tenacibaculum maritimum cells in salmon skin tissue. Viability conventional (vPCR) and quantitative PCR (v-qPCR) assays both had a limit of detection of 103 CFU mL−1 viable cells. The v-qPCR assay showed a linear quantification over 4 log units. Conventional vPCR showed complete signal suppression when only dead cells were present at concentrations lower than 106 CFU mL−1. While the v-qPCR did not result in complete suppression when only dead cells were present, a method was developed to determine if viable cells were present based on the % Δ in cycle threshold (Ct) value. The procedure was validated for high-throughput processing and an enrichment protocol was validated to reliably detect low concentrations of viable cells both with and without a high background of dead cells. Performing this protocol on naturally infected tissues showed that vPCR and v-qPCR reduced the potential for false positives compared to using conventional PCR and qPCR. The optimised protocol developed for this study provides an efficient, reliable and robust alternative for the detection of viable T. maritimum in skin tissue

Observation of Two-Photon Excitation for Three-Level Atoms in a Squeezed Vacuum

The two-photon transition (6S(sub 1/2) yields 6D(sub 5/2)) of atomic Cesium is investigated for excitation with squeezed vacuum generated via nondegenerate parametric down conversion. The two-photon excitation rate (R) is observed to have a non-quadratic dependence of R = aI(exp 2) + bI on the incident photon flux (I), reflecting the nonclassical correlations of the squeezed vacuum field

Phase-dependent spectra in a driven two-level atom

We propose a method to observe phase-dependent spectra in resonance fluorescence, employing a two-level atom driven by a strong coherent field and a weak, amplitude-fluctuating field. The spectra are similar to those which occur in a squeezed vacuum, but avoid the problem of achieving squeezing over a $4\pi$ solid angle. The system shows other interesting features, such as pronounced gain without population inversion.Comment: 4 pages and 4 figures. Submitted to Phys. Rev. Let