A novel absorption resonance for all-optical atomic clocks

We report an experimental study of an all-optical three-photon-absorption resonance (known as a "N-resonance") and discuss its potential application as an alternative to atomic clocks based on coherent population trapping (CPT). We present measurements of the N-resonance contrast, width and light-shift for the D1 line of 87Rb with varying buffer gases, and find good agreement with an analytical model of this novel resonance. The results suggest that N-resonances are promising for atomic clock applications.Comment: 4 pages, 6 figure

Cancellation of light-shifts in an N-resonance clock

We demonstrate that first-order light-shifts can be cancelled for an all-optical, three-photon-absorption resonance ("N-resonance") on the D1 transition of Rb87. This light-shift cancellation enables improved frequency stability for an N-resonance clock. For example, using a table-top apparatus designed for N-resonance spectroscopy, we measured a short-term fractional frequency stability (Allan deviation) 1.5e-11 tau^(-1/2) for observation times 1s< tau < 50s. Further improvements in frequency stability should be possible with an apparatus designed as a dedicated N-resonance clock.Comment: 4 pages, 4 figure

Comparison of 87Rb N-resonances for D1 and D2 transitions

We report an experimental comparison of three-photon-absorption resonances (known as "N-resonances") for the D_1 and D_2 optical transitions of thermal 87Rb vapor. We find that the D_2 N-resonance has better contrast, a broader linewidth, and a more symmetric lineshape than the D_1 N-resonance. Taken together, these factors imply superior performance for frequency standards operating on alkali D_2 N-resonances, in contrast to coherent population trapping (CPT) resonances for which the D_2 transition provides poorer frequency standard performance than the D_1 transition.Comment: 3 pages, 4 figure

The origins and spread of domestic horses from the Western Eurasian steppes

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: All collapsed and paired-end sequence data for samples sequenced in this study are available in compressed fastq format through the European Nucleotide Archive under accession number PRJEB44430, together with rescaled and trimmed bam sequence alignments against both the nuclear and mitochondrial horse reference genomes. Previously published ancient data used in this study are available under accession numbers PRJEB7537, PRJEB10098, PRJEB10854, PRJEB22390 and PRJEB31613, and detailed in Supplementary Table 1. The genomes of ten modern horses, publicly available, were also accessed as indicated in their corresponding original publications57,61,85-87.NOTE: see the published version available via the DOI in this record for the full list of authorsDomestication of horses fundamentally transformed long-range mobility and warfare. However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling at Botai, Central Asia around 3500 BC. Other longstanding candidate regions for horse domestication, such as Iberia and Anatolia, have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 BC, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 BC driving the spread of Indo-European languages. This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium BC Sintashta culture