"NIST Debuts Dual Atomic Clock - and a New Stability Record"
https://www.nist.gov/news-events/news/2016/11/nist-debuts-dual-atomic-clock-and-new-stability-record

"Ultrastable optical clock with two cold-atom ensembles"
http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.231.html

"Ultra-stable optical clock with two cold-atom ensembles"
https://arxiv.org/abs/1607.06867
https://arxiv.org/ftp/arxiv/papers/1607/1607.06867.pdf

This will be showing up in the popular press. Zero dead time Ytterbium lattice clock, PR release: "NIST Debuts Dual Atomic Clock - and a New Stability Record" https://www.nist.gov/news-events/news/2016/11/nist-debuts-dual-atomic-clock-and-new-stability-record Nature article (paywall, $32): "Ultrastable optical clock with two cold-atom ensembles" http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.231.html Open access: "Ultra-stable optical clock with two cold-atom ensembles" https://arxiv.org/abs/1607.06867 https://arxiv.org/ftp/arxiv/papers/1607/1607.06867.pdf No need to reply to this posting. FYI only. Not available on eBay yet (I checked). /tvb