Dr Joseph Cotter takes some unusual pieces of luggage on his trips on the London underground. They include a stainless steel vacuum chamber, a few billion atoms of rubidium and an array of lasers that are used to cool his equipment to a temperature just above absolute zero.While not the average kit you would expect to find being dragged into carriages on the District Line, this is the gear that Cotter – who works at Imperial College London’s Centre for Cold Matter – uses on his underground trave...