Another research group at the University of Wisconsin-Madison has also produced a new atomic clock set-up.
Shimon Kolkowitz and his colleagues used comparisons between six different strontium atomic clocks to measure a second. This comparative model, known as a multiplex clock, means the team can use a less stable laser than the JILA group’s clock, but still achieve a very high level of precision: the clock would lose just 1 second every 300 billion years.