Improvement of an Atomic Clock using Squeezed Vacuum

TLDR

Atom interferometers are used for precision metrology, but vacuum noise limits them to the standard quantum limit, which constrains the precision of microwave fountain clocks. We propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. The configuration employs squeezed vacuum in the empty input port and we evaluate the technical limitations and challenges for next‑generation fountain clocks based on atomic squeezed vacuum. The squeezed vacuum state containing an average of 0.75 atoms improves the clock sensitivity of 10,000 atoms by 2.05‑0.37+0.34 dB.

Abstract

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10000 atoms by 2.05-0.37+0.34 dB. The SQL poses a significant limitation for today's microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum.