0.75 atoms improve the clock signal of 10,000 atoms

TL;DR

This paper demonstrates that injecting a squeezed vacuum state with an average of 0.75 atoms into a 10,000-atom interferometer improves clock sensitivity beyond the standard quantum limit, advancing precision time measurement.

Contribution

The authors experimentally show that vacuum squeezing with a small atom number enhances atomic clock precision beyond the SQL.

Findings

Achieved 2.05 dB improvement in clock sensitivity.

Created a squeezed vacuum state with 0.75 atoms.

Identified technical challenges for next-generation fountain clocks.

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 10,000 atoms by 2.05 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.