Resolving the gravitational redshift across a millimetre-scale atomic sample.

Area of Science:

• Atomic physics
• General relativity
• Quantum mechanics

Background:

• Einstein's theory of general relativity predicts gravitational redshift, where clocks tick at different rates in varying gravitational potentials.
• Atomic clocks are crucial for testing general relativity across various distance scales.
• Future atomic clocks aim to probe the intersection of general relativity and quantum mechanics.

Purpose of the Study:

• To measure gravitational redshift within a millimetre-scale sample of ultracold strontium atoms.
• To advance atomic clock sensitivity for exploring fundamental physics.

Main Methods:

• Utilized ultracold strontium atoms in a millimetre-scale sample.
• Achieved a fractional frequency measurement uncertainty of 7.6 × 10^-21, an improvement of over 10x.
• Measured a linear frequency gradient consistent with gravitational redshift.

Main Results:

• Demonstrated a measurable gravitational redshift within a millimetre-scale sample.
• Achieved unprecedented measurement uncertainty in atomic clock frequency.
• Observed a linear frequency gradient attributable to gravitational potential differences.

Conclusions:

• The results confirm Einstein's prediction of gravitational redshift at the millimetre scale.
• This advancement opens a new era for atomic clocks, requiring intra-sample corrections for gravitational effects.
• Paves the way for atomic clocks to probe quantum gravity regimes.