Amplitude Sensing below the Zero-Point Fluctuations with a Two-Dimensional Trapped-Ion Mechanical Oscillator

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Sensing
• Condensed Matter Physics

Background:

• Precise measurement of collective ion motion is crucial for quantum technologies.
• Existing methods face limitations in sensitivity and precision for detecting small amplitudes.

Purpose of the Study:

• To develop and demonstrate a novel technique for measuring the center-of-mass (c.m.) motion amplitude of a 2D ion crystal.
• To achieve unprecedented measurement precision, resolving amplitudes significantly smaller than zero-point fluctuations.

Main Methods:

• Utilized a spin-dependent optical-dipole force to couple ion mechanical oscillations to electron spins.
• Measured one quadrature of the c.m. motion via spin state readout, with sensing far from resonance.
• Determined measurement imprecision by analyzing signals at frequencies away from the c.m. resonance.

Main Results:

• Successfully resolved motion amplitudes as small as 50 picometers (pm).
• Achieved a precision 40 times greater than the c.m. mode's zero-point fluctuations.
• Identified sensitivity limits imposed by spin projection noise and decoherence from off-resonant light scattering.

Conclusions:

• The demonstrated technique offers a pathway to ultra-precise measurements of ion crystal motion.
• On-resonance application can enable detection of ultra-weak forces and electric fields, probing quantum sensing limits.
• Provides a new tool for searching for physics beyond the Standard Model.