Entanglement-Enhanced Optical Ion Clock.

Area of Science:

• Quantum Information Science
• Atomic Physics
• Metrology

Background:

• Entangled states offer potential for enhanced quantum sensor precision and accuracy.
• Spectroscopy of optical clock transitions is a key area for metrology advancements.

Purpose of the Study:

• To experimentally demonstrate that entangled states in spectroscopy outperform classical methods for quantum sensors.
• To investigate the performance of an optical clock using entangled ^{40}Ca^{+} ions.

Main Methods:

• Entangling two ^{40}Ca^{+} ions in a quantum state with minimized magnetic field sensitivity.
• Utilizing near-lifetime-limited probe times up to 550 ms for spectroscopy.
• Comparing the frequency instability of the entangled ion clock with a ^{87}Sr lattice clock.

Main Results:

• Entangled ions achieved the same instability as uncorrelated ions but in half the probe time, enabling faster clock cycles.
• The entangled ^{40}Ca^{+} ion clock exhibited lower frequency instability than a clock using classically correlated states.
• Observed instabilities below the quantum projection noise limit for interrogation times under 100 ms.
• Achieved a fractional frequency instability of 7×10^{-16}/sqrt[τ/1 s] at 250 ms probe time, limited by laser phase noise.

Conclusions:

• Spectroscopy using entangled ^{40}Ca^{+} ions provides superior performance compared to classical approaches.
• This work establishes a new benchmark for instability in ^{40}Ca^{+} ion clocks.
• Entanglement-enhanced quantum sensors, specifically optical clocks, show significant promise for future metrology applications.