Multi-qubit gates and Schrödinger cat states in an optical clock

Area of Science:

• Quantum Metrology
• Atomic Physics
• Quantum Information Science

Background:

• Many-particle entanglement is crucial for quantum sensor precision.
• Optical atomic clocks represent the state-of-the-art in frequency precision.
• Entanglement-enhanced metrology is a key focus for improving optical clocks.

Purpose of the Study:

• To develop and utilize multi-qubit Rydberg gates for generating highly entangled states in optical atomic clocks.
• To explore the potential of Greenberger-Horne-Zeilinger (GHZ) states for enhancing clock precision.
• To overcome limitations of single-size GHZ states for improved phase estimation.

Main Methods:

• Development of multi-qubit Rydberg gates for programmable atom arrays.
• Generation of Schrödinger cat states of the GHZ type with up to nine optical clock qubits.
• Atom-laser comparison experiments to measure frequency instability.

Main Results:

• Demonstrated fractional frequency instability below the standard quantum limit (SQL) using GHZ states of up to four qubits.
• Observed that single-size GHZ states do not improve clock precision at optimal dark times.
• Successfully prepared a cascade of varying-size GHZ states for unambiguous phase estimation.

Conclusions:

• Multi-qubit Rydberg gates enable the creation of complex entangled states for quantum clocks.
• GHZ states show promise for surpassing the SQL in optical atomic clocks.
• Cascaded GHZ states offer a pathway towards Heisenberg-limited precision scaling in atomic clocks.