Quadrupole Coupling of Circular Rydberg Qubits to Inner Shell Excitations

Area of Science:

• Quantum simulation and computing
• Atomic physics
• Quantum information science

Background:

• Divalent atoms offer enhanced control in Rydberg atom-based quantum technologies due to their second optically active valence electron.
• Circular Rydberg atoms are particularly promising due to long-lived ionic core excitations and resistance to autoionization.

Purpose of the Study:

• To implement and demonstrate electric quadrupole coupling between a metastable ionic core level and a high-n circular Rydberg qubit.
• To explore optical control of highly excited circular Rydberg states via ionic core manipulation for quantum simulation.

Main Methods:

• Utilized doubly excited ^{88}Sr atoms prepared in an optical tweezer array.
• Implemented electric quadrupole coupling between the metastable 4D_{3/2} level and a high-n (n=79) circular Rydberg qubit.
• Employed beat-node Ramsey interferometry with spin echo to measure the differential level shift on the circular Rydberg qubit.

Main Results:

• Successfully measured kHz-scale differential level shifts, demonstrating electric quadrupole coupling.
• Achieved coherent interrogation of Rydberg states for over 100 μs, aided by tweezer trapping and enhanced circular state lifetime.
• Observed no significant loss of qubit coherence under continuous photon scattering on the ion core.

Conclusions:

• Demonstrated a new method for accessing weak electron-electron interactions in Rydberg atoms.
• Expanded the quantum simulation toolbox by enabling optical control of circular Rydberg qubits through ionic core manipulation.
• Paved the way for laser cooling and imaging of Rydberg atoms by confirming coherence under photon scattering.