Controllable coupling of superconducting flux qubits

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Information Science

Background:

• Superconducting flux qubits are promising candidates for quantum computation.
• Controlling and tuning qubit-qubit interactions is essential for scalable quantum processors.
• Existing coupling methods often lack in situ tunability.

Purpose of the Study:

• To demonstrate a novel tunable coupler for two three-junction flux qubits.
• To investigate the in situ tunability of coupling strength (J) between qubits.
• To explore the relationship between tunable two-qubit coupling and three-qubit behavior.

Main Methods:

• Insertion of an additional coupler loop with three Josephson junctions between two flux qubits.
• Utilizing a shared Josephson junction design for strong qubit-coupler interaction.
• Modulating the coupler's flux bias to tune the coupling strength J.

Main Results:

• Achieved controllable coupling strengths ranging from approximately 45 mK (antiferromagnetic) to -55 mK (ferromagnetic).
• Demonstrated that coupling strength J can be tuned in situ via the coupler's flux bias.
• Observed vanishing coupling strength at an intermediate coupler bias.
• Measurements on a second sample provided insights into three-qubit interactions.

Conclusions:

• The developed tunable coupler offers precise control over qubit-qubit interactions.
• This method is vital for building more complex and scalable superconducting quantum processors.
• The findings contribute to the fundamental understanding of multi-qubit dynamics in superconducting circuits.