How to Connect Quantum Computer Bits with a Superconducting Circuit

This patent describes a superconducting circuit called an rf-SQUID that can precisely turn on, turn off, or change the way two quantum computer bits (qubits) interact with each other.

What it covers

This system provides a way to controllably link two quantum bits, or qubits, using a special superconducting loop called an rf-SQUID (Claim 1). This rf-SQUID has a 'compound Josephson junction' and is connected to both a first qubit and a second qubit through magnetic fields (mutual inductance). A separate 'magnetic flux inductor' is also connected to the Josephson junction (Claim 1). By adjusting the magnetic field produced by this inductor, the system can control how the two qubits interact, allowing for different 'coupling states' such as anti-ferromagnetic coupling, ferromagnetic coupling, or even no coupling at all (Claim 3, Claim 5). For example, if you want two qubits in a quantum computer to perform a calculation together, this system could turn on their interaction, and then turn it off when they need to operate independently.

What it doesn't cover

• —Does not cover qubit coupling systems that do not use an rf-SQUID as the intermediate coupling device.
• —Does not cover coupling mechanisms that do not rely on mutual inductance between the rf-SQUID and the qubits.
• —Does not cover control methods for qubit coupling that do not involve a magnetic flux inductor adjusting flux through a compound Josephson junction.
• —Does not cover qubits that are not superconducting, as the claims specifically mention 'superconducting flux qubit' (Claim 2) and 'superconducting material' (Claim 1).
• —Does not cover direct coupling between qubits without an intermediate tunable coupler.

The clever bit

The cleverness lies in using an rf-SQUID with a compound Josephson junction as a tunable intermediary, allowing a magnetic flux inductor to precisely switch and adjust the quantum mechanical coupling between two qubits from zero to ferromagnetic or anti-ferromagnetic states.

Why it matters

Controlling how qubits interact is fundamental to building functional quantum computers. This patent offers a precise method to switch and tune these interactions, which is essential for executing quantum algorithms and building scalable quantum processors. Without such control, qubits would either always interact or never interact, severely limiting the types of computations possible.

Real-world examples

• 1.Superconducting quantum processors
• 2.Tunable couplers in quantum computing architectures
• 3.IBM Quantum computers
• 4.Google's Sycamore processor
• 5.Rigetti Computing quantum systems