Quantum bit with a multi-terminal junction and loop with a phase shift

A method of initializing a qubit, comprising:

• providing a qubit, the qubit including a superconducting loop coupled to a multi-terminal junction, the superconducting loop providing a phase shift;
• and
• passing current asymmetrically through the multi-terminal junction in a selected direction for a sufficient amount of time to induce a selected quantum state on the superconducting loop of the quantum qubit.

A method of performing a phase gate operation, comprising:

• providing a qubit, the qubit including superconducting loop coupled to a multi-terminal junction, the superconducting loop providing a phase shift;
• passing current through the multi-terminal junction.

A method of entangling two qubits in a qubit array, comprising:

• switchably capacitively coupling a voltage into an entanglement junction, the entanglement junction being coupled between superconducting loops of the two qubits.

The method of claim 97, wherein the quantum states of the two qubits are entangled in the absence of the voltage.

A method of tuning a qubit, comprising:

• providing a qubit, the qubit including a superconducting loop coupled to a multi-terminal junction, the superconducting loop providing a phase shift;
• providing a current symmetrically through the multi-terminal junction, the current adjusting a tunneling frequency between quantum states on the qubit.