XX coupler for flux qubits

A quantum circuit assembly comprising:

• a first flux qubit, having at least two potential energy minima;
• a second flux qubit, having at least two potential energy minima, such that a system formed by the first qubit and the second qubit has at least four potential energy minima prior to coupling, each of the four potential energy minima containing a quantum state of a system comprising the first flux qubit and the second flux qubit;
• and
• a coupler, comprising a plurality of tunable Josephson junctions and a capacitor, operatively connected to each of the first flux qubit and the second flux qubit, that creates a first tunneling path between a first potential energy minimum of the system and a second potential energy minimum of the system, and a second tunneling path between a third potential energy minimum of the system and a fourth potential energy minimum of the system, the coupler being tunable via a control signal applied to at least one of the plurality of tunable junctions to tune a first tunneling energy associated with the first tunneling path and a second tunneling energy associated with the second tunneling path, wherein the capacitor decreases a spread of a wave function of the system to decouple the first potential energy minimum of the system and the second potential energy minimum of the system from the third potential energy minimum of the system and the fourth potential energy minimum of the system.