The present invention provides a coupling mechanism, a coupling mechanism activation method, a square lattice including the coupling mechanism, and a quantum gate including the coupling mechanism. A coupling mechanism for a multi-qubit variable coupling architecture using fixed frequency superconducting qubits. The coupling mechanism comprises two qubits and a variably coupled qubit that causes the interaction between the two qubits by modulation of its frequency. A variable coupling qubit capacitively couples two qubits. The variable coupled qubit is modulated at the difference frequency of the two qubits. The difference frequency is much larger than the anharmonicity of the two qubits. The variably coupled qubit can be two by two electrodes separated by a superconducting quantum interference device (SQUID) loop having two Josephson junctions, or by a single electrode using a SQUID loop coupled to ground. It can be coupled to qubits. The SQUID loop is controlled by an inductively coupled flux bias line centrally located in the variable coupling qubit. [Selected figure] Figure 1
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