Exponential-Off Qubit Couplers

Creating qubit-qubit interactions that can be turned on or off is key to making multi-qubit circuits, whether for gate-based or quantum annealing applications. It is critical that the “off” state be robust, both in terms of residual coupling and sensitivity to flux noise. This ensures good isolation of the circuit elements and prevents unwanted terms from being introduced into the Hamiltonian. Here we present an extensible framework for a coupler consisting of a chain of elements connecting two qubits. While the “on” state coupling decreases polynomially in the length of the chain, the unwanted “off” coupling decreases exponentially, leading to a broad range of control flux with negligible “off” coupling for chains of reasonable length. Additionally, the individual elements may be engineered to control aspects of the “on” point, allowing one to mitigate noise or errors in fabrication.