Engineering Purely Nonlinear Coupling between Superconducting Qubits Using a Quarton

Summary

Proposes the quarton — a superconducting circuit element with purely quartic (${\phi }^4$) potential and no quadratic (${\phi }^2$) term — for engineering ultrastrong nonlinear coupling between linearly decoupled transmon qubits. Achieves gigahertz-scale cross-Kerr interaction (${\chi }_{zz}$), an order of magnitude stronger than conventional dispersive coupling. The circuit uses balanced series and lone Josephson junctions with tilt parameter $2\alpha \approx 1$. Applications include ultrafast entangling gates and single photon detection.

Cited In

• quarton-coupler