Nonlinearity-engineered Threaded SQUID: A Novel Nonlinear Device for Bosonic Quantum Error Correction

Bosonic error correction codes, such as cat codes, are promising candidates for quantum information processing. However, the stabilization and control of these codes require complicated high-order nonlinear Hamiltonians, which are challenging to implement in practice. The realization of effective high-order Hamiltonians usually demands strong drives at carefully selected frequencies, which also induce unavoidable residual Hamiltonians and decoherence effects. To get around, we design a novel multi-loop Josephson interference device that selectively produces odd-order nonlinear Hamiltonians when subjected to specific magnetic drives. Different from the anharmonic threaded SQUID (ATS) with two single-junction branches, this new device is expected to eliminate the residual first-order Hamiltonian and suppress static Kerr nonlinearity while retaining the third-order and higher ones by introducing a multi-junction branch. The device that we propose can be used for the implementation of bias-preserving CNOT gates and other gate operations on Kerr-cat qubits. In this talk, we will present the theoretical part related to this novel device.