Nonreciprocal interaction and entanglement between two superconducting qubits

TL;DR

This paper proposes a tunable scheme for achieving nonreciprocal interaction and entanglement between two superconducting qubits using combined coherent and dissipative couplings, facilitating nonreciprocal quantum devices.

Contribution

It introduces a novel method to realize nonreciprocal interaction and entanglement in superconducting qubits without relying on nonlinearity or complex setups.

Findings

Nonreciprocal interaction achieved at specific qubit separations.

Stable nonreciprocal entangled states can be generated.

The scheme is highly tunable and adaptable for quantum networks.

Abstract

Nonreciprocal interaction between two spatially separated subsystems plays a crucial role in signal processing and quantum networks. Here, we propose an efficient scheme to achieve nonreciprocal interaction and entanglement between two qubits by combining coherent and dissipative couplings in a superconducting platform, where two coherently coupled transmon qubits simultaneously interact with a transmission line waveguide. The coherent interaction between the transmon qubits can be achieved via capacitive coupling or via an intermediary cavity mode, while the dissipative interaction is induced by the transmission line via reservoir engineering. With high tunability of superconducting qubits, their positions along the transmission line can be adjusted to tune the dissipative coupling, enabling to tailor reciprocal and nonreciprocal interactions between the qubits. A fully nonreciprocal interaction can be achieved when the separation between the two qubits is $(4n+3)\lambda_{0} /4$, where $n$ is an integer and $\lambda_{0}$ is the photon wavelength. This nonreciprocal interaction enables the generation of nonreciprocal entanglement between the two transmon qubits. Furthermore, applying a drive field to one of the qubit can stabilize the system into a nonreciprocal steady-state entangled state. Remarkably, the nonreciprocal interaction in this work does not rely on the presence of nonlinearity or complex configurations, which has more potential applications in designing nonreciprocal quantum devices, processing quantum information, and building quantum networks.