Interqubit coupling mediated by a high-excitation-energy quantum object

TL;DR

This paper analyzes a quantum system with two qubits and a high-energy mediator, providing insights into mediated coupling, residual interactions, and entanglement, with implications for multi-qubit quantum computing architectures.

Contribution

It offers a detailed quantum mechanical analysis of qubit coupling via a high-energy mediator, including residual coupling and entanglement in multi-qubit systems, extending previous models.

Findings

Reproduces known mediated coupling results.

Derives expression for residual qubit coupling in off state.

Identifies errors unique to multi-qubit systems.

Abstract

We consider a system composed of two qubits and a high-excitation-energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well-known results concerning the leading term in the mediated coupling, we obtain an expression for the residual coupling between the qubits in the off state. We also analyze the entanglement between the three objects, i.e. the two qubits and the coupler, in the eigenstates of the total Hamiltonian. Although we focus on the application of our results to the recently realized parametric-coupling scheme with two qubits, we also discuss extensions of our results to harmonic-oscillator couplers, couplers that are near resonance with the qubits and multi-qubit systems. In particular, we find that certain errors that are absent for a two-qubit system arise when dealing with multi-qubit systems.