The qubit reveals a qubit-cavity system

TL;DR

This paper demonstrates that the coupling parameters and the state of a cavity mode can be inferred solely from qubit process tomography data, offering an alternative to existing methods.

Contribution

It introduces a method to estimate qubit-cavity coupling parameters and reconstruct the cavity state using only qubit measurements, simplifying the analysis process.

Findings

Coupling Hamiltonian parameters can be derived from qubit data.

The cavity's photon number statistics can be reconstructed.

The variance matrix of the cavity mode can be obtained from qubit measurements.

Abstract

We show that the coupling between a qubit and a single mode cavity can be estimated from the process tomography data for the qubit alone. All the parameters of the coupling Hamiltonian between the qubit and the cavity mode can be obtained from observations on the qubit. We also show that the variance matrix and the photon number statistics of the single mode cavity can be reconstructed. Our results provide an alternate means of obtaining the coupling and reconstructing the state of the cavity mode in comparison with the techniques presently used.