Quantum phase measurement for two-qubit states in an open waveguide

TL;DR

This paper introduces a novel quantum state tomography method for two-qubit states in an open waveguide, utilizing frequency modulation of an ancillary qubit to extract phase information unambiguously.

Contribution

The method enables phase measurement of two-qubit states in an open waveguide using a single-excitation subspace and frequency modulation techniques.

Findings

Successfully measures phase difference between edge qubits.

Provides a new approach for quantum state tomography in waveguide QED.

Demonstrates unambiguous phase extraction via ancillary qubit modulation.

Abstract

We present a new method for quantum state tomography within a single-excitation subspace of two-qubit states in an open waveguide. The system under investigation consists of three qubits in an open waveguide, separated by a distance comparable to the wavelength of the electromagnetic field. We show that the modulation of the frequency of the central ancillary qubit allows us to obtain unambiguous information about the initial phase difference $\varphi_1-\varphi_3$ of the edge qubits via the measurement of the evolution of their probability amplitudes.