Quantum witness of a damped qubit with generalized measurements

Manuel Bojer,Alexander Friedenberger,Eric Lutz

doi:10.1088/2399-6528/ab2209

Manuel Bojer, Alexander Friedenberger + Show 1 more

Open Access

https://doi.org/10.1088/2399-6528/ab2209

Copy DOI

Abstract

We evaluate the quantum witness based on the no-signaling-in-time condition of a damped two-level system for nonselective generalized measurements of varying strength. We explicitly compute its dependence on the measurement strength for a generic example. We find a vanishing derivative for weak measurements and an infinite derivative in the limit of projective measurements. The quantum witness is hence mostly insensitive to the strength of the measurement in the weak measurement regime and displays a singular, extremely sensitive dependence for strong measurements. We finally relate this behavior to that of the measurement disturbance defined in terms of the fidelity between pre-measurement and post-measurement states.

Highlights

What is the intrinsic difference between quantum and classical systems? This question has been at the core of quantum theory since its very beginning [1, 2]
This approach exploits the idea that the time evolution of a quantum system is perturbed by a measurement contrary to that of a classical system
Our aim in this paper is to investigate the quantum witness based on the no-signaling-in-time condition of a damped qubit when a generalized measurement with variable strength is used to perturb the system

Summary

INTRODUCTION

What is the intrinsic difference between quantum and classical systems? This question has been at the core of quantum theory since its very beginning [1, 2]. A third criterion based on the no-signaling-in-time condition has been developed [10, 11] This approach exploits the idea that the time evolution of a quantum system is perturbed by a measurement contrary to that of a classical system. In this context, quantum features are witnessed by the different population dynamics of a system in the presence and in the absence of a measurement. Our aim in this paper is to investigate the quantum witness based on the no-signaling-in-time condition of a damped qubit when a generalized measurement with variable strength is used to perturb the system. We relate this behavior to that of the measurement disturbance defined in terms of the fidelity between the states before and after the measurement

WITNESS OF A DAMPED QUBIT

MEASUREMENT DISTURBANCE

SUMMARY