Short-time coherence of a qubit and measurement apparatus

TL;DR

This paper investigates how a measurement apparatus influences the short-time quantum coherence of a qubit, showing that coherence can be manipulated through specific measurement schemes and temperature conditions.

Contribution

It introduces a model analyzing the effects of nonselective measurements on qubit coherence, highlighting the role of measurement schemes and temperature in coherence dynamics.

Findings

Maximum initial coherence is 1/2 under certain schemes and low temperature.

Coherence can increase, decrease, or remain constant over short times depending on measurement choice.

Measurement schemes and high temperature enhance the rate of coherence change.

Abstract

The effects of the measurement apparatus on quantum coherence are studied by considering a purely dephasing model of a qubit. The initial state is prepared from a thermal state of the whole system by performing a nonselective measurement on the qubit. The magnitude of the initial postmeasurement coherence is bounded by the value $1/2$, which is realized with special measurement schemes and in the low-temperature limit. The magnitude of coherence identically vanishes, increases or decreases with approximately constant velocity over a determined short time scale, according to the choice of the preparation measurement. The maximization of the short-time increasing or decreasing velocity is favored by the choice of further special measurement schemes and the high-temperature limit. The measurement apparatus allows to manipulate quantum coherence of the qubit over short times via nonselective preparation measurements.