Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2112.10776 · International Journal of Quantum Information

Short-time coherence of a qubit and measurement apparatus

Filippo Giraldi

Published Mar 7, 2022• 1 citation
arXivHTMLPDF

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 [Formula: see text], which is realized with special measurement schemes and in the low-temperature limit. The coherence magnitude identically vanishes, increases or decreases with an approximately constant rate over a determined short-time scale, according to the choice of the preparation measurement. The maximization of the short-time increasing or decreasing rate is favored by the choice of other special measurement schemes and the high-temperature limit. The measurement apparatus allows to manipulate the quantum coherence of the qubit over short times via nonselective preparation measurements.

DOI
10.1142/s0219749922500034

Related papers

Evolution of quantum coherence induced by band gaps and initial-state preparation measurements

Filippo Giraldi

The evolution of quantum coherence in a qubit is analyzed, over short and long times, in case the qubit interacts with a bosonic environment. The distribution of the frequency modes exhibits a low-frequency band gap. The initial conditions under study of the qubit and the bosonic environment are factorized or prepared with selective or nonselective measurements. The modulus of the coherence term of the reduced density matrix of the qubit evolves algebraically over short times and, due to the band gap, tends to the nonvanishing asymptotic value with damped oscillations. Depending on the measurement scheme, the nonselective preparation measurement can enhance quantum coherence or accelerate the decoherence process, over short times, according to dominant linear laws. Over long times, the nonselective preparation measurement produces the slowest-decaying envelope of the damped oscillations among the decoherence processes under study. Similar short- and long-time evolution is exhibited by the trace distance measure of two general states of the qubit.

International Journal of Quantum Information•Feb 1, 2020•1 citation

Preparing Decoherence-Recoherence Times of a Qubit with Special Nonselective Measurement Schemes

Filippo Giraldi

The appearance of decoherence-recoherence events is analyzed in a dephasing model of a qubit which interacts with a bosonic environment. The initial condition is prepared from the thermal state of the whole system by performing a nonselective measurement on the qubit. Decoherence-recoherence events appear in the reduced dynamics of the qubit uniquely if special nonselective preparation measurements are adopted and the spectral density of the system fulfills determined conditions. General lower bounds are found for the number of decoherence-recoherence events in terms of the properties of the measurement scheme and of the spectral density. The number is finite for canonical spectral densities which are super-ohmic, perturbed super-ohmic, or ohmic at low frequencies and are arbitrarily tailored at high frequencies. The number is infinite in the sub-ohmic regime and for perturbations of the sub-ohmic or ohmic regime. Decoherence-recoherence times are evaluated, analytically and numerically, for ohmic-like spectral densities with exponential high-frequency cutoffs.

Open Systems & Information Dynamics•Mar 1, 2021•1 citation

Enhancement of coherence in qubits due to interaction with the environment

V. V. Ignatyuk, V. G. Morozov

The influence of the initial preparation on dephasing in open quantum dynamics is studied using an exactly solvable model of a two-level system (qubit) interacting with a bosonic bath. It is found that, for some classes of nonselective preparation measurements, qubit-bath correlations lead to a significant enhancement of coherence in the qubit at the initial stage of evolution. The time behavior of the qubit purity and entropy in the regime of enhancement of coherence is considered for different temperatures and coupling strengths.

arXiv:1504.05244•Physical Review A•May 6, 2015•12 citations

Peculiarities of qubit initial-state preparation by nonselective measurements on an overcomplete basis

V. V. Ignatyuk

We consider the qubit initial-state preparation due to the nonselective measurements on an overcomplete basis, when the number of outcomes $N=3$. To be specific, we have chosen the dephasing model and applied the conditions for a post-measurement state to ensure a gradual coherence enhancement at the initial stage of the system evolution. It is shown that contrary to the von Neumann--L\"uders projection scheme with $N=2$, the most mixed post-measurement state of the qubit in the general case can depend on the bath temperature. This remarkable feature allows one to consider a ``temperature-controlled'' initial purification of the open quantum system. We also consider some kinds of the repeated nonselective measurements from the viewpoint of an eventual system purification and analyze the important peculiarities of such schemes.

arXiv:1511.05206•Physical Review A•Dec 9, 2015•4 citations

Beyond the standard quantum Zeno effect

Andrey A. Borisov, Anton A. Borisov, T. F. Kamalov

In this paper, we introduce a functional for the decoherence rate of a quantum system. The quantum system is modeled as a qubit that can be in the state |1〉, |0〉, or in a superposition. In addition to external dephasing and the Zeno attenuation rate acting on the quantum system, resource losses of the measuring channel are taken into account. It is shown that for the parameters corresponding to the limit of ideally frequent measurements in the quantum Zeno effect, the stability of the qubit state is not increased. The existence of optimal values of the measurement time interval and the measurement imperfection parameter is established; at these values, the decoherence rate of the qubit state reaches a minimum. Calculations show that in the case under consideration, the qubit coherence time increases by a factor of 11.5, which ensures an increase in the stability of the qubit state.

Physics of Complex Systems•Jan 1, 2026•0 citations

Measurement-induced quantum coherence recovery

Jin‐Shi Xu, Chuan‐Feng Li, Xu‐Bo Zou +4 more

We show that measurement can recover the quantum coherence of a qubit in a pure dephasing environment. The experimental demonstration of this in an optical system by comparing the visibilities (and fidelities) of the final states with and without measurement is provided here. This method can be extended to other two-level quantum systems and entangled states in a dephasing evolution environment. It may also be used to implement other types of quantum information processing.

arXiv:0810.5272•New Journal of Physics•Apr 3, 2009•7 citations
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 [Formula: see text], which is realized with special measurement schemes and in the low-temperature limit. The coherence magnitude identically vanishes, increases or decreases with an approximately constant rate over a determined short-time scale, according to the choice of the preparation measurement. The maximization of the short-time increasing or decreasing rate is favored by the choice of other special measurement schemes and the high-temperature limit. The measurement apparatus allows to manipulate the quantum coherence of the qubit over short times via nonselective preparation measurements.
The evolution of quantum coherence in a qubit is analyzed, over short and long times, in case the qubit interacts with a bosonic environment. The distribution of the frequency modes exhibits a low-frequency band gap. The initial conditions under study of the qubit and the bosonic environment are factorized or prepared with selective or nonselective measurements. The modulus of the coherence term of the reduced density matrix of the qubit evolves algebraically over short times and, due to the band gap, tends to the nonvanishing asymptotic value with damped oscillations. Depending on the measurement scheme, the nonselective preparation measurement can enhance quantum coherence or accelerate the decoherence process, over short times, according to dominant linear laws. Over long times, the nonselective preparation measurement produces the slowest-decaying envelope of the damped oscillations among the decoherence processes under study. Similar short- and long-time evolution is exhibited by the trace distance measure of two general states of the qubit.
The appearance of decoherence-recoherence events is analyzed in a dephasing model of a qubit which interacts with a bosonic environment. The initial condition is prepared from the thermal state of the whole system by performing a nonselective measurement on the qubit. Decoherence-recoherence events appear in the reduced dynamics of the qubit uniquely if special nonselective preparation measurements are adopted and the spectral density of the system fulfills determined conditions. General lower bounds are found for the number of decoherence-recoherence events in terms of the properties of the measurement scheme and of the spectral density. The number is finite for canonical spectral densities which are super-ohmic, perturbed super-ohmic, or ohmic at low frequencies and are arbitrarily tailored at high frequencies. The number is infinite in the sub-ohmic regime and for perturbations of the sub-ohmic or ohmic regime. Decoherence-recoherence times are evaluated, analytically and numerically, for ohmic-like spectral densities with exponential high-frequency cutoffs.
The influence of the initial preparation on dephasing in open quantum dynamics is studied using an exactly solvable model of a two-level system (qubit) interacting with a bosonic bath. It is found that, for some classes of nonselective preparation measurements, qubit-bath correlations lead to a significant enhancement of coherence in the qubit at the initial stage of evolution. The time behavior of the qubit purity and entropy in the regime of enhancement of coherence is considered for different temperatures and coupling strengths.
We consider the qubit initial-state preparation due to the nonselective measurements on an overcomplete basis, when the number of outcomes N=3N=3N=3. To be specific, we have chosen the dephasing model and applied the conditions for a post-measurement state to ensure a gradual coherence enhancement at the initial stage of the system evolution. It is shown that contrary to the von Neumann--L\"uders projection scheme with N=2N=2N=2, the most mixed post-measurement state of the qubit in the general case can depend on the bath temperature. This remarkable feature allows one to consider a ``temperature-controlled'' initial purification of the open quantum system. We also consider some kinds of the repeated nonselective measurements from the viewpoint of an eventual system purification and analyze the important peculiarities of such schemes.
In this paper, we introduce a functional for the decoherence rate of a quantum system. The quantum system is modeled as a qubit that can be in the state |1〉, |0〉, or in a superposition. In addition to external dephasing and the Zeno attenuation rate acting on the quantum system, resource losses of the measuring channel are taken into account. It is shown that for the parameters corresponding to the limit of ideally frequent measurements in the quantum Zeno effect, the stability of the qubit state is not increased. The existence of optimal values of the measurement time interval and the measurement imperfection parameter is established; at these values, the decoherence rate of the qubit state reaches a minimum. Calculations show that in the case under consideration, the qubit coherence time increases by a factor of 11.5, which ensures an increase in the stability of the qubit state.