Weak Measurement Reversal Research Articles

Enhancing the Precision of Phase Estimation by Weak Measurement and Quantum Measurement Reversal in High Dimensional Quantum System

We investigate the effect of the weak measurement (WM) and quantum measurement reversal (QMR) on the improvement of the parameter-estimation precision for a qurit interacting with a zero-temperature reservoir with both spontaneous emission and dephasing. We derive the exact expressions of the optimal quantum Fisher information (QFI), show explicitly that the WM and QMR operation indeed helps for enhancing the precision of parameter estimation from spontaneous emission damping, but not for dephasing damping. In particular, we found that the enhancement effect is work in high dimensional quantum system, which extends the applicable scope of the WM and QMR approach.

Improving the Capacity of Quantum Dense Coding Via Environment-Assisted Measurement and Quantum Measurement Reversal

We propose a novel method to enhance the capacity of quantum dense coding under local amplitude damping noise. With the assistance of environment-assisted measurement and quantum measurement reversal, we show that the amplitude damping noise could be completely eliminated and the capacity is exactly recovered with a certain probability. Comparing with the results obtained by the method of weak measurement and quantum measurement reversal, our results show notable superiorities on improving the capacity and successful probability. The key advantage of our scheme originates from the fact that environment-assisted measurement can extract additional information from the environment.

Entropic Uncertainty Relation for Dirac Particles in Garfinkle–Horowitz–Strominger Dilation Space–Time

AbstractThe quantum‐memory‐assisted entropic uncertainty relation for Dirac particles in the background of a Garfinkle–Horowitz–Strominger (GHS) dilation black hole is investigated, and the relationship between the entropy uncertainty and the quantum entanglement of a hybrid qubit–qutrit state in the GHS space–time analyzed. The results show that the physically accessible uncertainty increases while the inaccessible uncertainty decreases as the dilation parameter of the black hole enhances. Moreover, the evolution behavior of the uncertainty is inversely correlated with that of the entanglement between the quantum memory and the particle to be measured. Meanwhile, a method to steer the entropic uncertainty with the technique of weak measurement reversal is proposed. It is found that the uncertainty can be reduced effectively by adjusting the appropriate measurement strength. These findings may lead to a deeper understanding of entropy uncertainty dynamics, as well as its steering in a curved space–time.

Decoherence Suppression in Phase Decoherence Environment Using Weak Measurement and Quantum Measurement Reversal

Decoherence suppression from disturbance of the environment is an essential task in quantum information processing. We investigate decoherence suppression of a qubit system interacting with a heat bath with phase decoherence by employing the weak measurement (WM) and quantum measurement reversal (QMR) operation. We show explicitly that the qubit decoherence can be efficiently completely suppressed by means of the combination WM and QMR, which is independent of the form of the spectral density of the reservoir and the form of initial input state.

Enhancement of parameter-estimation precision by weak measurement and quantum measurement reversal under various non-Markovian decoherence sources

We investigate the effect of the weak measurement (WM) and quantum measurement reversal (QMR) on the improvement of the precision of parameter estimation for a qubit interacting with various non-Markovian decoherence sources: amplitude damping, dephasing damping and random unitary damping, respectively. We derive the exact expressions of the optimal quantum Fisher information, show explicitly that the WM and QMR operation indeed helps for enhancing the precision of parameter estimation from amplitude damping and phase damping, but not for random unitary damping. In particular, we found that the enhancement effect is independent of the specific form of the spectral density of the reservoir, which extends the applicable scope of the WM and QMR approach.

Analysing Nonlocal Correlations in Three-qubit Partially Entangled States Under Real Conditions

In this article, we readdress the question of importance of nonlocal correlations under real conditions. For characterizing nonlocal correlations, we use a three-qubit Svetlichny inequality whose violation confirms the existence of genuine nonlocal correlations between the qubits. For our purpose, we consider states in the three-qubit GHZ class states and establish an analytical relations between the expectation value of Svetlichny operator, state parameter, noise parameters, and weak measurement and its reversal operations. Interestingly, we found that the extent of violation of the Svetlichny inequality under the phase damping channel is independent of the state parameter and weak measurement strength for optimal weak measurement reversal strength, hence, bringing in the flexibility to start with any initial state instead of starting with a maximally entangled states only. On the other hand, if we fix the value of reverse weak measurement, then the expectation value of Svetlichny operator first increases, attains a maximum value and then decreases again. For depolarizing noise as well, we found that the weak measurements may be useful for protecting nonlocal correlations against the noise. Our analytical results further show an excellent agreement with numerical results in all above cases.

Protecting Entanglement in a Common Phase Decoherence Environment using Weak Measurement and Quantum Measurement Reversal

Protection of entanglement from disturbance of the environment is an essential task in quantum information processing. We investigate the entanglement protection of a qubit-qubit system interacting with a phase decoherence reservoir by employing the weak measurement (WM) and quantum measurement reversal (QMR). We show explicitly that the quantum entanglement can be obviously protected by means of the proper WM and QMR. In particular, we found that there is a specific initial state parameter region, the entanglement protection ratio, which is determined only by the initial state parameter and independent of the form of the spectral density of the reservoir.

Recovery of maximally entangled quantum states by weak-measurement reversal

Maximal quantum entanglement provided by N00N states is a unique resource in the quest for the ultimate precision in physical measurements. Such states, however, are fragile and prone to decoherence. Even in weak-measurement schemes, as we demonstrate in this work, the phase super-resolution provided by N00N states is achieved at a cost of an N-fold enhancement of amplitude damping. Still, as the analysis presented here shows, a partial collapse of N00N states induced by weak measurements can be reversed, despite the dramatic, N-fold enhancement of amplitude damping, through appropriate reversal operations on the post-measurement state, enabling a full restoration of the Heisenberg-limit phase super-resolution of N00N states.

Protecting quantum Fisher information in curved space-time

In this work, we investigate the quantum Fisher information (QFI) dynamics of a two-level atom interacting with quantized conformally coupled massless scalar fields in de Sitter-invariant vacuum. We first derive the master equation that governs its evolution. It is found that the QFI decays with evolution time. Furthermore, we propose two schemes to protect QFI by employing prior weak measurement (WM) and post measurement reversal (MR). We find that the first scheme can not always protect QFI and the second scheme has prominent advantage over the first scheme.

Dynamics of entropic uncertainty for atoms immersed in thermal fluctuating massless scalar field

In this article, the dynamics of quantum memory-assisted entropic uncertainty relation for two atoms immersed in a thermal bath of fluctuating massless scalar field is investigated. The master equation that governs the system evolution process is derived. It is found that the mixedness is closely associated with entropic uncertainty. For equilibrium state, the tightness of uncertainty vanishes. For the initial maximum entangled state, the tightness of uncertainty undergoes a slight increase and then declines to zero with evolution time. It is found that temperature can increase the uncertainty, but two-atom separation does not always increase the uncertainty. The uncertainty evolves to different relatively stable values for different temperatures and converges to a fixed value for different two-atom distances with evolution time. Furthermore, weak measurement reversal is employed to control the entropic uncertainty.

Controlling quantum memory-assisted entropic uncertainty in non-Markovian environments

Quantum memory-assisted entropic uncertainty relation (QMA EUR) addresses that the lower bound of Maassen and Uffink’s entropic uncertainty relation (without quantum memory) can be broken. In this paper, we investigated the dynamical features of QMA EUR in the Markovian and non-Markovian dissipative environments. It is found that dynamical process of QMA EUR is oscillation in non-Markovian environment, and the strong interaction is favorable for suppressing the amount of entropic uncertainty. Furthermore, we presented two schemes by means of prior weak measurement and posterior weak measurement reversal to control the amount of entropic uncertainty of Pauli observables in dissipative environments. The numerical results show that the prior weak measurement can effectively reduce the wave peak values of the QMA-EUA dynamic process in non-Markovian environment for long periods of time, but it is ineffectual on the wave minima of dynamic process. However, the posterior weak measurement reversal has an opposite effects on the dynamic process. Moreover, the success probability entirely depends on the quantum measurement strength. We hope that our proposal could be verified experimentally and might possibly have future applications in quantum information processing.

Quantum-memory-assisted entropic uncertainty in spin models with Dzyaloshinskii–Moriya interaction

In this article, we investigate the dynamics and correlations of quantum-memory-assisted entropic uncertainty, the tightness of the uncertainty, entanglement, quantum correlation and mixedness for various spin chain models with Dzyaloshinskii–Moriya (DM) interaction, including the XXZ model with DM interaction, the XY model with DM interaction and the Ising model with DM interaction. We find that the uncertainty grows to a stable value with growing temperature but reduces as the coupling coefficient, anisotropy parameter and DM values increase. It is found that the entropic uncertainty is closely correlated with the mixedness of the system. The increasing quantum correlation can result in a decrease in the uncertainty, and the robustness of quantum correlation is better than entanglement since entanglement means sudden birth and death. The tightness of the uncertainty drops to zero, apart from slight volatility as various parameters increase. Furthermore, we propose an effective approach to steering the uncertainty by weak measurement reversal.

Protection of Telecloning Over Noisy Channels with Environment-Assisted Measurements and Weak Measurements

We propose a scheme for protecting and improving the fidelity of quantum telecloning over the amplitude damping (AD) channels. By using the environment-assisted measurements and weak measurement reversals (WMR), the entanglement of quantum channel among three separated participants can be recovered probabilistically. Particularly, when the strength of WMRs is equal to the damping rate of the AD channels, the fidelity of the telecloning can be restored to the maximum value with a certain successful probability.

Enhancement of quantum Fisher information of quantum teleportation by optimizing partial measurements

The purpose of quantum teleportation is to achieve perfect transmission of quantum information from one site to another distant site. In the teleportation process, the quantum system is inevitably affected by its surrounding environment, causing the system to lose its coherence, which will result in distortion of the transmitted information. In recent years, weak measurement and measurement reversal have been proposed to suppress the decoherence of quantum entanglement and protect some quantum states. On the other hand, quantum Fisher information (QFI) is an important physical quantity in quantum metrology, which can give the optimal value estimating the accuracy of parameters. As is well known, QFI is highly susceptible to environmental noise and can lead its measurement accuracy to decrease. Therefore, it is of great importance to examine how to protect QFI from being influenced by the external circumstance during the teleportation procedure. In this paper, we study how to improve the QFI of teleporting a single-qubit state via a Greenberger-Horne-Zeilinger state in a finite temperature environment with the technique of weak measurement and weak measurement reversal. According to different qubit transmission cases of three quantum teleportation schemes, we consider their respective QFIs in detail. After constructing the quantum logic circuit of each teleportation scheme, we first analyze the variance trend of QFI against the generalized amplitude damping noise parameters. Then by introducing weak measurement and measurement reversal on each noise particle of the three schemes, we optimize the related partial measurement parameters and explore the corresponding improved QFI, namely, the difference between the QFI with optimal partial measurements and that without partial measurements. We find that optimizing partial measurements can efficiently enhance the QFI of the teleported state for the three kinds of teleportation schemes at finite temperature. Moreover, with the value of p fixed, the lower the environment temperature, the larger the value of the improved QFI is. Our results could be useful in further understanding the applications of weak measurement and measurement reversal to the quantum communication process and may shed light on estimating some relevant quantum parameters and implementing quantum information tasks.

EPR steering of polar molecules in pendular states and their dynamics under intrinsic decoherence.

Einstein–Podolsky–Rosen (EPR) steering gives evidence for the phenomenon called “spooky action at a distance” in quantum mechanics, and provides a useful resource for the implementation of quantum information tasks. In this paper, we consider a pair of ultracold polar molecules trapped in an external electric field as a promising quantum information carrier, and analyze the evolution behavior of EPR steering for the two coupled polar molecules in pendular states. Our results show that the steering of the two linear dipoles is remarkably reliant upon the Stark effect and dipole–dipole interaction. To be specific, the steerability degree is inversely associated with the intensity of the electric field while it is positively correlated with the coupling strength between the two polar molecules. Moreover, it is found that high ambient temperature can lead to a rapid loss of the steerable resource in thermal equilibrium. Further, we put forward an effective strategy to enhance the steerability using the technique of weak measurement reversal (WMR). By taking into account the influence of intrinsic decoherence on the steering dynamics, we found that robust EPR steering preservation can be realized for the initial state being in the Bell state . Our findings may shed some new light on molecular quantum information processing with pendular states.

Recovering the lost steerability of quantum states within non-Markovian environments by utilizing quantum partially collapsing measurements

In this letter, we mainly investigate the dynamic behavior of quantum steering and how to effectively recover the lost steerability of quantum states within non-Markovian environments. We consider two different cases (one-subsystem or all-subsystem interaction with dissipative environments), and find that the dynamical interaction between a system initialized by a Werner state and a non-Markovian environment can induce quasi-periodic quantum entanglement (concurrence) resurgence, however, quantum steering cannot be retrieved in such a condition. We also find that the resurgent quantum entanglement cannot be utilized to achieve quantum steering. Subsequently, we put forward a feasible physical scheme for recovering the steerability of quantum states within non-Markovian noises by prior weak measurement on each subsystem before interaction with dissipative environments, followed by post weak measurement reversal. It is shown that the steerability of quantum states and fidelity can be effectively restored. Furthermore, the results show that the larger the weak measurement strength, the better the effectiveness of the scheme. Consequently, our investigations might be beneficial to recover the lost steerability of quantum states within non-Markovian regimes.

Tripartite nonlocality for an open Dirac system in the background of Schwarzschild space–time

In this paper, the behavior of the tripartite nonlocality for a Dirac system in the background of Schwarzschild space–time is studied. It is shown that the nonlocality of the ultimate physical accessible state always decreases as the Hawking effect increases monotonically, which is independent of the number of particles located near the event horizon. Besides, the more particles there are located near the event horizon, the more difficult the violation of the Svetlichny inequality becomes. Furthermore, we investigate the property of these particles suffering from a non-Markovian environment, and derive that the nonlocality decreases quickly with the increasing decoherence time accompanied by damping revivals. To preserve tripartite nonlocality in the non-Markovian environment, we propose a scheme by means of prior weak measurement and post measurement reversal. It is worth noticing that the effect is better for larger measurement strengths, while it induces smaller success probability.

Enhancing the quantum state transfer between two atoms in separate cavities via weak measurement and its reversal

Taking the advantage of weak measurement and quantum measurement reversal, we propose a scheme to enhance the fidelity of transferring quantum state from one atom trapped in cavity to another distant one trapped in another cavity which is coupled by an optical fiber. It is turned out that the fidelity can be greatly improved even when the system is under serious dissipation. Moreover, the scheme works in both the strong-coupling and weak-coupling regimes. It is also robust to the ratio of the coupling constant between the atoms and the cavity modes to the coupling constant between the fiber and cavity modes. The underlying mechanism can be attributed to the probabilistic nature of weak measurements.

Entropic uncertainty for spin-1/2 XXX chains in the presence of inhomogeneous magnetic fields and its steering via weak measurement reversals

The uncertainty principle configures a low bound to the measuring precision for a pair of non-commuting observables, and hence is considerably nontrivial to quantum precision measurement in the field of quantum information theory. In this letter, we consider the entropic uncertainty relation (EUR) in the context of quantum memory in a two-qubit isotropic Heisenberg spin chain. Specifically, we explore the dynamics of EUR in a practical scenario, where two associated nodes of a one-dimensional XXX-spin chain, under an inhomogeneous magnetic field, are connected to a thermal entanglement. We show that the temperature and magnetic field effect can lead to the inflation of the measuring uncertainty, stemming from the reduction of systematic quantum correlation. Notably, we reveal that, firstly, the uncertainty is not fully dependent on the observed quantum correlation of the system; secondly, the dynamical behaviors of the measuring uncertainty are relatively distinct with respect to ferromagnetism and antiferromagnetism chains. Meanwhile, we deduce that the measuring uncertainty is dramatically correlated with the mixedness of the system, implying that smaller mixedness tends to reduce the uncertainty. Furthermore, we propose an effective strategy to control the uncertainty of interest by means of quantum weak measurement reversal. Therefore, our work may shed light on the dynamics of the measuring uncertainty in the Heisenberg spin chain, and thus be important to quantum precision measurement in various solid-state systems.

Protecting Quantum Correlation from Correlated Amplitude Damping Channel

In this work, we investigate the dynamics of quantum correlation measured by measurement-induced nonlocality (MIN) and local quantum uncertainty (LQU) in correlated amplitude damping (CAD) channel. We find that the memory parameter brings different influences on MIN and LQU. In addition, we propose a scheme to protect quantum correlation by executing prior weak measurement (WM) and post-measurement reversal (MR). However, better protection of quantum correlation by the scheme implies a lower success probability (SP).