The protection schemes of the entanglement in the system of two entangled atoms from nonMarkovian reservoirs via previous Weak measurement (pre-WM) and posterior Weak measurement reversal (post-WMR) are investigated. We firstly compare the effects of combination applying of pre-WM and post-WMR (scheme 1) and twice Weak measurements (WMs) (scheme 2) in the condition of different initial entangled states. The analysis indicates that the protection performance of scheme 1 is much better than that of scheme 2. The scheme 1 was utilized when the system of two entangled atoms suffers from the independent reservoirs. The numerical results show that the combination of pre-WM and post-WMR can effectively enhance entanglement and shorten the time of Entanglement sudden death (ESD) in non-Makovain environment. We have found the optimum of WM strengthens is drastically related to the initial entangled state.
The protection schemes of the entanglement in the system of two entangled atoms from nonMarkovian reservoirs via previous Weak measurement (pre-WM) and posterior Weak measurement reversal (post-WMR) are investigated. We firstly compare the effects of combination applying of pre-WM and post-WMR (scheme 1) and twice Weak measurements (WMs) (scheme 2) in the condition of different initial entangled states. The analysis indicates that the protection performance of scheme 1 is much better than that of scheme 2. The scheme 1 was utilized when the system of two entangled atoms suffers from the independent reservoirs. The numerical results show that the combination of pre-WM and post-WMR can effectively enhance entanglement and shorten the time of Entanglement sudden death (ESD) in non-Makovain environment. We have found the optimum of WM strengthens is drastically related to the initial entangled state.
Based on the quantum technique of the weak measurement and quantum measurement reversal (WMR), we propose a scheme to protect entanglement for an entangled two-qubit pure state from four typical quantum noise channels with memory, i.e., the amplitude damping channel, the phase damping channel, the bit flip channel, and the depolarizing channel. For a given initial state | ψ 〉 = a| 00 〉 + d| 11 〉, it is found that the WMR operation indeed helps to protect entanglement from the above four quantum channels with memory, and the protection effect of WMR scheme is better when the coefficient a is small. For the other initial state | ϕ 〉 = b| 01 〉 + c| 10 〉, the effect of the protection scheme is the same regardless of the coefficient b and the WMR operation can protect entanglement in the amplitude damping channel with memory. Moreover, the protection of entanglement in quantum noise channels without memory in contrast to the results of the channels with memory is more effective. For | ψ 〉 or | ϕ 〉, we also find that the memory parameters play a significant role in the suppression of entanglement sudden death and the initial entanglement can be drastically amplified. Another more important result is that the relationship between the concurrence, the memory parameter, the weak measurement strength, and quantum measurement reversal strength is found through calculation and discussion. It provides a strong basis for the system to maintain maximum entanglement in the nosie channel.
We investigate the protection of quantum correlations of two qubits in independent vacuum reservoirs by means of weak measurements. It is found that the weak measurement can reduce the amount of quantum correlation for one type of initial state at the beginning in a non-Markovian environment and meanwhile it can reduce the occurrence time of entanglement sudden death (ESD) in the process of time evolution. In a Markovian environment, the quantum entanglements of the two kinds of initial states decay rapidly and the weak measurement can further weaken the quantum entanglement, therefore in this case the entanglement cannot be optimized in the evolution process.
Abstract In this work, a scheme to protect quantum entanglement from a non‐Markovian noisy environment is proposed. By applying two quantum weak measurements before and after sending the quantum state into the noisy channel, the quantum state can be “pushed” closer to a decoherence‐free state, reducing decoherence during the time evolution. Then, the second weak measurement can partially retrieve the initial quantum state from the state corrupted by the noisy environment. The study involves a non‐Markovian dynamic equation to examine the impact of the memory effect on the protection scheme's performance. Various factors affecting the residual entanglement and the success probability are analyzed. The results suggest that two measurement strengths shall be chosen approximately in a linear relation, with the best ratio determined by the memory time of the environment. Additionally, it is demonstrated that the memory effect significantly enhances the protection efficiency. Lastly, the scheme's robustness against systematic errors is evaluated.
Abstract Entangled states with high-dimensional systems have been investigated widely because of its various advantages. This paper investigates the effect of the weak measurement and reversal (WMR) on the protection of the entanglement for an arbitrarily entangled qutrit–qutrit state from the amplitude-phase decoherence sources. By solving the master equation of the qutrit–qutrit system, we numerically get the maximal amount of entanglement. The numerical results show explicitly that the WMR operation indeed helps for protecting entanglement from amplitude-phase decoherence. In particular, WMR can protect entanglement more efficiently in the case of strong decay rates than those with small decay rates. These results shed new light on the protection of high-dimensional quantum entanglement in a complex quantum environment.
According to the map of a qubit, a scheme for protecting entanglement of two-qubit by the weak measurements at finite temperature is proposed. Since the choices of the channel parameters and initial states are very different for different weak measurement strengths, two local unitary equivalent initial entangled states |ψ> and |φ> are chosen. Weak measurements are performed when two initial entangled states go through the generalized amplitude damping channel, and the analytical expressions of getting maximum concurrence entanglement Cr and weak measurement parameters m and n can be obtained by performing an overall optimization for four weak measurement parameters. What is more, the relationship between the weak measurement parameters and the channel parameters is further explored. Theoretical results show the entanglement protection project based on weak measurements can effectively enhance the entanglement and even prevent the sudden death of entanglement in some cases. When the channel parameter r is fixed, for different values of parameter p, the concurrence is centered at p = 0.5, and the weak measurement parameters of the maximum concurrence entanglement are the same as those for initial state |ψ>, while they are different for initial state |φ>. Under the condition of different values of r, for the fixed p and initial state |ψ> or |φ>, the weak measurement parameters remain constant as the entanglement reaches the maximum and the concurrence decreases with the increase of parameter r. Through the analysis of channel parameters, higher entanglement can be obtained by choosing appropriate channel parameters and initial state.
Abstract The weak measurement (WM) and quantum measurement reversal (QMR) are crucial in protecting the collapse of quantum states. The idea of WM and QMR has recently been used to protect and enhance quantum correlations and universal quantum teleportation (UQT) protocols. Here, we study the quantum correlations, maximal fidelity, and fidelity deviation of the two-qubit negative quantum states developed using discrete Wigner functions with(without) WM and QMR. To take into account the effect of a noisy environment, we evolve the states via non-Markovian amplitude damping and random telegraph noise quantum channels. To benchmark the performance of negative quantum states, we calculate their success probability. We compare our results with the two-qubit maximally entangled Bell state. Interestingly, we observe that some negative quantum states perform better with WM and QMR than the Bell state for different cases under evolution via noisy quantum channels.