Correlated Amplitude Damping Research Articles

Quantum state reconstruction in a noisy environment via deep learning

Quantum noise is currently limiting efficient quantum information processing and computation, impacting on the fidelity and reliability of quantum states. In this work, we consider the tasks of reconstructing and classifying quantum states corrupted by the action of an unknown noisy channel using classical feed-forward neural networks. By framing reconstruction as a regression problem, we show how such an approach can be used to recover with fidelities exceeding 99% the noiseless density matrices of quantum states of up to three qubits undergoing noisy evolution, and we test its performance with both single-qubit (bit-flip, phase-flip, depolarizing, and amplitude damping) and two-qubit quantum channels (correlated amplitude damping). Furthermore, a critical aspect of our investigation involves also a comprehensive comparison between mean squared error and infidelity as loss functions. Our findings reveal that these two metrics yield comparable results in the context of state reconstruction. Moreover, we also consider the task of distinguishing between different quantum noisy channels, and show how a neural network-based classifier is able to solve such a classification problem with perfect accuracy.

Toward Realization of Universal Quantum Teleportation Using Weak Measurements

AbstractIn this manuscript, universal quantum teleportation in the presence of memory or memory‐less dynamics with applications of partial collapse measurement operators is analyzed. These results show that the combined effects of memory or non‐Markovianity, and weak measurements can lead to universal quantum teleportation (UQT). This study involves noise models of physical importance having characteristic Markovian and non‐Markovian regions, allowing one to observe a transition in quantum properties as one switches from non‐Markovian to Markovian dynamics. For this, the effects of different types of non‐Markovianity are characterized for efficient UQT, both due to the retention of correlations for a longer duration and due to information backflow. The memory effects arising from a correlated channel with or without weak measurements are analyzed further. Interestingly, this analysis for a correlated amplitude damping channel shows that memory effects are of significant advantage in minimizing the fidelity deviation. The presence of weak measurements further enhances the realization of UQT in the presence of memory. The ability of memory effects to achieve zero fidelity deviation at non‐zero time is interesting and of experimental importance.

Enhancing the capacity of quantum dense coding from correlated amplitude damping channel via non-Hermitian operation

Using the non-Hermitian operation approach, we propose a scheme to protect and enhance quantum dense coding from correlated amplitude damping (AD) decoherence. In contrast to the results of memoryless AD channel, we show that the memory effects play a significant role in the suppression of quantum dense coding sudden death. Moreover, we find that the damaged quantum dense coding can be effectively enhanced by using the non-Hermitian operation. Furthermore, the freezing phenomenon of quantum dense coding can be detected by using the optimal non-Hermitian operation.

Average steered coherence in correlated amplitude damping channel

The combined effects of memory effects due to correlated actions of the amplitude damping channel on two qubits and temporal correlations in the time evolution of each qubit on the average steered coherence (ASC) are explored. For the input Bell states, it is shown that the two kinds of memory effects are beneficial for enhancing ASC of the output states in a wide time region. In particular, the ASC is immune to decoherence for some input states if the actions of the amplitude damping channel are fully correlated. Moreover, in the infinite-time limit, the positive role of the non-Markovian effect on the steady-state ASC disappears, whereas the correlated actions of the channel are still beneficial to certain input states.

Enhancing the teleportation of quantum Fisher information under correlated amplitude damping decoherence

From the perspective of quantum information transmission, one may be interested in the teleportation of quantum Fisher information (QFI) which provides the optimal precision of parameter estimation. In this paper, we investigate the teleportation of QFI under the correlated amplitude damping (CAD) decoherence. It is found that the correlated effects play a positive role in improving the teleported QFI, but the impact of decoherence is still serious. Therefore, we propose two schemes, which are based on weak measurement (WM) and environment-assisted measurement (EAM), to enhance the teleportation of QFI under the CAD decoherence. The results show that both schemes can significantly improve the teleported QFI with a certain success probability. The findings of our study suggest that the correlated effects can significantly increase the success probabilities of these two schemes. A detailed comparison confirms that the EAM scheme is more efficient than the WM scheme in improving the teleportation of QFI.

Simulating open quantum dynamics on an NMR quantum processor using the Sz.-Nagy dilation algorithm

We experimentally implement the Sz.-Nagy dilation algorithm to simulate open quantum dynamics on a nuclear magnetic resonance quantum processor. The Sz.-Nagy algorithm enables the simulation of the dynamics of an $n$-qubit system using $n+1$ qubits. We experimentally simulate the action of three nonunitary processes, namely, a phase damping channel acting independently on two qubits, a two-qubit correlated amplitude damping channel, and a magnetic-field-gradient pulse acting on an ensemble of two coupled nuclear spin-$\frac{1}{2}$ particles. To evaluate the quality of the experimentally simulated quantum process, we perform convex-optimization-based full quantum process tomography to reconstruct the quantum process from the experimental data and compare it with the target quantum process to be simulated.

Protecting quantum coherence and entanglement in a correlated environment

Long-term preservation of quantum coherence and entanglement is indispensable for practical quantum computation. We study the evolution of quantum coherence and genuine multipartite concurrence of extended Werner like states transmitted through correlated amplitude damping (AD), phase damping (PD) and depolarizing (DP) channels. The results show that the decay rate of coherence is curtailed in the presence of correlation between successive actions of the channel. It is shown that the fragility of genuine multipartite entanglement due to decoherence can be protected to some significant amount by using the correlated channels. In fact, for even qubit Werner like states, coherence and entanglement exhibit freezing phenomenon, in which it remains intact against decohering environment in perfectly correlated phase damping and depolarizing channels. For multipartite GHZ-class states in a perfectly correlated channel, it is shown that entanglement sudden death (ESD) is circumvented in amplitude damping channel, and there is an entanglement sudden birth (ESB) for odd qubit systems in depolarizing channel. Further, we have established analytical relation between coherence and entanglement for completely uncorrelated and fully correlated quantum channels.

Protecting and enhancing entanglement from correlated amplitude damping channel via non-Hermitian operation

Using the non-Hermitian operation approach, we propose a scheme to protect and enhance entanglement from correlated amplitude damping decoherence. In contrast to the results of memoryless amplitude damping channel, we show that the memory effects play a significant role in the suppression of entanglement sudden death and induce the entanglement revival. Moreover, we find that the damaged entanglement can be effectively enhanced by using the non-Hermitian operation. Furthermore, the freezing phenomenon of entanglement can be detected by using the optimal non-Hermitian operation.

Complete Complementarity Relations in System–environment Decoherent Dynamics

We investigate the system-environment information flow from the point of view ofcomplete complementarity relations. We consider some commonly used noisy quantum channels:Amplitude damping, phase damping, bit flip, bit-phase flip, phase flip, depolarizing, and correlatedamplitude damping. By starting with an entangled bipartite pure quantum state, with the linearentropy being the quantifier of entanglement, we study how entanglement is redistributed and turnedinto general correlations between the degrees of freedom of the whole system. For instance, it ispossible to express the entanglement entropy in terms of the multipartite quantum coherence or interms of the correlated quantum coherence of the different partitions of the system. In addition,we notice that for the depolarizing and bit-phase flip channels the wave and particle aspects candecrease or increase together. Besides, by considering the environment as part of a pure quantumsystem, the linear entropy is shown to be not just a measure of mixedness of a particular subsystem,but a correlation measure of the subsystem with rest of the world.

Dense coding capacity in correlated noisy channels with weak measurement* *Project supported by the National Natural Science Foundation of China (Grant No. 12074027).

Capacity of dense coding via correlated noisy channel is greater than that via uncorrelated noisy channel. It is shown that the weak measurement and reversal measurement need to further improve their quantum dense coding capacity in correlated amplitude damping channel, but this improvement is very small in correlated phase damping channel and correlated depolarizing channel.

Enhancing entanglement of two-qubit states from amplitude damping channel using single-qubit unitary operation and local filtering operation

We propose a scheme to enhance entanglement from amplitude damping or correlated amplitude damping decoherence. We show that entanglement sudden death time can be prolonged by the initial single-qubit operation combined with local filtering operation. For the amplitude damping channel case, we give the optimal single-qubit operation for arbitrary pure state [Formula: see text]. For the correlated amplitude damping channel case, we find that single-qubit operation on the initial state can not only enhance the final entanglement but also avoid entanglement sudden death. Compared to the previous schemes, the optimal operations and local filtering operations used in our scheme are independent with the decay parameters of the environment.

Enhancing entanglement of assistance using weak measurement and quantum measurement reversal in correlated amplitude damping channel

Entanglement of assistance from multipartite to fewer partites (e.g., bipartite) entangled state via measurements is an important way for generating entanglement. Here, we study the dynamics of entanglement of assistance from a tripartite W-like state to a bipartite Bell-like state under correlated amplitude damping channel using weak measurement and quantum measurement reversal. Our results show that the correlation between environmental noises plays a positive role in enhancing the entanglement of assistance, and in particular, it also works very well for very large decoherence strength of channel. More importantly, we find that an almost maximal two-qubit entangled state in the total region of decoherence strength can be obtained from the originally W-like state with a better success probability. The proposed scheme provides an active way in combating the amplitude damping noises, which may have potential applications in quantum communication and distributed quantum computation.

The influence of correlated noise on the SDC protocol

In this paper, we study the simultaneous dense coding (SDC) protocol when the noise on consecutive uses of the channel has some partial correlations. Three typical kinds of correlated noise are studied, i.e., the correlated depolarizing channel, the correlated dephasing channel and the correlated amplitude damping channel. Three success probabilities of SDC are calculated to evaluate the influence of the correlated noise. The analytical expressions of the success probabilities as functions of the noise strength and the correlation level are given.

Quantum speed limit time for correlated quantum channel

Memory effects play a fundamental role in the dynamics of open quantum systems. There exist two different views on memory for quantum noises. In the first view, the quantum channel has memory when there exist correlations between successive uses of the channels on a sequence of quantum systems. These types of channels are also known as correlated quantum channels. In the second view, memory effects result from correlations which are created during the quantum evolution. In this work, we will consider the first view and study the quantum speed limit time for a correlated quantum channel. Quantum speed limit time is the bound on the minimal time which is needed for a quantum system to evolve from an initial state to desired states. The quantum evolution is fast if the quantum speed limit time is short. In this work, we will study the quantum speed limit time for some correlated unital and correlated non-unital channels. As an example for unital channels, we choose correlated dephasing colored noise. We also consider the correlated amplitude damping and correlated squeezed generalized amplitude damping channels as the examples for non-unital channels. It will be shown that the quantum speed limit time for correlated pure dephasing colored noise is increased by increasing correlation strength, while for correlated amplitude damping and correlated squeezed generalized amplitude damping channels quantum speed limit time is decreased by increasing correlation strength.

Enhanced Superdense Coding over Correlated Amplitude Damping Channel.

Quantum channels with correlated effects are realistic scenarios for the study of noisy quantum communication when the channels are consecutively used. In this paper, superdense coding is reexamined under a correlated amplitude damping (CAD) channel. Two techniques named as weak measurement and environment-assisted measurement are utilized to enhance the capacity of superdense coding. The results show that both of them enable us to battle against the CAD decoherence and improve the capacity with a certain probability. Remarkably, the scheme of environment-assisted measurement always outperforms the scheme of weak measurement in both improving the capacity and successful probability. These notable superiorities could be attributed to the fact that environment-assisted measurement can extract additional information from the environment and thus it performs much better.

Enhance quantum teleportation under correlated amplitude damping decoherence by weak measurement and quantum measurement reversal

A scheme which aims to protect the quantum teleportation from correlated amplitude damping decoherence is proposed. Comparing with the results of uncorrelated amplitude damping noise, we find that the correlated effects enable to improve the fidelity with the given decoherence parameter. Moreover, we show that the combination of weak measurement and quantum measurement reversal could drastically enhance the fidelity in both uncorrelated and correlated amplitude damping noise. Our results extend the ability of weak measurement as a technique in various quantum information processes which are affected by correlated noise.

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).

Protecting entanglement from correlated amplitude damping channel using weak measurement and quantum measurement reversal

Based on the quantum technique of weak measurement, we propose a scheme to protect the entanglement from correlated amplitude damping decoherence. In contrast to the results of memoryless amplitude damping channel, we show that the memory effects play a significant role in the suppression of entanglement sudden death and protection of entanglement under severe decoherence. Moreover, we find that the initial entanglement could be drastically amplified by the combination of weak measurement and quantum measurement reversal even under the correlated amplitude damping channel. The underlying mechanism can be attributed to the probabilistic nature of weak measurements.

Information transmission over an amplitude damping channel with an arbitrary degree of memory

We study the performance of a partially correlated amplitude damping channel acting on two qubits. We derive lower bounds for the single-shot classical capacity by studying two kinds of quantum ensembles, one which allows to maximize the Holevo quantity for the memoryless channel and the other allowing the same task but for the full-memory channel. In these two cases, we also show the amount of entanglement which is involved in achieving the maximum of the Holevo quantity. For the single-shot quantum capacity we discuss both a lower and an upper bound, achieving a good estimate for high values of the channel transmissivity. We finally compute the entanglement-assisted classical channel capacity.

Classical and quantum capacities of a fully correlated amplitude damping channel

We study information transmission over a fully correlated amplitude damping channel acting on two qubits. We derive the single-shot classical channel capacity and show that entanglement is needed to achieve the channel best performance. We discuss the degradability properties of the channel and evaluate the quantum capacity for any value of the noise parameter. We finally compute the entanglement-assisted classical channel capacity.