Abstract Variational quantum algorithms (VQAs) have dominated literature as tools for demonstrating quantum utility on near-term quantum hardware, with applications in optimisation, quantum simulation, and machine learning. While researchers have studied how easy VQAs are to train, the effect of quantum noise on the classical optimisation process is still not well understood. Contrary to expectations, we find that twirling, which is commonly used in standard error-mitigation strategies to symmetrise noise, actually degrades performance in the variational setting, whereas preserving biased or non-unital noise can help classical optimisers find better solutions. Analytically, we study a universal quantum regression model and demonstrate that relatively uniform Pauli channels suppress gradient magnitudes and reduce expressivity, making optimisation more difficult. Conversely, asymmetric noise such as amplitude damping or biased Pauli channels introduces directional bias that can be exploited during optimisation. Numerical experiments on a variational eigensolver for the transverse-field Ising model confirm that non-unital noise yields lower-energy states compared to twirled noise. Finally, we show that coherent errors are fully mitigated by re-parameterisation. These findings challenge conventional noise-mitigation strategies and suggest that preserving noise biases may enhance VQA performance.

Recent advances in quantum communication and quantum error correction (QEC) have motivated hybrid architectures that exploit quantum resources to enhance multimedia transmission. However, practical quantum hardware remains constrained in qubit count, making it unrealistic to apply full scale QEC to every pixel of an image. To address this, we propose a hybrid framework combining Adaptive Multi-Qubit Encoding (AMQE) with selective Quantum Low-Density Parity-Check (QLDPC) protection. The proposed solution is demonstrated for the case of image data. Our work provides a resource-efficient pathway for high-quality quantum media transmission. The system partitions the image into blocks and assigns an importance score based on local variance. High-importance blocks structural features are encoded into multi-qubit superposition states and embedded into the logical subspace of a high-rate lifted-product QLDPC code. Low-importance blocks background are transmitted with lightweight AMQE encoding. We model the channel using realistic amplitude - damping noise. Numerical simulations show that this selective protection strategy decouples perceptual quality from physical noise limits. The proposed architecture maintains a Peak Signal-to-Noise Ratio (PSNR) above 40 dB in noise regimes where classical baselines fail. The framework also retains high-structural fidelity, maintaining the Structural Similarity Index Measure (SSIM) more than 0.98, confirming robust preservation of key visual features under amplitude - damping noise. Furthermore, we demonstrate that the proposed QLDPC architecture outperforms Quantum Polar codes at finite block lengths due to the steeper error suppression slope of the Belief Propagation - Ordered Statistics Decoding (BP - OSD).

Abstract We explore how thermal fluctuations and noisy decoherence affect non-classical correlations and entropic uncertainty relations in a perylene-bisimide (PBI) dimer system represented by two coupled molecular two-level systems. The composite Hamiltonian includes dipole-dipole interaction between the monomers, and the system's initial state is considered the thermal Gibbs state, which exhibits entanglement at a finite temperature. Environmental noise is introduced through amplitude damping, phase damping, and phase-flip channels, allowing us to trace the evolution of logarithmic negativity, trace distance discord, and the quantum-memory-assisted entropic uncertainty relation (QMA-EUR). The investigation demonstrates that entanglement decays rapidly with increasing temperature and decoherence strength, whereas trace discord remains resilient over a more comprehensive parameter range. This robustness suggests that PBI dimers can retain useful quantum resources under realistic environmental conditions, highlighting their potential as building blocks for molecular quantum information devices.

Abstract We study the dynamics of skew information (SI)-based nonlocal advantage of quantum coherence (NAQC) in amplitude damping channels. For Bell states used as initial states, it is shown that the dynamics of SI-based NAQC is very similar, namely, it decreases monotonically and exists in finite time. To enhance SI-based NAQC for further applications, weak measurements and quantum measurement reversals (QMRs) are jointly performed for the initial Bell states <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mi>ϕ</mml:mi> <mml:mrow> <mml:mo>±</mml:mo> </mml:mrow> </mml:msub> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mn>00</mml:mn> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo>±</mml:mo> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mn>11</mml:mn> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msqrt> <mml:mn>2</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> . While for the initial Bell states <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mi>φ</mml:mi> <mml:mrow> <mml:mo>±</mml:mo> </mml:mrow> </mml:msub> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mn>01</mml:mn> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo>±</mml:mo> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mn>10</mml:mn> <mml:mo fence="false" stretchy="false">⟩</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msqrt> <mml:mn>2</mml:mn> </mml:msqrt> </mml:mrow> </mml:math> , SI-based NAQC can be remarkably enhanced only by QMRs. Finally, an all-optical experimental proposal is presented, and the experimental feasibility is also analyzed.

We study the dissipative dynamics of a hybrid qubit–qutrit system initially prepared in the interacting thermal (Gibbs) state of the full Hamiltonian and subsequently subjected to a non-Markovian amplitude-damping channel. To benchmark the persistence of nonclassical features in this noisy setting, we track four complementary quantum resources: entanglement via negativity (NEG), nonclassical correlations via geometric quantum discord (GQD), coherence via the [Formula: see text]-norm of coherence (LNC) and measurement-induced quantumness via local quantum uncertainty (LQU). We show that coherent exchange coupling g enhances both the initial magnitudes and lifetimes of all resources by strengthening qubit–qutrit hybridization, whereas strong dispersive (cross-Kerr) coupling [Formula: see text] suppresses thermal correlations already at [Formula: see text], thereby limiting the resources available before dissipation sets in. Environmental memory effects, controlled by the reservoir cutoff frequency, slow the decay and can induce some revival pattern–assisted decay, extending the operational time window slightly. Across a broad parameter range, coherence (LNC) is consistently the most robust resource, often persisting after entanglement and discord have decayed, indicating that coherence-based protocols may provide superior stability in noisy hybrid architectures.

Abstract I will investigate the capacities of noisy quantum channels through a combined analytical&amp;#xD;and numerical approach. First, I introduce novel flagged extension techniques that embed&amp;#xD;a channel into a higher-dimensional space, enabling single-letter upper bounds on&amp;#xD;quantum and private capacities. My results refine previous bounds and clarify noise&amp;#xD;thresholds beyond which quantum transmission vanishes. Second, I present a simulation&amp;#xD;framework that uses coherent information to estimate channel capacities in practice,&amp;#xD;focusing on two canonical examples: the amplitude damping channel (which we confirm is&amp;#xD;degradable and thus single-letter) and the depolarizing channel (whose capacity requires&amp;#xD;multi-letter superadditivity). By parameterizing input qubit states on the Bloch sphere, I&amp;#xD;numerically pinpoint the maximum coherent information for each channel and validate the&amp;#xD;flagged extension bounds. Notably, I capture the abrupt transition to zero capacity at high&amp;#xD;noise and observe superadditivity for moderate noise levels.

Abstract In this paper, we consider an efficient dual-hop quantum communication network with multiple senders or nodes, a repeater, and a receiver. We derive closed-form expressions for the system quantum outage probability (QOP) assuming time-varying amplitude damping (TVAD) quantum channels. In addition, closed-form expressions for the quantum hashing outage probability of two approximated quantum channels, namely TVAD Pauli twirl approximated (TVADPTA) and TVAD Clifford twirl approximated (TVADCTA) channels are also provided. These channels are efficient in modeling the simplest kind of noise in quantum devices. Opportunistic node scheduling is proposed, for the first time, to select among sending nodes, where the node of the largest relaxation time T 1 is allowed to transmit to repeater, which in turn communicates with receiver. The impact of various system parameters, including number of sending nodes K , coefficient of variation of relaxation time ϵ , code rates of both hops, channel damping parameter γ , and channel noise limit γ l ( R ) on the system performance is investigated. Findings show that for the case where first hop is dominating the system performance, the more the number of nodes, the better the achieved performance. This gain starts to vanish once the second hop starts dominating the system performance. For good quality channels, more nodes are needed in order for second hop to dominate the system performance compared to the case of low quality channels. Finally, results illustrate that for higher values of ϵ , and in order to achieve a certain target QOP, both nodes and repeater need to adapt their transmission rates to the optimum values.

Abstract This paper systematically investigates the coherence dynamics of a two-qubit system under correlated channels. Through density matrix transformation and operator algebra derivation, we analyze the regulatory effects of memory properties of correlated amplitude damping, phase damping, and depolarization channels on three kinds of coherence, namely l 2 -norm coherence, Tsallis 2-relative entropy coherence, and Rényi 2-relative entropy coherence. The results show that phase damping and depolarization channels induce coherence freezing under perfect memory conditions, where coherence values remain invariant with channel damping rate variations. In partial memory environments, l 2 -norm coherence exhibits superior stability and retains coherence more efficiently than the other two coherence measures. In addition, we quantitatively evaluate the cohering and decohering power of these coherences under the correlated amplitude damping channel. This work provides theoretical support for anti-noise design of quantum technologies in open quantum systems.

Abstract This work investigates the dynamics of quantum correlations and entanglement in a thermal bipartite dipolar spin system with Dzyaloshinskii–Moriya (DM) interaction, subjected to both Markovian and non-Markovian noise. By analyzing amplitude damping and random telegraph noise channels, we derive explicit analytic forms for the thermal density matrix and quantify coherence, concurrence, quantum discord, local quantum uncertainty (ℒ𝓠𝒰), and teleportation fidelity. Our results reveal that the interplay of temperature and DM interaction crucially governs the robustness of quantum resources. In particular, non-Markovian regimes exhibit memory-induced oscillatory revivals, while Markovian channels produce irreversible decay. Importantly, we identify a hierarchy of robustness, with coherence being more resilient than discord, which in turn surpasses entanglement and ℒ𝓠𝒰, providing design principles for preserving quantum correlations. These findings extend existing open-system studies by highlighting the role of DM interaction and dipolar coupling in tailoring noise resilience, offering practical implications for solid-state spintronics and quantum communication.

Abstract We study the influence of memory effects on quantum Stackelberg duopoly game through amplitude-damping channel where successive uses of the channels are correlated. It is shown that the memory effects can drastically change the Nash equilibrium and the payoffs of the two firms. As the degree of channels memory increases, there exists a Nash equilibrium for the entire range of entanglement parameter. Similarly, the presence of memory ensures existence of the Nash equilibrium for the whole range of decoherence parameter both for entangled and unentangled initial states. Moreover, quantum memory leads to a ’critical point’ of the damping parameter, at which both firms are equally benefited. With the maximum-memory effect, the position of the ’critical point’ moves to the place of fully decohered.

Abstract We present a theoretical investigation of weak-value amplification under decoherence, quantifying its metrological capabilities through the quantum Fisher information. By modeling decoherence via Kraus operators acting before and after the weak measurement interaction, we derive exact expressions for the QFI governing parameter estimation of a weak coupling strength. These analytical results reveal the fundamental limitation imposed by decoherence on the QFI achievable via WVA. From these results, the optimal post-selection state that maximizes the QFI can be derived for different noise environments. Through paradigmatic examples including amplitude damping and depolarizing channels, we demonstrate a key distinction: the optimal post-selection evolves with the noise strength in the amplitude damping channel, but is fixed in the depolarizing channel. This work provides both theoretical insights and practical guidance for optimizing metrological schemes based on weak-value amplification in realistic decoherent environments.

Abstract We study the performance of high-dimensional superdense coding (HD-SDC) over an amplitude damping (AD) channel with memory, and propose a protocol that leverages partial measurement and its reversal to enhance the channel capacity. By considering two qutrit-based system, we model the memory AD noise using a convex mixture of memoryless and perfectly memory AD channels. We demonstrate that memory effect alone can mitigate the decay of the SDC capacity under noise. More significantly, we show that the application of partial measurement before the channel and its reversal after the channel can not only recover the capacity degraded by noise but, for certain non-maximally entangled initial states, even amplify it beyond the initial capacity. This amplification effect is governed by three key factors: the ground-state probability in the initial entangled state, the memory strength, and the partial measurement strength. Our results provide a practical strategy for enhancing quantum communication protocols in realistic noisy environments and highlight the synergistic benefits of memory noise and measurement-based control.

We introduce a universal method for accelerating Lindblad dynamics that preserves the original trajectory through Hilbert space. The technique provides exact, fast processes analytically, which are Markovian and do not require manipulation of the environment properties, by time-rescaling a reference dynamics. In particular, the engineered control protocols are based only on local interactions, and no additional control fields are required compared to the reference protocol. We demonstrate the scheme with two examples: a driven two-level system in an amplitude damping channel and the dissipative transverse field Ising model. We also show that, by starting with a reference process, which is the fastest connecting two states under a certain constraint, the method provides other optimal processes satisfying modified constraints. Our approach can help advance techniques for quantum control and computation toward more complex noisy systems.

Abstract In the field of quantum error mitigation, most current research separately addresses quantum gate noise mitigation and measurement noise mitigation. However, due to the typically high complexity of measurement noise mitigation methods, such as those based on estimating response matrices, the overall complexity of noise mitigation schemes increases when combining measurement noise mitigation with other quantum gate noise mitigation approaches. This paper proposes a low-complexity quantum error mitigation scheme that jointly mitigates quantum gate and measurement noise, specifically when measurement noise manifests as an amplitude damping channel. The proposed scheme requires estimating only three parameters to jointly mitigate both types of noise, whereas the zero-noise extrapolation method enhanced by response matrix estimation requires estimating at least six parameters under the same conditions.

In this paper, we present an application of the variational quantum simulation (VQS) framework to capture finite temperature open system dynamics on near-term quantum hardware. By embedding the generalized amplitude damping channel into the VQS algorithm, we model energy exchange with a thermal bath through its Lindblad representation and thereby simulate realistic dissipative effects. To explore a wide range of activation behaviors, we introduce a nonadditive relaxation time model using a generalized form of the Arrhenius law, based on the phenomenological parameter q. We compare our method on driven qubit systems subject to both static and composite time-dependent fields, comparing population evolution and trace distance errors against reference numerical solutions. Our results demonstrate that (1) VQS accurately maps the effective nonunitary generator under GAD, (2) smoother drive envelopes induced by nonaddtive parameters suppress high-frequency components and yield lower simulation errors, and (3) the variational manifold exhibits dynamical selectivity, maintaining mapping fidelity even as the reference numerical solution's sensitivity to q increases.

Measuring complex properties in quantum systems, such as measures of quantum entanglement and Bell nonlocality, is inherently challenging. Traditional methods, like quantum state tomography (QST), require a full reconstruction of the density matrix for a given system and demand resources that scale exponentially with system size. We propose an alternative strategy that reduces the required information by combining multicopy measurements with artificial neural networks (ANNs), resulting in a 67% reduction in measurement requirements compared to QST. We have successfully measured two-qubit quantum correlations of Bell states subjected to a depolarizing channel (resulting in Werner states) and an amplitude-damping channel (leading to Horodecki states) using the multicopy approach on real quantum hardware. Our experiments, conducted with transmon qubits on IBMQ quantum processors, quantified the violation of Bell's inequality and the negativity of two-qubit entangled states. We compared these results with those obtained from the standard QST approach and applied a maximum likelihood method to mitigate noise. We trained ANNs to estimate degrees of entanglement and nonlocality measures using optimized sets of projections identified through Shapley's (SHAP) analysis for the Werner and Horodecki states. The ANN output, based on this reduced set of projections, aligns well with expected values and enhances noise robustness. This approach simplifies and improves the error robustness of multicopy measurements, eliminating the need for complex nonlinear equation analysis. It represents a significant advancement in AI-assisted quantum measurements, making the practical implementation on current quantum hardware more feasible. The experimental results demonstrate improved noise robustness on the current noisy intermediate-scale quantum (NISQ) hardware, representing a practical advance in resource-efficient characterization of quantum correlations.

We give the detailed processes for sharing a four-qubit pure entangled state as quantum channel in amplitude damping (AD) network channel via entanglement compensation.We propose a secure (2,2)-type quantum teleportation (QT) scheme based on this AD network channel, which allows 2-dimensional quantum information shared by 2 senders to be teleported to 2 receivers in such a way that after performing two Bell-state measurements by two senders, the original target state can be probabilistically reconstructed through introducing an auxiliary qubit and executing appropriate local unitary operations provided that all the receivers collaborate. We then extend it to the transmission of a 2-dimensional quantum secret state shared by n senders to m receivers (i.e., (n,m)-type QT of shared 2-dimensional quantum secret) from the perspectives of projective measurement, positive-operator-valued measurement (POVM) and generalized Bell-state measurement. Furthermore, we generalize the above (n,m)-type QT to the case of transmitting a shared d-dimensional quantum secret state. Our approach enables efficient and distributed quantum information relay, eliminating the need for a fully trusted central or intermediary node. The results show that our schemes achieve unit fidelity, though the success probabilities are less than 1. More interestingly, the QT protocol for high-dimensional quantum states exhibits a higher success probability than low-dimensional states under equivalent AD conditions.

Abstract Achieving high‐fidelity quantum teleportation requires the distribution of maximally entangled states through noiseless channels, a condition rarely met in practical implementations. In realistic environments, decoherence processes, such as amplitude damping, severely degrade entanglement quality. In this study, a universal strategy is proposed for protecting entanglement against amplitude damping noise by introducing escort qubits—ancillary qubits specifically designed to assist in the distribution process. This method involves CNOT operations and measurement of the escort qubits. Modeling the amplitude damping channel with a Lindblad master equation, it is showed analytically that the method achieves unit fidelity under ideal operations, independent of the damping rate, with a certain success probability. This method is applied to teleportation with Bell and W states, and compare its performance with weak measurement and environment‐assisted measurement protocols. This approach offers superior fidelity, experimental feasibility, and independence from noise parameters, as confirmed through simulation and Qiskit implementation.

In this paper, two conclusive three-party cyclic assisted cloning protocols in amplitude damping (AD) channel are put forward that, respectively clone three arbitrary unknown single-qubit states and single-qutrit states with the help of a state preparer. Each of our protocols includes three consecutive stages: quantum channel preparation, cyclic quantum teleportation (CQT), and multi-party assisted cloning. The first stage of each protocol proposes the detailed processes of sharing a pure entangled quantum state as a component of a quantum channel in AD channel via entanglement compensation. In second stage, a three-party CQT is presented where three unknown single-qubit states (or single-qutrit states) are reconstructed simultaneously in three different places, respectively, by introducing auxiliary qubits and performing appropriate operations. In the third stage, the state preparer Victor performs one multi-qubit measurement (or one unitary transformation and one multi-qutrit measurement) and informs the three communicators of his outcome, three distinct unknown single-qubit states or their orthogonal complement states (or single-qutrit states) are cloned simultaneously and with probability at three separate locations,respectively. Furthermore, we extend the above protocols from two aspects: (i) the extension to the case of participants; (ii) extension to the case of d-dimensional unknown single-qudit state cycle-assisted cloning.

Alzheimer's disease (AD) presents significant diagnostic challenges owing to the subtle morphological similarities observed in the early stages, with traditional deep learning approaches often struggling to distinguish between the various stages of disease progression via structural Magnetic Resonance Imaging (MRI) data. Quantum computing offers unique advantages for medical image analysis, leveraging superposition and entanglement capabilities to process high-dimensional feature spaces beyond the limits of classical computation. This study introduces a hybrid quantum-classical neural network architecture (HQC-Net) for accurate four-class Alzheimer's disease classification, which uses quantum processing to detect patterns that are often invisible to classical spatial analysis methods. The proposed framework integrates classical feature extractors, including a custom CNN and modified ResNet18, with six-qubit variational quantum circuits that employ multiaxis rotation encoding (RY→RZ→RX), a quantum Fourier transform for spectral decomposition, and multihead attention for effective quantum-classical feature fusion. Comprehensive evaluations were conducted on the Kaggle dataset (5,121 samples) and the OASIS dataset (20,000 samples), incorporating realistic quantum noise modelling, including depolarising, amplitude damping, and phase damping channels. The modified QResNet18 configuration achieved a test accuracy of 99.67%, with perfect discriminative capability (AUC = 1.0000) on the OASIS dataset. Quantum processing demonstrated superior detection of very mild dementia (99.86% accuracy), which is crucial for early intervention. The proposed approach outperformed existing quantum-enhanced methods by 3.57 percentage points while effectively handling the increased diagnostic complexity associated with four-class classification. This study demonstrates a practical quantum advantage for multiclass neuroimaging classification, achieving superior diagnostic accuracy while maintaining computational efficiency and clinical deployment feasibility under current Noisy Intermediate-Scale Quantum (NISQ) hardware constraints.