Pseudo-entropy is a complex-valued generalization of entanglement entropy defined on non-Hermitian transition operators and induced by post-selection. We present a simulation-based protocol for detecting nonclassicality and coherent errors in quantum circuits using this pseudo-entropy measure Sˇ, focusing on its imaginary part ℑSˇ as a diagnostic tool. Our method enables resource-efficient classification of phase-coherent errors, such as those from miscalibrated CNOT gates, even under realistic noise conditions. By quantifying the transition between classical-like and quantum-like behavior through threshold analysis, we provide theoretical benchmarks for error classification that can inform hardware calibration strategies. Numerical simulations demonstrate that 55% of the parameter space remains classified as classical-like (below classification thresholds) at hardware-calibrated sensitivity levels, with statistical significance confirmed through rigorous sensitivity analysis. Robustness to noise and comparison with standard entropy-based methods are demonstrated in a simulation. While hardware validation remains necessary, this work bridges theoretical concepts of nonclassicality with practical quantum error classification frameworks, providing a foundation for experimental quantum computing applications.
Pseudo-entropy is a complex-valued generalization of entanglement entropy defined on non-Hermitian transition operators and induced by post-selection. We present a simulation-based protocol for detecting nonclassicality and coherent errors in quantum circuits using this pseudo-entropy measure Sˇ, focusing on its imaginary part ℑSˇ as a diagnostic tool. Our method enables resource-efficient classification of phase-coherent errors, such as those from miscalibrated CNOT gates, even under realistic noise conditions. By quantifying the transition between classical-like and quantum-like behavior through threshold analysis, we provide theoretical benchmarks for error classification that can inform hardware calibration strategies. Numerical simulations demonstrate that 55% of the parameter space remains classified as classical-like (below classification thresholds) at hardware-calibrated sensitivity levels, with statistical significance confirmed through rigorous sensitivity analysis. Robustness to noise and comparison with standard entropy-based methods are demonstrated in a simulation. While hardware validation remains necessary, this work bridges theoretical concepts of nonclassicality with practical quantum error classification frameworks, providing a foundation for experimental quantum computing applications.
This research paper provides an in-depth examination of verification and testing approaches for quantum circuits, focusing on methodologies essential for ensuring the correctness, reliability and operational efficiency of quantum computing systems. Since quantum circuits function on the fundamental principles of superposition and entanglement, they present verification challenges that cannot be effectively addressed using conventional classical testing techniques. As a result, the development of specialized quantum-specific verification strategies has become critically important. The study highlights simulation-based verification as a foundational technique, wherein the outcomes of quantum circuit simulations are systematically compared with results obtained from physical quantum hardware. This process enables the identification of functional inconsistencies and supports iterative refinement of circuit designs. In addition, randomized benchmarking is examined as a key evaluation method for estimating circuit fidelity and quantifying error rates through the application of random gate sequences and performance comparisons against established benchmarks. To further improve system robustness, the research investigates fault-tolerant mechanisms, particularly quantum error correction codes, which play a vital role in minimizing the effects of noise, decoherence and hardware imperfections. The integration of advanced quantum metrology and characterization techniques is also explored, enabling precise measurement and detailed analysis of quantum system behavior. These techniques provide deeper insights into circuit performance and contribute significantly to validation processes. By combining simulation-based verification, randomized benchmarking, fault-tolerant protocols and quantum metrology, this study proposes a comprehensive and reliable framework for quantum circuit verification and testing. The findings contribute to the advancement of dependable quantum technologies and support their growing applications in areas such as cryptography, materials science and other emerging domains.
Abstract Quantum discord has emerged as a resource that extends beyond entanglement, yet its operational role remains underexplored. In this work, we introduce the Measurement-Induced Coherence Transfer (MICT) framework as both a theoretical and experimental diagnostic for coherence transfer. The MICT-Discord analysis establishes thresholds, scaling behavior, and noise resilience, mapping the geometry of discord across entanglement and measurement parameters. Complementing this, the MICT-Benchmark validates these predictions on IBM Quantum hardware through teleportation, superdense coding, and QKD protocols. The comparative results between the simulator, the ideal state vector,and the hardware output reveal discord as a sensitive witness of backend stability and coherence degradation. Together, MICT-Discord and MICT-Benchmark provide a reproducible suite for evaluating quantum platforms, positioning Discord as a practical diagnostic tool. Future directions include multipartite discord (GHZ/W states), error correction primitives, dynamic circuits with feed-forward, and cross-architecture reproducibility.
A bstract Quantum informatic quantities such as entanglement entropy are useful in detecting quantum phase transitions. Recently, a new entanglement measure called pseudo-entropy was proposed which is a generalization of the more well-known entanglement entropy. It has many nice properties and is useful in the study of post-selection measurements. In this paper, one of our goals is to explore the properties of pseudo-entropy and study its effectiveness as a quantum chaos diagnostic, i.e., as a tool to distinguish between chaotic and integrable systems. Using various variants of the SYK model, we study the signal of quantum chaos captured in the pseudo-entropy and relate it to the spectral form factor (SFF) and local operator entanglement (LOE).
Measurement-induced phase transitions are a central paradigm in non-unitary quantum dynamics, arising from the interplay between unitary evolution and projective measurements. In this study, we analyze the robustness of measurement-induced Ising order under combined coherent rotation errors and stochastic measurement noise, using echo-protected quantum circuits simulated for system sizes .Our results show that magnetization remains above 0.8 for measurement noise up to in the largest system, demonstrating a substantial enhancement compared to unprotected circuits where the same threshold drops below 0.12. Finite-size scaling confirms consistent crossing of magnetization curves at the critical noise , independent of system size within numerical resolution. Fidelity analysis further reveals that global quantum coherence is more sensitive: decreases to 0.5 near , while magnetization still exceeds 0.7, emphasizing the difference between classical order and quantum state integrity.The derivative of fidelity with respect to measurement noise, exhibits a sharp peak around for , providing a clear numerical indicator of the critical point. The robustness metric highlights an operationally useful ordered phase that persists for quantifying the combined effect of classical correlations and state fidelity. Overall, echo protection improves the threshold by more than 50% compared to unprotected dynamics and stabilizes both classical and quantum observables under realistic noise.These findings demonstrate quantitatively that coherent error mitigation, combined with fidelity-based diagnostics, significantly enhances the stability and detectability of measurement-induced phases on near-term quantum devices
The nonclassicality of quantum states is a fundamental resource for quantum technologies and quantum information tasks, in general. In particular, a pivotal aspect of quantum states lies in their coherence properties, encoded in the nondiagonal terms of their density matrix in the Fock-state bosonic basis. We present operational criteria to detect the nonclassicality of individual quantum coherences that use only data obtainable in experimentally realistic scenarios. We analyze and compare the robustness of the nonclassical coherence aspects when the states pass through lossy and noisy channels. The criteria can be immediately applied to experiments with light, atoms, solid-state system, and mechanical oscillators, thus providing a toolbox allowing practical experiments to more easily detect the nonclassicality of generated states.
This manuscript introduces a computationally efficient method to calculate the nonlinearity of a quantum feature map, as well as a method for determining whether a quantum feature map will have a high concentration of quantum states. The technique analyzes quantum operators, through an extension of the functions of von Neumann entropy and state-transition pseudo-entropy, by deriving a method to extract the entropy of an operator. The technique is denoted as operator pseudo-entropy, is rigorously derived, and is generally complex valued; as with state-transition pseudo-entropy, complex values contain a lot of information about entanglement or nonlinearity. The characteristics of a class of quantum feature maps are rigorously shown. The operator pseudo-entropy is illuminated through experiments and compared with von Neumann entropy and state-transition pseudo-entropy. We end the manuscript with open questions and potential directions for further research.