Quantum Information Processing最新文献

We present three measures of the dynamical coherence of channels, which generalize several previous results. The measures are based on a generalized distance-like function between channels, such as a quantum divergence of channels, including the relative entropy and diamond distance. Free operations are considered to be detection-incoherent, creation-incoherent, and detection-creation incoherent. We consider free superchannels constructed from free pre- and post-processing channels. The new measures are monotone under free superchannels and convex.

An evolutionarily stable strategy (ESS) is a strategy that, once adopted by a population, cannot be invaded by any sufficiently rare alternative (mutant) strategy. We analyze evolutionary stability in an Eisert–Wilkens–Lewenstein (EWL) quantization of a symmetric (2times 2) coordination game, whose classical mixed equilibrium (p^*=1/2) is not an ESS. In the restricted two-parameter EWL strategy space, the corresponding quantum strategy is a strict symmetric Nash equilibrium and an ESS for every entanglement strength (gamma >0). In the full SU(2) strategy space it remains a Nash equilibrium, but in the unreduced game, in which every unitary is a distinct strategy, exact payoff duplicates preclude strictness and ESS for every pure strategy. For the agreement-payoff class, the payoff factors through a Bloch map; identifying payoff-equivalent unitaries gives the reduced space (U(1)backslash SU(2)cong S^2), where strictness and ESS are restored for (gamma >0). An arbitrarily small perturbation outside this class that preserves (p^*=1/2) yields a profitable deviation, so the reduced-space result is not generic.

Topological phases are widely expected to protect quantum information through symmetry-enforced degeneracies, yet the operational mechanisms underlying coherence protection are rarely resolved. We perform a mechanism-resolved study of a logical qubit encoded in the edge modes of the Su–Schrieffer–Heeger (SSH) model, using Lindblad master equation simulations to disentangle two independent protective effects: spatial localization of the edge-state wavefunctions and chiral symmetry pinning of the edge-state degeneracy. By continuously interpolating between chiral symmetry-breaking (on-site) and chiral symmetry-preserving (bond) noise, we find that the topological encoding shows a larger dynamical coherence advantage under on-site noise than under bond noise (protection factors 3.15 versus 2.12). Because the two channels carry different effective dephasing power, we normalize them to equal dissipation power and to equal trivial-encoding decay rate; the on-site advantage persists ((1.6times )) whenever the dissipation rate exceeds the finite-size edge splitting, so it is not a channel power artifact. The on-site protection factor grows with chain length (from 1.4 to 3.5) and saturates; the saturation value is (gamma )-independent below the bulk gap while the saturation length follows (N_{textrm{sat}}simeq 2+ln (1.68,w/gamma )/ln (w/v)). We derive the logical dephasing rate analytically from the Lindbladian and show that it reproduces the simulated coherence floor with no free parameters. The mechanism is subtle: Chiral symmetry contributes through an exact cancellation of the pure dephasing channel between the two edge states—which we confirm by a chiral-breaking control—while the length dependence is set by the edge hybridization splitting (Delta sim w(v/w)^N), whose scale is the localization length. Neither localization nor symmetry alone is the sole driver; symmetry fixes the height of the coherence floor while localization sets its length dependence. As a hardware benchmark, we execute the Trotterized dynamics on the IBM ibm_kingston superconducting processor: The qualitative dynamical contrast between encodings—monotonic edge population decay versus ballistic bulk oscillation—survives device noise up to a transpiled depth of 222, and a device-calibrated noise simulation with no fitted parameters reproduces the trivial-encoding loss and the depth dependence of the topological loss. This is a proof of execution of the dynamical signature, not a measurement of logical coherence.

We investigate how the quantum advantage in quantum illumination is determined by an interplay between entanglement and discord of the probe state. In particular, we consider a setup in which the probe is a maximally mixed marginal (MMM) state and the environmental state is completely mixed where the quantum advantage equals the amount of discord consumed for illumination. Through a conditional extremal analysis, we determine the range of accessible advantages for given values of entanglement and discord. At fixed discord, higher entanglement restricts the accessible advantage to higher values, making high entanglement sufficient for achieving high advantage. Conversely, at fixed entanglement, low discord limits the advantage to low values, indicating that high discord is necessary for high advantage in MMM states. These conclusions remain unchanged when alternative correlation measures, including relative entropy and Bures entanglement and geometric discord, are used. The consistency of our results across multiple conceptually distinct measures indicates that the observed resource-advantage relation is not an artifact of a specific quantifier, but a robust feature of the protocol within the family of MMM states. We finally find that in the high-noise regime (near-maximally-mixed state), quantum advantage is, to leading order, a linear function of the initial discord highlighting discord as the key resource for resilience to noise in the protocol.

We investigate the Dirac oscillator in the spacetime of a spinning cosmic string in the presence of a uniform magnetic field and an Aharonov–Bohm flux, obtaining exact analytical solutions for the relativistic spectrum and wave functions. The combined effects of curvature, rotation, and electromagnetic flux produce controllable shifts in the effective angular momentum and in the localization properties of the states. We compute the Shannon entropies in coordinate and momentum spaces and show that the geometric and topological parameters act as tunable resources for manipulating quantum uncertainty and information distribution in relativistic systems. Our results reveal how nontrivial spacetime backgrounds can be exploited to engineer quantum–information-relevant features, offering new pathways for relativistic quantum control and entropy-based quantum diagnostics.

Quantum key distribution (QKD) guarantees the theoretical security of communication based on the principles of quantum mechanics and serves as a core component of quantum communication networks. To address the challenge of enabling multi-user concurrent communication and improving transmission efficiency, the integration of dense wavelength division multiplexing (DWDM) technology with QKD protocols has emerged as an important research direction. This paper focuses on the performance of the MP-QKD protocol based on DWDM in multi-user scenarios, analyzing the impact of key parameters such as the number of channels, different noise type, channel isolation, classical channel power, and detector configuration on the system noise rate and secret key rate through numerical simulations. The results demonstrate that DWDM technology can enhance the total secret key capacity through multi-channel parallel transmission, while optimizing channel isolation, classical channel power, channel count, and detector configuration can effectively suppress noise interference and improve system performance. These findings provide useful guidance for the practical deployment of multi-user quantum communication networks with low noise and high performance.

The rapid development of quantum communication networks has highlighted the urgent need for physical-layer protection mechanisms that complement cryptographic protocols. While photonic systems provide low-loss transmission and high-fidelity quantum state manipulation, they remain vulnerable to side-channel leakage and electromagnetic probing. Plasmonic nanostructures, on the other hand, offer extreme field confinement and tunable resonance properties, enabling adaptive shielding against external interrogation. In this work, we propose a hybrid plasmonic–photonic cloaking framework designed to enhance the security of quantum communication channels. The architecture integrates metamaterial-based plasmonic layers with photonic waveguides to dynamically suppress scattering signatures, minimize information leakage, and preserve quantum coherence. Analytical modeling and numerical simulations demonstrate that the hybrid cloak achieves attenuation exceeding 40 dB in targeted probing bands while maintaining entanglement visibility above 90%. The results indicate that combining plasmonic resonance with photonic interference provides a scalable and reconfigurable defense strategy for next-generation quantum networks, including fiber-based, free-space, and satellite communication systems. This study establishes a foundation for multi-layered quantum security architectures where physical cloaking complements protocol-level cryptography.

Byzantine agreement (BA) enables all honest nodes in a decentralized network to reach consensus. In the era of emerging quantum technologies, classical cryptography-based BA protocols face inherent security vulnerabilities. By leveraging information-theoretically secure keys generated by quantum processing, such as quantum key distribution (QKD), and utilizing the one-time pad (OTP) and one-time universal hashing (OTUH) classical methods, we propose a quantum signed Byzantine agreement (QSBA) protocol based on the quantum signed message (QSM) scheme. This protocol achieves information-theoretic security using only QKD-shared key resources between network nodes, without requiring quantum entanglement or other advanced quantum resources. Compared to the recently proposed quantum Byzantine agreement (QBA), our QSBA achieves superior fault tolerance, extending the threshold from nearly 1/2 to an arbitrary number of malicious nodes. Furthermore, our QSBA significantly reduces communication complexity under the same number of malicious nodes. Simulation results in a 5-node twin-field QKD network highlight the efficiency of our protocol, showcasing its potential for secure and resource-efficient consensus in quantum networks.

While the effects of intrinsic decoherence on homogeneous Heisenberg spin chains are widely documented, hybrid lower-dimensional architectures remain less explored. In this work, we investigate a heterogeneous quantum system comprising a spin-1 (qutrit) and a spin-(frac{1}{2}) (qubit) coupled under the influence of an inhomogeneous magnetic field. Under the assumption that the system originates from an initial thermal state, we derive an exact analytical solution for the density matrix using the Milburn master equation. We monitor the dynamical evolution of several key quantumness measures including geometric quantum discord, von Neumann entropy, and concurrence with a particular focus on how intrinsic decoherence reshapes their temporal profiles. Our numerical and analytical results demonstrate that robust quantum correlations and high-degree entanglement can be successfully generated and preserved by carefully tuning both the decoherence rate and the magnetic field inhomogeneity parameter. Furthermore, we test the ultimate bounds of parameter estimation within this framework by evaluating the Quantum Fisher Information (QFI). The results reveal that estimation precision is highly sensitive to both the relative magnitude of the parameters and the specific QFI metric employed. Crucially, optimal estimation accuracy remains strictly confined to early interaction intervals, experiencing severe degradation as the system evolves toward its long-time steady state.

Quantum network routing is an area of research that primarily involves finding paths for entanglement swapping to distribute entangled qubit pairs (EPR) between two quantum nodes. This paper considers a “burst” variant of the problem. In this variant, if (d_{i}) EPR pairs are to be shared between quantum nodes (s_i) and (e_i), they have to be shared within a short pre-specified time interval that starts at time instant (ST_{i}) and ends at (ET_{i}). This is a natural requirement in the case of applications that need several shared EPR pairs, and the quantum memory is not long-lived, thereby imposing timing constraints. We first investigate a simple variant of the problem. Although simpler, it is still easily shown to be NP-hard. We study this variant by formulating and solving it as an integer linear programming (ILP), and designing a fast greedy heuristic algorithm for it. While the heuristic algorithm takes significantly less time to solve the problem than the ILP, we empirically observe that the solution seems to mimic that of the ILP formulation. Motivated by this, we generalize the greedy heuristic into a framework that can be easily adapted to yield different heuristics for different objective functions. A crucial feature of this greedy framework is that it splits the demands for EPR pairs among multiple paths and temporally. We finally present several heuristics under this framework for different variants of the problem—like starvation avoidance and minimizing the number of “spatial splits”—and compare their performance.