Quantum Information Processing最新文献

The advanced encryption standard (AES) is widely used and well studied for its efficiency and strong security. This paper presents well-balanced quantum circuit designs for the AES S-box by introducing the composite field ( F((2^4)^2) ) to replace the traditional field ( F(2^8) ), enabling the inversion to be decomposed into operations over ( F(2^4) ). This work reduces the quantum resource overhead required for implementing the S-box by decreasing the number of CNOT gates in the matrix multiplication, lowering the depth of T gates in both the inversion circuit and the multiplication circuit. Besides, the width for the S-box quantum circuits is also optimized in the inversion circuit and multiplication circuit. With the nonlinear key schedule, the resulting quantum circuit AES-128 reduces the product of the circuit width and T depth to 102,800, which is the lowest known to date.

In this work, we investigate the performance of non-Gaussian entangled resources in continuous-variable quantum teleportation within a realistic setting. We describe the characteristic functions of three distinct entangled resources, a two-mode squeezed vacuum state, a two-mode photon-subtracted squeezed state, and a two-mode photon-added squeezed state. We extend the theoretical analysis by Yang et al. (Phys Rev A 80:022315, 2009) to include the realistic experimental conditions such as photon losses, imperfect measurements which typically affect continuous-variable quantum teleportation. Our results demonstrate that even in non-ideal situations, the photon-subtracted squeezed state outperforms the other two resources in the low squeezing regime, keeping fidelity above the classical threshold that suggests the robustness of photon-subtracted squeezed state in practical teleportation applications. We further analyze the EPR correlations of these entangled resources, revealing that the photon-subtracted squeezed state exhibits stronger EPR correlations than the original two-mode squeezed vacuum state and the two-mode photon-added squeezed state. We incorporate an entanglement-based and a prepare-and-measure continuous-variable quantum key distribution (CV-QKD) schemes to illustrate the practical feasibility of the proposed model. We calculate the secure key rate for the two-mode squeezed state in the entanglement-based protocol, linking the analyzed correlations directly to practical quantum communication performance. Besides photon addition or subtraction, we employ zero-photon quantum catalysis operation that significantly improves the performance of continuous-variable quantum key distribution without adding photons. This study considers theoretical models with realistic imperfections and employs non-Gaussian entanglement to enable high-fidelity quantum teleportation.

We propose a straightforward method to determine the maximal entanglement of pure states using the criterion of maximal I-concurrence, a measure of entanglement. The square of concurrence for a bipartition (X|X^prime ) of a pure state is defined as (E^2_{X| X ^prime }=2[1-textrm{tr}({rho _X}^2)]). From this, we can infer that the concurrence (E_{X| X ^prime }) reaches its maximum when (textrm{tr}({rho _X}^2)) is minimised. Using this approach, we have established the connection to the entanglement entropy to identify numerous Absolutely Maximally Entangled (AME) pure states that exhibit maximal entanglement across all possible bipartitions. Conditions are derived for pure states to achieve maximal mixedness in all bipartitions, revealing that any pure state with an odd number of subsystem coefficients does not meet the AME criterion. Furthermore, we obtain Equal Maximally Entangled (EME) pure states across all bipartitions using our maximal concurrence criterion.

Recently, Ma et al. proposed an efficient semi-quantum secret sharing protocol (SQSSP) for sharing specific secret information. In their protocol, quantum resources are provided by a trusted third party. The other participants, who act as classical parties, merely need to carry out classical operations to realize the sharing of specific secret information. Unfortunately, according to our security analysis, their protocol is insecure. When an external attacker conducts a Controlled-NOT (CNOT) attack, he/she can obtain the shared secret information without anyone's assistance. What is more, the attacker’s eavesdropping cannot be detected by the participants. During the execution of the protocol, the third party and the outside adversary can also obtain the shared secret information. Then, an improved scheme is proposed. The improved protocol can make up for the security defects of the original protocol, and it is secure against various types of attacks, including eavesdropping attacks and CNOT attack. Furthermore, it has enhanced security so that even trusted third party cannot obtain useful information about the shared secret. This protocol requires only semi-quantum capabilities for both the secret dealer and participants, and demonstrates advantages in quantum resources, security, and qubit efficiency compared to similar protocols.

We investigate the impact of a small deformation of the electromagnetic Lagrangian on the entanglement properties of photonic quantum states. Using the von Neumann entropy as a quantitative measure, we analyze how such deformations modify reduced density matrices of entangled photons. For two-photon polarization states, we show that maximally entangled states exhibit a universal quadratic reduction of entropy with respect to the deformation parameter, reflecting the fact that maximal entanglement is a local maximum of the entropy. We extend the analysis to multi-photon systems and find that GHZ states display a quadratic scaling of entropy reduction with subsystem size, indicating pronounced fragility, whereas W-type multipartite photonic entangled states exhibit linear scaling, reflecting greater robustness under deformation. We further clarify that normalization factors in reduced density matrices arise from sums of squared amplitudes rather than products, as a direct consequence of the orthogonality of the superposed components. When the deformation parameter is allowed to acquire scale dependence, as expected in effective field-theoretic extensions, the entanglement entropy inherits a corresponding dependence on photon frequency. These results establish a direct connection between field-theoretic modifications of the electromagnetic Lagrangian and quantum entanglement in photonic systems, and suggest that precision measurements of entanglement may serve as sensitive probes of weak nonlinearities in electromagnetic dynamics.

Quantum auction protocols are designed to ensure the confidentiality, authenticity, and integrity of submitted bids, but in practice their deployment remains vulnerable to attacks that exploit imperfections in measurement devices. To address this challenge, we introduce a measurement-device-independent quantum auction (MDI-QA) protocol that eliminates the need to trust the measurement apparatus while still preserving both bid privacy and bidder identity anonymity. The protocol is structured around three key components: (i) mutual identity authentication achieved through entanglement swapping combined with decoy-state checks; (ii) Pauli-based bid encoding that is further masked by hash-derived ephemeral identifiers, preventing information leakage; and (iii) the distribution of pseudonymous identifiers across multiple rounds to strengthen anonymity. We rigorously analyze the security against several classes of adversaries, including measure–resend, entangle–measure, and dishonest-relay strategies, and derive an asymptotic lower bound on secrecy capacity against collective attacks via a Bell-diagonal reduction. Furthermore, public verifiability of the final winning bid is guaranteed through a hash-commitment mechanism, which deters auctioneer misreporting. Finally, we validate the protocol’s fundamental subroutines on IBM Quantum simulators, confirming the predicted entanglement-swapping correlations.

Quantum error-correcting codes are an important coding technique used to protect quantum information from noise and errors. Recently, researchers have been increasingly interested in the study of quantum error-correcting codes. In order to provide more research ideas and methods on error-correcting codes, in this paper, we study a topological error-correcting code called (textrm{XYZ}^{2}), which is encoded similar to the Kitaev honeycomb model lattice. Designing efficient decoders for quantum error-correcting codes remains a challenge. Here, we use a reinforcement learning algorithm to decode the (textrm{XYZ}^{2}) code, which considers only the logical states associated with the (textrm{XYZ}^{2}) code during the decoding process when training the reward agent. Considering the complexity of the (textrm{XYZ}^{2}) code lattice computation, the spin property of the code is exploited to transform the honeycomb qubit lattice into a square lattice, and then, deep convolutional networks and experience replay techniques are used to implement the decoding design. Under the depolarizing noise model, we evaluate the training accuracy at different code distance, and the decoder can achieve about 83.33% error correction accuracy. We measured the threshold performance of the (textrm{XYZ}^{2}) code at the maximum code distance of 7 and 9, which are 0.19029 and 0.21936, respectively. Finally, we utilized the deep Q-network to improve the decoding accuracy and successfully improved the fidelity of the qubits from 0.21513 to 0.76609. Our study provides directions and ideas for the application of reinforcement learning decoding schemes to other topological quantum error-correcting codes.

We construct a hybrid quantum–classical Viterbi decoder for the classical error-correcting codes. Viterbi decoding is a trellis-based procedure for maximum likelihood decoding of classical error-correcting codes. In this article, we demonstrate that the quantum approximate optimization algorithm can find any path on the trellis with the minimum Hamming distance relative to the received erroneous vector. We construct a generalized method to map the Viterbi decoding problem into optimization of a parameterized quantum circuit for any classical linear block code. Also, we propose a uniform parameter optimization strategy to optimize the parameterized quantum circuit using a classical optimizer. We observe that the proposed method efficiently generates low-depth trainable parameterized quantum circuits. Our approach makes the hybrid decoder more efficient than previous attempts at making quantum Viterbi algorithm. We show that using uniform parameter optimization, we obtain parameters more efficiently for the parameterized quantum circuit than previously used methods such as random sampling and fixing the parameters.

The rapid development of quantum networks has created an urgent need to investigate quantum steering in networks and its role in quantum information protocols. By leveraging joint measurability theory and the concept of steering-equivalent-observable (SEO) measurement assemblages, this work establishes two necessary and sufficient conditions (distinct from conventional inequality-based criteria) for determining the steerability of network states in an entanglement-swapping network. Additionally, since quantum steering operates via one-way local operations and classical communication (LOCC), such as local filtering on the trusted party, we establish a necessary and sufficient condition for the convertibility between steering assemblages under local filtering operations in the entanglement-swapping network. To enhance the practical relevance and readability of our theoretical results, we provide a concrete example in which incompatible measurements acting on the untrusted party are shown to necessarily induce network steering.

We investigate ground-state quantum correlations in the spin-1/2 XX chain with anisotropic four-spin interaction (AFSI) using exact fermionization techniques. The system exhibits three quantum critical lines separating topological phases with winding numbers (nu = pm 1) and (nu = pm 3). To explore its critical and topological properties, we analyze concurrence and quantum discord (QD) between nearest-neighbor spins. Our results show that while concurrence fails to detect all critical lines—especially in phases with higher winding numbers—QD reliably identifies every quantum phase transition through cusps or discontinuities in its first derivative. Moreover, QD reaches higher values in phases with lower winding numbers, indicating that the structure and localization of quantum correlations are shaped by topological order. These findings establish QD as a sensitive probe of both quantum criticality and topology in many-body systems, offering insights for correlation-based diagnostics in quantum information science and highlighting the potential of topological spin chains in future quantum technologies.