Quantum Information Processing最新文献

In this paper, thermofield dynamics (TFD) is applied to map a quantum optics nonlinear master equation into a Schrödinger-like equation for any arbitrary initial condition. This formalism provides a more efficient way for solving open quantum system problems. Then we use the Hartree–Fock approximation to solve the master equations of two separate noisy quantum systems analytically, which allows us to analyze the entanglement and quantum mutual information in each case using the eigenvalues of a covariance matrix, followed by two-mode and single-mode squeezed states.

The rapid development of neutral atom quantum hardware provides a unique opportunity to design hardware-centered algorithms for solving real-world problems aimed at establishing quantum utility. In this work, we study the performance of two such algorithms on solving MaxCut problem for various weighted graphs. The first method uses a state-of-the-art machine learning tool to optimize the pulse shape and embedding of the graph using an adiabatic Ansatz to find the ground state. We tested the performance of this method on finding maximum power section task of the IEEE 9-bus power system and obtaining MaxCut of randomly generated problems of size up to 12 on QuEra’s Aquila quantum processor. To the best of our knowledge, this work presents the first MaxCut results on Aquila quantum hardware. Our experiments run on Aquila demonstrate that even though the probability of obtaining the solution is reduced, one can still solve the MaxCut problem on cloud-accessed neutral atom analog quantum hardware, with an average 60% overlap for the graphs of 8 to 12 vertices studied. The second method uses local detuning, which is an emergent update on the Aquila hardware, to obtain a near exact realization of the standard QAOA Ansatz with similar performance. Finally, we study the fidelity throughout the time evolution realized in the adiabatic method as a benchmark for the IEEE 9-bus power grid graph state.

This paper presents a connection between the quantum walk and the absolute mathematics. The quantum walk is a quantum counterpart of the classical random walk. We especially deal with the Grover walk on the graph, which is a typical model of quantum walks. The time evolution of the Grover walk is obtained by a unitary matrix called the Grover matrix. We define a new type of the zeta function determined by the Grover matrix. Then, we consider to construct the absolute zeta function. In the previous paper [10], it is pointed out that there is a relationship between quantum walk and absolute zeta function. In the first half of this paper, we briefly describe the results of the previous research. In the latter part, we compute the absolute zeta function of the quantum walk by two different methods. One is calculated by the cyclotomic polynomial. The other is based on the series expansion. Its explicit derivation can be extended to a broader class of quantum walks on graphs.

SHA-256 exhibits strong resistance to collision attacks, a property attributed to its intricate design. Recently, Li et al. proposed a novel semi-free-start (SFS) collision attack targeting 39-step SHA-256, advancing prior methodologies. Despite these advancements, increasing the number of attackable rounds for SHA-256 remains challenging. This study demonstrates the conversion of a semi-free-start collision into a full collision attack through a specialized quantum technique. Using a quantum approach, our method targets 39-round SHA-256, leveraging frameworks that transform SFS collisions into two-block collisions, thereby establishing a new benchmark for collision attacks.

The quantum analysis method proposed in this paper achieves a circuit depth of (T_F le 3.4) and a circuit width of (S_F le 2.4). With a quantum computer of size S, this attack achieves a collision within time (t = 2^{124}/sqrt{S}). The attack is effective when the quantum computer size satisfies (2.4 le S < 2^8). Furthermore, this study investigates the conditions required to transform a semi-free-start collision into a two-block collision. It also examines the conversion of semi-free-start or free-start collision attacks into two-block collisions across various hash functions. The results indicate that the unique properties of quantum computing establish new benchmarks for collision attacks on hash functions.

This paper introduces a theoretical framework for asymmetric quad-directional controlled quantum teleportation (AQDCQT), offering a novel approach to simultaneous quantum state transmission among four users. In this protocol, any of the four users can concurrently transmit their entangled state to others, facilitated by a supervisory controller, utilizing a network of 29 qubits as the quantum channel. Quad-directional teleportation enables all four users to act simultaneously as both sender and receiver. Using the IBM Quantum platform, the quantum channel is implemented in practice. The protocol leverages Bell state measurement (BSM), GHZ state measurement (GHZ), and single-qubit measurement (SQM) for efficient quantum state teleportation. Regarding security, we address communication security measures against two potential attacks. The comparative analysis demonstrates the superior intrinsic efficiency of the proposed scheme when compared to previous approaches. Furthermore, we examine the impact of environmental noise on the channel, revealing that the protocol’s fidelity is influenced by the initial state's amplitude coefficient and the noise intensity.

Preparing multipartite entangled states under restricted qubit access is a key challenge for modular and distributed quantum architectures. We address this by presenting two complementary circuits. First, we propose a resource-efficient deterministic circuit for preparing the four-qubit Dicke state with two excitations, requiring only six two-qubit controlled gates, which is fewer than previously reported schemes. Second, we introduce a probabilistic expansion protocol that transforms a four-qubit Dicke state with two excitations into a five-qubit Dicke state with three excitations, even when only a subset of qubits is accessible and one qubit remains untouched. The expansion succeeds with a probability of 5/6; in the remaining 1/6 of cases, the post-measurement state is a recyclable three-qubit W-like state that can be used to regenerate the initial four-qubit Dicke state. We provide an analytical derivation of the success bound, explicit circuit constructions, and numerical simulations over (10^5) runs that confirm the predicted statistics. A robustness analysis using a coherent over-rotation error model applied uniformly to all controlled gates shows that the output fidelity remains high for experimentally relevant deviations, indicating resilience to realistic imperfections. By operating without global access to every qubit, the proposed methods advance Dicke-state generation in settings where direct control is limited and offer practical building blocks for scalable state growth in near-term quantum processors.

Multi-hop quantum teleportation is a fundamental technique for enabling scalable, long-distance quantum communication, making it a key building block for future quantum networks. In this paper, we present a generalized multi-hop quantum controlled teleportation (MQCT) protocol that enables more flexible transfer across complex network architectures. We perform a detailed analysis of the protocol’s performance under realistic noise conditions, focusing on the impact of various noise sources on both the teleportation process and the underlying quantum channels. To assess its practical performance, we implemented the protocol on an IBM quantum (IBMQ) computer. The experimental results demonstrate the feasibility of the protocol in near-term quantum devices and provide valuable insights into its behavior under real-world quantum noise, paving the way for more reliable quantum communication systems.

A theoretical scheme is proposed to enhance the entanglement in a hybrid cavity magnonics system by exploiting the synergistic effect of two-magnon squeezing and coherent feedback. The system comprises the cavity mode, magnon Kittel mode and HMS mode. Compared to using either squeezing alone or feedback alone, the cavity–Kittel entanglement and the cavity–HMS entanglement are significantly enhanced. The optimal enhancement of genuine tripartite entanglement is realized through the simultaneous presence of these two mechanisms. Moreover, the robustness of entanglement against thermal effects can also be significantly improved. This work offers a viable approach for achieving high-quality entanglement resources in cavity magnonics, with potential applications in quantum information processing.

This paper introduces a novel lower bound on communication complexity using quantum relative entropy and mutual information, refining previous classical entropy-based results. By leveraging Uhlmann’s lemma and quantum Pinsker inequalities, the authors establish tighter bounds for information-theoretic security, demonstrating that quantum protocols inherently outperform classical counterparts in balancing privacy and efficiency. This paper also explores several symmetric Quantum Private Information Retrieval (QPIR) protocols that achieve sublinear communication complexity while ensuring robustness against specious adversaries: (i) a post-quantum cryptography-based protocol that can be authenticated for the specious server; (ii) a homomorphic encryption-based protocol in a single-server setting, ensuring robustness against quantum attacks; (iii) a multi-server protocol optimized for hardware practicality, reducing implementation overhead while maintaining sublinear efficiency. These protocols address critical gaps in secure database queries, offering exponential communication improvements over classical linear complexity methods. The work also analyzes security trade-offs under quantum specious adversaries, providing theoretical guarantees for privacy and correctness.

The measurement-based quantum computing paradigm relies on entangling the qubits of a register into a graph state and on measuring subsets of such register in order to condition the unmeasured qubits. The computation therefore, instead of being carried on only by one-qubit and two-qubits logic gates, is largely based on entanglement and measurement processes. Compared to the gate model architecture, in MBQC the overhead in terms of computation resources to synthesize logical qubits is higher. While gate model relies on a register of logical qubits whose number is set at the beginning of the computation and remains constant during the computation, in the MBQC the input qubits outnumber the output ones, due to the destructive nature of measurement processes. Still, we analytically prove and experimentally confirm that MBQC can be efficiently emulated on a classical software, reaching equal loads with respect to the gate-based approach in terms of average runtime and storage of memory. The numerical results confirm that despite the potential computational overhead due to the high entanglement of the initial graph state, the MBQC paradigm carries similar computational complexity, both in terms of time and memory, with respect to the gate-based approach.