Quantum key distribution (QKD) promises theoretically secure communication. However, it encounters challenges in implementation security and performance due to inevitable device imperfections. Since the proposal of measurement-device-independent (MDI) QKD, the critical step toward practical security is to secure QKD with imperfect sources. The source imperfections manifest as state-preparation uncertainty (SPU) in various aspects, e.g., encoding uncertainty, intensity fluctuation, and imperfect vacuum states. Here, we perform an MDI-QKD experiment and achieve both high practical security and superior performance. We address the general form of SPU and guarantee a tight estimation of the secret key rate based on the operator dominance method. We achieve secure key distribution over 303.37 km, which not only represents the farthest distance in experiments involving SPU but also considers the most SPU scenarios. Our experimental results represent a significant step toward promoting practical and secure quantum communication.

Abstract The growing public fascination with quantum technologies has inadvertently fueled the rise of pseudoscientific claims, particularly the misuse of quantum terminology in fields such as alternative medicine. This phenomenon poses a challenge for physics education, where the distinction between legitimate science and pseudoscience is essential. This paper examines how pre-service physics teachers (N = 28) respond to pseudoscientific uses of quantum terminology, particularly in the context of quantum healing. Therefore, the participants were asked to evaluate a pseudoscientific text about quantum healing in a classroom-like vignette, responding as if they were addressing a student. Their responses were analyzed using qualitative content analysis to categorize the types of reasoning used. Most participants were successful in identifying scientific inaccuracies and misuse of technical terms, although only a proportion applied broader Nature of Science (NOS)-related critiques. The findings suggest that although pre-service teachers are adept at identifying pseudoscientific claims, more emphasis on the principles of NOS could improve their ability to make comprehensive judgements.

Abstract This study investigates the quantum information dynamics of a multi-level atomic system interacting with an SU(1;1) quantum system, focusing on atomic inversion, entropy, coherence, and skew information. The system is specified as a two-level and three-level Λ-type configuration, incorporating multi-mode SU(1;1) quantum systems and the Stark effect. Numerical simulations are performed to solve the time-dependent density matrix equations under varying shift, intensity, and Stark parameters. Results show that increasing the shift stabilizes inversion but raises statistical uncertainty, while greater field intensity amplifies entropy. The Stark amplitude suppresses decoherence and improves quantum information retention. Negativity is used to quantify entanglement between the first two SU(1;1) modes, showing that stronger Stark shifts stabilize entanglement and coherence. Three-level systems consistently outperform two-level ones in preserving coherence and entanglement due to enhanced interference and spectral separation. Eigenvalue analysis reveals the nonlinear structure of three-level systems, explaining their robustness. These findings are supported by recent experiments in SU(1;1) interferometry and Stark-tuned quantum systems, offering insights for quantum sensing, computation, and communication.

The quantum measurement of the microwave electric field based on Rydberg atoms developed in recent years has shown promise for enhancing accuracy, sensitivity and stability. However, the study of ultra-low frequency electric field measurements in power systems is still in its early stages, presenting new challenges for Rydberg-based measurement techniques. In this work, a ladder-type two-photon three-level structure of Cs atoms is selected, and the corresponding experimental system is constructed. Two kinds of laser control schemes, which are referred to as mismatch and match measurement schemes, are then proposed, and the quantum effect’s optical spectrum is obtained by using the two measurement schemes. After these measured spectral properties are compared, the match measurement scheme is chosen for real-time measurement of ultra-low frequency electric fields. Additionally, dynamic models of the interactions among the laser field, ultra-low frequency electric field and atoms are derived, on the basis of which theoretical simulations are being conducted to study the effects of the input parameters of the electric field and laser power on the optical spectrum. On the basis of the optical spectral features, an inversion method for the excitation electric field in real time is proposed, and its effectiveness is demonstrated.

Biomolecular residue pairs have been utilized in constructing quantum logic gates (QLGs), significantly reducing the hardware size to the subnanoscale level. However, the development of molecular fault-tolerant topological quantum computers (TQCs) presents challenges in error reduction and hardware size minimization. This study presents the manipulation of molecular QLGs (MQLGs) by utilizing protein residue pairs as molecular transistors, enabling the construction of molecular topological QLGs. This innovative approach leverages molecular functionality in quantum computer (QC) designs to build sub-nanometer transistors that significantly reduce size, enhance efficiency, and accelerate computing. The transmission spectra of electron transfer in molecular junction systems were analyzed using the non-equilibrium Green’s function method. The molecular field effect led to the observation of four quantum states on a two-dimensional potential energy surface with two degrees of freedom—proton translation and molecular rotation. These states form a quaternary QLG, similar to a 2-qubit controlled-NOT logic gate. By applying the Kitaev honeycomb lattice model, MQLGs were employed to generate nonabelian anyons that adhere to fusion rules, such as Ising and Fibonacci anyons. Furthermore, quantum circuits incorporating nonabelian anyons and their fusion processes were developed for practical applications. These findings underscore the shift away from conventional atom-based silicon technology and highlight the potential for innovative applications of molecular universal QLGs, particularly in the advancement of sub-nanometer molecular fault-tolerance TQCs.

Scalable solutions are essential to achieving the long-term goal of building a fault-tolerant quantum computer and energy-power consumption are fundamental limiting factors for this target. Among the available types of silicon qubits, this work focuses on Flip-Flop (FF) qubits. Energy consumption and power requirements are estimated for a square array of qubits that hosts the logical qubit. The logical qubit is implemented using the rotated Surface Code (SC) for Quantum Error Correction (QEC). By using a universal set of quantum gates, the energy usage, time and power requirements for a SC cycle are estimated based on noise level, code distance and control levels. These estimates are used to provide insights into the main scaling-up challenges for quantum computer development. This is achieved by extending a thermal model that includes energy contributions from both the cryogenic components (such as the qubit array, the cryogenic control electronics, and the cryostat) and the room temperature (RT) section (RT electronics and heat dissipation systems). The maximum numbers of physical and logical qubits are provided, as well as power consumption across the different temperature sections.

Quantum circuits for multiplication are necessary for scientific computing on quantum computers. Clifford + T circuits are widely used in fault-tolerant implementations. The costs of implementing T and double-qubit gates are higher than those of other one-qubit gates in the Clifford + T group. In addition, the small number of qubits available in existing quantum devices is another constraint on quantum circuits. Therefore, we reduce T and CNOT gates and circuit width as the primary optimization goal in this paper. We propose an algorithm for multiplication with two unchanged operands. Preserving both operands of the multiplication is important for realizing some quantum algorithms, such as quantum bilinear interpolation. Using this algorithm, we design the circuit of the integer multiplier with two unchanged operands reducing CNOT gates. Next, we develop a Clifford + T circuit for the multiplier and introduce new optimization rules to reduce T gates. Comparative analysis shows that the proposed multiplier achieves the best width among existing multipliers. Compared to multipliers with two unchanged operands that use at most one ancillary qubit, our proposed multiplier has the best T-count, T-depth, and CNOT-count.

This paper introduces the design process of a multiparty quantum key agreement protocol based on the Greenberger-Horne-Zeilinger state in detail. Building on the traditional circle-type quantum key agreement protocol, we introduce a star structure, which significantly improves the speed and efficiency of key agreement. To facilitate the reader’s understanding, we provide an example of a four participants quantum key agreement protocol. In the process of quantum state transmission, we perform operations using the Pauli matrix and the Hadamard matrix to ensure that the quantum state remains in one of the four basis states. This significantly enhances the security of the protocol. After rigorous security analysis, we find that the protocol can effectively resist intercept-resend attack, entangle-measure attack, collective attack, and dishonest participant attack. Under a collective attack, if the first particle is subjected to bit-flipping noise, then p<0.2430 only guarantees r>0.20.2$\\end{document}]]> when a=1. Additionally, we conduct a fairness analysis and evaluate the practical performance of the proposed protocol. In an ideal depolarization noise-free environment, the protocol can achieve a positive key rate only when the global detection efficiency exceeds 0.9636. Finally, we conduct a comprehensive comparative analysis of the protocols. The results show that our proposed protocol is superior to other existing schemes in terms of efficiency and running time.

Effectively managing various types of decoherence is crucial for leveraging entanglement in quantum information processing and quantum computing. In this paper, we propose purification circuits that deterministically produce a maximally entangled state from a single copy of an imperfect entangled pair affected by various noise sources. Unlike conventional methods, our approach eliminates the need for multiple copies of the entangled state, pre-purification operations, and imposes no restrictions on the initial entanglement fidelity of the imperfect pair. Our method utilizes ancilla qubits and CNOT gates to address errors from Pauli X and Z (bit flip and phase flip), as well as combinations of these errors that create general mixed entangled states and amplitude-damped entangled states. Our analysis shows that noisy CNOT gates impact fidelity minimally, with only the final two gates being critical. We validate our approach through mathematical analysis and practical implementation in Qiskit, demonstrating its effectiveness and robustness.

While it is possible to estimate the dark matter density at the Sun distance from the galactic center, this does not give information on actual dark matter density in the Solar system. There can be considerable local enhancement of dark matter density in the vicinity of gravitating centers, including the Sun, the Earth, as well as other planets in the solar system. Generic mechanisms for the formation of such halos were recently elucidated. In this work, we studies the possible halo dark matter overdensities and corresponding dark matter masses allowed for various objects in the solar system. We explore spacecraft missions to detect such halos with instruments such as quantum clocks, atomic and molecular spectrometers designed to search for fast (tens of hertz to gigahertz) oscillations of fundamental constants, highly sensitive comagnetometers, and other quantum sensors and sensor networks.