EPJ Quantum Technology最新文献

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>0.2) 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.

In practical satellite-based quantum key distribution (QKD) systems, the preparation and transmission of polarization-encoding photons suffer from complex environmental effects and high channel loss. Consequently, the hinge to enhancing the secure key rate (SKR) lies in achieving robust, low-error, and high-speed polarization modulation. Although the schemes that enable self-compensation demonstrate remarkable robustness, their modulation speed is limited to around 2 GHz to prevent the interaction between the electrical signal and the reverse optical pulses. Here, we utilize the non-reciprocity of the lithium niobate modulators and eliminate the modulation on the reverse optical pulses. This characteristic is widely available in the radio-frequency band, allowing the modulation speed to no longer be limited by the self-compensating optics and enabling further increases. The measured average intrinsic quantum bit error rate of the four polarization states at 10 GHz system repetition frequency is as low as 0.53% over 10 min without any compensation. The simulation results show that our scheme can maintain a SKR of about 5 kbps even at the extreme communication distances between the satellite and the earth. Our work can be efficiently applied in high-speed, high-loss satellite-based quantum communication scenarios.

Precise control of atomic systems has led to an array of emerging ‘quantum’ sensor concepts ranging from Rydberg-atom RF-electric probes to cold-atom interferometer gravimeters. Looking forward, the potential impact of these technologies hinges on their capability to be adapted from laboratory-scale experiments to compact and low-power field-deployable instruments. However, existing setups typically require a bulky and power-hungry laser and optics system (LOS) to prepare, control, and interrogate the relevant atomic system using a variety of frequency-referenced and rapidly reconfigurable laser beams. In this work, we investigate the feasibility of using semiconductor optical amplifiers (SOAs) to replace high-power pump lasers and acousto-optic modulators within a simple atom cooling apparatus, looking forward to the ultimate goal of a space-deployable atom interferometer. We find that existing off-the-shelf SOA components operating at relevant wavelengths for Cs and Rb atom cooling (852 and 780 nm, respectively) are able to permit an attractive combination of rapid (sub-microsecond), high extinction ratio (>60-65 dB) switching while acting as power boosters prior to the atom physics package. These attributes enable a radically different, power-efficient approach to LOS design, reducing or eliminating the need for Watt-class laser amplifiers that are unsuitable for flight deployment. Building on these results, we construct a simple and compact all-semiconductor laser/amplifier LOS for atom cooling that is integrated with custom path-to-flight drive electronics. Up to 125 mW of total optical power is delivered to six fiber-coupled channels for magneto-optical-trap-based cooling of a cloud of neutral Cs atoms. The entire LOS, including reference and cooling laser subsystems and control electronics, occupies a volume of 20×20×15 cm and totals DC power consumption of around 13.5 W, and is designed in a modular format so that additional hardware for synthesizing atom interferometry beams may be added through future development efforts. These results indicate the utility of all-semiconductor laser systems for future low-power flyable atom-based sensor instruments.

In quantum physics (QP) education, the use of representations such as diagrams and visual aids that connect to mathematical concepts is crucial. Research in representation theory indicates that combining symbolic-mathematical elements (e.g., formulae) with visual-graphical representations enhances conceptual understanding more effectively than representations that merely depict phenomena. However, common representations vary widely, and existing category systems do not adequately distinguish between them in QP. To address this, we developed a new set of differentiation criteria based on insights from representation research, QP education, and specific aspects of the quantum sciences. We created a comprehensive category system for evaluating visual QP representations for educational use, grounded in Ainsworths (2006) DeFT Framework.

Twenty-one experts from four countries evaluated this category system using four qubit representations: the Bloch sphere, Circle Notation, Quantum Bead, and the pie chart (Qake) model. This evaluation enabled us to assess the discriminative power of our criteria and to gain expert-based insights into the perceived effectiveness of each representation in supporting the learning of QP concepts. It evaluated how well each representation conveyed quantum concepts such as quantum state, measurement, superposition, entanglement, and quantum technologies (X-, Z-, and H-gates) across 16 criteria.

The results showed significant differences in the effectiveness of these representations, particularly in conveying key concepts like superposition and measurement from an expert perspective. Additionally, expert ratings indicated notable variations in the potential of each representation to induce misconceptions, linked to differences in shape, measurement behaviour, and requirements for understanding entanglement. We also discuss considerations for developing new representations and suggest directions for future empirical studies.

This paper examines the intersection of goals and values within grassroots organizations operating in the realm of quantum technologies (QT) education. It delineates a fundamental distinction between the objective to provide education and the drive to democratize learning through principles of inclusivity, accessibility, and diversity. The analysis reveals how these organizations navigate their nascent stages, grappling with the dual challenge of adhering to their foundational values while aspiring for sustainable growth and development in the highly specialized field of QT. The study uncovers the strategic approaches adopted by these entities, including efforts to create educational ecosystems and foster community engagement. The research underscores the potential vulnerabilities of these grassroots organizations, particularly in relation to the longevity and evolution of their initiatives as members transition into professional roles within the quantum sector. Through this investigation, the paper contributes to a nuanced understanding of how emerging educational organizations in the QT field balance their ideological commitments with practical growth considerations, highlighting the critical factors that influence their trajectory and impact.

This summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024 (Second Terrestrial Very-Long-Baseline Atom Interferometry Workshop, Imperial College, April 2024), building on the initial discussions during the inaugural workshop held at CERN in March 2023 (First Terrestrial Very-Long-Baseline Atom Interferometry Workshop, CERN, March 2023). Like the summary of the first workshop (Abend et al. in AVS Quantum Sci. 6:024701, 2024), this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions (Memorandum of Understanding for the Terrestrial Very Long Baseline Atom Interferometer Study).

Imaginary-time evolution is a powerful tool for obtaining the ground state of a quantum system, but the complexity of classical algorithms designed for simulating imaginary-time evolution will increase significantly as the size of the quantum system becomes larger. Here, a probabilistic quantum algorithm based on Taylor expansion for implementing imaginary-time evolution is introduced. For Hamiltonians composed of Pauli product terms, the quantum circuit requires only a single ancillary qubit and is exclusively constructed using elementary single-qubit and two-qubit gates. Furthermore, similar principles are used to extend the algorithm to the case where the Hamiltonian takes a more general form. The algorithm only requires negligible precomputed numerical calculations, without the need for complex classical pre-mathematical calculations or optimization loops. We demonstrate the algorithm by solving the ground state energy of hydrogen molecules and Heisenberg Hamiltonians. Moreover, we conducted experiments on real quantum computers through the quantum cloud platform to find the ground state energy of Heisenberg Hamiltonians. Our work extends the methods for realizing imaginary-time evolution on quantum computers, and our algorithm exhibits potential for implementation on near-term quantum devices, particularly when the Hamiltonian consists of Pauli product terms.

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.

In response to numerous programs seeking to advance quantum education and workforce development in the United States, experts from academia, industry, government, and professional societies convened for a National Science Foundation-sponsored workshop in February 2024 to explore the benefits and challenges of establishing a national center for quantum education. Broadly, such a center would foster collaboration and build the infrastructure required to develop a diverse and quantum-ready workforce. The workshop discussions focused on how a center could uniquely address gaps in public, K-12, and undergraduate quantum information science and engineering (QISE) education. Specifically, the community identified activities that, through a center, could lead to an increase in student awareness of quantum careers, boost the number of educators trained in quantum-related subjects, strengthen pathways into quantum careers, enhance the understanding of the US quantum workforce, and elevate public engagement with QISE. Core proposed activities for the center include professional development for educators, coordinated curriculum development and curation, expanded access to educational laboratory equipment, robust evaluation and assessment practices, network building, and enhanced public engagement with quantum science.

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.