EPJ Quantum Technology最新文献

The Quantum Approximate Optimization Algorithm (QAOA) is a hybrid quantum-classical algorithm that shows promise in efficiently solving the Max-Cut problem, a representative example of combinatorial optimization. However, its effectiveness heavily depends on the parameter optimization pipeline, where the parameter initialization strategy is nontrivial due to the non-convex and complex optimization landscapes characterized by issues with low-quality local minima. Recent inspiration comes from the diffusion of classical neural network parameters, which has demonstrated that neural network training can benefit from generating good initial parameters through diffusion models. However, whether the diffusion model can enhance the parameter optimization and performance of QAOA by generating well-performing initial parameters is still an open topic. Therefore, in this work, we formulate the problem of finding good initial parameters as a generative task and propose the initial parameter generation scheme through dataset-conditioned pre-trained parameter sampling. Concretely, the generative machine learning model, specifically the denoising diffusion probabilistic model (DDPM), is trained to learn the distribution of pre-trained parameters conditioned on the graph dataset. Intuitively, the proposed framework aims to effectively distill knowledge from pre-trained parameters to generate well-performing initial parameters for QAOA. To benchmark our framework, we adopt trotterized quantum annealing (TQA)-based and graph neural network (GNN) prediction-based initialization protocols as baselines. Through numerical experiments on Max-Cut problem instances of various sizes, we show that conditional DDPM can consistently generate high-quality initial parameters, improve convergence to the approximation ratio, and exhibit greater robustness against local minima over baselines. Additionally, the experimental results also indicate that the conditional DDPM trained on small problem instances can be extrapolated to larger ones, thus demonstrating the extrapolation capacity of our framework in terms of the qubit number.

Leveraging the properties of quantum entanglement and squeezing, quantum clock synchronization offers significant advantages in improving precision and security. For scalable quantum clock synchronization networks, developing an accurate time deviation analysis model is essential to characterize long-term timing stability and enable reliable deployment in real-world systems. This paper proposes a synchronization stability analysis model that establishes the theoretically achievable time deviation based on the Cramér-Rao lower bound. We experimentally validate this model using a round-trip quantum clock synchronization protocol over 50 km of fiber, employing an integrated silicon-photonic chip that generates frequency-entangled photon pairs via four-wave mixing. Results show a synchronization accuracy of 15.08 ps and a time deviation of 901 fs at an averaging time of 10,240 seconds, while our model analysis shows a standard deviation of 12.21 ps. This work provides a fundamental framework for building robust, large-scale quantum networks.

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.

High-dimensional (HD) quantum systems are capable of processing more complex information and performing a wider array of quantum operations, in contrast to low-dimensional (LD) quantum systems, thereby improving the speed and fault tolerance of quantum computing. In the study, we propose a deterministic qudit-encoded (4times 4times 4)-dimensional (64D) controlled-controlled-SUM (CCSUM) gate based on weak Kerr effect. The 64D CCSUM gate leverages the polarization and spatial degrees of freedom (DoFs) of three photons to encode 4D control and target qudits, thereby optimizing quantum resources and reducing costs. Moreover, the HD CCSUM gate functionality is implemented in a deterministic way by employing the X-Homodyne detector to measure coherent states, combined with related classical feed-forward operations. Through detailed analyses, the proposed HD CCSUM gate, under current technological conditions, exhibits robust fidelity and feasibility, offering a promising path toward the realization of HD quantum computing.

In this note, we clarify a small problem concerning our recent work “On validity of quantum partial adiabatic search”. The conclusion here is that, the success probability of the quantum partial adiabatic search algorithm in the paper indeed can be bounded by the same quantity as that of early work of Kay’s, even though the Hamiltonian settings in those works are different. This fact is not mentioned in our prior paper, so the purpose here is to explicitly point it out for clarity.

We consider the strong-coupling limit of lattice QCD with massless staggered quarks and study the resource requirements for quantum simulating the theory in its Hamiltonian formulation. The bosonic Hilbert space of the color-singlet degrees of freedom grows quickly with the number of quark flavors (N_{f}), making it a suitable testing ground for resource considerations across different platforms. In particular, in addition to the standard model of computation with qubits, we consider mapping the theory to qudits ((d>2)) and qumodes, as used on atomic systems and photonic devices, respectively. We subsequently derive the resource requirements to quantum simulate the theory, for varying number of quark flavors (N_{f}=1) and (N_{f} = 2), using a first-order product formula.

By considering linear scattering of laser-driven cold atoms inside an undriven high-finesse optical resonator, we experimentally demonstrate effects unique to a strongly coupled vacuum field. Arranging the atoms in an incommensurate lattice with respect to the radiation wavelength, the Bragg scattering into the cavity can be suppressed by destructive interference: the atomic array is subradiant to the cavity mode under transverse illumination. We show however, that strong collective coupling leads to a drastic modification of the excitation spectrum, as evidenced by well-resolved vacuum Rabi splitting in the intensity of the fluctuations. Furthermore, we demonstrate a significant polarization rotation in the linear scattering off the subradiant array via Raman scattering induced by the strongly coupled vacuum field.

Space quantum communications is a potential means for establishing global secure communications and quantum networking. Despite pioneering demonstrations of satellite quantum key distribution, considerable challenges remain for wide deployment such as the local effects of the atmosphere on the transmission of single-photon level quantum signals. As part of Ireland’s efforts to establish quantum links with the rest of Europe and further afield, we present a preliminary study of the feasibility of satellite quantum key distribution taking into account geographic and weather effects on the space-Earth channel. Weather data over 5 years covering 4 locations across Ireland were used to assess performance and the prospects of optical ground station (OGS) geographic diversity to improve service availability. Despite significant cloud cover that may reduce the performance of a single OGS location, the use of a 4-OGS network can provide up to 45% improvement for a single satellite exploiting anti-correlation in cloud cover, though most gains are achieved with 2 or 3 OGSs.

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.

This study investigates the experiences of pre-high and high school teachers in implementing QuanTime and other quantum-related activities aiming to promote quantum literacy and introduce foundational quantum concepts to K-12 students. The ultimate goal is to help prepare a diverse future workforce in quantum information science and technology (QIST). Teachers were divided into two groups: pre-high school (grades 4-8) and high school (grades 9-12). We used a survey featuring 12 Likert-scale questions and 14 open-ended responses to assess teachers’ perceptions, engagement, and feedback about engaging in QuanTime and other quantum-related activities. Approximately two-thirds of the teachers responding to the survey implemented QuanTime activities in their classes. High school teachers who responded to the survey were most likely to use activities like Wave-Particle Duality and Electron Transitions while pre-high school teachers showed a strong interest in Art & Polarization. Open-ended feedback highlighted the ease of integrating these activities into existing curricula and the minimal preparation required, making them accessible for educators. The positive reception across both groups indicates that QuanTime and other quantum-related activities are valuable tools for early-age quantum education. By engaging students with quantum concepts from a young age, these activities have the potential to spark interest, which may contribute to their future engagement over time. It can inspire a diverse group of students and has the potential to get them interested in future opportunities in the growing field of QIST.