EPJ Quantum Technology最新文献

Quantum computing offers transformative potential for simulating real-world materials, providing a powerful platform to investigate complex quantum systems across quantum chemistry and condensed matter physics. In this work, we leverage this capability to simulate the Hubbard model on a six-site graphene hexagon using Qiskit, employing the Iterative Quantum Phase Estimation (IQPE) and adiabatic evolution algorithms to determine its ground-state properties. Our results show that a single Slater determinant is sufficient to initialize IQPE and accurately recover ground-state energies (GSEs) in small-scale Hubbard systems. In noiseless simulations, IQPE converges within a few iterations to exact GSEs, while adiabatic simulations yield charge and spin densities and correlation functions in excellent agreement with exact diagonalization. However, deploying IQPE and adiabatic evolution on today’s noisy quantum hardware remains highly challenging. To investigate these limitations in IQPE, we use the Qiskit Aer simulator with a custom noise model tailored to the characteristics of IBM’s real hardware. This model includes realistic depolarizing gate errors, thermal relaxation, and readout noise, allowing us to explore how these factors degrade simulation accuracy. Further, we implement the IQPE algorithm on IBM’s ibm_strasbourg and ibm_fez devices for a reduced three-site Hubbard model, enabling direct comparison between simulated and real hardware noise. While ibm_fez runs closely match exact results, discrepancies highlight the gap between modeled and physical noise. Extending the study to systems up to (N=6) sites, we benchmark IQPE’s scalability, demonstrating its potential and current limitations for simulating strongly correlated materials under realistic conditions.

Quantum teleportation enables a way to transmit an arbitrary qubit state from one location to another. The standard scheme for teleportation in optical setups involves three photons: an entangled photon pair and a photon carrying the quantum state to be teleported. The interaction between photons in such schemes makes quantum teleportation probabilistic. Here, we demonstrate a novel scheme for deterministic quantum teleportation of an arbitrary qubit state using only a polarization-entangled photon pair in a linear optical setup. By introducing the path degree of freedom (DOF) to one of the entangled photons and encoding the arbitrary qubit state into it, we achieve complete Bell state discrimination within our measurement strategy. This enables deterministic teleportation of a qubit state in an optical scheme with high fidelity. We report an average teleportation fidelity of (0.88 pm 0.04). The dependence of fidelity on the visibility of single-photon interference used in our scheme highlights the possibility of further improving the teleportation fidelity.

Quantum information science and technology provide contemporary contexts for teaching and learning foundational principles of quantum physics by accessing them via two-state systems. In this study, a teaching approach based on a Spin First approach is developed for introducing quantum physics at lower secondary level in a qualitative way. The teaching approach follows research-based design principles. It introduces electron spin as an exemplary two-state system and embeds basic concepts of quantum physics related to the context of quantum computing. To examine the feasibility and suitability of this teaching approach in principle and to formatively evaluate the content structure, semi-structured individual interviews with alternating intervention and survey phases (“Teaching Experiments”) were conducted with (N=11) grade 9 students. Learning outcomes were assessed based on an evaluative qualitative content analysis, and further general assessments regarding learning difficulties, prior knowledge and student assessment could be derived based on the interviews. The results of this evaluation reveal the approach to appear suitable for the addressed target group. Students seem to qualitatively understand foundational principles of quantum physics, and no significant mixing of classical and quantum physical principles is observed. Nevertheless, evidence of potential learning difficulties becomes apparent (e.g., adequate use of language and verbal reasoning, unreflective reasoning based on hidden variables, inert knowledge and lacks of prior knowledge), which in turn results in amendments to the teaching approach and supports the further development of ready-to-use teaching materials and the preparation of an extensive field study in the future.

The study introduces a hybrid computational framework that combines neuro-inspired information processing using spiking neural networks (SNNs) and quantum information processing using quantum kernels to develop quantum-enhanced machine learning models for spatio-temporal data, demonstrated through the classification of EEG data as a case study. In the proposed SNN-quantum computation (SNN-QC) framework, SNN with spike time information representation is employed to learn spatio-temporal interactions (EEG recorded from multiple channels over time). Frequency-based (rate-based) information as spike frequency state vectors are extracted from the SNN and classified using a quantum classifier. In the latter part, we use the quantum kernel approach utilising feature maps for classification tasks. The proposed SNN-QC is demonstrated on a benchmark EEG dataset to classify three distinct wrist movement tasks in six binary classification setups as a proof of concept. We introduce a novel high-order nonlinear feature map that demonstrates improved performance over state-of-the-art feature maps and several machine learning methods across most of the tasks studied. Furthermore, the role of hyperparameters for enhanced feature maps is also highlighted. The performance of SNN-QC is evaluated using statistical metrics and cross-validation techniques, demonstrating its efficacy across multiple binary classifiers. Quantum hardware validation is conducted using both a superconducting IBM-QPU and a high-fidelity noisy simulation that replicates a real QPU. Furthermore, the results demonstrate that the SNN-QC outperforms models that use statistical features rather than features extracted from the SNN, as the SNN accounts for the temporal interaction between the spatio-temporal input variables. Finally, we conclude that the SNN-QC offers a potential pathway for developing more accurate neuromorphic-quantum enhanced systems that are both energy-efficient and biologically-inspired, well-suited for dealing with spatio-temporal data.

Quantum networks aim to facilitate the fault-tolerant and secure transmission of quantum states across distant devices. The widely adopted quantum teleportation scheme requires multiple rounds of entanglement swapping and purification, leading to significant resource overhead and operational complexity. In this study, we propose a novel fault-tolerant and secure quantum communication scheme based on uncorrectable error injection. Our method exploits a quantum state encoding scheme based on quantum error correction codes, which strategically introduces uncorrectable errors to enhance security. It eliminates the need for entanglement distribution while reducing resource requirements. The injected errors protect against eavesdropping by preventing unauthorized parties from retrieving meaningful information. Security analysis shows that as the data length and encoded message size increase, information leakage becomes negligible relative to the size of the total message. Comparative performance analysis with existing approaches indicates that our method reduces transmission overhead while maintaining comparable fidelity in low-error regimes. These findings suggest that the proposed method offers a scalable and practical alternative for secure long-distance quantum communication, distributed quantum computing, and future quantum internet applications.

Authenticated Key Exchange (AKE) is a foundational cryptographic building block that plays a critical role in safeguarding digital networks and infrastructures. In PQCrypto 2023, Bruckner, Ramacher, and Striecks proposed a novel hybrid AKE (HAKE) protocol dubbed Muckle+, which is particularly useful in large quantum-safe networks consisting of a large number of nodes. The Muckle+ protocol is of a hybrid nature, in that it facilitates the incorporation of key material from conventional, post-quantum, and quantum cryptography primitives into a unified authenticated shared key.

To achieve the desired authentication properties, Muckle+ utilizes post-quantum digital signatures. However, the efficiency of available instantiations of such signature schemes is not yet comparable to that of their post-quantum key-encapsulation mechanism (KEM) counterparts, particularly in large networks with potentially several connections in a short period of time. In order to address this discrepancy, the present work proposes Muckle#, a protocol that aims to expand the existing boundaries of efficiency within the HAKE framework. Muckle# utilizes post-quantum KEMs for implicit authentication, drawing inspiration from recent advancements in the domain of Transport Layer Security (TLS) protocols, particularly in KEMTLS (CCS’20).

Our KEM-based approach results in a slightly different message flow compared to prior work and we developed novel proof techniques in the process. Moreover, we implemented a proof of concept, thereby demonstrating practicality of this alternative approach to authentication within HAKE.

Time-bin encoding of quantum information is highly advantageous for long-distance quantum communication protocols over optical fibres due to its inherent robustness in the channel and the possibility of generating high-dimensional quantum states. The most common implementation of time-bin quantum states using unbalanced interferometers presents challenges in terms of stability and flexibility of operation. In particular, a limited number of states can be generated without modifying the optical scheme. Here we present the implementation of a fully controllable arbitrary time-bin quantum state encoder, which is easily scalable to arbitrary dimensions and time-bin separations. The encoder presents high stability and low quantum bit error rate (QBER) for all the tested repetition rates and time-bin separations, without requiring hardware modifications. We further demonstrate phase randomisation and phase encoding without the need for additional resources.

This study presents the design and implementation of a university course for physics teacher training with a focus on quantum technologies and quantum information science. The course aims to equip prospective teachers with the knowledge and skills to teach quantum physics at upper secondary level and provide their students with insights into the professional world of quantum technologies. To this end, the course comprises three parts: a theoretical seminar at university, a didactic internship at quantum technology companies and a transfer phase implementing corresponding teaching units at school. The course was developed and implemented in several cycles within the framework of design-based research. The effect of the course was evaluated by an exploratory interview study. The focus was on its impact on prospective teachers’ attitudes and knowledge concerning quantum technologies, as well as on the implementation of career-oriented teaching units in the classroom. The results show that the internship was considered interesting and motivating by the prospective teachers, who valued the opportunity to gain insights into professional fields. However, transferring the content and experiences from the internship into actual school practice proved to be challenging. This process was perceived as difficult and required extensive support from university supervisors. From the results it can be concluded that the approach achieves its aims of providing prospective teachers with an introduction to quantum technologies and related professions and of stimulating students interest in the subject.

A hybrid optomechanical system incorporating a two-level atom is utilized to realize phonon blockade, with the large-detuned optical mode decoupled from the system via adiabatic approximation. This process establishes an exchange interaction between the two-level atom and the mechanical mode. The findings indicate that both conventional and unconventional phonon blockade mechanisms coexist within the system. By tuning the driving frequency of the two-level atom, the system can be dynamically switched between these two mechanisms. The phonon blockade effect exhibits remarkable robustness against optical dissipation due to the adiabatic elimination of the cavity mode, enabling its realization even in low-Q cavities. In this study, the two-level atom serves not only as a critical component for achieving phonon blockade but also as an additional tool for manipulating the blockade mechanism. Our results provide a promising framework for hybrid optomechanical systems aiming to achieve switchable and robust single-phonon sources.

Efficient adiabatic control schemes, where one steers a quantum system along an adiabatic path ensuring minimal excitations while achieving a desired final state, that enable fast, high-fidelity operations are essential for any practical quantum computation. However, current optimization protocols are not universally tractable due to stringent requirements imposed by the microscopic systems encoding the qubit, including complex energy level structures and unwanted transitions, and generally require a trade-off between speed and fidelity of the operation. Here, we address these challenges by developing a general framework for optimal control based on the quantum metric tensor. This framework allows for fast and high-fidelity adiabatic pulses, even for a dense energy spectrum, based solely on the Hamiltonian of the system instead of the time evolution propagator and independent of the size of the underlying Hilbert space. Furthermore, our framework suppresses diabatic transitions and state-dependent crosstalk effects without the need for additional control fields. As an example, we study the adiabatic charge transfer in a double quantum dot to find optimal control pulses with improved performance. We show that for the geometric protocol, the transfer fidelities are lower bounded (mathcal{F}>99%) for ultrafast (20~mbox{ns}) pulses, regardless of the size of the anti-crossing, while being robust against miscalibration errors and quasistatic noise.