EPJ Quantum Technology最新文献

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.

Quantum information hiding, as an extension of classical information hiding techniques into the realm of quantum information, currently focuses on embedding classical bits (0/1) within quantum carriers. This includes methods such as disguising classical secret information as channel noise and embedding it within quantum error correction codes. However, the embedding mechanism for arbitrary quantum states (alpha |0rangle + beta |1rangle ) is still in the exploratory stage. This paper proposes an innovative framework that leverages the redundant space of quantum error correction codes to construct a nonlinear decoding architecture with quantum neural networks. This approach simultaneously achieves both carrier state error correction and secret state embedding and extraction functions. Specifically, the [5,1,3] stabilizer code is used as the carrier, with secret state embedding achieved through single-qubit substitution, and a quantum autoencoder is designed for steganographic state information decoding. The proposed framework features fully quantum-based input/output systems, overcoming the limitations of traditional variational quantum circuits that rely on probabilistic measurements for output generation. By performing full ground-state measurements at the autoencoder bottleneck layer and optimizing the parallel sub-network architecture, the network achieves efficient convergence and effective extraction of single-copy quantum states. Experimental results show that under the conditions of optimized parameters and data size of 20, the training losses for the carrier and secret states are 0.03 and 0.08, respectively, with test fidelities of 0.92 and 0.93. For a data size of 50, the secret states recovery fidelity exceeds 0.87. KS test analysis indicates that the full ground-state measurement and parallel sub-network are key strategies for achieving network performance. Equivalent error analysis shows that this approach successfully utilizes the potential redundant space of quantum error correction codes, providing new research directions for quantum state information hiding.

Two sets of quantum entangled states that are equivalent under local unitary transformations may exhibit identical effectiveness and versatility in various quantum information processing tasks. Consequently, classification under local unitary transformations has become a fundamental issue in the theory of quantum entanglement. The primary objective of this work is to establish a practical LU-classification for all sets of (l (geq 2)) generalized Bell states (GBSs), high-dimensional generalizations of Bell states, in a bipartite system (mathbb{C}^{d}otimes mathbb{C}^{d}) with (dgeq 3). Based on this classification, we determine the minimal cardinality of indistinguishable GBS sets in (mathbb{C}^{6}otimes mathbb{C}^{6}) under one-way local operations and classical communication (one-way LOCC). We first propose two classification methods based on LU-equivalence for all sets of l GBSs (l-GBS sets). We then establish LU-classification for all 2-GBS, 3-GBS, 4-GBS and 5-GBS sets in (mathbb{C}^{6}otimes mathbb{C}^{6}). Since LU-equivalent sets share identical local distinguishability, it suffices to examine representative GBS sets from equivalent classes. Notably, we identify a one-way LOCC indistinguishable 4-GBS set among these representatives, thereby resolving the case of (d = 6) for the problem of determining the minimum cardinality of one-way LOCC indistinguishable GBS sets in (Yuan et al. in Quantum Inf Process. 18:145, 2019) or (Zhang et al. in Phys Rev A 91:012329, 2015).

Photoluminescent point defects, such as nitrogen vacancy (NV) color centers in diamond, have attracted much attention as solid-state qubits. In recent years, a method has been developed to dope ions one-by-one into a solid substrate with Ångström position accuracy using a Paul trap. However, the dopant atoms must be laser-cooled, and the atoms that are promising dopants for solid-state quantum devices, such as nitrogen, cannot be directly applied. In the previous studies, the cooling of the dopant ions has been achieved using a sympathetic cooling technique, in which the laser-cooled atoms are sandwiched, but this method has several problems such as the need for a mechanism to remove the laser-cooled atoms and the inability to distinguish between the dopant atoms and contaminations. We show that these problems can be overcome by directly cooling the hydrogenated ions instead of sympathetically cooling the ions, and the position accuracy can be improved.

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.