Advanced quantum technologies最新文献

The quantum entanglement between the coin state and the position in nonlinear quantum walks is investigated. This study reveals that the nonlinearity of the quantum walk has a significant impact on the enhancement of quantum entanglement in an initially separable bipartite system. It is demonstrated that by selecting appropriate nonlinear parameters the initial separable states may turn to be entangled, and even approach to maximal entangled states.

Deutsch's algorithm is the first quantum algorithm to demonstrate an advantage over classical algorithms. Here, Deutsch's problem is generalized to $�n$ functions and a quantum algorithm with an indefinite causal order is proposed to solve this problem. The algorithm not only reduces the number of queries to the black box by half compared to the classical algorithm, but also significantly decreases the complexity of the quantum circuit and the number of required quantum gates compared to the generalized Deutsch's algorithm. The algorithm is experimentally demonstrated in a stable Sagnac loop interferometer with a common path, which overcomes the obstacles of both phase instability and low fidelity of the Mach–Zehnder interferometer. The experimental results show both ultrahigh and robust success probabilities $��\approx ��99.7��\%�$. This study opens a path toward solving practical problems with indefinite cause-order quantum circuits.

Quantum Machine Learning (QML) leverages the transformative power of quantum computing to explore a broad range of applications, including optimization, data analysis, and complex problem-solving. Central to this study is the using of an innovative intrusion detection system leveraging QML models, with a preference for Quantum Neural Network (QNN) architectures for classification tasks. The inherent advantages of QNNs, notably their parallel processing capabilities facilitated by quantum computers and the exploitation of quantum superposition and parallelism, are elucidated. These attributes empower QNNs to execute certain classification tasks expediently and with heightened efficiency. Empirical validation is conducted through the deployment and testing of a QNN-based intrusion detection system, employing a subset of the CIC-DDoS 2019 dataset. Notably, despite employing a reduced feature set, the QNN-based system exhibits remarkable classification accuracy, achieving a commendable rate of 92.63%. Moreover, the study advocates for the utilization of quantum computing libraries such as Qiskit, facilitating QNN training on local machines or quantum simulators. The findings underscore the efficacy of a QNN-based intrusion detection system in attaining superior classification accuracy when confronted with large-scale training datasets. However, it is imperative to acknowledge the constraints imposed by the limited number of qubits available on local machines and simulators.

Critical phenomena of quantum systems are useful for enhancement of quantum sensing. However, experimental realizations of criticality enhancement are confined to very few systems, owing to the stringent requirements, including the thermodynamical or scaling limit, and fine control of interacting quantum subsystems or particles. Here, a simple critical quantum sensing scheme is proposed that requires neither of these conditions. The critical system is realized with a single parametrically-driven bosonic mode involving many non-interacting bosons. The quantum Fisher information is calculated, which confirms the criticality-enabled enhancement. The response of one of the quadratures to the variation of the control parameter is further detailed. The numerical results reveal that its inverted variance exhibits a diverging behavior at the critical point. Based on the presently available control techniques of parametric driving, it is expected that scheme can be realized in different systems, e.g., ion traps and superconducting circuits.

QSimon algorithm (a full quantum version of Simon's algorithm) is used to find periods in commitment functions and does not require classical calculations. However, QSimon algorithm circuit is incomplete, and the implementation of an essential component (solving boolean linear equations) has high resource consumption. This work further studies QSimon algorithm and applies QSimon algorithm to attack the offset two-round (OTR) scheme. QSimon algorithm is established by quantum boolean linear equations solving algorithm and general quantum truncation technique, which can obtain the period of any truncated function with overwhelming probability. The confidentiality and integrity of the OTR scheme are compromised by employing QSimon algorithm. The attacks ensure a high success rate and realize exponential speedup compared with classical versions.

A cyclic four-mode optical system is investigated with anti-parity-time symmetry. The energy spectra is analyzed and reveal the topological phase transition under different parameter regimes. In the topological phase regions, it is found that the degree of localization of the edge states can be tuned by modulating the vertical hopping strength. Moreover, it is observed that the emergence of nonzero energy edge states and the expansion of the topological phase regions. Meanwhile, it is found that the nonzero energy edge states still adhere to the bulk boundary correspondence, and which can be demonstrated by the bulk bandgap. Zero and nonzero energy edge states are also characterized by Zak phase and hidden Chern number. These results enrich the study of topological phases and edge states in non-Hermitian optical systems.

In this study, the influence of the nonlinear magneto–optical rotation effect on a spin-exchange relaxation-free (SERF) atomic magnetometer is analyzed. The nonlinear effect is described by saturation parameters obtained from the density matrix model considering the Rabi oscillation of the probe light. For better sensitivity, the nonlinear effect is suppressed, and larger output signals are achieved. Based on the nonlinear effect analysis, the relationship between the probe sensitivity and light power density is obtained, and the optimal probe light power density is measured with best probe sensitivity. The best probe sensitivity improves by ≈6 times at the optimal probe light power density compared with that in the conventional linear optical rotation detection. The proposed method can be applied to SERF magnetometers, co-magnetometers, and atomic spin gyroscopes.

Polarization moments play a crucial role in measuring magnetic fields for nonlinear magneto-optical rotation (NMOR) atomic magnetometers. However, it is challenging to distinguish between each polarization moment and evaluate its effect on the magnetic resonance response signal in an alkali vapor cell with buffer gas. To address this issue, a method is proposed to identify different polarization moments through the frequency shift of the magnetic resonance response signal. The proportion of each polarization moment is determined, and it is demonstrated that the magnetic resonance response signal is affected by the hexadecapole moment, resulting in a frequency shift and a decrease in signal amplitude. To mitigate this effect, an approach is investigated to manipulate the polarization moments by flipping the phase of the pump light. Ultimately, a 15.19% increase in response amplitude is achieved in the simulated geomagnetic environment within the magnetic shield barrel. The theory and method presented here provide strong support for the study of the polarization moments in an alkali vapor cell with buffer gas, which potentially enhance the performance of NMOR atomic magnetometers.

Quantum Hall insulators in artificial systems have become a rapidly developing research field in recent years, and have made significant breakthroughs in observing many novel topological phenomena. However, there are few reports about quantum magnon-photon Hall insulators. Here, a scheme is proposed for implementing a 1D cavity magnonics lattice that exhibits quantum magnon-photon Hall insulator behaviors, where each unit cell comprises cavity photons and magnons. By adjusting the system parameters, it is found that not only different energy spectrum structures can be triggered, but also the distribution of the edge states can show the flipping process, which allows the achievement of the multi-channel topological quantum state transmission. In addition, considering the presence of defects, dissipation, and disorder, it is found that appropriate defects can trigger new topological phases, while dissipation only causes shifts in energy levels without changing the position and period of edge states, and disorder leads to shifts in band structures and edge states, thus demonstrating the robustness of edge states. This work offers an effective way to study topological magnon-photon Hall insulators, which will have promising applications in magnon-based quantum information processing.

In the atomic comagnetometer, nuclear spin relaxation is a core parameter that affects the magnetic field suppression ability and stability, and is influenced by various gradient fields. It is necessary to measure and separate the effects of different gradients on nuclear spin, which helps to effectively suppress them separately. This article proposes a periodic optical pumping method for separating and measuring polarization gradient relaxation and magnetic field gradient relaxation, considering the effects of pump light and applied magnetic field. The comprehensive influence model for pump light on transverse nuclear spin relaxation is established, and the measurement steps and parameter selection criteria for the proposed method considering signal decay characteristics are provided. Furthermore, the proportion of various gradient relaxations is quantified. This work provides an evaluation method for gradient relaxation suppression, supporting the improvement of the measurement sensitivity and stability of the atomic comagnetometer.