Advanced quantum technologies最新文献

This work presents an all-fiber telecom-range optical gyroscope employing a spontaneous parametric down conversion crystal to produce ultra-low intensity thermal light by tracing-out one of the heralded photons. The prototype exhibits a detection limit on photon delay measurements of 249 zs over a 72 s averaging time and 26 zs in differential delay measurements at $��t�=�{10}^4�$ s averaging. The detection scheme proves to be the most resource-efficient possible, saturating $��>�99.5�\%�$ of the Cramér–Rao bound. These results are groundbreaking in the context of low-photon regime quantum metrology, paving the way to novel experimental configurations to bridge quantum optics with special or general relativity.

Classification is at the core of data-driven prediction and decision-making, representing a fundamental task in supervised machine learning. Recently, several quantum machine learning algorithms that use quantum kernels as a measure of similarities between data have emerged to perform binary classification on datasets encoded as quantum states. The potential advantages of quantum kernels arise from the ability of quantum computers to construct kernels that are more effective than their classical counterparts in capturing patterns in data or computing kernels more efficiently. However, existing quantum kernel-based classification algorithms do not harness the capability of having data samples in quantum superposition for additional enhancements. This work demonstrates how such capability can be leveraged in quantum kernelized binary classifiers (QKCs) through Quantum Amplitude Estimation (QAE) for quadratic speed-up. Additionally, new quantum circuits are proposed for the QKCs in which the number of qubits is reduced by one, and the circuit depth is reduced linearly with respect to the number of sample data. The quadratic speed-up over previous methods is verified through numerical simulations on the Iris dataset.

Quantum battery (QB) is an energy storage and extraction device conforming to the principles of quantum mechanics. In this study, the characteristics of QBs are considered for the Heisenberg spin chain models in the absence and presence of Dzyaloshinskii-Moriya (DM) interaction. The results show that the DM interaction can enhance the ergotropy and power of QBs, which shows the collective charging can outperform parallel charging regarding QB's performance. Besides, it turns out that first-order coherence is a crucial quantum resource during charging, while quantum steering between the cells is not conducive to the energy storage of QBs. The investigations offer insight into the properties of QBs with Heisenberg spin chain models with DM interaction and facilitate us to acquire the performance in the framework of realistic quantum batteries.

Cavity magnonics has become an intriguing field due to its potential to enable next-generation technologies centered around controlling information exchange in hybrid resonant systems. Investigating the tunability of magnon-photon coupling is key to advancing the field. Here, the observation of coupling between the first order magnon mode in a metallic thin film with a cavity photon mode is reported. An electromagnetic perturbation theory that takes account of perpendicular standing spin waves and their respective dissipation is utilized to estimate the coupling strength. The metallic thin film exhibits notably lower dissipation for the higher-order magnon mode, which is not observed in a thin film magnetic insulator. As such, and given that metallic Kittel magnons typically exhibit lower coherence times than their insulator counterparts, the excitation and coupling to specific higher order modes could lengthen these times compared to previous observations, which may be useful for future integration into quantum devices.

An online estimated state feedback control for trajectory tracking in stochastic open quantum systems is proposed in this paper, which is based on the Lyapunov-based control method. By inducing the error between the controlled state, and the target state as the error state, the trajectory tracking problem of the quantum system is transformed into the error state transition control problem. The quantum state online estimation method QST-OADM is applied to estimate the state of the error state system online, and the tracking control laws are designed by using the quantum Lyapunov stability theorem for driving the stochastic open quantum system from an arbitrary initial state to an arbitrary trajectory. The numerical simulation experiments and results analyses are given.

A basic element of a quantum network based on two single-mode waveguides is proposed with different frequencies connected by a solid-state qubit. Using a simple example of a possible superconducting implementation, the usefulness of the simplifications used in the general theoretical consideration has been justified. The non-classical field in a single-mode with a frequency of $�{\omega }_1$ is fed to the input of a qubit controller and transformed into a non-classical field in an output single-mode with a frequency of $�{\omega }_2$. The interface can establish a quantum connection between solid-state and photonic flying qubits with adjustable pulse shapes and carrier frequencies. This allows quantum information to be transferred to other superconducting or atomic-based quantum registers or chips. The peculiarities of the wave-qubit interactions are described, showing how they help to control the quantum state of the non-classical field. On this basis, the operating principles of solid-state and flying qubits for the future quantum information platforms are considered.

Nondeterministic measurement-based techniques are efficient in reshaping the population distribution of a quantum system but suffer from a limited success probability of holding the system in the target state. To save the experimental cost, a two-step protocol is proposed to cool a resonator down to the ground state with a near-unit probability by exploiting the state-engineering mechanisms of both conditional and unconditional measurements on an ancillary qubit. In the first step, the unconditional measurements on the ancillary qubit are applied to reshape the target resonator from a thermal state to a reserved Fock state. The measurement sequence can be efficiently optimized by reinforcement learning for maximum fidelity. In the second step, the population on the reserved state can be faithfully transferred in a stepwise way to the resonator's ground state with a near-unit fidelity by the conditional measurements on the qubit. Properly designing the projection operator and the measurement interval enables the Kraus operator to act as a lowering operator for neighboring Fock states. Through dozens of measurements in all, the initial thermal average population of the resonator can be reduced by five orders in magnitude with a success probability of over 95%.

In recent years, mediated semi-quantum key distribution (MSQKD) has become a hot topic in quantum cryptography. In this study, the original MSQKD protocol is revisited and a new scheme for proving security based on information theory is developed. At first, a new bound on the key rate of the protocol is derived using an entropic uncertainty relation, thus proving the unconditional security of the protocol. In addition, in the asymptotic scenario, a higher noise tolerance that improves the previous results is found. The legitimate communicating parties have to abort the protocol when they observe the error rate is larger than the noise tolerance. Furthermore, the security of a single-state MSQKD protocol and a single-state semi-quantum key distribution (SQKD) protocol is proven using a similar scheme.

Phonon lasers have long been a subject of interest and possess broad application prospects. Much effort is devoted to lay the foundation of realizing phonon lasers using cavity magnomechanical systems, but up to now no related work is carried out to explore the quantum-squeezing-engineered phonon laser action in cavity magnomechanics. Here, the phonon laser action is investigated in a three-mode cavity magnomechanical system built based on a microwave resonator-yttrium iron garnet sphere composite device, focusing on the effect induced by the magnon-mode squeezing. It is found that the magnon squeezing can improve the effective magnon–photon and magnon–phonon coupling rates. It is demonstrated that the phonon laser action can be engineered and enhanced by changing the squeezing strength. This scheme provides a new mechanism to improve the effective magnon–photon and magnon–phonon couplings for various applications, and demonstrates the feasibility of realizing high-gain and low-threshold phonon lasers with cavity magnomechanical platforms.

In this work, a scalable quantum gate-based algorithm for accelerating causal inference is introduced. Specifically, the formalism of causal hypothesis testing presented in [Nat Commun 10, 1472 (2019)] is considered. Through the algorithm, the existing definition of error probability is generalized, which is a metric to distinguish between two competing causal hypotheses, to a practical scenario. The results on the Qiskit validate the predicted speedup and show that in the realistic scenario, the error probability depends on the distance between the competing hypotheses. To achieve this, the causal hypotheses are embedded as a circuit construction of the oracle. Furthermore, by assessing the complexity involved in implementing the algorithm's subcomponents, a numerical estimation of the resources required for the algorithm is offered. Finally, applications of this framework for causal inference use cases in bioinformatics and artificial general intelligence are discussed.