Advanced quantum technologies最新文献

Photon-number-splitting (PNS) is a well-known theoretical attack on quantum key distribution (QKD) protocols that employ weak coherent states produced by attenuated laser pulses. However, beyond the fact that it has not yet been demonstrated experimentally, its plausibility and effect on quantum bit error rate are questioned. In this work, an experimental scheme is presented for PNS attack employing demonstrated technological capabilities, specifically a single-photon Raman interaction (SPRINT) in a cavity-enhanced three-level atomic system. Several aspects of the proposed implementation are addressed, analytically and simulatively, and the eavesdropper's information gain by the attack is calculated. Furthermore, it is analytically shown that the scheme results in a small (yet non-zero) quantum bit error rate, and a comparison to purely theoretical analyses in the literature is presented. It is believed that the inherent nonlinearity of the PNS attack unavoidably affects the optical modes sent to the receiver, and accordingly will always result in some error rate.

Donor-atom-based nano-devices in silicon represent a breakthrough for individual control of electrons at atomic scale. Here, a finite-bias characterization of electrical transport through such a device, fabricated on a silicon-on-insulator (SOI) wafer with low phosphorus (P) doping, is presented. In this device, multiple quasi-periodic current peaks are observed at low temperatures in the electrical transfer characteristics. Such behavior of the transport characteristics is generally observed in devices having high doping concentration or with selective doping in the channel region to form a multi-donor cluster quantum dot. However, in the present device donor–cluster formation is highly improbable owing to low doping concentration. The observed electrical transport characteristics of the device are explained with a model of two non-interacting donors coupled in series with an unintentionally larger quantum dot, likely formed within the channel due to roughness. Theoretical simulation is also presented here for such a circuit supporting the experimental observations.

Genuine multipartite non-locality is not only of fundamental interest but also serves as an important resource for quantum information theory. The $�N$-partite scenario and provide an analytical upper bound on the maximal expectation value of the generalized Svetlichny inequality achieved by an arbitrary $�N$-qubit system is considered. Furthermore, the constraints on quantum states for which the upper bound is tight are also presented and illustrated by noisy generalized Greenberger-Horne-Zeilinger states. Especially, the new techniques proposed to derive the upper bound allow more insights into the structure of the generalized Svetlichny operator and enable us to systematically investigate the relevant properties. As an operational approach, the variation of the correlation matrix defined makes it more convenient to search for suitable unit vectors that satisfy the tightness conditions. Finally, the results give feasible experimental implementations in detecting the genuine multipartite non-locality and can potentially be applied to other quantum information processing tasks.

Phonon statistics in a hybrid optomechanical system, where a mechanical resonator is quadratically coupled to a cavity and couples with another resonator via Coulomb interaction is studied. It is found that the conventional and unconventional phonon blockade can be both achieved at the same parameter regime, which is confirmed by analytical and numerical results. By analyzing the energy level structure, it is found that the anharmonicity of the system is the joint action of both the Coulomb interaction and the optomechanical coupling, where the nonlinearity introduced by the latter has a more significant effect on one branch of the conventional phonon blockade. In addition, the phonon blockade can be enhanced by introducing the mechanical parametric amplifier with optimal parameters, where the physical mechanism underlying comes from the multi-pathway destructive interference. It is found that the phonon blockade is fragile toward thermal noise due to the weak quantum interference, which can be overcome by increasing the driving strength and applying the mechanical parametric amplifier with suitable parameters. This work may provide a way to manipulate the phonon blockade and can be helpful to the application of quantum information processing.

The vehicle routing problem with time windows (VRPTW) is a common optimization problem faced within the logistics industry. In this work, the use of a previously-introduced qubit encoding scheme is explored to reduce the number of qubits, to evaluate the effectiveness of Noisy Intermediate-Scale Quantum (NISQ) devices when applied to industry relevant optimization problems. A quantum variational approach is applied to a testbed of multiple VRPTW instances ranging from 11 to 3964 routes. These intances are formulated as quadratic unconstrained binary optimization (QUBO) problems based on realistic shipping scenarios. The results are compared with standard binary-to-qubit mappings after executing on simulators as well as various quantum hardware platforms, including IBMQ, AWS (Rigetti), and IonQ. These results are benchmarked against the classical solver, Gurobi. The approach can find approximate solutions to the VRPTW comparable to those obtained from quantum algorithms using the full encoding, despite the reduction in qubits required. These results suggest that using the encoding scheme to fit larger problem sizes into fewer qubits is a promising step in using NISQ devices to find approximate solutions for industry-based optimization problems, although additional resources are still required to eke out the performance from larger problem sizes.

The Jaynes–Cummings Model (JCM) is a fundamental model and building block for light-matter interactions, quantum information and quantum computation. The present work analytically analyzes the topological feature manifested by the JCM in the presence of non-Hermiticity which may arise from dissipation and decay rates. Indeed, the eigenstates of the JCM are topologically characterized by spin windings in 2D plane. The non-Hermiticity tilts the spin-winding plane and induces an out-of-plane component, while the topological feature is maintained. In particular, besides the invariant spin texture nodes, the study reveals a non-Hermiticity-induced reversal transition of the tilting angle and spin winding direction with a fractional phase gain at gap closing, a partially level-independent reversal transition without gap closing, and a completely level-independent super-invariant point with untilted angle and also without gap closing. The result demonstrates that the topological feature is robust against non-Hermiticity, which may be favorable in practical applications. On the other hand, one may conversely make use of the disadvantageous dissipation and decay rates to reverse the spin winding direction, which may add a controlled way for topological manipulation of quantum systems in light-matter interactions.

Stochastic magnetic field noise has a non-negligible negative impact on the performance of quantum precision measurement instruments such as spin-exchange relaxation-free (SERF) co-magnetometer in terms of sensitivity and stability. Conventional magnetic field error analysis and suppression methods are not applicable to stochastic magnetic field noise. In this paper, a stochastic model of the SERF co-magnetometer is proposed to analyze the mechanism of stochastic magnetic field noise. The mean and covariance propagation model of the SERF co-magnetometer is given based on the stochasticity model and statistical principles. The analysis of simulation experiments reveals that reducing the longitudinal electron spin polarization can somewhat reduce the standard deviation of the system output caused by stochastic magnetic field noise. And the atomic ensembles are most resistant to stochastic magnetic field noise when the electron spin polarization strongly couples with the nuclear spin polarization. Finally, the experiments verified the above conclusions. In conclusion, this paper provides theoretical and experimental support for analyzing and suppressing the effect of stochastic magnetic field noise on the SERF co-magnetometer, which is of great significance for improving the sensitivity and stability of the measurement.

Finding parent thermoelectric materials with a high figure of merit is a direction that people pursue. However, the interplay and constraints among the Seebeck coefficient, electrical conductivity, and thermal conductivity pose formidable challenges. In this review, the decoupling effect of anisotropic electronic energy band and multi-valley band structures are initially introduced on the Seebeck coefficient and electrical conductivity. Subsequently, an overview of how materials with a host-guest structure enable the coexistence of high electrical conductivity and low thermal conductivity through unique transport mechanisms is provided. Finally, deliberating on approaches to achieve intrinsic low lattice thermal conductivity, encompassing low dimensionality, low phonon group velocities, and substantial anharmonicity. Moreover, a detailed analysis is conducted to dissect the physical mechanisms through which strong higher-order anharmonicity restricts lattice thermal transport. It is believed that this review serves as a guiding resource for the quest for and design of efficient thermoelectric materials.

Quantum circuits of a general quantum gate acting on multiple $�d$-level quantum systems play a prominent role in multi-valued quantum computation. A recursive Cartan decomposition of semi-simple unitary Lie group $��U�\left(�3^n�\right)�$ (arbitrary $�n$-qutrit gate) is first proposed with a rigorous proof, which completely decomposes an $�n$-qutrit gate into local and non-local operations. On this basis, an explicit quantum circuit is designed for implementing arbitrary two-qutrit gates, and the cost of the construction is 21 generalized controlled $�X$ (GCX) and controlled increment (CINC) gates less than the earlier best result of 26 GGXs. Furthermore, the program is extended to the $�n$-qutrit system, and the quantum circuit of generic $�n$-qutrit gates contained $��\frac{41}{96}�·�3^{�2�n�}�-�4�·�3^{�n�-�1�}�-��(�\frac{n^2}{}$

The development of single-platform qubits, predominant for most of the last few decades, has driven the progress of quantum information technologies but also highlighted the limitations of various platforms. Some inherent issues, such as charge/spin noise in materials hinder certain platforms, while increased decoherence upon attempts to scale up severely impacts qubit quality and coupling on others. In addition, a universal solution for coherent information transfer between quantum systems remains lacking. By combining one or more qubit platforms, one could potentially create new hybrid platforms that might alleviate significant issues that current single-platform qubits suffer from, and in some cases, even facilitate the conversion of static to flying qubits on the same hybrid platform. While nascent, this is an area of rising importance that could shed new light on robust and scalable qubit development and provide new impetus for research directions. Here, the requirements for hybrid systems are defined with artificial atoms in the solid state, exemplified with systems that are proposed or attempted, and conclude with the outlook for such hybrid quantum systems.