Advanced quantum technologies最新文献

Employing the constructs of density functional theory (DFT) and the Nonequilibrium Green's Function (NEGF), the investigation extensively explores the electronic and transport properties of zigzag graphene nanoribbons (ZGNRs) doped with vanadium (V). Notably, this inquiry unveils that strategic doping can transform V-doped ZGNRs into spintronic nanodevices with distinctive transport attributes. Initially, the simulations showcase remarkably high spin-filtering efficiencies (SFEs) at certain bias voltages. Furthermore, a giant magnetoresistance (GMR) peaking at 6.87 $�\times$ 10$�{}^3$ is detected. In conclusion, the examination discerns a spin rectifier that exhibits a significant rectification ratio (RR) of 9.62 $�\times$ 10$�{}^2$. This research delineates a viable trajectory for the refinement of high-performance spintronics in ZGNRs via vanadium doping. The implications of this study indicate that the model harbors considerable promise for application in miniature spintronic devices.

Recent work has proposed solving the k-means clustering problem on quantum computers via the Quantum Approximate Optimization Algorithm (QAOA) and coreset techniques. Although the current method demonstrates the possibility of quantum k-means clustering, it does not ensure high accuracy and consistency across a wide range of datasets. The existing coreset techniques are designed for classical algorithms, and there is no quantum-tailored coreset technique designed to boost the accuracy of quantum algorithms. This study proposes solving the k-means clustering problem with the variational quantum eigensolver (VQE) and a customized coreset method, the Contour coreset, which is formulated with a specific focus on quantum algorithms. Extensive simulations with synthetic and real-life data demonstrated that the VQE+Contour Coreset approach outperforms existing QAOA+Coreset k-means clustering approaches with higher accuracy and lower standard deviation. This research demonstrates that quantum-tailored coreset techniques can remarkably boost the performance of quantum algorithms compared to generic off-the-shelf coreset techniques.

Recently, a groundbreaking advancement known as multimode photon blockade (MPB) is proposed by S. Chakram et al. [Nature. Phys. 18, 879-884 (2022)], showcasing its ability to generate multimode W states. Inspired by their work, in this paper, an interesting method is proposed to investigate MPB by engineering the eigenstates of the system Hamiltonian, which is defined as the reverse design method. It is demonstrated that an entangled state is created with a certain probability by sharing a single photon between two coupled Kerr-nonlinear cavities. This entangled state in the two-coupled cavities blocks the creation of the subsequent photons. The system is in a superposition of only the entangled state and the vacuum state. And the photon blockade (PB) exists in two cavities simultaneously. The reversed design method can also be utilized to study MPB in three coupled cavities with Kerr nonlinearities by creating a three-qubit W state.

Quantum secret sharing has many important applications in quantum communication and secure multiparty computing. In this work, a novel measurement-device-independent protocol for three-party quantum secret sharing is put forward, in which the dealer and two sharers are required to prepare Greenberger-Horne-Zeilinger states and single particles, respectively, but they only need to perform single-particle measurement. As a result, this protocol is feasible in experiments by using current technologies. More importantly, it can extend the spatial distance among three participants for quantum state transmissions at least 15.47% compared to the previous protocols.

Experimental implementations of quantum simulation must balance control-field-induced decoherence with the controllability of the quantum system. The ratio of coherent interaction strength to decoherence induced by stimulated emission in atomic systems is typically determined by hardware constraints, limiting the flexibility needed to explore different operating regimes. Here, an optomechanical system is presented for in situ tuning of the coherent spin-motion and spin-spin interaction strength in 2D ion crystals in a Penning trap. Enabled by precision closed-loop piezo-actuated positioners integrated into the confined space of a superconducting magnet's bore, the system allows tuning of the angle-of-incidence of Raman laser beams up to $��{\theta }_{\mathrm{ODF}}�\approx �{28}^{\circ }�$, governing the ratio of coherent to incoherent light-matter interaction for fixed optical power. System characterization involves measurements of the induced mean-field spin precession under the application of an optical dipole force in ion crystals cooled below the Doppler limit through electromagnetically induced transparency cooling. These experiments show approximately a $��\times �2�$ variation in the coherent to incoherent interaction ratio with changing $�{\theta }_{\text{ODF}}$, consistent with theoretical predictions. The system stability is characterized over 6000 s, resulting in a drift rate of $��0�.�{002}^{\circ }�$ h^–1. These technical developments will be crucial in future quantum simulations and sensing applications.

Quantum utility is severely limited in superconducting quantum hardware until now by the modest number of qubits and the relatively high level of control and readout errors, due to the intentional coupling with the external environment required for manipulation and readout of the qubit states. Practical applications in the Noisy Intermediate Scale Quantum (NISQ) era rely on Quantum Error Mitigation (QEM) techniques, which are able to improve the accuracy of the expectation values of quantum observables by implementing classical post-processing analysis from an ensemble of repeated noisy quantum circuit runs. In this work, a recent QEM technique that uses Fuzzy C-Means (FCM) clustering to specifically identify measurement error patterns is focused. For the first time, a proof-of-principle validation of the technique on a two-qubit register, obtained as a subset of a real NISQ five-qubit superconducting quantum processor based on transmon qubits is reported. It is demonstrated that the FCM-based QEM technique allows for reasonable improvement of the expectation values of single- and two-qubit gates-based quantum circuits, without necessarily invoking state-of-the-art coherence, gate, and readout fidelities.

In article number 2300335, Wai Yuen Fu and Hoi Wai Choi review nano-optical techniques for characterising InGaN quantum wells. The study contrasts scanning near-field optical microscopy (SNOM) with electron microscopy-cathodoluminescence (EM-CL), emphasising their crucial roles in revealing the structural and optical properties of InGaN quantum wells. The cover image illustrates these techniques in action, exciting luminescence from the quantum well within the atomic structure of the GaN/InGaN/GaN heterostructure.

Prospective application of quantum technologies for reinforcement learning (RL) is an exciting surge in quantum fields. Quantum random number generators (QRNGs) produce high-frequency random bits, with advantages of true randomness and device independence over pseudo-random numbers. This work explores a new approach, called the quantum random numbers for multi-armed bandit (QRN-MAB) algorithm, for multi-user access in wireless communication system upon random bits. The primary objective of the algorithm is to attain a stable assignment state without further exchange. QRN-MAB utilizes random bits to learn channel features and conducts concurrent exchange to attain stability. This work finds that the intrinsic randomness property used in QRN-MAB enables arrangement to maintain high accuracy and outperforms other classical algorithms. Additionally, the algorithm exhibits strong adaptability when the environment changes over time and quantum random numbers are advantageous over other pseudo-random methods in achieving the target. This work provides an effective way for quantum technologies applications in RL and unfolds a promising avenue to stabilize assignment among multiple users.

Recently, quantum harmonic oscillator (QHO) battery models have been studied with importance because these experimentally realizable batteries have high ergotropy and capacity to store more than one quanta of energy. However, the following fundamental questions are not yet answered: Do these models have any benefit? Are these models stable against the environment? These questions are answered both numerically and analytically by considering a model that allows a laser to shine on a QHO charger, which interacts with a QHO battery. The laser frequency is tuned with the local frequencies of the charger and battery (off-resonance) or the frequency of the global charger-battery system (on-resonance). It is shown that for a fixed laser field amplitude, in the off-resonance (on-resonance) charging process, the maximum energy stored in a battery depends on the detuning and coupling strength (charger dissipation constant). The charging process of the open QHO, which is a simplified model, is also discussed. Further, the charging process of QHO in the simplified model is observed to be faster than the same for the catalytic and non-catalytic batteries. The self-discharging process is found to be almost doubly faster than the charging process, implying that the QHO batteries are unstable against the environment.