Advanced quantum technologies最新文献

This cover image is the 3D rendering of a quantum photonic device concept consisting of a whispering gallery mode microlaser coupled to a ridge waveguide. Such a device could potentially be used to resonantly excite a single-photon emitter that is subsequently integrated into a ridge waveguide. This allows for on-chip and on-demand generation of single photons in the context of integrated quantum photonic circuits. In article number 2400195, Stephan Reitzenstein and co-workers use finite element simulations to investigate the resonance quality of the cavity and its coupling efficiency.

In recent years, rapid advances in non-Hermitian physics and PT-symmetry have brought new opportunities for ultra-sensitive sensing. Especially the presence of controllable non-conservative processes in optical and photonic systems has triggered the development of singularity-based sensing. By flexibly tuning gain, loss, and coupling strength, a series of high-resolution sensing approaches can be realized, with the potential of on-chip integration. Another important non-Hermitian singularity is the coherent perfect absorption-lasing (CPAL) point in the PT-broken phase, which manifests the coexistence of lasing and CPA, exhibiting intriguing properties with considerable sensing potential. As a crucial method for quantum sensing and metrology, the interaction between light and alkali-metal atomic ensembles promises unprecedented sensitivity in the measurement of ultra-weak magnetic field, inertia, and time. Therefore, extending the study of PT-symmetry and singularity-based sensing from conventional solid-state wave systems to diffusive systems such as atomic ensembles is attracting wide attention. In this review, the development of singularity-based sensing in PT/anti-PT symmetric non-Hermitian systems is summarized, with a special focus on photonic platforms including integration with waveguides, microcavities, metasurface, etc. In addition, sensing applications with discussion further extended to atomic ensembles, projecting future research trends in the field.

A quantum polarimetry method using entangled photons to improve measurement precision is introduced in article number 2400059 by Ali Pedram, Vira R. Besaga, Frank Setzpfandt, and Özgür E. Müstecaplıoğlu. By calculating precision bounds and estimating the rotation angle of optical elements, both theoretically and experimentally, it is shown that the capability of entanglement to enhance accuracy is diminished with noise. Experimental noise induces bias in estimators, reducing accuracy and precision depending on chosen estimators and noise channels.

The cover image depicts coupling of the light emission of single quantum emitters to single mode fibers. 3D printed microoptics are used to create the aspheric optics that matches the numerical apertures of light emission cone and fibers to each other. Additionally, a 3D printed chuck is used to place the fiber in the correct distance and with the correct horizontal alignment over the quantum emitters. The article by Harald Giessen and co-workers (article number 2400135) describes the quantification of the alignment accuracy and reproducibility of such 3D printed couplers. [Cover image: © Florian Sterl, Sterltech Optics.]

In article number 2400149, Arindam Dutta and co-workers study the implementation of high-dimensional quantum key distribution protocols, HD-Ext-B92 and HD-BB84, via satellite. The study modifies key rate calculations to explore variations in key rate, probability distribution, and quantum bit error rate (QBER) with respect to dimension and noise. The research examines how the average key rate changes with zenith angle and link length under different weather conditions, showing HD-BB84's superior performance in higher dimensions despite higher QBER saturation. The down-link configuration is shown to be preferable over the up-link configuration.

Since the initial observation of quantum effects, scientists have worked diligently to understand and harness their potential. Thanks to many pioneers, a level where quantum effects can be exploited is reached. Numerous cutting-edge technologies, such as quantum sensing and quantum computing, are proposed. A common trait in all technologies is the need to manipulate and read out their states; therefore, the quantum characteristics of the building blocks must adhere to strict guidelines. Magnetic Molecules (MMs) are promising candidates. They can be obtained indistinguishably, and the control over their structural and electronic properties, makes them appealing to act as quantum bits or “qubits”. MMs can be connected to other units while preserving their coherence properties, enabling the implementation of quantum gates. Furthermore, the low-lying energy levels can be exploited as qudits, which can exist in more than 2 states simultaneously (d > 2), allowing them to hold more information efficiently. The larger electronic/nuclear space in qudits can decrease the number of physical units and enhance computational efficiency, reducing error and making them promise for complex problem-solving. In this perspective article, the physical characteristics of MMs and key achievements that position them as promising candidates for quantum technologies, are described.

Entanglement is a key element in quantum information processing. The detection of entanglement is crucial in many long-range quantum information tasks, including secure communication and fundamental tests of quantum physics, but it is also highly resource-intensive. Even for simple 2-qubits systems, satisfactory detection is challenging. In this work, a modified entanglement detection model combining a convolutional neural network (CNN) and a bidirectional long short-term memory network (BiLSTM) is proposed. It shows that the proposed model can effectively extract the deep features and correlations, enabling accurate classification of simple quantum states, even with only a few tens of training samples. When trained with a large number of highly random samples, the model exhibits outstanding fitting capability, resulting in the reliable classification of nearly all common 2-qubits systems. Furthermore, the model exhibits exceptional adaptability and significant application potential in higher-dimensional systems.

The four-intensity protocol for measurement-device-independent (MDI) quantum key distribution (QKD) is renowned for its excellent performance and extensive experimental implementation. To enhance this protocol, a machine learning-driven rapid parameter optimization method is developed. This initial step involved a speed-up technique that quickly pinpoints the worst-case scenarios with minimal data points during the optimization phase. This is followed by a detailed scan in the key rate calculation phase, streamlining data collection to fit machine learning timelines effectively. Several machine learning models are assessed—Generalized Linear Models (GLM), k-Nearest Neighbors (KNN), Decision Trees (DT), Random Forests (RF), XGBoost (XGB), and Multilayer Perceptron (MLP)—with a focus on predictive accuracy, efficiency, and robustness. RF and MLP were particularly noteworthy for their superior accuracy and robustness, respectively. This optimized approach significantly speeds up computation, enabling complex calculations to be performed in microseconds on standard personal computers, while still achieving high key rates with limited data. Such advancements are crucial for deploying QKD under dynamic conditions, such as in fluctuating fiber-optic networks and satellite communications.

Chiral interaction between light and quantum emitters leads to emergence development of chiral quantum optics and stimulates a wide range of practical applications in quantum regime, such as single-photon isolation and photon unidirectional emission. Cavity optomechanics studying the interaction between optical and mechanical resonators plays an important role in the field of quantum optics. However, how to achieve the chiral interaction between light and mechanical oscillators and explore the applications of the chiral optomechanical systems are still difficult encountered in cavity optomechanics. Here, a method is proposed to achieve chiral optomechanical interaction by exploiting directional squeezed light in a multimode optomechanical system. Based on the chiral interaction between photon and phonon, the nonreciprocal photon transport at a single-photon level can be realized. An isolation ratio of $��>�40��\text{dB}�$ and a negligible insertion loss for the photonic isolator are obtained. This method paves the way to realize chiral optomechanical interaction for conducting chiral optomechanics and opens up the prospect of exploring and utilizing chiral photon–phonon manipulation in the quantum regime.