Superposition Of States Research Articles

Longitudinal encoding of focused vector vortex beams empowered by silicon metasurfaces

Vector vortex beams (VVBs) have attracted considerable applications due to their unique properties, such as vortex filtering, particle trapping, and quantum information. Recently, information coding methods based on metasurface strategies show excellent performance in remote sensing and communication, but the implementation of the longitudinal dimension of the optical field in information coding remains to be developed. Here, we provide a strategy for constructing all-dielectric terahertz (THz) metasurface designs for longitudinal codecs, with the individual focal planes carrying specific encrypted information. Benefiting from the joint modulation of the geometrical and propagation phases, the physical mechanism of spin-polarization multiplexing realizes the coherent superposition of multidimensional focused orbital angular momentum (OAM) modes. As a bridge between Poincaré sphere (PS) and the higher-order Poincaré sphere (HOPS), the proposed design produces a longitudinally controllable variation of OAM mode superposition states. A series of metasurface examples for generating specific coding sequences are characterized by manipulating topological charges and phase factors embedded within orthogonal circularly polarized channels. The longitudinal dimension, as a new coding degree of freedom, can be further expanded for meta-optical applications with the assistance of the VVB pattern.

QPEN: Quantum Projection and Quantum Entanglement Enhanced Network for Cross-Lingual Aspect-Based Sentiment Analysis

Aspect-based sentiment analysis (ABSA) has attracted much attention due to its wide application scenarios. Most previous studies have focused solely on monolingual ABSA, posing a formidable challenge when extending ABSA applications to multilingual scenarios. In this paper, we study upgrading monolingual ABSA to cross-lingual ABSA. Existing methods usually exploit pre-trained cross-lingual language to model cross-lingual ABSA, and enhance the model with translation data. However, the low-resource languages might be under-represented during the pre-training phase, and the translation-enhanced methods heavily rely on the quality of the translation and label projection. Inspired by the observation that quantum entanglement can correlate multiple single systems, we map the monolingual expression to the quantum Hilbert space as a single quantum system, and then utilize quantum entanglement and quantum measurement to achieve cross-lingual ABSA. Specifically, we propose a novel quantum neural model named QPEN (short for quantum projection and quantum entanglement enhanced network). It is equipped with a proposed quantum projection module that projects aspects as quantum superposition on a complex-valued Hilbert space. Furthermore, a quantum entanglement module is proposed in QPEN to share language-specific features between different languages without transmission. We conducted simulation experiments on the classical computer, and experimental results on SemEval-2016 dataset demonstrate that our method achieves state-of-the-art performance in terms of F1-scores for five languages.

Quantum Interference Model for Semantic Biases of Glosses in Word Sense Disambiguation

Word Sense Disambiguation (WSD) aims to determine the meaning of the target word according to the given context. Currently, a single representation enhanced by glosses from different dictionaries or languages is used to characterize each word sense. By analyzing the similarity between glosses of the same word sense, we find semantic biases among them, revealing that the glosses have their own descriptive perspectives. Therefore, the traditional approach of integrating all glosses by a single representation results in failing to present the unique semantics revealed by the individual glosses. In this paper, a quantum superposition state is employed to formalize the representations of multiple glosses of the same word sense to reveal their distributions. Furthermore, the quantum interference model is leveraged to calculate the probability that the target word belongs to this superposition state. The advantage is that the interference term can be regarded as a confidence level to guide word sense recognition. Finally, experiments are performed under standard WSD evaluation framework and the latest cross-lingual datasets, and the results verify the effectiveness of our model.

Cellular automaton ontology, bits, qubits and the Dirac equation

Cornerstones of the Cellular Automaton Interpretation of Quantum Mechanics are its ontological states that evolve by permutations, in this way never creating would-be quantum mechanical superposition states. We review and illustrate this with a classical Ising spin chain. It is shown that it can be related to the Weyl equation in the continuum limit. Yet, the model of discrete spins or bits unavoidably becomes a model of qubits by generating superpositions, if only slightly deformed. We study modifications of its signal velocity which, however, do not relate to mass terms. To incorporate the latter, we consider the Dirac equation in 1+1 dimensions and sketch an underlying discrete deterministic “necklace of necklaces” automaton that qualifies as ontological.

Superposition-enhanced quantum neural network for multi-class image classification

Quantum neural networks have made progress in classification tasks. However, they face challenges when applied to multi-class image classification tasks. In this paper, we propose a superposition-enhanced quantum neural network(SEQNN). Comprising image superposition and quantum binary classifiers(QBCs), SEQNN addresses the following challenges. Firstly, the inherent linearity of quantum evolution is overcome by the one-vs-all strategy combined with QBCs, thereby circumventing the nonlinearity. Subsequently, the second challenge pertains to data imbalance within the subtasks of the one-vs-all strategy. Drawing inspiration from the mixup technique, image superposition is employed to alleviate this imbalance. Two image superposition methods, quantum state superposition(QSS) and angle superposition(AS), are proposed. The simulated experiments on MNIST and Fashion-Mnist show that AS is better than QSS in multi-class image classification tasks. Equipped with AS, SEQNN outperforms existing models and achieves an accuracy of 87.56% on MNIST.

Numerical simulation of large-scale nonlinear open quantum mechanics

We introduce a method to solve nonlinear open quantum dynamics of a particle in situations where its state undergoes significant expansion in phase space while generating small quantum features at the phase-space Planck scale. Our approach involves simulating two steps. First, we transform the Wigner function into a time-dependent frame that leverages information from the classical trajectory to efficiently represent the quantum state in phase space. Next, we simulate the dynamics in this frame using a numerical method that implements this time-dependent nonlinear change of variables. To demonstrate the capabilities of our method, we examine the open quantum dynamics of a particle evolving in a one-dimensional weak quartic potential after initially being ground-state cooled in a tight harmonic potential. This approach is particularly relevant to ongoing efforts to design, optimize, and understand experiments targeting the preparation of macroscopic quantum superposition states of massive particles through nonlinear quantum dynamics. Published by the American Physical Society 2024

Investigation on the Significance of Incorporating Quantum Computing Technology into the Prevailing Curriculum

In conventional data processing, the use of binary bits is required. Online education is most beneficial to those who are already comfortable with technology. It's possible that classical mechanics will be replaced by quantum mechanics in near future. The processing speed of quantum computers is million times faster than that of traditional computer. Qubits are quantum bits. In the quantum technology, superposition and entanglement are important concepts. Traditional computers can benefit from the complex computational problems that are solved by quantum computing. Astrology, cryptography, and weather forecasting can all be simplified using quantum technology. Quantum theory should be studied by students majoring in Science, Technology, Engineering and Mathematics related fields. This paper discusses the advantages, applications, and tactics that can be used to enhance graduate and undergraduate courses in this rapidly expanding field of work.

Nonclassicalities of the Superposition State of Coherent and Photon-Added-Coherent State

Nonclassicalities of the Superposition State of Coherent and Photon-Added-Coherent State

All-optical Stern-Gerlach effect in the time domain.

The Stern-Gerlach experiment, a seminal quantum physics experiment, demonstrated the intriguing phenomenon of particle spin quantization, leading to applications in matter-wave interferometry and weak-value measurements. Over the years, several optical experiments have exhibited similar behavior to the Stern-Gerlach experiment, revealing splitting in both spatial and angular domains. Here we show, theoretically and experimentally, that the Stern-Gerlach effect can be extended into the time and frequency domains. By harnessing Kerr nonlinearity in optical fibers, we couple signal and idler pulses using two pump pulses, resulting in the emergence of two distinct eigenstates whereby the signal and idler are either in phase or out of phase. This nonlinear coupling emulates a synthetic magnetization, and by varying it linearly in time, one eigenstate deflects towards a higher frequency, while the other deflects towards a lower frequency. This effect can be utilized to realize an all-optical, phase-sensitive frequency beam splitter, establishing a new paradigm for classical and quantum data processing of frequency-bin superposition states.

Coherent x-ray spontaneous emission spectroscopy of conical intersections.

Conical intersections are known to play a vital role in many photochemical processes. The breakdown of the Born-Oppenheimer approximation in the vicinity of a conical intersection causes exciting phenomena, such as the ultrafast radiationless decay of excited states. The passage of a molecule through a conical intersection creates a coherent superposition of electronic states via nonadiabatic couplings. Detecting this coherent superposition may serve as a direct probe of the conical intersection. In this paper, we theoretically demonstrate the use of coherent spontaneous emission in samples with long-range order for probing the occurrence of a conical intersection in a molecule. Our simulations show that the spectrum contains clear signatures of the created coherent superposition of electronic states. We investigate the bandwidth requirements for the x-ray probes, which influence the observation of coherent superposition generated by the conical intersection.

Cooperative properties of multiple quantum scattering: II. Coherentlasing

The description model of the multiple scattering lasers using the superposition states between the generated photons in the ensemble of bi-modes of the resonator field, we introduced a concept of indistinguishable energy portions generated in the resonator following multiple scattering. Each of these quasi-quanta has energy equal to the difference between the pumping and scattering quantum energies at each step of multiple scattering. The conversion of the photons in the external electromagnetic mode of the resonator destroys this cooperative correlation between the bi-modes and established conservation lows during the cooperative emission. The master equation containing two parameters connected with the gain of quasi-energy portions, and their annihilation due to the losses from the resonator, is proposed. The competition between these two processes is numerically studied. An attractive problem is connected with established quantum correlations between the photons belonging to non-adjacent modes of the cavity. The time behavior of the evolution of correlations between such modes is observed. This conception may be used for the teleportation of information in other modes during the multiple Raman conversion.

Elastic bit and Berry phase: Investigating topological phenomena in a classical granular network

This study investigates the Berry phase, a key concept in classical and quantum physics, and its manifestation in a classical system. We achieve controlled accumulation of the Berry phase by manipulating the elastic bit (a classical analogue to a quantum bit) in an externally driven, homogeneous, spherical, nonlinear granular network. This is achieved through the classical counterpart of quantum coherent superposition of states. The elastic bit's state vectors are navigated on the Bloch sphere using external drivers' amplitude, phase, and frequency, yielding specific Berry phases. These phases distinguish between trivial and nontrivial topologies of the elastic bit, with the zero Berry phase indicating pure states of the linearized granular system and the nontrivial π phase representing equal superposed states. Other superposed states acquire different Berry phases. Crucially, these phases correlate with the structure's eigenmode vibrations: trivial phases align with distinct, in-phase, or out-of-phase eigenmodes, while nontrivial phases correspond to coupled vibrations where energy is shared among granules, alternating between oscillation and rest. Additionally, we explore Berry's phase generalizations for non-cyclic evolutions. This research paves the way for advanced quantum-inspired sensing and computation applications by utilizing and controlling the Berry phase.

Toward a dual-species atom interferometer with cadmium and strontium

We report on the progress toward a dual-species cadmium and strontium atom interferometer for fundamental physics tests. We have developed and characterized a complete baseline laser system for cadmium, which provides the high power and narrow linewidth necessary for laser cooling and trapping and for performing atom interferometry, with upgraded systems for strontium also implemented. An overview of a design for cooling cadmium is presented, and we outline the basic design of a Cd–Sr atomic fountain, discussing atom launching techniques and the possible role of blackbody radiation. The excellent properties of cadmium and strontium, both individually and as a test pair, are discussed along with the enabled fundamental physics program of tests of the weak equivalence principle and the measurement of relativistic time dilation effects in quantum superpositions of clocks.

A Robust Networking Model With Quantum Evolution for Internet of Things

The Internet of Things (IoT), which includes massive energy-limited sensor nodes, has become the foundation of smart city. Improving the ability of network topology to resist node cascading failures, namely robustness, is the key for IoT to provide stable data-aware services for upper-layer applications. However, the robustness optimization problem of complex topology is an NP-hard problem and cannot be optimally solved in polynomial time. The existing researches try to find the approximate solution by heuristic algorithms, but there are problems of slow convergence and easy to fall into local optimum. Quantum computing has more diverse search spaces due to the existence of quantum superposition states, which can jump out of the local optimum. Therefore, this paper firstly combines quantum computing with topology robustness evolution, and proposes a robust networking model based on quantum evolution. By using the quantum encoding, we design a novel quantum measurement method to collapse quantum states towards a more robust network topology. The experimental results show that our model can jump out of the local optimum with fewer population individuals and achieve higher robustness.

Quantum Computing

Abstract: The revolutionary technology known as quantum computing has the potential to completely transform several industries, including material research, medicine development, optimization, and cryptography. Quantum computers use the ideas of quantum mechanics to harness the power of quantum bits, or qubits, in contrast to classical computers, which function using binary digits, or bits. These qubits, which exist in a superposition of states, allow quantum computers to operate at a computational rate never before possible, potentially tackling challenging issues that are beyond the capabilities of classical systems

Dynamically encircling exceptional points for robust eigenstate generation and all-optical logic operations in a three-dimensional photonic chip

Dynamically encircling exceptional points (EEPs) in non-Hermitian systems have been utilized to realize robust on-chip mode conversions by taking the advantage that the output states are usually fixed and independent of the input states. This highly protects one of the specific eigenstates, but restricts their practical applications requiring superposition states. Here, we realize an on-chip robust eigenstate generator using a depth-varying 3D waveguide to overpass the EEP system. It not only preserves the robustness of the EEP system to generate one determinate eigenstate, but also generates another two-level eigenstate and arbitrary superposition states. Furthermore, by ingeniously combining two identical generators with a symmetric Y combiner, both the all-optical XOR and OR logic operations insensitive to the variations in the input light are realized by the destructive or constructive interference between the two generators' near-neighboring output signals. This paper paves the way for applications of EEP systems to highly robust state manipulations and information processing in integrated photonic and quantum devices. Published by the American Physical Society 2024

Quantum Dynamics of Cavity–Bose–Einstein Condensates in a Gravitational Field

We theoretically studied the quantum dynamics of a cavity–Bose–Einstein condensate (BEC) system in a gravitational field, which is composed of a Fabry–Pérot cavity and a BEC. We also show how to deterministically generate the transient macroscopic quantum superposition states (MQSSs) of the cavity by the use of optomechanical coupling between the cavity field and the BEC. The quantum dynamics of the cavity–BEC system specifically include phase space trajectory dynamics, system excitation number dynamics, quantum entanglement dynamics, and quantum coherence dynamics. We found that the system performs increasingly complex trajectories for larger values of the Newtonian gravity parameter. Moreover, the number of phonon excitations of the system can be increased by coupling the cavity–BEC system to Newtonian gravity, which is analogous to an external direct current drive. The scattering of atoms inside the BEC affects the periodicity of the quantum dynamics of the system. We demonstrate a curious complementarity relation between the quantum entanglement and quantum coherence of cavity–BEC systems and found that the complementarity property can be sustained to some extent, despite being in the presence of the cavity decay. This phenomenon also goes some way to show that quantum entanglement and quantum coherence can be referred to together as quantum resources.

Spontaneous collapse models lead to the emergence of classicality of the Universe

Assuming that Quantum Mechanics is universal and that it can be applied over all scales, then the Universe is allowed to be in a quantum superposition of states, where each of them can correspond to a different space-time geometry. How can one then describe the emergence of the classical, well-defined geometry that we observe? Considering that the decoherence-driven quantum-to-classical transition relies on external physical entities, this process cannot account for the emergence of the classical behaviour of the Universe. Here, we show how models of spontaneous collapse of the wavefunction can offer a viable mechanism for explaining such an emergence. We apply it to a simple General Relativity dynamical model for gravity and a perfect fluid. We show that, by starting from a general quantum superposition of different geometries, the collapse dynamics leads to a single geometry, thus providing a possible mechanism for the quantum-to-classical transition of the Universe. Similarly, when applying our dynamics to the physically-equivalent Parametrised Unimodular gravity model, we obtain a collapse on the basis of the cosmological constant, where eventually one precise value is selected, thus providing also a viable explanation for the cosmological constant problem. Our formalism can be easily applied to other quantum cosmological models where we can choose a well-defined clock variable.

Micrometer-size spatial superpositions for the QGEM protocol via screening and trapping

The quantum gravity-induced entanglement of masses (QGEM) protocol for testing quantum gravity using entanglement witnessing utilizes the creation of spatial quantum superpositions of two neutral, massive matter-wave interferometers kept adjacent to each other, separated by a distance d. The mass and the spatial superposition should be such that the two quantum systems can entangle solely via the quantum nature of gravity. Despite being charge-neutral, many electromagnetic backgrounds can also entangle the systems such as the dipole-dipole and Casimir-Polder interactions. To minimize electromagnetic-induced interactions between the masses, it is pertinent to isolate the two superpositions by a conducting plate. However, the conducting plate will also exert forces on the masses and hence the trajectories of the two superpositions would be affected. To minimize this effect, we propose to trap the two interferometers such that the trapping potential dominates over the attraction between the conducting plate and the matter-wave interferometers. The superpositions can still be created via the Stern-Gerlach effect in the direction parallel to the plate, where the trapping potential is negligible. The combination of trapping and shielding provides a better parameter space for the parallel configuration of the experiment, where the requirement on the size of the spatial superposition, to witness the entanglement between the two masses purely due to their quantum nature of gravity, decreases by at least two orders of magnitude as compared to the original protocol paper. Published by the American Physical Society 2024

Measuring gravity with milligram levitated masses.

Gravity differs from all other known fundamental forces because it is best described as a curvature of space-time. For that reason, it remains resistant to unifications with quantum theory. Gravitational interaction is fundamentally weak and becomes prominent only at macroscopic scales. This means, we do not know what happens to gravity in the microscopic regime where quantum effects dominate and whether quantum coherent effects of gravity become apparent. Levitated mechanical systems of mesoscopic size offer a probe of gravity, while still allowing quantum control over their motional state. This regime opens the possibility of table-top testing of quantum superposition and entanglement in gravitating systems. Here, we show gravitational coupling between a levitated submillimeter-scale magnetic particle inside a type I superconducting trap and kilogram source masses, placed approximately half a meter away. Our results extend gravity measurements to low gravitational forces of attonewton and underline the importance of levitated mechanical sensors.