Some aspects of atom-field interactions in curved spacetime are reviewed. Of great interest are quantum radiative and entanglement processes arising out of Rindler and black hole spacetimes, which involve the role of Hawking−Unruh and dynamical Casimir effects. Most of the discussion surrounds the radiative part of interactions. For this, we specifically reassess the conventional understandings of atomic radiative transitions and energy level shifts in curved spacetime. We also briefly outline the status quo of entanglement dynamics study in curved spacetime, and highlight literature related to some novel insights, like entanglement harvesting. On one hand, the study of the role played by spacetime curvature in quantum radiative and informational phenomena has implications for fundamental physics, notably the gravity-quantum interface. In particular, one examines the viability of the Equivalence Principle, which is at the heart of Einstein’s general theory of relativity. On the other hand, it can be instructive for manipulating quantum information and light propagation in arbitrary geometries. Some issues related to nonthermal effects of acceleration are also discussed.
Based on the AdS/CFT correspondence, this study employs an oscillating Gaussian source to numerically study the holographic images of an AdS black hole under
We studied the quantum correlations of a three-body Unruh−DeWitt detector system using genuine tripartite entanglement (GTE) and geometric quantum discord (GQD). We considered two representative three-body initial entangled states, namely the GHZ state and the W state. We demonstrated that the quantum correlations of the tripartite system are completely destroyed at the limit of infinite acceleration. In particular, it is found that the GQD of the two initial states exhibits “sudden change” behavior with increasing acceleration. It is shown that the quantum correlations of the W state are more sensitive than those of the GHZ state under the effect of Unruh thermal noise. The GQD is a more robust quantum resource than the GTE, and we can achieve robustness in discord-type quantum correlations by selecting the smaller energy gap in the detector. These findings provide guidance for selecting appropriate quantum states and resources for quantum information processing tasks in a relativistic setting.
Since the isolation of graphene, two-dimensional (2D) materials have attracted increasing interest because of their excellent chemical and physical properties, as well as promising applications. Nonetheless, particular challenges persist in their further development, particularly in the effective identification of diverse 2D materials, the domains of large-scale and high-precision characterization, also intelligent function prediction and design. These issues are mainly solved by computational techniques, such as density function theory and molecular dynamic simulation, which require powerful computational resources and high time consumption. The booming deep learning methods in recent years offer innovative insights and tools to address these challenges. This review comprehensively outlines the current progress of deep learning within the realm of 2D materials. Firstly, we will briefly introduce the basic concepts of deep learning and commonly used architectures, including convolutional neural and generative adversarial networks, as well as U-net models. Then, the characterization of 2D materials by deep learning methods will be discussed, including defects and materials identification, as well as automatic thickness characterization. Thirdly, the research progress for predicting the unique properties of 2D materials, involving electronic, mechanical, and thermodynamic features, will be evaluated succinctly. Lately, the current works on the inverse design of functional 2D materials will be presented. At last, we will look forward to the application prospects and opportunities of deep learning in other aspects of 2D materials. This review may offer some guidance to boost the understanding and employing novel 2D materials.
We present a theoretical investigation of Majorana zero mode (MZM) assisted spin pumping which consists of a quantum dot (QD) and two normal leads. When the coupling between the MZM and the QD is absent, d.c. pure spin current can be excited by a rotating magnetic field where low energy spin down electrons are flipped to high energy spin up electrons by absorbing photons. However, when the coupling is turned on, the d.c. pure spin current vanishes, and an a.c. charge current emerges with its magnitude independent of the coupling strength. We reveal that this change is due to the formation of a highly localized MZM assisted topological Andreev state at the Fermi level, which allows only the injection of electron pairs with opposite spin into the QD. By absorbing or emitting photons, the electron pairs are separated to opposite spin electrons, and then return back to the lead again, generating an a.c. charge current without spin polarization. We demonstrate the switching from d.c. pure spin current to a.c. charge current based on both Kitaev model and a more realistic topological superconductor nanowire. Although this switching can also be induced by partially separated Andreev bound state (ps-ABS) in the topological trivial phase, it is extremely unstable and highly sensitive to the Zeeman field, which is different from the switching induced by MZM. Our result suggests that quantum spin pumping may be a feasible local transport method for detecting the presence of MZMs at the ends of a superconducting nanowire.
Van der Waals epitaxy allows heterostructure formation without considering the lattice match requirement, thus is a promising method to form 2D/2D and 2D/3D heterojunction. Considering the unique optical properties of CsPbI3 and transition metal dichalcogenides (TMDCs), their heterostructure present potential applications in both photonics and optoelectronics fields. Here, we demonstrate selective growth of cubic phase CsPbI3 nanofilm with thickness as thin as 4.0 nm and Zigzag/armchair orientated nanowires (NWs) on monolayer WSe2. Furthermore, we show growth of CsPbI3 on both transferred WSe2 on copper grid and WSe2 based optoelectrical devices, providing a platform for structure analysis and device performance modification. Transmission electron microscopy (TEM) results reveal the epitaxial nature of cubic CsPbI3 phase. The revealed growth fundamental of CsPbI3 is universal valid for other two-dimensional substrates, offering a great advantage to fabricate CsPbI3 based van der Waals heterostructures (vdWHs). X-ray photoelectron spectroscopy (XPS) and optical characterization confirm the type-II band alignment, resulting in a fast charger transfer process and the occurrence of a broad emission peak with lower energy. The formation of WSe2/CsPbI3 heterostructure largely enhance the photocurrent from 2.38 nA to 38.59 nA. These findings are vital for bottom-up epitaxy of inorganic semiconductor on atomic thin 2D substrates for optoelectronic applications.
MXenes, a novel class of 2D transition metal carbides and nitrides, have recently emerged as a promising candidate in the quest for efficient catalysts for the hydrogen evolution reaction. To enhance the performance of 2D MXenes with modest or poor catalytic efficiency, a particularly prosperous strategy involves doping with transition and noble metal atoms. Taking the Nb4C3O2 monolayer as a model, we explore substitutional metallic impurities, which serve as single-atom catalysts embedded within the Nb4C3O2 surface. Our findings demonstrate the ability to finely tune the atomic H binding energy within a 0.6 eV range, showing the potential for precise control in catalytic applications. Across different transition and noble metals, the single atoms integrated into Nb4C3O2 effectively adjust the free energy of H adsorption at nearby O atoms, achieving values comparable to or superior to Pt catalysts. A comprehensive examination of the electronic properties around the impurities reveals a correlation between changes in local reactivity and charge transfer to neighboring O atoms, where H atoms bind.
In order to fulfill the urgent requirements of functional products, circuit integration of different functional devices are commonly utilized. Thus, issues including production cycle, cost, and circuit crosstalk will get serious. Neuromorphic computing aims to break through the bottle neck of von Neumann architectures. Electronic devices with multi-operation modes, especially neuromorphic devices with multi-mode cognitive activities, would provide interesting solutions. Here, pectin/chitosan hybrid electrolyte gated oxide neuromorphic transistor was fabricated. With extremely strong proton related interfacial electric-double-layer coupling, the device can operate at low voltage of below 1 V. The device can also operate at multi-operation mode, including bottom gate mode, coplanar gate and pseudo-diode mode. Interestingly, the artificial synapse can work at low voltage of only 1 mV, exhibiting extremely low energy consumption of ~7.8 fJ, good signal-to-noise ratio of ~229.6 and sensitivity of ~23.6 dB. Both inhibitory and excitatory synaptic responses were mimicked on the pseudo-diode, demonstrating spike rate dependent plasticity activities. Remarkably, a linear classifier is proposed on the oxide neuromorphic transistor under synaptic metaplasticity mechanism. These results suggest great potentials of the oxide neuromorphic devices with multi-mode cognitive activities in neuromorphic platform.
High-quality antiferromagnetic Mott insulator thin films of LaTiO3 (LTO) were epitaxially grown onto SrTiO3 (STO) (110) substrates using the pulsed laser deposition. The LTO/STO heterostructures are not only highly conducting and ferromagnetic, but also show Kondo effect, Shubnikov‒de Haas (SdH) oscillations with a nonzero Berry phase of
Dielectric engineering plays a crucial role in the process of device miniaturization. Herein we investigate the electrical properties of bilayer GaSe metal-oxide-semiconductor field-effect transistors (MOSFETs), considering hetero-gate-dielectric construction, dielectric materials and GaSe stacking pattern. The results show that device performance strongly depends on the dielectric constants and locations of insulators. When high-k dielectric is placed close to the drain, it behaves with a larger on-state current (Ion) of 5052 μA/μm when the channel is 5 nm. Additionally, when the channel is 5 nm and insulator is HfO2, the largest Ion is 5134 μA/μm for devices with AC stacking GaSe channel. In particular, when the gate length is 2 nm, it still meets the HP requirements of ITRS 2028 for the device with AA stacking when high-k dielectric is used. Hence, the work provides guidance to regulate the performance of the two-dimensional nanodevices by dielectric engineering.
Spin−rotation coupling (SRC) is a fundamental interaction that connects electronic spins with the rotational motion of a medium. We elucidate the Einstein−de Haas (EdH) effect and its inverse with SRC as the microscopic mechanism using the dynamic spin−lattice equations derived by elasticity theory and Lagrangian formalism. By applying the coupling equations to an iron disk in a magnetic field, we exhibit the transfer of angular momentum and energy between spins and lattice, with or without damping. The timescale of the angular momentum transfer from spins to the entire lattice is estimated by our theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm. Moreover, we discover a linear relationship between the magnetic field strength and the rotation frequency, which is also enhanced by a higher ratio of Young’s modulus to Poisson’s coefficient. In the presence of damping, we notice that the spin−lattice relaxation time is nearly inversely proportional to the magnetic field. Our explorations will contribute to a better understanding of the EdH effect and provide valuable insights for magneto-mechanical manufacturing.
Orbital angular momentums (OAMs) greatly enhance the channel capacity in free-space optical communication. However, demodulation of superposed OAM to recognize them separately is always difficult, especially upon multiplexing more OAMs. In this work, we report a directly recognition of multiplexed fractional OAM modes, without separating them, at a resolution of 0.1 with high accuracy, using a multi-task deep learning (MTDL) model, which has not been reported before. Namely, two-mode, four-mode, and eight-mode superposed OAM beams, experimentally generated with a hologram carrying both phase and amplitude information, are well recognized by the suitable MTDL model. Two applications in information transmission are presented: the first is for 256-ary OAM shift keying via multiplexed fractional OAMs; the second is for OAM division multiplexed information transmission in an eightfold speed. The encouraging results will expand the capacity in future free-space optical communication.
We investigated 1-μm multimode fiber laser based on carbon nanotubes, where multiple typical pulse states were observed, including Q-switched, Q-switched mode-locked, and spatiotemporal mode-locked pulses. Particularly, stable spatiotemporal mode-locking was realized with a low threshold, where the pulse duration was 37 ps and the wavelength was centred at 1060.5 nm. Moreover, both the high signal to noise and long-term operation stability proved the reliability of the mode-locked laser. Furthermore, the evolution of the spatiotemporal mode-locked pulses in the cavity was also simulated and discussed. This work exhibits the flexible outputs of spatiotemporal phenomena in multimode lasers based on nanomaterials, providing more possibilities for the development of high-dimensional nonlinear dynamics.
While the common practice of decomposing general quantum algorithms into a collection of single- and two-qubit gates is conceptually simple, in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used. In the noisy intermediate-scale quantum (NISQ) era where a universal error correction is still unavailable, this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms. In this work, we experimentally investigate a three-qubit Controlled-CPHASE-SWAP (CCZS) gate on superconducting quantum circuits. By exploiting the higher energy levels of superconducting qubits, we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns, which is comparable to typical single- and two-qubit gates realized on the same platform. By performing quantum process tomography for the two target qubits, we obtain a process fidelity of
We show that the manifold of quantum states is endowed with a rich and nontrivial geometric structure. We derive the Fubini−Study metric of the projective Hilbert space of a multi-qubit quantum system, endowing it with a Riemannian metric structure, and investigate its deep link with the entanglement of the states of this space. As a measure, we adopt the entanglement distance E preliminary proposed in Phys. Rev. A 101, 042129 (2020). Our analysis shows that entanglement has a geometric interpretation:
We study mathematical, physical and computational aspects of the stabilizer formalism arising in quantum information and quantum computation. The measurement process of Pauli observables with its algorithm is given. It is shown that to detect genuine entanglement we need a full set of stabilizer generators and the stabilizer witness is coarser than the GHZ (Greenberger–Horne–Zeilinger) witness. We discuss stabilizer codes and construct a stabilizer code from a given linear code. We also discuss quantum error correction, error recovery criteria and syndrome extraction. The symplectic structure of the stabilizer formalism is established and it is shown that any stabilizer code is unitarily equivalent to a trivial code. The structure of graph codes as stabilizer codes is identified by obtaining the respective stabilizer generators. The distance of embeddable stabilizer codes in lattices is obtained. We discuss the Knill−Gottesman theorem, tableau representation and frame representation. The runtime of simulating stabilizer gates is obtained by applying stabilizer matrices. Furthermore, an algorithm for updating global phases is given. Resolution of quantum channels into stabilizer channels is shown. We discuss capacity achieving codes to obtain the capacity of the quantum erasure channel. Finally, we discuss the shadow tomography problem and an algorithm for constructing classical shadow is given.
Principal component analysis (PCA) is a widely used tool in machine learning algorithms, but it can be computationally expensive. In 2014, Lloyd, Mohseni & Rebentrost proposed a quantum PCA (qPCA) algorithm [Nat. Phys. 10, 631 (2014)] that has not yet been experimentally demonstrated due to challenges in preparing multiple quantum state copies and implementing quantum phase estimations. In this study, we presented a hardware-efficient approach for qPCA, utilizing an iterative approach that effectively resets the relevant qubits in a nuclear magnetic resonance (NMR) quantum processor. Additionally, we introduced a quantum scattering circuit that efficiently determines the eigenvalues and eigenvectors (principal components). As an important application of PCA, we focused on classifying thoracic CT images from COVID-19 patients and achieved high accuracy in image classification using the qPCA circuit implemented on the NMR system. Our experiment highlights the potential of near-term quantum devices to accelerate qPCA, opening up new avenues for practical applications of quantum machine learning algorithms.
Quantum secure direct communication (QSDC) can transmit secret messages without keys, making it an important branch of quantum communication. We present a hybrid entanglement-based quantum secure direct communication (HE-QSDC) protocol with simple linear optical elements, combining the benefits of both continuous variables (CV) and discrete variables (DV) encoding. We analyze the security and find that the QSDC protocol has a positive security capacity when the bit error rate is less than 0.073. Compared with previous DV QSDC protocols, our protocol has higher communication efficiency due to performing nearly deterministic Bell-state measurement. On the other hand, compared with CV QSDC protocol, this protocol has higher fidelity with large
