When the energy of a quantum emitter aligns with the photonic bandgap of the waveguide, variety of distinct quantum optical phenomena emerges. The paradigmatic example of such nontrivial interaction results in the formation of a qubit-photon bound state (QPBS) where a single photon is exponentially localized around the qubit position. Superconducting quantum circuits has been extensively used for studying QPBS where the photonic band gaps are generated in two-dimensional periodic structures such as photonic crystals and metamaterials. Nonetheless, in all the experiments reported so far, the exponential nature of the bound state wave function is justified by making two assumptions (1) that the waveguide is infinite in length and (2) the coupling to the external ports are absent. These assumptions are difficult to achieve for a physical device and the transition from an experimentally realizable finite-size system to the theoretically assumed infinite device size has never been thoroughly understood. Here, we have realized an alternative platform based on a three-dimensional (3D) rectangular waveguide that has a naturally occurring low-frequency cutoff for generating QPBS as proposed in Shahmoon and Kurizki [Phys. Rev. A 87, 033831 (2013)]. In its theoretical description, we explicitly take into consideration the finite nature of the 3D waveguide arising due to its metallic boundaries and coupling to microwave ports and demonstrate how the infinite waveguide limit arises in such a finite system.

A nanoscale dielectric gap clamped between two metal electrodes may undergo a large resistance change from insulating to highly conducting upon applying an electrical stress. This sudden resistive switching is largely exploited in memristors for emulating synapses in neuromorphic neural networks. Here, we show that volatile resistive switching can be accompanied by a release of electromagnetic radiation spanning the visible spectral region. Of note, we find that the spectrum is characterized by photon energies exceeding the maximum kinetic energy of electrons provided by the switching voltage. This so-called overbias emission can be described self-consistently by a thermal radiation model featuring an out-of-equilibrium electron distribution generated in the device with an effective temperature exceeding 2000 K. The emitted spectrum is understood in terms of hot electrons radiatively decaying to resonant optical modes occurring in a nanoscale ${\mathrm{Si}\mathrm{O}}_2$ matrix located between two $\mathrm{Ag}$ electrodes. We further show that the same device can sustain different emission mechanisms depending on the nature, the intricacy and historicity of its memristive gap. Specifically, when operated in a nonvolatile state, we identify inelastic electron tunneling as an additional process providing photon emission from the device. The correlation between resistive switching and the onset of light emission in atomic scale photonic memristor brings alternative venues to generate light on chip and their exploitation in optical interconnects. Photons emitted during memristive switching can also be monitored to follow the neural activation pathways in memristor-based networks.

The lattice strain induced by metallic electrodes can impair the functionality of advanced quantum devices operating with electron or hole spins. Here, we investigate the deformation induced by CMOS-manufactured titanium nitride electrodes on the lattice of a buried 10-nm-thick $\mathrm{Si}/{\mathrm{Si}}_{0.66}{\mathrm{Ge}}_{0.34}$ quantum well by means of nanobeam scanning x-ray diffraction microscopy. We are able to measure $\mathrm{Ti}\mathrm{N}$-electrode-induced local modulations of the strain tensor components in the range of 2–8 × ${10}^{-4}$ with about 60-nm lateral resolution. We evaluate that these strain fluctuations are reflected in local modulations of the potential of the $\mathrm{Si}$ conduction-band minimum larger than 2 meV, which is close to the orbital energy of an electrostatic quantum dot. We observe that the sign of the strain modulations at a given depth of the quantum-well layer depends on the lateral dimensions of the electrodes. Since our work explores the impact of device geometry on the strain-induced energy landscape, it enables further optimization of the design of scaled CMOS-processed quantum devices.

Mott-insulator-to-metal transitions under an applied electric field are currently the subject of numerous fundamental and applied studies. Exploring the electronic parameters contributing to the external control of conductivity of correlated systems like ${\mathrm{V}}_2{\mathrm{O}}_3$ is an indispensable requirement for next-generation Mottronic devices. Here, we demonstrate a resistive-switching (RS) phenomenon, i.e., a flip from the high-resistance state (HRS) to the low-resistance state in a ${\mathrm{V}}_2{\mathrm{O}}_3$ thin film grown on $\mathrm{Si}$ (001) substrate by applying a dc voltage as external perturbation. The RS effect is explained in connection with the electronic structure by overcoming the electronic correlations and, in the HRS, the ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{Si}$ film is realized to lie in the intermediate regime between the Mott-Hubbard and charge-transfer insulating states. Interestingly, our study reveals an electrically induced nonthermal RS effect in the ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{Si}$ film in terms of different energetics like on-site Coulomb repulsion (U) and charge-transfer energy (Δ), which regulate the exotic properties of this metal oxide and its functionality.

Quantum-disordered models provide a versatile platform to explore the emergence of quantum excitations in many-body systems. The engineering of spin models at the atomic scale with scanning tunneling microscopy and the local imaging of excitations with electrically driven spin resonance has risen as a powerful strategy to image spin excitations in finite quantum spin systems. Here, focusing on $S=1/2$ lattices as realized by $\mathrm{Ti}$ in $\mathrm{Mg}\mathrm{O}$, we show that dynamical spin excitations provide a robust strategy to infer the nature of the underlying Hamiltonian. We show that finite-size interference of the dynamical many-body spin excitations of a generalized long-range Heisenberg model allows the underlying spin couplings to be inferred. We show that the spatial distribution of local spin excitations in $\mathrm{Ti}$ islands and ladders directly correlates with the underlying ground state in the thermodynamic limit. Using a supervised-learning algorithm, we demonstrate that the different parameters of the Hamiltonian can be extracted by providing the spatially dependent and frequency-dependent local excitations that can be directly measured by electrically driven spin resonance with scanning tunneling microscopy. Our results put forward local dynamical excitations in confined quantum spin models as versatile witnesses of the underlying ground state, providing an experimentally robust strategy for Hamiltonian inference in complex real spin models.

Mechanical resonators that possess coupled modes with harmonic frequency relations have recently sparked interest due to their suitability for controllable energy transfer and non-Hermitian dynamics. Here we show coupling between high-$Q$-factor (greater than ${10}^4$) resonances with a nearly 1:1 frequency relation in spatially symmetric microresonators. We develop and demonstrate a method to analyze their dynamical behavior based on the simultaneous and resonant detection of both spectral peaks, and validate this with experimental results. The frequency difference between the peaks modulates their ringdown, and creates a beat pattern in the linear decay. This method applies to both the externally driven regime and the Brownian-motion (thermal) regime, and allows characterization of both linear and nonlinear parameters. The mechanism behind this method renders it broadly applicable to both optical and electrical readout, as well as to different mechanical systems. This will aid studies using near-degenerate mechanical modes, for example, optomechanical energy transfer, synchronization, and gyroscopic sensors.

Teleporting physical quantities to remote locations remains a key challenge for quantum information science and technology. Quantum teleportation has enabled the transfer of quantum information, but teleportation of quantum physical quantities has not yet been realized. Here we report the realization and observation of quantum energy teleportation on real superconducting quantum hardware. We achieve this by using several IBM superconducting quantum computers. The results are consistent with the exact solution of the theory and are improved by the mitigation of measurement error. Quantum energy teleportation requires only local operations and classical communication. Therefore, our results provide a realistic benchmark that is fully achievable with current quantum computing and communication technologies.

We propose compact plasmonic-power-splitters with arbitrary phase responses in the millimetre waveband based on spoof surface plasmon polaritons (SSPPs). Benefitting from the strong field confinements of SSPPs, the branches of the proposed plasmonic-power-splitters can be flexibly bent to meet the design requirement of various situations, while their transmission performance is nearly not affected. Of note, the output phase responses of the plasmonic-power-splitters can be flexibly controlled by adjusting the SSPP propagation constant of each branch only via optimizing the unit size, without changing the overall layout of the power splitter. At a proof of concept, two eight-way plasmonic-power-splitters with exactly the same layout are designed, simulated and measured. They can achieve eight-way equal output powers, but their output phase shifts are 0° and 45°, respectively, at the center frequency of 26 GHz. We show that the designed power splitters have good power allocation performance in an ultrawideband range from 5 to 30 GHz. Though the phase responses cannot maintain good consistency in such a wide bandwidth, it can be designed at any center frequency in the band. The proposed power splitters show big advantages of path compatibility, high compactness, and customizable phase response, which is promising in large-scale integrated circuits.

The synthesized two-dimensional (2D) Ruddlesden-Popper (RP) all-inorganic mixed halogen perovskite, ${\mathrm{Cs}}_2{\mathrm{Pb}\mathrm{I}}_x{\mathrm{Cl}}_{4-x}$ (x = 2) has attracted extensive attention due to its excellent luminescence properties and environmental stability. However, the regulation of halogen ratio and halogen replacement sites on the luminescence properties of 2D RP inorganic mixed halogen perovskite remains unknown. In this paper, the luminescence properties containing band structures, effective mass, exciton-binding energies, photoluminescence emission energy, and the transition dipole moment of 2D RP perovskite ${\mathrm{Cs}}_2{\mathrm{Pb}\mathrm{I}}_x{\mathrm{Cl}}_{4-x}$ (x = 0,1,2,3,4) were studied via density-functional theory. To systematically represent different replacement sites, according to the halogens on the equatorial plane of the octahedron, we divide it into three types. [(1) the halogens on the equatorial plane are $\mathrm{I}$ atoms; (2) the halogens on the equatorial plane are $\mathrm{Cl}$ atoms; (3) the halogens on the equatorial plane are composed of $\mathrm{I}$ and $\mathrm{Cl}$ atoms]. The calculation results show that for structures with replacement sites of the same kind, the band gap, photoluminescence emission energy, and transition dipole moment decrease with the increase of the proportion of $\mathrm{I}$ atoms, while the opposite is true for exciton-binding energy and effective mass. In addition, among the three types of replacement sites, the quadratic eigenvalue problem-Mix (equatorial plane is composed of $\mathrm{I}$ and $\mathrm{Cl}$) type replacement site is the most conducive to the luminescence performance of the material. Our theoretical study will provide guidance for the design and fabrication of highly luminescent 2D RP perovskite.

Quantum key distribution provides a promising solution for sharing secure keys between two distant parties with unconditional security. Nevertheless, quantum key distribution is still severely threatened by the imperfections of devices. In particular, the classical pulse correlation threatens security when sending decoy states. To address this problem and simplify experimental requirements, we propose a phase-matching quantum key distribution protocol without intensity modulation. Instead of using decoy states, we propose an alternative method to estimate the theoretical upper bound on the phase error rate contributed by even-photon-number components. Simulation results show that the transmission distance of our protocol could reach 305 km in telecommunication fiber. Furthermore, we perform a proof-of-principle experiment to demonstrate the feasibility of our protocol, and the key rate reaches 22.5 bit/s under a 45-dB channel loss. Addressing the security loophole of pulse intensity correlation and replacing continuous random phase with a six- or eight-slice random phase, our protocol provides a promising solution for constructing quantum networks.

The classical Drude model provides an accurate description of the plasma resonance of three-dimensional materials, but only partially explains two-dimensional systems where quantum mechanical effects dominate such as P:$\delta$ layers—atomically thin sheets of phosphorus dopants in silicon that induce electronic properties beyond traditional doping. Previously it was shown that P:$\delta$ layers produce a distinct Drude tail feature in ellipsometry measurements. However, the ellipsometric spectra could not be properly fit by modeling the $\delta$ layer as a discrete layer of classical Drude metal. In particular, even for large broadening corresponding to extremely short relaxation times, a plasma resonance feature was anticipated but not evident in the experimental data. In this work, we develop a physically accurate description of this system, which reveals a general approach to designing thin films with intentionally suppressed plasma resonances. Our model takes into account the strong charge-density confinement and resulting quantum mechanical description of a P:$\delta$ layer. We show that the absence of a plasma resonance feature results from a combination of two factors: (i) the sharply varying charge-density profile due to strong confinement in the direction of growth; and (ii) the effective mass and relaxation time anisotropy due to valley degeneracy. The plasma resonance reappears when the atoms composing the $\delta$ layer are allowed to diffuse out from the plane of the layer, destroying its well-confined two-dimensional character that is critical to its distinctive electronic properties.

Experimentally achieving optimal performance of quantum sensors, such as optically pumped magnetometers, is usually challenging and time consuming due to the complexity of the physical system. For a given experiment scheme, there are usually many experiment parameters that need to be fine tuned for achieving a satisfying performance of the quantum sensor. By employing global optimization algorithms, we propose an automatic and efficient way to optimize the sensor performance. We take the most sensitive magnetic field sensor, i.e., the optically pumped magnetometer, as an example to demonstrate how these algorithms facilitate the automatic optimization of quantum sensors. Both the optimization of zero-field magnetometers in a magnetic shield and the finite-field magnetometers in open Earth’s field are demonstrated. A noise floor of approximately $10\mathrm{fT}/{\mathrm{Hz}}^{1/2}$ is achieved within a short time. This method provides an efficient way for quantum sensor optimization and will be helpful for the quantum sensor design.

Atoms are ideal quantum sensors and quantum light emitters. Interfacing atoms with nanophotonic devices promises nanoscale sensing and quantum optical functionalities. But precise optical control of atomic states in these devices is challenged by the spatially varying light-atom coupling strength, which is generic to nanophotonic devices. We demonstrate numerically that despite the inhomogeneity, composite picosecond optical pulses with optimally tailored phases are able to evanescently control the atomic electric dipole transitions nearly perfectly, with fidelity $f>99\mathrm{\%}$ across volumes large enough for, e.g., controlling cold atoms confined in near-field optical lattices. Our proposal is followed by a proof-of-principle demonstration with a ${}^{85}$$\mathrm{Rb}$-vapor–optical-nanofiber interface, where the excitation by an $N=3$ sequence of guided picosecond $D_1$ control pulses reduces the absorption of a coguided nanosecond $D_2$ probe pulse by up to approximately $70\mathrm{\%}$. The close-to-ideal performance is corroborated by comparing the absorption data across the parameter space with first-principles modeling of the mesoscopic atomic vapor response. Extension of the composite technique to $N\ge 5$ appears highly feasible to support arbitrary local control of atomic dipoles with exquisite precision. This unprecedented ability would allow error-resilient atomic spectroscopy and open up a variety of research opportunities in nanophotonic quantum optics.

Topological interface states and the associated enhancement of sound intensity in periodic systems is of fundamental interest in wave physics and may have wide applications, such as in sound detection and biomedical imaging. Yet their occurrence is hitherto limited to the topological transition where the bands inverse. Here we theoretically design and experimentally demonstrate an “acoustic heterostructure” capable of giving rise to interface states at arbitrary frequency within the topological band gap, which is accomplished by adjusting a single structural parameter. The remarkable sound-intensity enhancement, which reaches ${10}^4$, is not affected by this change but remains near constant within the said frequency range and is tested in both a sonic and an elastic wave setting. We envision our strategy to be useful in the design of alternative acoustic sensors and detectors with high flexibility and sensitivity in diverse scenarios, such as nondestructive detection and medical imaging.