We report the successful adaptation of the quasi-boson approximation, a technique traditionally employed in nuclear physics, to the analysis of the two-dimensional electron gas. We show that the correlation energy estimated from this approximation agrees closely with the results obtained from quantum Monte Carlo simulations. Our methodology comprehensively incorporates the exchange self-energy, direct scattering, and exchange scattering for a particle-hole pair excited out of the mean-field ground state within the equation-of-motion framework. The linearization of the equation of motion leads to a generalized random phase approximation (gRPA) eigenvalue equation whose spectrum indicates that the plasmon dispersion remains unaffected by exchange effects, while the particle-hole continuum experiences a marked upward shift due to the exchange self-energy. Using the gRPA excitation spectrum, we calculate the zero-point energy of the quasi-boson Hamiltonian, thereby approximating the correlation energy of the original Hamiltonian. This research highlights the potential and effectiveness of applying the quasi-boson approximation to the gRPA spectrum, a fundamental technique in nuclear physics, to extended condensed matter systems.

We propose an efficient, scalable, and deterministic scheme to generate multiple indistinguishable photons over independent channels, on demand. Our design relies on multiple single-photon sources, each coupled to a waveguide, all interacting with a common cavity mode. The cavity synchronizes and triggers the simultaneous emission of one photon by each source, which are collected by the waveguides. In a state-of-the-art circuit QED implementation, this scheme supports the creation of single photons with $99\%$ purity, indistinguishability, and efficiency at rates of $\sim \mathrm{MHz}$. We also discuss conditions to produce up to 100 photons simultaneously with generation rates of hundreds of kHz. This is orders of magnitude more efficient than previous demultiplexed sources for boson sampling and enables the realization of deterministic multiphoton sources and scalable quantum information processing with photons.

In this article, we consider a realistic waveguide implementation of a quantum network that serves as a testbed to show how to maximize the storage and manipulation of quantum information in QED setups. We analyze two approaches using wavepacket engineering and quantum state transfer protocols. First, we propose and design a family of orthogonal photons in the time domain. These photons allow for a selective interaction with distinct targeted qubits. Yet, mode multiplexing employing resonant nodes is largely spoiled by cross-talk effects. This motivates the second approach, namely, frequency multiplexing. Here we explore the limits of frequency multiplexing through the waveguide, analyzing its capabilities to host and faithfully transmit photons of different frequencies within a given bandwidth. We perform detailed one- and two-photon simulations and provide theoretical bounds for the fidelity of coherent quantum state transfer protocols under realistic conditions. Our results show that state-of-the-art experiments can employ dozens of multiplexed photons with global fidelities fulfilling the requirements imposed by fault-tolerant quantum computing. This is with the caveat that the conditions for single-photon fidelity are met.

Ultracold fermionic atoms, having two valence electrons, exhibit a distinctive internal state structure, wherein the nuclear spin becomes decoupled from the electronic degrees of freedom in the ground electronic state. Consequently, the nuclear spin states are well isolated from the environment, rendering these atomic systems an opportune platform for quantum computation and quantum simulations. Coupling with off-resonance light is an essential tool to selectively and coherently manipulate the nuclear spin states. In this paper, we present a systematic derivation of the effective Hamiltonian for the nuclear spin states of ultracold fermionic atoms due to such an off-resonance light. We obtain compact expressions for the scalar, vector, and tensor light shifts taking into account both linear and quadratic contributions to the hyperfine splitting. The analysis has been carried out using the Green operator approach and solving the corresponding Dyson equation. Finally, we analyze different scenarios of light configurations which lead to the vector- and tensor-light shifts, as well as the pure spin-orbit coupling for the nuclear spin.

We investigate how squeezing techniques can improve the measurement precision in multiphase quantum metrology. While these methods are well studied and effectively used in single-phase estimations, their usage in multiphase situations has yet to be examined. We fill this gap by investigating the mechanism of quantum enhancement in the multiphase scenarios. Our analysis provides theoretical and numerical insights into the optimal condition for achieving the quantum Cramér-Rao bound, helping us understand the potential and mechanism for quantum-enhanced multiphase estimations with squeezing. In this paper, we open possibilities for advancements in quantum metrology and sensing technologies.

We propose an approach for learning probability distributions as differentiable quantum circuits (DQC) that enable efficient quantum generative modeling (QGM) and synthetic data generation. Contrary to existing QGM approaches, we perform training of a DQC-based model, where data is encoded in a latent space with the proposed phase feature map of exponential capacity. This is followed by a trainable quantum circuit, forming the model. We then map the trained model to the bit basis using a fixed unitary transformation, in this case corresponding to a quantum Fourier transform circuit. It allows fast sampling from parametrized distributions using a single-shot readout. Importantly, latent space training provides models that are automatically differentiable, and we show how samples from solutions of stochastic differential equations (SDEs) can be accessed by solving stationary and time-dependent Fokker-Planck equations with a quantum protocol. Our approach opens a route to multidimensional generative modeling with qubit registers explicitly correlated via a (fixed) entangling layer. In this case quantum computers can offer advantage as efficient samplers, which perform complex inverse transform sampling enabled by the fundamental laws of quantum mechanics. On a technical side the advances are multiple, as we introduce the phase feature map, analyze its properties, and develop frequency-taming techniques that include qubitwise training and feature map sparsification.

We theoretically predict a kind of power-law-exponential (PLE) dipole-dipole interaction between quantum emitters in a 1D waveguide QED system. This unconventional long-range interaction is the combination of power-law growth and exponential decay couplings. Applying the PLE interaction to a spin model, we uncover the rich many-body phases. Most remarkably, we find that the PLE interaction can induce the ordered and critical spiral phases. These spiral phases emerge from the strong frustration generated by the power-law factor of the PLE interaction; hence they are absent for other types of long-range interaction, e.g., pure exponential and power-law decay interactions. Our work is also applicable for the higher-dimensional systems. It fundamentally broadens the realm of many-body physics and has significant applications in quantum simulation of strongly correlated matter.

We investigate the topological phase transitions driven by band warping, $\lambda$, and a transverse magnetic field, $B$, for three-dimensional Weyl semimetals. First, we use the Chern number as a mathematical tool to derive the topological $\lambda \times B$ phase diagram. Next, we associate each of the topological sectors to a given angular momentum state of a rotating wave packet. Then we show how the position of the Weyl nodes can be manipulated by a transverse external magnetic field that ultimately quenches the wave packet rotation, first partially and then completely, thus resulting in a sequence of field-induced topological phase transitions. Finally, we calculate the current-induced magnetization and the anomalous Hall conductivity of a prototypical warped Weyl material. Both observables reflect the topological transitions associated with the wave packet rotation and can help to identify the elusive 3D quantum anomalous Hall effect in three-dimensional, warped Weyl materials.

This paper supports the idea that some out-of-equilibrium systems can be described by universality classes. A specific out-of-equilibrium fusing particles model is studied in detail, resulting in a method for determining the number and mass of the final particles based solely on the initial conditions, eliminating the need to evolve the particle system. This method reveals the basis for a universality class encompassing theorem, which is developed to define other models within the same universality class. This result establishes an infinite number of models with the same behavior and scaling, two of which are described in detail.

The Leidenfrost temperature ($T_L$), at which the liquid drop lifetime peaks on a superheated surface, is believed to be wettability dependent. Here, we show that the wettability effect on $T_L$ is subject to the history of the surface temperature. Observing a water drop evaporating on a polished stainless-steel surface heated from 100 to $400{}^{\circ }\mathrm{C}$ in argon gas, we find $T_L\approx 265{}^{\circ }\mathrm{C}$. We then repeat the experiment along decreasing temperature and find a $T_L$ increase by 10 K, i.e., $T_L\approx 275{}^{\circ }\mathrm{C}$. This thermal hysteresis is due to a reduced contact angle during heating. Once hydrophilized, the hysteresis disappears until the contact angle recovers. Similar observations are made in the air where oxidation is possible.

Recently, the physics of many-body quantum chaotic systems close to their ground states has come under intensified scrutiny. Such studies are motivated by the emergence of model systems exhibiting chaotic fluctuations throughout the entire spectrum [the Sachdev-Ye-Kitaev (SYK) model being a renowned representative] as well as by the physics of holographic principles, which likewise unfold close to ground states. Interpreting the edge of the spectrum as a quantum critical point, here we combine a wide range of analytical and numerical methods to the identification and comprehensive description of two different universality classes: the near edge physics of “sparse” and the near edge of “dense” chaotic systems. The distinction lies in the ratio between the number of a system's random parameters and its Hilbert space dimension, which is exponentially small or algebraically small in the sparse and dense case, respectively. Notable representatives of the two classes are generic chaotic many-body models (sparse) and invariant random matrix ensembles or chaotic gravitational systems (dense). While the two families share identical spectral correlations at energy scales comparable to the level spacing, the density of states and its fluctuations near the edge are different. Considering the SYK model as a representative of the sparse class, we apply a combination of field theory and exact diagonalization to a detailed discussion of its edge spectrum. Conversely, Jackiw-Teitelboim gravity is our reference model for the dense class, where an analysis of the gravitational path integral and random matrix theory reveal universal differences to the sparse class, whose implications for the construction of holographic principles we discuss.

Trotterization is the most common and convenient approximation method for Hamiltonian simulations on digital quantum computers, but estimating its error accurately is computationally difficult for large quantum systems. Here, we develop a method for measuring the Trotter error without ancillary qubits on quantum circuits by combining the $m\text{th}$- and $n\text{th}$-order ($m<n$) Trotterizations rather than consulting with mathematical error bounds. Using this method, we make Trotterization precision guaranteed, developing an algorithm named Trotter$(m,n)$, in which the Trotter error at each time step is within an error tolerance $\epsilon$ preset for our purpose. Trotter$(m,n)$ is applicable to both time-independent and -dependent Hamiltonians, and it adaptively chooses almost the largest step size $\delta t$, which keeps quantum circuits shallowest, within the error tolerance. Benchmarking it in a quantum spin chain, we find the adaptively chosen $\delta t$ to be about 10 times larger than that inferred from known upper bounds of Trotter errors.

We propose a scheme to enhance the sensitivity of non-Hermitian optomechanical mass sensors. The benchmark system consists of two coupled optomechanical systems where the mechanical resonators are mechanically coupled. The optical cavities are driven either by a blue-detuned or red-detuned laser to produce gain and loss, respectively. Moreover, the mechanical resonators are parametrically driven through the modulation of their spring constant. For a specific strength of the optical driving field and without parametric driving, the system features an exceptional point (EP). Any perturbation to the mechanical frequency (dissipation) induces a splitting (shifting) of the EP, which scales as the square root of the perturbation strength, resulting in a sensitivity-factor enhancement compared with conventional optomechanical sensors. The sensitivity enhancement induced by the shifting scenario is weak as compared to the one based on the splitting phenomenon. By switching on parametric driving, the sensitivity of both sensing schemes is greatly improved, yielding to a better performance of the sensor. We have also confirmed these results through an analysis of the output spectra and the transmissions of the optical cavities. In addition to enhancing EP sensitivity, our scheme also reveals nonlinear effects on sensing under splitting and shifting scenarios. This work sheds light on mechanisms of enhancing the sensitivity of non-Hermitian mass sensors, paving a way to improve sensors performance for better nanoparticles or pollutants detection and for water treatment.

We analyze the real-time electron-photon dynamics in long- and short-range energy transfer using a real-time quantum electrodynamics coupled cluster model, which allows for spatial and temporal visualization of transport processes. We compute the time evolution of photonic and molecular observables, such as the dipole moment and the photon coordinate, following the excitation of the system induced by short laser pulses. Our simulations show that intermolecular interactions and light-matter strong coupling lead to modified electronic polarization compared to the undressed molecules. The developed method can simulate multiple high-intensity laser pulses while explicitly retaining electronic and electron-photon correlation and is thus suited for nonlinear optics and transient absorption spectroscopies of molecular polaritons.

The transport of neutral atoms in Rydberg quantum computers is a crucial step for the initial arrangement of the grid as well as the dynamic connectivity, recently successfully demonstrated. We study the application of optimal control and the quantum speed limit for the transport of neutral atoms in optical tweezers at finite temperatures and analyze how laser noise affects transport fidelity. Open-loop optimal control significantly enhances transport fidelity, achieving an improvement up to 89% for the lowest analyzed temperature of $1\mu \mathrm{K}$ for a distance of $3\mu \mathrm{m}$. Furthermore, we simulate how the transport fidelity behaves in release-and-capture measurements, which are realizable in the experiment to estimate transport efficiency and implement closed-loop optimal control.

Hybrid superconductor(S)-semiconductor(Sm) devices bring a range of functionalities into superconducting circuits. In particular, hybrid parity-protected qubits and Josephson diodes were recently proposed and experimentally demonstrated. Such devices leverage the nonsinusoidal character of the Josephson current-phase relation (CPR) in highly transparent S-Sm-S junctions. Here, we report an experimental study of superconducting quantum-interference devices (SQUIDs) embedding Josephson field-effect transistors fabricated from a SiGe/Ge/SiGe heterostructure grown on a 200-mm silicon wafer. The single-junction CPR shows up to three harmonics with gate-tunable amplitude. In the presence of microwave irradiation, the ratio of the first two dominant harmonics, corresponding to single and double Cooper-pair transport processes, is consistently reflected in relative weight of integer and half-integer Shapiro steps. A combination of magnetic-flux and gate-voltage control enables tuning the SQUID functionality from a nonreciprocal Josephson-diode regime with 27% asymmetry to a $\pi$-periodic Josephson regime suitable for the implementation of parity-protected superconducting qubits. These results illustrate the potential of Ge-based hybrid devices as versatile and scalable building blocks of superconducting quantum circuits.

The characterization of continuous-variable quantum states is crucial for applications in quantum communication, sensing, simulation, and computing. However, a full characterization of multimode quantum states requires a number of experiments that grows exponentially with the number of modes. Here we propose an alternative approach where the goal is not to reconstruct the full quantum state, but rather to estimate its characteristic function at a given set of points. For multimode states with reflection symmetry, we show that the characteristic function at $M$ points can be estimated using only $O(logM)$ copies of the state, independently of the number of modes. When the characteristic function is known to be positive, as in the case of squeezed vacuum states, the estimation is achieved by an experimentally friendly setup using only beamsplitters and homodyne measurements.

Music, enchanting and poetic, permeates every corner of human civilization. Although music is not unfamiliar to people, our understanding of its essence remains limited, and there is still no universally accepted scientific description. This is primarily due to music being regarded as a product of reason and emotion, making it difficult to define. This article treats musical texts as a complex system. This view echoes linguist John Rupert Firth's insight that understanding a word involves defining it through its surrounding relationships. To construct the network we first build a linear regression model with threshold values to assign conditions to the links among note, time, and volume. Then a clustering coefficient representing regional characteristics is utilized to define the word. Finally, the statistical distribution of the text is strictly required to adhere to the grammatical properties of statistical linguistics, such as Zipf's law, to adjust the weights of the linear regression model and achieve optimal results. These processes enable us to comprehend the structural differences in music across different periods with scientific rigor. Relying on the advantages of structuralism, we concentrate on the relationships and order between the physical elements of music, rather than getting entangled in the blurred boundaries of science and philosophy. Aside from serving as a bridge connecting music to natural language processing and knowledge graphs, the technical methods developed in this work offer a more intuitive approach to elucidate the relationships among elements of a complex network.