The moiré pattern induced by lattice mismatch in transition metal dichalcogenide heterobilayers causes the formation of flat bands, where interactions dominate the kinetic energy. At fractional fillings of the flat valence band, the long-range electron interactions then induce Wigner-Mott crystals. In this paper we investigate the nontrivial electronic phases appearing away from fractional fillings. Either competing phases arise that are characterized as doped Wigner-Mott charge transfer insulators, or alternatively a novel state with frozen charge order is conducting the “electron slush.” We propose that an extremely spatially inhomogeneous local density of states can serve as a key signature of the electron slush.

The concept of local symmetry dynamics has recently been used to demonstrate the evolution of discrete symmetries in one-dimensional chains leading to emergent periodicity. Here we go one step further and show that the unboundedness of this dynamics can lead to chains that consist of subunits of ever-increasing lengths which results in a scaled chain. Mapping this scaled chain onto a corresponding tight-binding Hamiltonian we investigate its spectral and transmission properties. Varying the off-diagonal coupling the eigenvalue spectrum shows different branches with characteristic transitions and peaks in the corresponding density of states. The fluctuations of the energy levels exhibit a hierarchy of minigaps each one accompanied by a characteristic sequence of energy spacings. We develop a local resonator model to describe the spectral properties and gain a deeper understanding of it in the weak-to-intermediate coupling regime. Eigenstate maps together with the inverse participation ratio are used to unravel the characteristic (de)localization properties of the scaled chain with varying coupling strength. Finally, we probe the energy-dependent transmission profile of the scaled chain.

The charge-density-wave (CDW) amplitude mode of the high-pressure sulfur-IV phase is observed between 83 and 146 $\mathrm{G}\mathrm{Pa}$ using Raman spectroscopy. The energy of this excitation softens with pressure yet remains finite at ${\nu }_{\mathrm{CDW}}>100\mathrm{c}{\mathrm{m}}^{-1}$ up to the critical pressure, which is indicative of a weakly first-order transition. Our ab initio calculations show that the finite energy of the excitation originates from the coupling and mutual stabilization of the CDW modulation and a monoclinic lattice distortion. At the critical pressure, both the CDW modulation and lattice distortion disappear simultaneously. Due to the prevalence of CDW phases, this coupling between the CDW modulation and lattice distortion is expected to be relevant for a wide variety of elements and compounds.

We use network theory to study topological features in the hierarchical clustering of dark matter halos. We use public halo catalogs from cosmological $N$-body simulations and construct tree graphs that connect halos within main halo systems. Our analysis shows that these graphs exhibit a power-law degree distribution with an exponent of $-2$, and possess scale-free and self-similar properties according to the criteria of graph metrics. We propose a random graph model with preferential attachment kernels, which effectively incorporate the effects of minor mergers, major mergers, and tidal stripping. The model reproduces the structural, topological properties of simulated halo systems, providing a new way of modeling complex gravitational dynamics of structure formation.

We introduce DeeLeMa, a deep learning-based network for the analysis of energy and momentum in high-energy particle collisions. This novel approach is specifically designed to address the challenge of analyzing collision events with multiple invisible particles, which are prevalent in many high-energy physics experiments. DeeLeMa is constructed based on the kinematic constraints and symmetry of the event topologies. We show that DeeLeMa can robustly estimate mass distribution even in the presence of combinatorial uncertainties and detector smearing effects. The approach is flexible and can be applied to various event topologies by leveraging the relevant kinematic symmetries. This work opens up exciting opportunities for the analysis of high-energy particle collision data, and we believe that DeeLeMa has the potential to become a valuable tool for the high-energy physics community.

We investigate the thermodynamics and fluctuations of a finite-time quantum Otto engine alter- natively driven by a hot-squeezed and a cold thermal reservoir. We show that reservoir squeezing significantly enhances the performance by increasing the thermodynamic efficiency and the power and enables higher stability by decreasing the relative power fluctuations and speeding up the convergence of quantum efficiency to its most probable value. We also demonstrate the counterintuitive result that the efficiency can be larger than the Otto limit in the finite-time operation. Experimental demonstration of this quantum heat engine can be available, based on a single-electron spin pertaining to a trapped ${}^{40}\mathrm{Ca}^{+}$ ion [D. von Lindenfels et al., Phys. Rev. Lett. 123, 080602 (2019)]. We provide a general framework for reliably studying the finite-time nanoengine in finite-time operation which accounts for quantum friction and coherence, deriving important insights into the thermodynamic behaviors beyond the classical thermal machines.

The precise measurement of low temperatures is significant for both the fundamental understanding of physical processes and technological applications. In this work, we present a method for low-temperature measurement that improves thermal range and sensitivity by generating quantum coherence in a thermometer probe. Typically, in temperature measurements, the probes thermalize with the sample being measured. However, we use a two-level quantum system, or qubit, as our probe and prevent direct probe access to the sample by introducing a set of ancilla qubits as an interface. We describe the open system dynamics of the probe using a global master equation and demonstrate that while the ancilla-probe system thermalizes with the sample, the probe per se evolves into a nonthermal steady state due to nonlocal dissipation channels. The populations and coherences of this steady state depend on the sample temperature, allowing for precise and wide-range low-temperature estimation. We characterize the thermometric performance of the method using quantum Fisher information and show that the quantum Fisher information can exhibit multiple and higher peaks at different low temperatures with increasing quantum coherence and the number of ancilla qubits. Our analysis reveals that the proposed approach, using a nonthermal qubit thermometer probe with temperature-dependent quantum coherence generated by a multiple qubit interface between a thermal sample and the probe qubit, can enhance the sensitivity of temperature estimation and broaden the measurable low-temperature range.

Exciton condensation is a phenomenon that indicates the spontaneous formation of electron-hole pairs, which can lead to a phase transition from a semimetal to an excitonic insulator by opening a gap at the Fermi surface. Although the idea of an excitonic insulator has been proposed for several decades, current theoretical approaches can only provide qualitative descriptions, and a quantitative predictive tool is still lacking. To shed light on this issue, we developed an ab initio method based on finite-temperature density functional theory and many-body perturbation theory to calculate the critical behavior of exciton condensation. Utilizing our methodology on monolayer $\mathrm{TiSe}{}_2$, we identify a phase transition involving lattice distortion and nontrivial electron-hole correlation at a temperature exceeding the critical temperature of phonon softening. By breaking down the components within the gap equation, we demonstrate that exciton condensation, mediated by electron-phonon interaction, is the underlying cause of the charge-density-wave state observed in this compound. Overall, the methodology introduced in this work is general and sets the stage for searching for potential excitonic insulators in natural material systems.

Artificial Kitaev chains, formed by quantum dots coupled via superconductors, have emerged as a promising platform for realizing Majorana bound states. Even a minimal Kitaev chain (a quantum dot–superconductor–quantum dot setup) can host Majorana states at discrete sweet spots. However, unambiguously identifying Majorana sweet spots in such a system is still challenging. In this work, we propose an additional dot coupled to one side of the chain as a tool to identify good sweet spots in minimal Kitaev chains. When the two Majorana states in the chain overlap, the extra dot couples to both and thus splits an even-odd ground-state degeneracy when its level is on resonance. In contrast, a ground-state degeneracy will persist for well-separated Majorana states. This difference can be used to identify points in parameter space with spatially separated Majorana states, using tunneling spectroscopy measurements. We perform a systematic analysis of different relevant situations. We show that the additional dot can help distinguish between Majorana sweet spots and other trivial zero-energy crossings. We also characterize the different conductance patterns, which can serve as a guide for future experiments aiming to study Majorana states in minimal Kitaev chains.

Multiband effects in hybrid structures provide a rich playground for unconventional superconductivity. We combine two complementary approaches based on density-functional theory (DFT) and effective low-energy model theory in order to investigate the proximity effect in a Rashba surface state in contact with an $s$-wave superconductor. We discuss these synergistic approaches and combine the effective model and DFT analysis at the example of a Au/Al heterostructure. This allows us to predict finite-energy superconducting pairing due to the interplay of the Rashba surface state of Au, and hybridization with the electronic structure of superconducting Al. We investigate the nature of the induced superconducting pairing, and we quantify its mixed singlet-triplet character. Our findings demonstrate general recipes to explore real material systems that exhibit interorbital pairing away from the Fermi energy.

We demonstrate the Doppler laser cooling of ${}^{40}\mathrm{Ca}^{+}$ ions confined in a segmented linear Paul trap in the presence of a strong quadrupolar magnetic field generated by two permanent ring magnets. Magnetic field gradients of 800 to 1600 G/mm give rise to a highly position-dependent Zeeman shift on the energy levels of the trapped ions. Efficient laser cooling is demonstrated using two 397 nm cooling laser beams with appropriate wavelengths and polarizations and one 866 nm repumper laser beam. Coulomb crystals of ions are found to exhibit similar secular temperatures to those trapped in absence of the magnetic field. In addition, the position dependency of the Zeeman effect is used to generate a map of the field strength. This work forms the basis for developing hybrid trapping experiments for cold ions and neutral molecules that consist of an ion and a magnetic trap to study cold interactions between these species, and opens up new possibilities for quantum-science experiments that employ trapped ions in inhomogeneous magnetic fields.

Twin-field quantum key distribution (TF-QKD) can change the channel-loss dependence of key rates from $O\left(\eta \right)$ to $O\left(\sqrt{\eta }\right)$ and thus significantly increase the secure key rate compared with other existing quantum key distribution protocols. However, it does not take the source security into account in most present TF-QKD protocols. Here, we propose to employ the Hong-Ou-Mandel interference to characterize the source security, i.e., to use the interference visibility to quantify the information leakage from detectable side channels of sources. Furthermore, we establish a corresponding theoretical model and calculate the final key rate, by using the three-intensity decoy-state method and taking finite-data-size effects into account. Consequently, by employing our present scheme, the secure transmission distance can be longer than 100 km under current experimental conditions, significantly surpassing present device-independent QKD systems.

Charged particle tracking has played a key role in the development of particle physics, particularly for understanding phenomena involving short-lived particles precisely. As a platform for high-resolution charged particle tracking, an array of Rydberg atoms is theoretically analyzed. Utilizing the Ramsey sequence to accumulate the phase shift between the ground and a Rydberg excited state induced by the time-dependent Stark shift due to a moving charge, a nonrelativistic charged particle can be tracked with a precision of $\sim 10$ nm, with a potential of higher resolution by optimizing reconstruction algorithm. Although a lot of technical difficulties need to be resolved, the proposed scheme can potentially serve as a charge tracker for relativistic charged particles as well. Also, this analysis can explain potential decoherence in the quantum computation with Rydberg atoms induced by residual ions and cosmic rays.

The Kondo effect is one of the most studied examples of strongly correlated quantum many-body physics. Another type of strongly correlated physics that has only recently been explored in detail (and become experimentally accessible) is that of ultrastrong coupling between light and matter. Here, we study a system which we denote as “Kondo QED” that combines both phenomena, consisting of a two-impurity Anderson model ultrastrongly coupled to a single-mode cavity. While presented as an abstract model, it is relevant for a range of future hybrid cavity-QED systems. Using the hierarchical equations of motion approach we show that the ultrastrong coupling of cavity photons to the electronic states (impurity) noticeably suppresses the electronic Kondo resonance due to the destruction of many-body correlations of the Kondo cloud. We observe this transfer of correlations from the Kondo cloud to the cavity by computing the entropy and mutual information of the impurity-cavity subsystems. In addition, in the weak lead-coupling limit and at zero bias, the model exhibits a ground-state photon accumulation effect originating entirely from counter-rotating terms in the impurity-cavity interaction. Interestingly, in the strong lead-coupling limit, this accumulation is “Kondo enhanced” by new transition paths opening when increasing the hybridization to the leads. This suggests a new mechanism for the generation of real photons from virtual states. We further show that the suppression of the Kondo effect is stable under broadening of the cavity resonance as a consequence of the interaction to an external bosonic continuum. Our findings pave the way for the simultaneous control of both the Kondo QED effect and a photon accumulation effect using the ultrastrong coupling of light and matter.

We consider suspended bilayer graphene under applied perpendicular electric bias field that is known to generate a single particle gap $2\mathrm{\Delta }$ and a related electric polarization $\mathcal{P}$. We argue that the bias also drives a quantum phase transition from band insulator to superfluid exciton condensate. The transition occurs when the exciton binding energy exceeds the band gap $2\mathrm{\Delta }$. We predict the critical bias (converted to band gap), ${\mathrm{\Delta }}_c\approx 60$ meV, below which the excitons condense. The critical temperature, $T_c\left(\mathrm{\Delta }\right)$, is maximum at $\mathrm{\Delta }\approx 25$ meV, $T_c^{max}\approx 115$ K, decreasing significantly at smaller $\mathrm{\Delta }$ due to thermal screening. Entering the condensate phase, the superfluid transition is accompanied by a cusp in the electric polarization $\mathcal{P}\left(\mathrm{\Delta }\right)$ at $\mathrm{\Delta }\to {\mathrm{\Delta }}_c$, which provides a striking testable signature. Additionally, we find that the condensate prefers to form a pair density wave.