Quantum State Engineering by Shortcuts to Adiabaticity in Interacting Spin-Boson Systems.

We present a fast and robust framework to prepare nonclassical states of a bosonic mode exploiting a coherent exchange of excitations with a two-level system ruled by a Jaynes-Cummings interaction mechanism. Our protocol, which is built on shortcuts to adiabaticity, allows for the generation of arbitrary Fock states of the bosonic mode, as well as coherent quantum superpositions of a Schrödinger cat-like form. In addition, we show how to obtain a class of photon-shifted states where the vacuum population is removed, a result akin to photon addition, but displaying more nonclassicality than standard photon-added states. Owing to the ubiquity of the spin-boson interaction that we consider, our proposal is amenable for implementations in state-of-the-art experiments.

Universal Anti-Kibble-Zurek Scaling in Fully Connected Systems.

We investigate the quench dynamics of an open quantum system involving a quantum phase transition. In the isolated case, the quench dynamics involving the phase transition exhibits a number of scaling relations with the quench rate as predicted by the celebrated Kibble-Zurek mechanism. In contact with an environment however, these scaling laws break down and one may observe an anti-Kibble-Zurek behavior: slower ramps lead to less adiabatic dynamics, increasing thus nonadiabatic effects with the quench time. In contrast to previous works, we show here that such anti-Kibble-Zurek scaling can acquire a universal form in the sense that it is determined by the equilibrium critical exponents of the phase transition, provided the excited states of the system exhibit singular behavior, as observed in fully connected models. This demonstrates novel universal scaling laws granted by a system-environment interaction in a critical system. We illustrate these findings in two fully connected models, namely, the quantum Rabi and the Lipkin-Meshkov-Glick models. In addition, we discuss the impact of nonlinear ramps and finite-size systems.

Probing the Dynamics of a Superradiant Quantum Phase Transition with a Single Trapped Ion.

We demonstrate that the quantum phase transition (QPT) of the Rabi model and critical dynamics near the QPT can be probed in the setup of a single trapped ion. We first demonstrate that there exists equilibrium and nonequilibrium scaling functions of the Rabi model by finding a proper rescaling of the system parameters and observables, and show that those scaling functions are representative of the universality class to which the Rabi model belongs. We then propose a scheme that can faithfully realize the Rabi model in the limit of a large ratio of the effective atomic transition frequency to the oscillator frequency using a single trapped ion and, therefore, the QPT. It is demonstrated that the predicted universal functions can indeed be observed based on our scheme. Finally, the effects of realistic noise sources on probing the universal functions in experiments are examined.

Quantum Phase Transition and Universal Dynamics in the Rabi Model.

We consider the Rabi Hamiltonian, which exhibits a quantum phase transition (QPT) despite consisting only of a single-mode cavity field and a two-level atom. We prove QPT by deriving an exact solution in the limit where the atomic transition frequency in the unit of the cavity frequency tends to infinity. The effect of a finite transition frequency is studied by analytically calculating finite-frequency scaling exponents as well as performing a numerically exact diagonalization. Going beyond this equilibrium QPT setting, we prove that the dynamics under slow quenches in the vicinity of the critical point is universal; that is, the dynamics is completely characterized by critical exponents. Our analysis demonstrates that the Kibble-Zurek mechanism can precisely predict the universal scaling of residual energy for a model without spatial degrees of freedom. Moreover, we find that the onset of the universal dynamics can be observed even with a finite transition frequency.

Effect of Socialization on Alzheimer's Disease During the COVID-19 Pandemic.

Age is the strongest risk factor for Alzheimer's disease, a neurodegenerative disease where beta-amyloid plaques accumulate in the brain. Elderly individuals, especially those in nursing homes, were burdened by social isolation during the COVID-19 pandemic. The purpose of this literature review is to describe the effectiveness of social engagement and how combating isolation can have a neuroprotective effect on individuals at risk for Alzheimer's disease. We conducted a search in PubMed examining articles from 2010 to 2023 that discussed the impact of socialization on Alzheimer's disease, particularly during the COVID-19 pandemic. Our search terms were "Alzheimer's Disease + Socialization," "Social Isolation + Alzheimer's Disease," "Alzheimer's Disease + COVID-19," "COVID-19 + Social Isolation," and "Social Interventions + Alzheimer's Disease." Inclusion criteria consisted of patients ages 60 and older with Alzheimer's disease, mention of social isolation or engagement, and any relationship between COVID-19 and Alzheimer's disease. Exclusion criteria were defined as other dementias, non-social interventions, and the effects of different viruses on Alzheimer's disease. After the screening process, 30 articles were included, along with six articles that were suitable to the topic. Of the 36 total articles, 19 focused on an intervention involving socialization; eight explored the effect of social isolation during COVID-19 on patients with Alzheimer's disease; five articles examined social isolation as a risk factor for dementia; and four articles discussed the effect of socialization on Alzheimer's disease. A few studies reported that having a large social network can improve cognition and mood for patients with Alzheimer's disease. Studies reported that interventions such as volunteering, video calls, group art classes, animal interactions, and others produced positive outcomes in Alzheimer's patients, but not all were statistically significant. Our review found a consistent association between a socially integrated lifestyle and a decreased incidence of early-onset dementia. Although not all interventions were solely social, a strong social structure remained at the core of a healthy aging process.

Work statistics and symmetry breaking in an excited-state quantum phase transition.

We examine how the presence of an excited-state quantum phase transition manifests in the dynamics of a many-body system subject to a sudden quench. Focusing on the Lipkin-Meshkov-Glick model initialized in the ground state of the ferromagnetic phase, we demonstrate that the work probability distribution displays non-Gaussian behavior for quenches in the vicinity of the excited-state critical point. Furthermore, we show that the entropy of the diagonal ensemble is highly susceptible to critical regions, making it a robust and practical indicator of the associated spectral characteristics. We assess the role that symmetry breaking has on the ensuing dynamics, highlighting that its effect is only present for quenches beyond the critical point. Finally, we show that similar features persist when the system is initialized in an excited state and briefly explore the behavior for initial states in the paramagnetic phase.

Irreversible processes without energy dissipation in an isolated Lipkin-Meshkov-Glick model.

For a certain class of isolated quantum systems, we report the existence of irreversible processes in which the energy is not dissipated. After a closed cycle in which the initial energy distribution is fully recovered, the expectation value of a symmetry-breaking observable changes from a value differing from zero in the initial state to zero in the final state. This entails the unavoidable loss of a certain amount of information and constitutes a source of irreversibility. We show that the von Neumann entropy of time-averaged equilibrium states increases in the same magnitude as a consequence of the process. We support this result by means of numerical calculations in an experimentally feasible system, the Lipkin-Meshkov-Glick model.