Robust Measurements of n-Point Correlation Functions of Driven-Dissipative Quantum Systems on a Digital Quantum Computer.

We propose and demonstrate a unified hierarchical method to measure n-point correlation functions that can be applied to driven, dissipative, or otherwise open or nonequilibrium quantum systems. In this method, the time evolution of the system is repeatedly interrupted by interacting an ancilla qubit with the system through a controlled operation, and measuring the ancilla immediately afterward. We discuss the robustness of this method as compared to other ancilla-based interferometric techniques (such as the Hadamard test), and highlight its advantages for near-term quantum simulations of open quantum systems. We implement the method on a quantum computer in order to measure single-particle Green's functions of a driven-dissipative fermionic system. This Letter shows that dynamical correlation functions for driven-dissipative systems can be robustly measured with near-term quantum computers.

Impact of SARS-CoV2 infection on mortality and hospitalization in nursing home residents during the "Omicron era".

BACKGROUND: Widespread vaccination and emergence of less aggressive SARS-CoV2 variants may have blunted the unfavourable outcomes of COVID-19 in nursing home (NH) residents. We analysed the course of COVID-19 epidemic in NHs of Florence, Italy, during the "Omicron era" and investigated the independent effect of SARS-CoV2 infection on death and hospitalization risk. METHODS: Weekly SARS-CoV2 infection rates between November 2021 and March 2022 were calculated. Detailed clinical data were collected in a sample of NHs. RESULTS: Among 2044 residents, 667 SARS-CoV2 cases were confirmed. SARS-CoV2 incidence sharply increased during the Omicron era. Mortality rates did not differ between SARS-CoV2-positive (6.9%) and SARS-CoV2-negative residents (7.3%, p = 0.71). Chronic obstructive pulmonary disease and poor functional status, but not SARS-CoV2 infection independently predicted death and hospitalization. CONCLUSIONS: Despite that SARS-CoV2 incidence increased during the Omicron era, SARS-CoV2 infection was not a significant predictor of hospitalization and death in the NH setting.

Mechanism of superconductivity in the Hubbard model at intermediate interaction strength.

We study the fluctuations responsible for pairing in the d-wave superconducting state of the two-dimensional Hubbard model at intermediate coupling within a cluster dynamical mean-field theory with a numerically exact quantum impurity solver. By analyzing how momentum- and frequency-dependent fluctuations generate the d-wave superconducting state in different representations, we identify antiferromagnetic fluctuations as the pairing glue of superconductivity in both the underdoped and the overdoped regime. Nevertheless, in the intermediate coupling regime, the predominant magnetic fluctuations may differ significantly from those described by conventional spin fluctuation theory.

Alzheimer's Disease CSF Biomarker Profiles in Idiopathic Normal Pressure Hydrocephalus.

Patients with idiopathic normal pressure hydrocephalus (iNPH) frequently show pathologic CSF Aß42 levels, comparable with Alzheimer's Disease (AD). Nevertheless, the clinical meaning of these findings has not been fully explained. We aimed to assess the role of AD CSF biomarkers (Aß42, Aß42/Aß40, p-tau, t-tau) in iNPH. To this purpose, we enrolled 44 patients diagnosed with iNPH and 101 with AD. All the patients underwent CSF sampling. We compared CSF biomarker levels in iNPH and AD: Aß42 levels were not different between iNPH and AD, while Aß42/Aß40, p-tau, and t-tau were significantly different and showed excellent accuracy in distinguishing iNPH and AD. A multiple logistic regression analysis showed that Aß42/Aß40 was the variable that most contributed to differentiating the two groups. Furthermore, iNPH patients with positive Aß42/Aß40 had higher p-tau and t-tau than iNPH patients with negative Aß42/Aß40. Those iNPH patients who showed cognitive impairment had lower Aß42/Aß40 and higher p-tau than patients without cognitive impairment. We concluded that positive CSF Aß42 with negative Aß42/Aß40, p-tau, and t-tau is a typical CSF profile of iNPH. On the contrary, positive Aß42/Aß40 in iNPH patients, especially when associated with positive p-tau, may lead to suspicion of a coexistent AD pathology.

Photonic polarization gears for ultra-sensitive angular measurements.

Quantum metrology bears a great promise in enhancing measurement precision, but is unlikely to become practical in the near future. Its concepts can nevertheless inspire classical or hybrid methods of immediate value. Here we demonstrate NOON-like photonic states of m quanta of angular momentum up to m=100, in a setup that acts as a 'photonic gear', converting, for each photon, a mechanical rotation of an angle θ into an amplified rotation of the optical polarization by mθ, corresponding to a 'super-resolving' Malus' law. We show that this effect leads to single-photon angular measurements with the same precision of polarization-only quantum strategies with m photons, but robust to photon losses. Moreover, we combine the gear effect with the quantum enhancement due to entanglement, thus exploiting the advantages of both approaches. The high 'gear ratio' m boosts the current state of the art of optical non-contact angular measurements by almost two orders of magnitude.