Signatures of Dissipation Driven Quantum Phase Transition in Rabi Model.

By using the worldline Monte Carlo technique, matrix product state, and a variational approach à la Feynman, we investigate the equilibrium properties and relaxation features of the dissipative quantum Rabi model, where a two level system is coupled to a linear harmonic oscillator embedded in a viscous fluid. We show that, in the Ohmic regime, a Beretzinski-Kosterlitz-Thouless quantum phase transition occurs by varying the coupling strength between the two level system and the oscillator. This is a nonperturbative result, occurring even for extremely low dissipation magnitude. By using state-of-the-art theoretical methods, we unveil the features of the relaxation towards the thermodynamic equilibrium, pointing out the signatures of quantum phase transition both in the time and frequency domains. We prove that, for low and moderate values of the dissipation, the quantum phase transition occurs in the deep strong coupling regime. We propose to realize this model by coupling a flux qubit and a damped LC oscillator.

Chronic inflammatory demyelinating polyradiculoneuropathy: can a diagnosis be made in patients not fulfilling electrodiagnostic criteria?

BACKGROUND AND PURPOSE: The aim was to identify the clinical and diagnostic investigations that may help to support a diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) in patients not fulfilling the European Federation of Neurological Societies and Peripheral Nerve Society (EFNS/PNS) electrodiagnostic criteria. METHODS: The data from patients with a clinical diagnosis of CIDP included in a national database were retrospectively reviewed. RESULTS: In all, 535 patients with a diagnosis of CIDP were included. This diagnosis fulfilled the EFNS/PNS criteria in 468 patients (87.2%) (definite in 430, probable in 33, possible in three, while two had chronic immune sensory polyradiculopathy). Sixty-seven patients had a medical history and clinical signs compatible with CIDP but electrodiagnostic studies did not fulfill the EFNS/PNS criteria for CIDP. These patients had similar clinical features and frequency of abnormal supportive criteria for the diagnosis of CIDP compared to patients fulfilling EFNS/PNS criteria. Two or more abnormal supportive criteria were present in 40 (61.2%) patients rising to 54 (80.6%) if a history of a relapsing course as a possible supportive criterion was also included. Increased cerebrospinal fluid proteins and response to immune therapy most frequently helped in supporting the diagnosis of CIDP. Response to therapy was similarly frequent in patients fulfilling or not EFNS/PNS criteria (87.3% vs. 85.9%). CONCLUSIONS: Patients with a clinical diagnosis of CIDP had similar clinical findings, frequency of abnormal supportive criteria and response to therapy compared to patients fulfilling EFNS/PNS criteria. The presence of abnormal supportive criteria may help in supporting the diagnosis of CIDP in patients with a medical history and clinical signs compatible with this diagnosis but non-diagnostic nerve conduction studies.

Phase-Preserving Linear Amplifiers Not Simulable by the Parametric Amplifier.

It is commonly accepted that a parametric amplifier can simulate a phase-preserving linear amplifier regardless of how the latter is realized [C. M. Caves et al., Phys. Rev. A 86, 063802 (2012)PLRAAN1050-294710.1103/PhysRevA.86.063802]. If true, this reduces all phase-preserving linear amplifiers to a single familiar model. Here we disprove this claim by constructing two counterexamples. A detailed discussion of the physics of our counterexamples is provided. It is shown that a Heisenberg-picture analysis facilitates a microscopic explanation of the physics. This also resolves a question about the nature of amplifier-added noise in degenerate two-photon amplification.

Risk factors for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP): antecedent events, lifestyle and dietary habits. Data from the Italian CIDP Database.

BACKGROUND AND PURPOSE: The role of lifestyle and dietary habits and antecedent events has not been clearly identified in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). METHODS: Information was collected about modifiable environmental factors and antecedent infections and vaccinations in patients with CIDP included in an Italian CIDP Database. Only patients who reported not having changed their diet or the lifestyle habits investigated in the study after the appearance of CIDP were included. The partners of patients with CIDP were chosen as controls. Gender-matched analysis was performed with randomly selected controls with a 1:1 ratio of patients and controls. RESULTS: Dietary and lifestyle data of 323 patients and 266 controls were available. A total of 195 cases and 195 sex-matched controls were used in the analysis. Patients eating rice at least three times per week or eating fish at least once per week appeared to be at decreased risk of acquiring CIDP. Data on antecedent events were collected in 411 patients. Antecedent events within 1-42 days before CIDP onset were reported by 15.5% of the patients, including infections in 12% and vaccinations in 1.5%. Patients with CIDP and antecedent infections more often had an acute onset of CIDP and cranial nerve involvement than those without these antecedent events. CONCLUSIONS: The results of this preliminary study seem to indicate that some dietary habits may influence the risk of CIDP and that antecedent infections may have an impact on the onset and clinical presentation of the disease.

Orthogonality Catastrophe in Dissipative Quantum Many-Body Systems.

We present an analog of the phenomenon of orthogonality catastrophe in quantum many-body systems subject to a local dissipative impurity. We show that the fidelity F(t), giving a measure for distance of the time-evolved state from the initial one, displays a universal scaling form F(t)∝t^{θ}e^{-γt}, when the system supports long-range correlations, in a fashion reminiscent of traditional instances of orthogonality catastrophe in condensed matter. An exponential falloff at rate γ signals the onset of environmental decoherence, which is critically slowed down by the additional algebraic contribution to the fidelity. This picture is derived within a second-order cumulant expansion suited for Liouvillian dynamics, and substantiated for the one-dimensional transverse field quantum Ising model subject to a local dephasing jump operator, as well as for XY and XX quantum spin chains, and for the two-dimensional Bose gas deep in the superfluid phase with local particle heating. Our results hint that local sources of dissipation can be used to inspect real-time correlations and to induce a delay of decoherence in open quantum many-body systems.

Boundary Time Crystals.

In this work we introduce boundary time crystals. Here continuous time-translation symmetry breaking occurs only in a macroscopic fraction of a many-body quantum system. After introducing their definition and properties, we analyze in detail a solvable model where an accurate scaling analysis can be performed. The existence of the boundary time crystals is intimately connected to the emergence of a time-periodic steady state in the thermodynamic limit of a many-body open quantum system. We also discuss connections to quantum synchronization.

Majorana Quasiparticles Protected by Z_{2} Angular Momentum Conservation.

We show how angular momentum conservation can stabilize a symmetry-protected quasitopological phase of matter supporting Majorana quasiparticles as edge modes in one-dimensional cold atom gases. We investigate a number-conserving four-species Hubbard model in the presence of spin-orbit coupling. The latter reduces the global spin symmetry to an angular momentum parity symmetry, which provides an extremely robust protection mechanism that does not rely on any coupling to additional reservoirs. The emergence of Majorana edge modes is elucidated using field theory techniques, and corroborated by density-matrix-renormalization-group simulations. Our results pave the way toward the observation of Majorana edge modes with alkaline-earth-like fermions in optical lattices, where all basic ingredients for our recipe-spin-orbit coupling and strong interorbital interactions-have been experimentally realized over the last two years.

Exotic Attractors of the Nonequilibrium Rabi-Hubbard Model.

We explore the phase diagram of the dissipative Rabi-Hubbard model, as could be realized by a Raman-pumping scheme applied to a coupled cavity array. There exist various exotic attractors, including ferroelectric, antiferroelectric, and incommensurate fixed points, as well as regions of persistent oscillations. Many of these features can be understood analytically by truncating to the two lowest lying states of the Rabi model on each site. We also show that these features survive beyond mean field, using matrix product operator simulations.

Neuromyelitis optica spectrum disorders: long-term safety and efficacy of rituximab in Caucasian patients.

OBJECTIVE: To assess the long-term benefit-risk profile of repeated courses of rituximab in Caucasian patients affected by neuromyelitis optica (NMO) and related disorders, in everyday clinical practice. METHODS: This is a prospective observational study performed at San Raffaele Hospital, Milan, Italy. From February 2006, we recruited 21 patients affected by NMO and NMO spectrum of disorders (NMOSD) whom underwent at least one cycle of intravenous (i.v.) rituximab and then were followed for at least 2 years. RESULTS: At a mean follow-up time of 48 months, we observed a significant reduction of the annualized relapse rate (ARR), from 2.0 to 0.16 (p < 0.01); and of the median Expanded Disability Status Scale (EDSS), from 5.5 to 4.0 (p < 0.013). There were 12 patients (57%) who remained disease free during the follow-up period. Five patients (24%) reported mild hematological adverse events. Serious infectious adverse events were reported by another four patients: These were all wheelchair bound at the beginning of their rituximab treatment. CONCLUSIONS: A fixed treatment scheme of rituximab, with re-treatment every 6 months, was efficacious for NMO and NMOSD, with a good safety profile; however, to obtain an even better benefit-risk ratio, close monitoring of CD19(+) B cells should be performed before the re-treatment of patients with high-level disability, concomitant leukopenia and hypogammaglobulinemia.

Measures of quantum synchronization in continuous variable systems.

We introduce and characterize two different measures which quantify the level of synchronization of coupled continuous variable quantum systems. The two measures allow us to extend to the quantum domain the notions of complete and phase synchronization. The Heisenberg principle sets a universal bound to complete synchronization. The measure of phase synchronization is, in principle, unbounded; however, in the absence of quantum resources (e.g., squeezing) the synchronization level is bounded below a certain threshold. We elucidate some interesting connections between entanglement and synchronization and, finally, discuss an application based on quantum optomechanical systems.

Environment-governed dynamics in driven quantum systems.

We show that the dynamics of a driven quantum system weakly coupled to the environment can exhibit two distinct regimes. While the relaxation basis is usually determined by the system+drive Hamiltonian (system-governed dynamics), we find that under certain conditions it is determined by specific features of the environment, such as, the form of the coupling operator (environment-governed dynamics). We provide an effective coupling parameter describing the transition between the two regimes and discuss how to observe the transition in a superconducting charge pump.

Extracting quantum work statistics and fluctuation theorems by single-qubit interferometry.

We propose an experimental scheme to verify the quantum nonequilibrium fluctuation relations using current technology. Specifically, we show that the characteristic function of the work distribution for a nonequilibrium quench of a general quantum system can be extracted by Ramsey interferometry of a single probe qubit. Our scheme paves the way for the full characterization of nonequilibrium processes in a variety of quantum systems, ranging from single particles to many-body atomic systems and spin chains. We demonstrate our idea using a time-dependent quench of the motional state of a trapped ion, where the internal pseudospin provides a convenient probe qubit.

Consistence and discrepancy of neuropathic pain screening tools DN4 and ID-Pain.

Pain is a subjective condition that cannot be objectively measured; for this reason, self patient-perspective is crucial. Recently, several screening tools to discriminate between nociceptive and neuropathic pain have been developed. We aimed at assessing the consistence and discrepancy of two widely used screening tools, The Douleur Neuropathique 4 (DN4) and the 6-item questionnaire (ID-Pain), by comparing their ability in discriminating neuropathic from nociceptive pain. DN4 and ID-Pain were administered to 392 Italian patients attending 16 outpatient services for peripheral nerve diseases. Based on medical history, clinical findings and diagnostic tools, patients were divided into two groups (neuropathic and nociceptive). Globally, ID-Pain identified neuropathic pain in 60 % of patients (38 % probable, 22 % likely). Interestingly also DN4 diagnosed neuropathic pain in 60 % of cases. A discrepancy was observed in 16 % of cases. DN4 and ID-Pain resulted to be highly interrelated in the identification of neuropathic pain. Sensitivity of DN4 was 82 % and specificity was 81 %, while ID-Pain (considering both probable and likely groups) showed sensitivity 78 % and specificity 74 %. Reliable screening tools for neuropathic pain are well related between them; hence, they are available for researchers and clinicians who may choose the most appropriate for their activity. Since the gold standard for the diagnosis and treatment of neuropathic pain cannot do without a neurological evaluation, perhaps DN4, that includes physician objective measures, may help reducing the percentage of dubious cases. Conversely, when needing a more agile tool (not needing a physician) ID-Pain may be adopted.

Photon production from the vacuum close to the superradiant transition: linking the dynamical Casimir effect to the Kibble-Zurek mechanism.

The dynamical Casimir effect (DCE) predicts the generation of photons from the vacuum due to the parametric amplification of the quantum fluctuations of an electromagnetic field. The verification of such an effect is still elusive in optical systems due to the very demanding requirements of its experimental implementation. We show that an ensemble of two-level atoms collectively coupled to the electromagnetic field of a cavity, driven at low frequencies and close to a quantum phase transition, stimulates the production of photons from the vacuum. This paves the way to an effective simulation of the DCE through a mechanism that has recently found experimental demonstration. The spectral properties of the emitted radiation reflect the critical nature of the system and allow us to link the detection of the DCE to the Kibble-Zurek mechanism for the production of defects when crossing a continuous phase transition.

Deep-learning density functionals for gradient descent optimization.

Machine-learned regression models represent a promising tool to implement accurate and computationally affordable energy-density functionals to solve quantum many-body problems via density functional theory. However, while they can easily be trained to accurately map ground-state density profiles to the corresponding energies, their functional derivatives often turn out to be too noisy, leading to instabilities in self-consistent iterations and in gradient-based searches of the ground-state density profile. We investigate how these instabilities occur when standard deep neural networks are adopted as regression models, and we show how to avoid them by using an ad hoc convolutional architecture featuring an interchannel averaging layer. The main testbed we consider is a realistic model for noninteracting atoms in optical speckle disorder. With the interchannel average, accurate and systematically improvable ground-state energies and density profiles are obtained via gradient-descent optimization, without instabilities nor violations of the variational principle.

Rituximab in patients with chronic inflammatory demyelinating polyradiculoneuropathy: a report of 13 cases and review of the literature.

BACKGROUND: A few case reports have shown controversial results of rituximab efficacy in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). OBJECTIVE: To analyse the efficacy of rituximab in a large CIDP cohort. METHODS: A retrospective, observational and multicentre study on the use of rituximab in CIDP. 13 Italian CIDP patients were treated with rituximab after the partial or complete lack of efficacy of conventional therapies. Eight patients had co-occurring haematological diseases. Patients who improved by at least two points in standard clinical scales, or who reduced or discontinued the pre-rituximab therapies, were considered as responders. RESULTS: Nine patients (seven with haematological diseases) responded to rituximab: six of them, who were non-responders to conventional therapies, improved clinically, and the other three maintained the improvement that they usually achieved with intravenous immunoglobulin or plasma exchange. Significantly associated with shorter disease duration, rituximab responses started after a median period of 2.0 months (range, 1-6) and lasted for a median period of 1 year (range, 1-5). CONCLUSIONS: Rituximab seems to be a promising therapeutic choice when it targets both CIDP and co-occurring haematological diseases. Timely post-onset administration of rituximab seems to be associated with better responses.

Immunosuppressive treatment in refractory chronic inflammatory demyelinating polyradiculoneuropathy. A nationwide retrospective analysis.

BACKGROUND AND PURPOSE: There are other options open to patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) who are non-responders to conventional treatment, including immunosuppressive and immunomodulatory agents (IA). The aim of this study was to assess whether the use of IA is able to increase the number of responders. METHODS: Clinical and electrophysiological data of patients with refractory CIDP, followed at 10 Italian centres, were collected, and the clinical outcome (Rankin Scale) and drug side effects (SE) for the different therapies were analysed. RESULTS: A total of 110 patients were included. These patients underwent 158 different therapeutic procedures with IA. Seventy-seven patients were treated with azathioprine, 18 rituximab, 13 cyclophosphamide, 12 mycophenolate mofetil, 12 cyclosporine, 12 methotrexate, 11 interferon-alpha and three interferon beta-1a. The percentage of patients who responded to azathioprine (27%) was comparable to the percentage of responders to other therapies, after the exclusion of interferon beta-1a that was not effective in any of the three patients treated. The percentage of SE ranges from 8% (methotrexate) to 50% (cyclosporine). CONCLUSIONS: One-fourth of patients, refractory to conventional treatment, showed an improvement in their disability with IA. Methotrexate had the lowest SE; cyclosporine was associated with severe SE and often led to drug discontinuation.

Coherent detection of electron dephasing.

We show that an Aharonov-Bohm ring with asymmetric electron injection can act as a coherent detector of electron dephasing. The presence of a dephasing source in one of the two arms of a moderately-to-highly asymmetric ring changes the response of the system from total reflection to complete transmission while preserving the coherence of the electrons propagating from the ring, even for strong dephasing. We interpret this phenomenon as an implementation of an interaction-free measurement.

A nationwide retrospective analysis on the effect of immune therapies in patients with chronic inflammatory demyelinating polyradiculoneuropathy.

BACKGROUND AND PURPOSE: The guidelines for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) therapy suggest to use immunoglobulins (IVIg) and steroid as first-line therapies. Patients who do not respond to one of the two drugs should be switched to the other drug. We collected therapeutic outcome data in patients followed at 11 centres in order to document the clinical practice in Italy. METHODS: Clinical and electrophysiological data of patients with CIDP were entered into a central database. The clinical outcome (Rankin Scale) and drug side effects (SE) for first- and second-line therapies were recorded. RESULTS: A total of 267 patients were included. The percentage of responders (R) to first-line therapy [steroid or IVIg or plasma exchange (PE)] was 69%; this number increased to 81% when patients who switched to different therapies were included. Overall, the percentage of R to IVIg was similar to R to steroids (P = 0.07) and higher than R to PE (P < 0.001). Of the main therapies, PE frequently caused SE (19%), followed by steroids (12.5%) and IVIg (4%). CONCLUSIONS: Switching between traditional therapies increases the number of responder patients. IVIg was confirmed to be a therapy with low SE.

Detection of geometric phases in superconducting nanocircuits

When a quantum-mechanical system undergoes an adiabatic cyclic evolution, it acquires a geometrical phase factor' in addition to the dynamical one; this effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnology should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be realized, and show how the effect may be applied to the design of gates for quantum computation.