Entanglement Storage Units

We introduce a protocol based on optimal control to drive many body quantum systems into long-lived entangled states, protected from decoherence by big energy gaps, without requiring any apriori knowledge of the system. With this approach it is possible to implement scalable entanglement-storage units. We test the protocol in the Lipkin-Meshkov-Glick model, a prototype many-body quantum system that describes different experimental setups, and in the ordered Ising chain, a model representing a possible implementation of a quantum bus

Weak localization effects in granular metals

The weak localization correction to the conductivity of a granular metal is calculated using the diagrammatic technique in the reciprocal grain lattice representation. The properties of this correction are very similar to that one in disordered metal, with the replacement of the electron mean free path $\ell$ by the grain diameter $d$ and the dimensionless conductance $g$ by the tunnelling dimensionless conductance $g_{T}$. In particular, we demonstrate that at zero temperature no conducting phase can exist for dimensions $D\leq 2$. We also analyze the WL correction to magnetoconductivity in the weak field limit.Comment: 4 pages, 3 figures; minor corrections adde

Quantum dynamics of propagating photons with strong interactions: a generalized input-output formalism

There has been rapid development of systems that yield strong interactions between freely propagating photons in one dimension via controlled coupling to quantum emitters. This raises interesting possibilities such as quantum information processing with photons or quantum many-body states of light, but treating such systems generally remains a difficult task theoretically. Here, we describe a novel technique in which the dynamics and correlations of a few photons can be exactly calculated, based upon knowledge of the initial photonic state and the solution of the reduced effective dynamics of the quantum emitters alone. We show that this generalized "input-output" formalism allows for a straightforward numerical implementation regardless of system details, such as emitter positions, external driving, and level structure. As a specific example, we apply our technique to show how atomic systems with infinite-range interactions and under conditions of electromagnetically induced transparency enable the selective transmission of correlated multi-photon states

Noise-resistant optimal spin squeezing via quantum control

Entangled atomic states, such as spin squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a protocol that is robust to noise which outperforms conventional methods. Potential experimental implementations are discussed.Comment: 5 pages of main tex

Noise-Resistant Optimal Spin Squeezing via Quantum Control

Entangled atomic states, such as spin squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a time-optimal protocol that yields more than two orders of magnitude improvement with respect to conventional adiabatic preparation. Potential experimental implementations are discussed.Physic

Suicide and suicides attempts in Italian prison epidemiological findings from the “Triveneto” area, 2010-2016

The aim of this observational study was to assess rates of suicide and suicide attempts, in relation to gender, age, place of birth and security levels, in north-eastern Italian prisons during 2010-2016, and investigate associations with prison overcrowding, offence type and prior self-harm and suicide attempts. The study was based on individual data on suicides and suicide attempts from 16 prisons, with an average yearly number of 3,900 inmates during the study period, for all prisons combined. Descriptive and binomial regression analyses were performed. Rates of suicide and suicide attempts in Triveneto prisons were 1and 15 per 1,000 inmates, respectively. More than 90% of suicides and suicide attempters were men aged between 21 and 49 years old, and most had committed violent offences. Only half the prisoners who died by suicide and 30% of those who made a suicide attempt in custody were Italians. ‘Cooperative witnesses’ had the highest mean suicide attempt rate (30/1,000 inmates). Fourteen per cent of suicides and 19% of attempters had a prior history of suicide attempts and self-injury. In binomial regression analyses, predictors of suicidal behaviour were being a male inmate in standard security conditions, with a mean age of 30 years. The study highlighted that there is a need for suicide prevention policies in Triveneto; these should take into account predictors of suicidal behaviours and individual characteristics of suicidal inmates. More research is warranted in order to both evaluate the effectiveness of prevention plans and better assess risk of suicide in specific groups, such as cooperative witnesses

Exact time evolution of space- and time-dependent correlation functions after an interaction quench in the 1D Bose gas

We consider the non-equilibrium dynamics of the interacting Lieb-Liniger gas after instantaneously switching the interactions off. The subsequent time evolution of the space- and time-dependent correlation functions is computed exactly. Different relaxation behavior is observed for different correlation functions. The long time average is compared with the predictions of several statistical ensembles. The generalized Gibbs ensemble restricted to a fixed number of particles is shown to give correct results at large times for all length scales.Comment: 9 pages, 11 figure

Breakdown of the adiabatic limit in low dimensional gapless systems

It is generally believed that a generic system can be reversibly transformed from one state into another by sufficiently slow change of parameters. A standard argument favoring this assertion is based on a possibility to expand the energy or the entropy of the system into the Taylor series in the ramp speed. Here we show that this argumentation is only valid in high enough dimensions and can break down in low-dimensional gapless systems. We identify three generic regimes of a system response to a slow ramp: (A) mean-field, (B) non-analytic, and (C) non-adiabatic. In the last regime the limits of the ramp speed going to zero and the system size going to infinity do not commute and the adiabatic process does not exist in the thermodynamic limit. We support our results by numerical simulations. Our findings can be relevant to condensed-matter, atomic physics, quantum computing, quantum optics, cosmology and others.Comment: 11 pages, 5 figures, to appear in Nature Physics (originally submitted version

Flat Spectrum Radio Quasars through the MAGIC glasses

The detection of Flat Spectrum Radio Quasars (FSRQs) in the Very High Energy (VHE, E > 100 GeV) range is challenging, mainly because of their steep spectra in this energy band. Up to now, only five FSRQs are known to be VHE γ-ray emitters, all of them have been detected by the MAGIC telescopes, that discovered four of them in the VHE band. The observations in the VHE band are crucial to understand their emission, specially to constrain the location of the emitting region within the jet due to the absorption from their broad line region (BLR). Typically, FSRQs are detected during high flux states, enhancing the probability of detection with the current instruments sensitivities. However, the last observation campaigns performed with the MAGIC telescopes show emission during moderate states, thus challenging our understanding of the emission mechanisms in FSRQs. In this contribution, we give an overview and present the most recent results of the three FSRQs 3C279, PKS1222+21 and PKS1510-089 in a multi-wavelength context with special focus on MAGIC and Fermi-LAT simultaneous observations

High-fidelity quantum driving

The ability to accurately control a quantum system is a fundamental requirement in many areas of modern science such as quantum information processing and the coherent manipulation of molecular systems. It is usually necessary to realize these quantum manipulations in the shortest possible time in order to minimize decoherence, and with a large stability against fluctuations of the control parameters. While optimizing a protocol for speed leads to a natural lower bound in the form of the quantum speed limit rooted in the Heisenberg uncertainty principle, stability against parameter variations typically requires adiabatic following of the system. The ultimate goal in quantum control is to prepare a desired state with 100% fidelity. Here we experimentally implement optimal control schemes that achieve nearly perfect fidelity for a two-level quantum system realized with Bose-Einstein condensates in optical lattices. By suitably tailoring the time-dependence of the system's parameters, we transform an initial quantum state into a desired final state through a short-cut protocol reaching the maximum speed compatible with the laws of quantum mechanics. In the opposite limit we implement the recently proposed transitionless superadiabatic protocols, in which the system perfectly follows the instantaneous adiabatic ground state. We demonstrate that superadiabatic protocols are extremely robust against parameter variations, making them useful for practical applications.Comment: 17 pages, 4 figure