44 research outputs found
Exact spectral function of a Tonks-Girardeau gas in a lattice
The single-particle spectral function of a strongly correlated system is an
essential ingredient to describe its dynamics and transport properties. We
develop a general method to calculate the exact spectral function of a strongly
interacting one-dimensional Bose gas in the Tonks-Girardeau regime, valid for
any type of confining potential, and apply it to bosons on a lattice to obtain
the full spectral function, at all energy and momentum scales. We find that it
displays three main singularity lines. The first two can be identified as the
analogs of Lieb-I and Lieb-II modes of a uniform fluid; the third one, instead,
is specifically due to the presence of the lattice. We show that the spectral
function displays a power-law behaviour close to the Lieb-I and Lieb-II
singularities, as predicted by the non-linear Luttinger liquid description, and
obtain the exact exponents. In particular, the Lieb-II mode shows a divergence
in the spectral function, differently from what happens in the dynamical
structure factor, thus providing a route to probe it in experiments with
ultracold atoms.Comment: 10 pages, 3 figure
Local control of entanglement in a spin chain
In a ferromagnetic spin chain, the control of the local effective magnetic
field allows to manipulate the static and dynamical properties of entanglement.
In particular, the propagation of quantum correlations can be driven to a great
extent so as to achieve an entanglement transfer on demand toward a selected
site
Decoherence in a fermion environment: Non-Markovianity and Orthogonality Catastrophe
We analyze the non-Markovian character of the dynamics of an open two-level
atom interacting with a gas of ultra-cold fermions. In particular, we discuss
the connection between the phenomena of orthogonality catastrophe and Fermi
edge singularity occurring in such a kind of environment and the memory-keeping
effects which are displayed in the time evolution of the open system
Quantum Otto cycle with inner friction: finite-time and disorder effects
The concept of inner friction, by which a quantum heat engine is unable to
follow adiabatically its strokes and thus dissipates useful energy, is
illustrated in an exact physical model where the working substance consists of
an ensemble of misaligned spins interacting with a magnetic field and
performing the Otto cycle. The effect of this static disorder under a
finite-time cycle gives a new perspective of the concept of inner friction
under realistic settings. We investigate the efficiency and power of this
engine and relate its performance to the amount of friction from misalignment
and to the temperature difference between heat baths. Finally we propose an
alternative experimental implementation of the cycle where the spin is encoded
in the degree of polarization of photons.Comment: Published version in the Focus Issue on "Quantum Thermodynamics
Finite-Temperature Scaling of Magnetic Susceptibility and Geometric Phase in the XY Spin Chain
We study the magnetic susceptibility of 1D quantum XY model, and show that
when the temperature approaches zero, the magnetic susceptibility exhibits the
finite-temperature scaling behavior. This scaling behavior of the magnetic
susceptibility in 1D quantum XY model, due to the quantum-classical mapping,
can be easily experimentally tested. Furthermore, the universality in the
critical properties of the magnetic susceptibility in quantum XY model is
verified. Our study also reveals the close relation between the magnetic
susceptibility and the geometric phase in some spin systems, where the quantum
phase transitions are driven by an external magnetic field.Comment: 6 pages, 4 figures, get accepted for publication by J. Phys. A: Math.
Theo
Small-scale perturbation on soft bottom macrozoobenthos after mechanical cleaning operations in a Central-Western Mediterranean lagoon
1 - Sardinia Island (Italy), even if relatively small, has over 100 lagoons totalling some 12,000 ha. Yet their potential yield remain often unexpressed because they are subjected to environmental stress and degradation. As far as benthic communities are concerned, one of the main disturbances is certainly the accumulation of shell detritus, which progressively modifies the way benthic organisms interact with the sediment.
2 - An experimental dredging study was therefore performed in the Calich lagoon (NW Sardinia), due to its particular interest for fishing activities and potential semi-intensive mollusc culture. Changes in benthic community structure were examined in two areas of the lagoon by analysing both the demographic profile of several abundant species and the features of sedimentary matrix immediately after the cleaning operations and seven months later. Data obtained were compared with those collected in undisturbed areas of the lagoon. This allowed us to evaluate the effects of dredging operations on the benthic assemblages unaffected by natural temporal shifts of the system.
3 - Univariate and multivariate analyses indicated a strong relationship between macrofaunal community structure and intensity of the cleaning activities. At the dredged sites benthic fauna was not depleted but did exhibit higher diversity and evenness indexes than at the undisturbed sites. This seemed to be a consequence of decrease in the density of some abundant species at the dredged sites. Furthermore, a general reduction of total organic content was observed in the upper sediment layer. Lastly, the cleaning method employed is discussed in relation to its potential for impacting the benthos
Charge and current fluctuations in a superconducting single electron transistor near a Cooper pair resonance
We analyze charge tunneling statistics and current noise in a superconducting
single-electron transistor in a regime where the Josephson-quasiparticle cycle
is the dominant mechanism of transport. Due to the interplay between Coulomb
blockade and Josephson coherence, the probability distribution for tunneling
events strongly deviates from a Poissonian and displays a pronounced even--odd
asymmetry in the number of transmitted charges. The interplay between charging
and coherence is reflected also in the zero-frequency current noise which is
significantly quenched when the quasi-particle tunneling rates are comparable
to the coherent Cooper-pair oscillation frequency. Furthermore the finite
frequency spectrum shows a strong enhancement near the resonant transition
frequency for Josephson tunneling.Comment: 10 pages, 11 figure
Irreversible Work and Inner Friction in Quantum Thermodynamic Processes
We discuss the thermodynamics of closed quantum systems driven out of equilibrium by a change in a control parameter and undergoing a unitary process. We compare the work actually done on the system with the one that would be performed along ideal adiabatic and isothermal transformations. The comparison with the latter leads to the introduction of irreversible work, while that with the former leads to the introduction of inner friction. We show that these two quantities can be treated on an equal footing, as both can be linked with the heat exchanged in thermalization processes and both can be expressed as relative entropies. Furthermore, we show that a specific fluctuation relation for the entropy production associated with the inner friction exists, which allows the inner friction to be written in terms of its cumulants.All the authors acknowledge support from COST MP1209 Action. F. P., G. F., and N. L. G. acknowledge insightful discussions with Michele Campisi, John Goold, and Mauro Paternostro. T. J. G. A. is supported by the European Commission, the European Social Fund, and the Region Calabria through the program POR Calabria FSE 2007-2013-Asse IV Capitale Umano-Obiettivo Operativo M2. F. G. and R. Z. acknowledge MINECO, CSIC, the EU commission, UIB and FEDER funding under Grants FIS2011-23526 (TIQS), postdoctoral JAE program (ESF) and Invited professors program.Peer reviewe
Optical signatures of quantum phase transitions in a light-matter system
Information about quantum phase transitions in conventional condensed matter
systems, must be sought by probing the matter system itself. By contrast, we
show that mixed matter-light systems offer a distinct advantage in that the
photon field carries clear signatures of the associated quantum critical
phenomena. Having derived an accurate, size-consistent Hamiltonian for the
photonic field in the well-known Dicke model, we predict striking behavior of
the optical squeezing and photon statistics near the phase transition. The
corresponding dynamics resemble those of a degenerate parametric amplifier. Our
findings boost the motivation for exploring exotic quantum phase transition
phenomena in atom-cavity, nanostructure-cavity, and
nanostructure-photonic-band-gap systems.Comment: 4 pages, 4 figure