5,072 research outputs found
Cavity assisted measurements of heat and work in optical lattices
We propose a method to experimentally measure the internal energy of a system
of ultracold atoms trapped in optical lattices by coupling them to the fields
of two optical cavities. We show that the tunnelling and self-interaction terms
of the one-dimensional Bose-Hubbard Hamiltonian can be mapped to the field and
photon number of each cavity, respectively. We compare the energy estimated
using this method with numerical results obtained using the density matrix
renormalisation group algorithm. Our method can be employed for the assessment
of power and efficiency of thermal machines whose working substance is a
strongly correlated many-body system.Comment: Accepted version in Quantum. Updates: New results for the work in
quenching a Bose-Hubbard model; new references; v3 fixed doi links in
references to make paper compliant with Quantu
Detection of entanglement in ultracold lattice gases
We propose the use of quantum polarization spectroscopy for detecting
multi-particle entanglement of ultracold atoms in optical lattices. This
method, based on a light-matter interface employing the quantum Farady effect,
allows for the non destructive measurement of spin-spin correlations. We apply
it to the specific example of a one dimensional spin chain and reconstruct its
phase diagram using the light signal, readily measurable in experiments with
ultracold atoms. Interestingly, the same technique can be extended to detect
quantum many-body entanglement in such systems.Comment: Submitted to the Special Issue: "Strong correlations in Quantum
Gases" in The Journal of Low Temperature Physic
Genuine quantum correlations in quantum many-body systems: a review of recent progress
Quantum information theory has considerably helped in the understanding of
quantum many-body systems. The role of quantum correlations and in particular,
bipartite entanglement, has become crucial to characterise, classify and
simulate quantum many body systems. Furthermore, the scaling of entanglement
has inspired modifications to numerical techniques for the simulation of
many-body systems leading to the, now established, area of tensor networks.
However, the notions and methods brought by quantum information do not end with
bipartite entanglement. There are other forms of correlations embedded in the
ground, excited and thermal states of quantum many-body systems that also need
to be explored and might be utilised as potential resources for quantum
technologies. The aim of this work is to review the most recent developments
regarding correlations in quantum many-body systems focussing on multipartite
entanglement, quantum nonlocality, quantum discord, mutual information but also
other non classical measures of correlations based on quantum coherence.
Moreover, we also discuss applications of quantum metrology in quantum
many-body systems.Comment: Review. Close to published version. Comments are welcome! Please
write an email to g.dechiara[(at)]qub.ac.u
Evaluation of political control instruments for the Swiss alpine region
This paper analyses different direct payments system for the Swiss alpine region based on the multi-agent model SWISSland. Moreover, the future demand and management of the alpine pastures are simulated under different scenarios until 2020. In the model, agents are representing existing summer farms and are able to interact with each other. The results imply that the current direct payment system for the Swiss alpine region is effective and able to maintain a stable development until 2020. Since the land management in the alpine region is the activity that provides public goods, it would be reasonable to enforce payments that maximize the area of summered land. A change to contributions coupled to the surfaces could achieve the desired management of the alpine pastures meaning, at the same time, a need of proper monitoring systems.multi-agent models, policy analysis, simulation, alpine region, Agricultural and Food Policy, C16, Q18.,
Quantum correlations and thermodynamic performances of two-qubit engines with local and collective baths
We investigate heat engines whose working substance is made of two coupled
qubits performing a generalised Otto cycle by varying their applied magnetic
field or their interaction strength during the compression and expansion
strokes. During the heating and cooling strokes, the two qubits are coupled to
local and common environments that are not necessarily at equilibrium. We find
instances of quantum engines coupled to non equilibrium common environments
exhibiting non-trivial connections to quantum correlations as witnessed by a
monotonic dependence of the work produced on quantum discord and entanglement.Comment: Close to published versio
Equilibration and nonclassicality of a double-well potential
A double well loaded with bosonic atoms represents an ideal candidate to
simulate some of the most interesting aspects in the phenomenology of
thermalisation and equilibration. Here we report an exhaustive analysis of the
dynamics and steady state properties of such a system locally in contact with
different temperature reservoirs. We show that thermalisation only occurs
'accidentally'. We further examine the nonclassical features and energy fluxes
implied by the dynamics of the double-well system, thus exploring its
finite-time thermodynamics in relation to the settlement of nonclassical
correlations between the wells.Comment: 10 pages, 7 figures, Close to published versio
The Rhombi-Chain Bose-Hubbard Model: geometric frustration and interactions
We explore the effects of geometric frustration within a one-dimensional
Bose-Hubbard model using a chain of rhombi subject to a magnetic flux. The
competition of tunnelling, self-interaction and magnetic flux gives rise to the
emergence of a pair-superfluid (pair-Luttinger liquid) phase besides the more
conventional Mott-insulator and superfluid (Luttinger liquid) phases. We
compute the complete phase diagram of the model by identifying characteristic
properties of the pair-Luttinger liquid phase such as pair correlation
functions and structure factors and find that the pair-Luttinger liquid phase
is very sensitive to changes away from perfect frustration (half-flux). We
provide some proposals to make the model more resilient to variants away from
perfect frustration. We also study the bipartite entanglement properties of the
chain. We discover that, while the scaling of the block entropy pair-superfluid
and of the single-particle superfluid leads to the same central charge, the
properties of the low-lying entanglement spectrum levels reveal their
fundamental difference.Comment: 12 pages, 11 figure
Global and local thermometry schemes in coupled quantum systems
We study the ultimate bounds on the estimation of temperature for an
interacting quantum system. We consider two coupled bosonic modes that are
assumed to be thermal and using quantum estimation theory establish the role
the Hamiltonian parameters play in thermometry. We show that in the case of a
conserved particle number the interaction between the modes leads to a decrease
in the overall sensitivity to temperature, while interestingly, if particle
exchange is allowed with the thermal bath the converse is true. We explain this
dichotomy by examining the energy spectra. Finally, we devise experimentally
implementable thermometry schemes that rely only on locally accessible
information from the total system, showing that almost Heisenberg limited
precision can still be achieved, and we address the (im)possibility for
multiparameter estimation in the system.Comment: 16 pages, 5 figures. Close to published versio
Cost of counterdiabatic driving and work output
Unitary processes allow for the transfer of work to and from Hamiltonian
systems. However, to achieve nonzero power for the practical extraction of
work, these processes must be performed within a finite time, which inevitably
induces excitations in the system. We show that depending on the time scale of
the process and the physical realization of the external driving employed, the
use of counterdiabatic quantum driving to extract more work is not always
effective. We also show that by virtue of the two-time energy measurement
definition of quantum work, the cost of counterdiabatic driving can be
significantly reduced by selecting a restricted form of the driving Hamiltonian
that depends on the outcome of the first energy measurement. Lastly, we
introduce a measure, the exigency, that quantifies the need for an external
driving to preserve quantum adiabaticity which does not require knowledge of
the explicit form of the counterdiabatic drivings, and can thus always be
computed. We apply our analysis to systems ranging from a two-level
Landau-Zener problem to many-body problems, namely, the quantum Ising and
Lipkin-Meshkov-Glick models.Comment: 9 pages, 4 figure
Dynamics and Asymptotics of Correlations in a Many-Body Localized System
We examine the dynamics of nearest-neighbor bipartite concurrence and total
correlations in the spin-1/2 model with random fields. We show, starting
from factorized random initial states, that the concurrence can suffer
entanglement sudden death in the long time limit and therefore may not be a
useful indicator of the properties of the system. In contrast, we show that the
total correlations capture the dynamics more succinctly, and further reveal a
fundamental difference in the dynamics governed by the ergodic versus many-body
localized phases, with the latter exhibiting dynamical oscillations. Finally,
we consider an initial state composed of several singlet pairs and show that by
fixing the correlation properties, while the dynamics do not reveal noticeable
differences between the phases, the long-time values of the correlation
measures appear to indicate the critical region.Comment: 5 pages, 5 figures. Close to published versio
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