96 research outputs found
Non-equilibrium readiness and accuracy of Gaussian Quantum Thermometers
The dimensionality of a thermometer is key in the design of quantum
thermometry schemes. In general, the phenomenology that is typical of
finite-dimensional quantum thermometry does not apply to infinite dimensional
ones. We analyse the dynamical and metrological features of non-equilibrium
Gaussian Quantum Thermometers: on one hand, we highlight how quantum
entanglement can enhance the readiness of composite Gaussian thermometers; on
the other hand, we show that non-equilibrium conditions do not guarantee the
best sensitivities in temperature estimation, thus suggesting the reassessment
of the working principles of quantum thermometry
Quantum Simulation of single-qubit thermometry using linear optics
Standard thermometry employs the thermalisation of a probe with the system of
interest. This approach can be extended by incorporating the possibility of
using the non-equilibrium states of the probe, and the presence of coherence.
Here, we illustrate how these concepts apply to the single-qubit thermometer
introduced by Jevtic et al. by performing a simulation of the qubit-environment
interaction in a linear-optical device. We discuss the role of the coherence,
and how this affects the usefulness of non-equilibrium conditions. The origin
of the observed behaviour is traced back to the propensity to thermalisation,
as captured by the Helmholtz free energy.Comment: 6 pages, 6 figure
Speed of qubit states during thermalisation
Classifying quantum states usually demands to observe properties such as the
amount of correlation at one point in time. Further insight may be gained by
inspecting the dynamics in a given evolution scheme. Here we attempt such a
classification looking at single-qubit and two-qubit states at the start of
thermalisation with a heat bath. The speed with which the evolution starts is
influenced by quantum aspects of the state, however, such signatures do not
allow for a systematic classification
Monitoring dispersive samples with single photons: the role of frequency correlations
The physics that governs quantum monitoring may involve other degrees of
freedom than the ones initialised and controlled for probing. In this context
we address the simultaneous estimation of phase and dephasing characterizing a
dispersive medium, and we explore the role of frequency correlations within a
photon pair generated via parametric down-conversion, when used as a probe for
the medium. We derive the ultimate quantum limits on the estimation of the two
parameters, by calculating the corresponding quantum Cram\'er-Rao bound; we
then consider a feasible estimation scheme, based on the measurement of Stokes
operators, and address its absolute performances in terms of the correlation
parameters, and, more fundamentally, of the role played by correlations in the
simultaneous achievability of the quantum Cram\'er-Rao bounds for each of the
two parameters.Comment: to appear in Quantum Measurements and Quantum Metrolog
Assessing frequency correlation through a distinguishability measurement
The simplicity of a question such as wondering if correlations characterize
or not a certain system collides with the experimental difficulty of accessing
such information. Here we present a low demanding experimental approach which
refers to the use of a metrology scheme to obtain a conservative estimate of
the strength of frequency correlations. Our testbed is the widespread case of a
photon pair produced per downconversion. The theoretical architecture used to
put the correlation degree on a quantitative ground is also described
Entropy Production in Continuously Measured Gaussian Quantum Systems
The entropy production rate is a key quantity in non-equilibrium
thermodynamics of both classical and quantum processes. No universal theory of
entropy production is available to date, which hinders progress towards its
full grasping. By using a phase space-based approach, here we take the current
framework for the assessment of thermodynamic irreversibility all the way to
quantum regimes by characterizing entropy production -- and its rate --
resulting from the continuous monitoring of a Gaussian system. This allows us
to formulate a sharpened second law of thermodynamics that accounts for the
measurement back-action and information gain from a continuously monitored
system. We illustrate our framework in a series of physically relevant
examples.Comment: 15+6 pages, 2 figures. This version matches the one accepted for
publication in npj Quantum In
In-between forest expansion and cropland decline: A revised USLE model for soil erosion risk under land-use change in a Mediterranean region
The present study illustrates an original approach for the long-term assessment of soil erosion risk under land-use changes in a Mediterranean region (Matera, southern Italy). The study has been focused on the implementation of a modified Universal Soil Loss Equation (USLE) model at three time points (1960, 1990, 2010) with the objective to evaluate the contribution of each component to model's performance and model outcomes’ reliability. A modified USLE model was proposed for the assessment of soil erosion risk, based on the simplification of model's parameters and the use of high spatial resolution datasets. Spatio-temporal variability in the model's outcomes was analyzed for basic land-use classes. Our approach has improved model's flexibility with the use of high spatial resolution layers, producing reliable long-term estimates of soil loss for the study area
Geometrical bounds on irreversibility in open quantum systems
Clausius inequality has deep implications for reversibility and the arrow of
time. Quantum theory is able to extend this result for closed systems by
inspecting the trajectory of the density matrix on its manifold. Here we show
that this approach can provide an upper and lower bound to the irreversible
entropy production for open quantum systems as well. These provide insights on
the thermodynamics of the information erasure. Limits of the applicability of
our bounds are discussed, and demonstrated in a quantum photonic simulator
Multiparameter quantum estimation of noisy phase shifts
Phase estimation is the most investigated protocol in quantum metrology, but
its performance is affected by the presence of noise, also in the form of
imperfect state preparation. Here we discuss how to address this scenario by
using a multiparameter approach, in which noise is associated to a parameter to
be measured at the same time as the phase. We present an experiment using
two-photon states, and apply our setup to investigating optical activity of
fructose solutions. Finally, we illustrate the scaling laws of the attainable
precisions with the number of photons in the probe state
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