183 research outputs found
Towards the Extremely Large Telescopes era in exoplanetary science: simulation tools, instrumental optimization and design for high resolution spectroscopy. The cases of ESPRESSO and ELT-HIRES.
No full textIn this thesis I present my PhD activities concerning the development of simulation tools both for ground-based high resolution spectrograph design, ESPRESSO and ELT-HIRES, and for scientific investigations in the field of exoplanetary high-dispersion transmission spectroscopy. In the ESPRESSO (the Echelle SPectrograph for Rocky Exoplanets Super Stable Observations) project, the instrument modeling through ray-tracing bsoftware and ad-hoc developed sensivity analysis tool were fruitfully used for component optimization and alignment verification. In the framework of the ELT-HIRES (the HIgh REsolution Spectrograph for the ELT) project, an End-to-End simulator and a parametric paraxial model of the spectrograph were developed with the purpose to evaluate the different effects which can affect the final instrument performances, since they directly influence the scientific data observational performances. The synthetic echellogram (raw frame) produced and successfully processed by the CRIRES+ instrument data reduction pipeline are presented, thus probing the full chain feasibility and consistency of the system. Large telescopes allowing very high contrast, could also imply the possibility to detect the light emitted from background sources and/or from gravitationally bounded companion of exoplanetary system, which could act as signal contamination. A transmission spactra simulator, a tool aimed at generating synthetic spectra, was developed and used to show that the maximum contamination occurs for background stars of G-to-M type, even though for high resolution spectra with a 4m class telescope this contamination seems to not introduce obvious shifts or line broadening in the exoplanet atmospheric features
Optimal quantum repeaters for qubits and qudits
No full textA class of optimal quantum repeaters for qubits is suggested. The schemes are minimal, i.e., they involve a single additional probe qubit, and optimal, i.e., they provide the maximum information adding the minimum amount of noise. Information gain and state disturbance are quantified by fidelities which, for our schemes, saturate the ultimate bound imposed by quantum mechanics for randomly distributed signals. Special classes of signals are also investigated, in order to improve the information-disturbance trade-off. Extension to higherdimensional signal
Information-disturbance tradeoff in continuous variable Gaussian systems
No full textWe address the information–disturbance tradeoff for state measurements on continuous variable Gaussian systems and suggest minimal schemes for implementations. In our schemes, the symbols from a given alphabet are encoded in a set of Gaussian signals which are coupled to a probe excited in a known state. After the interaction the probe is measured, in order to infer the transmitted state, while the conditional state of the signal is left for the subsequent user. The schemes are minimal, i.e., involve a single additional probe, and allow for the nondemolitive transmission of a continuous real alphabet over a quantum channel. The tradeoff between information gain and state disturbance is quantified by fidelities and, after optimization with respect to the measurement, analyzed in terms of the energy carried by the signal and the probe. We found that transmission fidelity only depends on the energy of the signal and the probe, whereas estimation fidelity also depends on the alphabet size and the measurement gain. Increasing the probe energy does not necessarily lead to a better tradeoff, the most relevant parameter being the ratio between the alphabet size and the signal width, which in turn determine the allocation of the signal energy
Metrology with Unknown Detectors
No full textThe best possible precision is one of the key figures in metrology, but this is established by the exact response of the detection apparatus, which is often unknown. There exist techniques for detector characterization that have been introduced in the context of quantum technologies but apply as well for ordinary classical coherence; these techniques, though, rely on intense data processing. Here, we show that one can make use of the simpler approach of data fitting patterns in order to obtain an estimate of the Cramér-Rao bound allowed by an unknown detector, and we present applications in polarimetry. Further, we show how this formalism provides a useful calculation tool in an estimation problem involving a continuous-variable quantum state, i.e., a quantum harmonic oscillator
Detecting Gaussian entanglement via extractable work
No full textWe show how the presence of entanglement in a bipartite Gaussian state can be detected by the amount of work extracted by a continuous-variable Szilard-like device, where the bipartite state serves as the working medium of the engine. We provide an expression for the work extracted in such a process and specialize it to the case of Gaussian states. The extractable work provides a sufficient condition to witness entanglement in generic two-mode states, becoming also necessary for squeezed thermal states. We extend the protocol to tripartite Gaussian states and show that the full structure of inseparability classes cannot be discriminated based on the extractable work. This suggests that bipartite entanglement is the fundamental resource underpinning work extraction
Noisy Quantum Metrology Enhanced by Continuous Nondemolition Measurement
No full textWe show that continuous quantum nondemolition (QND) measurement of an atomic ensemble is able to improve the precision of frequency estimation even in the presence of independent dephasing acting on each atom. We numerically simulate the dynamics of an ensemble with up to N=150 atoms initially prepared in a (classical) spin coherent state, and we show that, thanks to the spin squeezing dynamically generated by the measurement, the information obtainable from the continuous photocurrent scales superclassically with respect to the number of atoms N. We provide evidence that such superclassical scaling holds for different values of dephasing and monitoring efficiency. We moreover calculate the extra information obtainable via a final strong measurement on the conditional states generated during the dynamics and show that the corresponding ultimate limit is nearly achieved via a projective measurement of the spin-squeezed collective spin operator. We also briefly discuss the difference between our protocol and standard estimation schemes, where the state preparation time is neglected
The Role of Monitoring Time and Detectors Efficiencies in Time-Continuous Quantum Magnetometry
No full textWe consider the estimation of a weak magnetic field B acting on a continuously monitored ensemble of atoms subjected to collective transverse noise. If N atoms are prepared in a coherent spin state and are not continuously monitored, the estimation precision scales with the total number of atoms according to the standard quantum limit δB2∼1/NδB2∼1/N. Remarkably, time-continuous monitoring of light that is coupled with the atomic ensemble, allows to achieve a Heisenberg limited precision δB2∼1/N2δB2∼1/N2. However this is typically obtained only for a large enough number of atoms N and with an asymptotic constant factor depending on the parameters characterizing the experiment. In this proceeding, after reviewing the analytical derivation of the effective quantum Fisher information that quantifies the ultimate precision achievable, we specifically address the role played by monitoring time and detectors measurement efficiency in obtaining a Heisenberg limited scaling. In particular we analyze the dependence on these experimentally relevant parameters of the asymptotic constant factor characterizing the effective quantum Fisher information, and, more importantly, the minimum value of atoms needed to observe the desired quantum enhancement
Quantifying the nonlinearity of a quantum oscillator
No full textWe address the quantification of nonlinearity for quantum oscillators and introduce two measures based on the properties of the ground state rather than on the form of the potential itself. The first measure is a fidelity-based one and corresponds to the renormalized Bures distance between the ground state of the considered oscillator and the ground state of a reference harmonic oscillator. Then, in order to avoid the introduction of this auxiliary oscillator, we introduce a different measure based on the non-Gaussianity (nG) of the ground state. The two measures are evaluated for a sample of significant nonlinear potentials and their properties are discussed in some detail. We show that the two measures are monotone functions with respect to each other in most cases, and this suggests that the nG-based measure is a suitable choice to capture the anharmonic nature of a quantum oscillator, and to quantify its nonlinearity independently of the specific features of the potential. We also provide examples of potentials where the Bures measure cannot be defined, due to the lack of a proper reference harmonic potential, while the nG-based measure properly quantifies their nonlinear features. Our results may have implications in experimental applications where access to the effective potential is limited, e.g., in quantum control, and protocols rely on information about the ground or thermal stat
Quantifying non-Gaussianity for quantum information
No full textWe address the quantification of non-Gaussianity (nG) of states and operations in continuous-variable systems
and its use in quantum information. We start by illustrating in detail the properties and the relationships of two recently proposed measures of nG based on the Hilbert-Schmidt distance and the quantum relative entropy (QRE) between the state under examination and a reference Gaussian state. We then evaluate the non-Gaussianities of several families of non-Gaussian quantum states and show that the two measures have the same basic properties and also share the same qualitative behavior in most of the examples taken into account. However, we also show
that they introduce a different relation of order; that is, they are not strictly monotone to each other. We exploit the nG measures for states in order to introduce a measure of nG for quantum operations, to assess Gaussification and de-Gaussification protocols, and to investigate in detail the role played by nG in entanglement distillation protocols. Besides, we exploit the QRE-based nG measure to provide different insight on the extremality of
Gaussian states for some entropic quantities such as conditional entropy, mutual information, and the Holevo bound. We also deal with parameter estimation and present a theorem connecting the QRE nG to the quantum
Fisher information. Finally, since evaluation of the QRE nG measure requires the knowledge of the full density matrix, we derive some experimentally friendly lower bounds to nG for some classes of states and by considering the possibility of performing on the states only certain efficient or inefficient measurements
Management and Nutrition of Neonates during the COVID-19 Pandemic: A Review of the Existing Guidelines and Recommendations
No full textWe aimed at reviewing the currently available guidelines and scientific recommendations regarding the neonatal in-hospital management and feeding in the light of the coronavirus disease 2019 (COVID-19) pandemic
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