arXiv subjects

Jefferson G. Filgueiras

Publications and source records attributed to Jefferson G. Filgueiras.

9 recordsLinked to original sources

arXiv2024

Experimental Investigation of Geometric Quantum Speed Limits in an Open Quantum System

We studied geometric quantum speed limits (QSL) of a qubit subject to decoherence in an ensemble of chloroform molecules in a Nuclear Magnetic Resonance experiment. The QSL is a fundamental lower bound on the evolution time for quantum systems undergoing general physical processes. To do so, we controlled the system-reservoir interaction and the spin relaxation rates by adding a paramagnetic salt, which allowed us to observe both Markovian and non-Markovian open system dynamics for the qubit. We used two distinguishability measures of quantum states to assess the speed of the qubit evolution: the quantum Fisher information (QFI) and Wigner-Yanase skew information (WY). For non-Markovian dynamics and low salt concentrations, we observed crossovers between QSLs related to the QFI and WY metrics. The WY metric sets the tighter QSL for high concentrations and Markovian dynamics. We also show that QSLs are sensitive even to small fluctuations in spin magnetization.

quant-ph↗

arXiv2023

Effects of clays on spin-spin relaxation: a route for non-invasive total clay content quantification

Clay minerals are important components of sandstone rocks, due to their significant role in petrophysical properties like porosity and permeability. These minerals have a particular impact on Nuclear Magnetic Resonance measurements since the iron inside clays generates internal gradients that impact the transverse relaxation directly. Here, we apply a methodology recently developed to a set of 20 sandstones with diverse clay content and mineralogy to estimate the total clay content. This estimation relies on the effect of internal gradients and restricted diffusion on transverse relaxation. Our analysis revealed a linear correlation between the total clay content and the displacement of the peak of the T$_2$ distribution as a function of $τ$, which is half the echo time in the CPMG sequence. Based on these measurements, we propose a geochemical rock typing from quantities determined by our measurements, namely total clay content and porosity.

physics.geo-ph↗

arXiv2018

Coherence orders, decoherence and quantum metrology

Since the dawn of quantum theory, coherence was attributed as a key to understand the weirdness of fundamental concepts like the wave-particle duality and the Stern-Gerlach experiment. Recently, based on a resource theory approach, the notion of quantum coherence was revisited and a plethora of coherence quantifiers were proposed. In this work, we address this issue using the language of coherence orders, developed by the NMR community. This allowed us to investigate the role played by different subspaces of the Hilbert-Schmidt space into physical processes and quantum protocols. We found some links between decoherence and each coherence order. Moreover, we propose a sufficient and straightforward criterion to testify the usefulness of a given state for quantum enhanced phase estimation, relying on a minimal set of elements belonging to the density matrix.

quant-ph↗

arXiv2017

Dipolar Filtered magic-sandwich-echoes as a tool for probing molecular motions using time domain NMR

We present a simple $^1$H NMR approach for characterizing intermediate to fast regime molecular motions using $^1$H time-domain NMR at low magnetic field. The method is based on a Goldmann Shen dipolar filter (DF) followed by a Mixed Magic Sandwich Echo (MSE). The dipolar filter suppresses the signals arising from molecular segments presenting sub kHz mobility, so only signals from mobile segments are detected. Thus, the temperature dependence of the signal intensities directly evidences the onset of molecular motions with rates higher than kHz. The DF-MSE signal intensity is described by an analytical function based on the Anderson Weiss theory, from where parameters related to the molecular motion (e.g. correlation times and activation energy) can be estimated when performing experiments as function of the temperature. Furthermore, we propose the use of the Tikhonov regularization for estimating the width of the distribution of correlation times.

physics.chem-ph↗

arXiv2017

Continuous variables quantum computation over the vibrational modes of a single trapped ion

We consider the quantum processor based on a chain of trapped ions to propose an architecture wherein the motional degrees of freedom of trapped ions (position and momentum) could be exploited as the computational Hilbert space. We adopt a continuous-variables approach to develop a toolbox of quantum operations to manipulate one or two vibrational modes at a time. Together with the intrinsic non-linearity of the qubit degree of freedom, employed to mediate the interaction between modes, arbitrary manipulation and readout of the ionic wave function could be achieved.

quant-ph↗

arXiv2016

NMR Contributions to the study of Quantum Correlations

In this chapter we review the contributions of Nuclear Magnetic Resonance to the study of quantum correlations, including its capabilities to prepare initial states, generate unitary transformations, and characterize the final state. These are the three main demands to implement quantum information processing in a physical system, which NMR offers, nearly to perfection, though for a small number of qubits. Our main discussion will concern liquid samples at room temperature.

quant-ph↗

arXiv2016

Using the Quantum Zeno Effect for Suppression of Decoherence

Projective measurements are an essential element of quantum mechanics. In most cases, they cause an irreversible change of the quantum system on which they act. However, measurements can also be used to stabilize quantum states from decay processes, which is known as the quantum Zeno effect (QZE). Here, we demonstrate this effect for the case of a superposition state of a nuclear spin qubit, using an ancilla to perform the measurement. As a result, the quantum state of the qubit is protected against dephasing without relying on an ensemble nature of NMR experiments. We also propose a scheme to protect an arbitrary state by using QZE.

quant-ph↗

arXiv2014

Construction of Arbitrary Robust One-Qubit Operations Using Planar Geometry

We show how to construct an arbitrary robust one-qubit unitary operation with a control Hamiltonian of $A_x(t) σ_x + A_y(t) σ_y$, where $σ_i$ is a Pauli matrix and $A_i(t)$ is piecewise constant. Our method, based on planar geometry, admits a simple and intuitive interpretation. Furthermore, the total execution time and the number of elementary gates of the obtained sequence are comparable to those of the shortest known concatenated composite pulses.

quant-ph↗

arXiv2014

Quantum discord determines the interferometric power of quantum states

Quantum metrology exploits quantum mechanical laws to improve the precision in estimating technologically relevant parameters such as phase, frequency, or magnetic fields. Probe states are usually tailored on the particular dynamics whose parameters are being estimated. Here we consider a novel framework where quantum estimation is performed in an interferometric configuration, using bipartite probe states prepared when only the spectrum of the generating Hamiltonian is known. We introduce a figure of merit for the scheme, given by the worst case precision over all suitable Hamiltonians, and prove that it amounts exactly to a computable measure of discord-type quantum correlations for the input probe. We complement our theoretical results with a metrology experiment, realized in a highly controllable room-temperature nuclear magnetic resonance setup, which provides a proof-of-concept demonstration for the usefulness of discord in sensing applications. Discordant probes are shown to guarantee a nonzero precision in the estimation procedure for different generating Hamiltonians, while classically correlated probes are unable to accomplish the estimation in a worst case setting. This work establishes a rigorous and direct operational interpretation for general quantum correlations, shedding light on their potential for quantum technology.

quant-ph↗