@PRL Irreversibility and the emergence of the arrow of time in quantum systems
Entropy production, a quantity associated with the emergence of the arrow of time, has been successfully measured in a microscopic quantum system. Irreversibility is one of the most intriguing concepts in physics. While microscopic physical laws are perfectly reversible, macroscopic average behavior has a preferred direction of time. According to the second law of thermodynamics, this arrow of time is associated with a positive mean entropy production. Using a nuclear magneti
New two-way quantum-key-distribution prototocol
Within the broad research scenario of quantum secure communication, two-way quantum-key-distribution (TWQKD) is a relatively new proposal for sharing secret keys that is not fully explored yet. We analyse the security of TWQKD schemes that use qubits prepared in non-orthogonal states to transmit the key. Investigating protocols that employ an arbitrary number of bases for the channel preparation, we show, in particular, that the security of the LM05 protocol can not be improv
The role of coherent interactions in quantum metrology
It is well known that a quantum correlated probe can yield better precision in estimating an unknown parameter than classically possible. However, how such a quantum probe should be measured remains somewhat elusive. We examine the role of measurements in quantum metrology by considering two types of readout strategies: coherent, where all probes are measured simultaneously in an entangled basis; and adaptive, where probes are measured sequentially, with each measurement one
@PRL The first experimental verification of fluctuation relations in "Quantum Thermodynamics&qu
Highlighted as Editors’ Suggestion. Research on the out-of-equilibrium dynamics of quantum systems has so far produced important statements on the thermodynamics of small systems undergoing quantum mechanical evolutions. Key examples are provided by the Crooks and Jarzynski relations: taking into account fluctuations in non-equilibrium dynamics, such relations connect equilibrium properties of thermodynamic relevance with explicit non-equilibrium features. Although the experi
Jonas Maziero (former PhD student) awarded the CAPES Thesis Prize
Our former PhD student, Dr Jonas Maziero was awarded a couple of prizes: (1) the best thesis Grand Prize in Natural Sciences and Engineering awarded by the Coordination for the Improvement of Higher Education Personnel (CAPES) and the Conrado Wessel Foundation (CWF); (2) the Best Physics Thesis Prize awarded by CAPES; (3) and his work also received honor mention in the José Leite Lopes Prize of the Brazilian Physical Society (SBF). Dr. Maziero’s thesis was recognize
Information Processing in NMR: theory and experiment
A new issue on Quantum information processing (QIP) in Nuclear Magnetic Resonance (NMR) was published in Philosophical Transactions of the Royal Society. This was compiled and edited by Ivan S. Oliveira and Roberto M. Serra.
This special issue gathers the state-of-art of NMR-QIP. It covers new experimental techniques, which combine NMR and EPR, perspectives for NMR-QIP in Solid-State and implementation of quantum algorithms and protocols in liquid-state samples, including qu
An NMR experiment on the full quantum version of the complementarity principle
One of the milestones of quantum mechanics is Bohr's complementarity principle. It states that a single quantum can exhibit a particlelike or a wavelike behavior, but never both at the same time. These are mutually exclusive and complementary aspects of the quantum system. This means that we need distinct experimental arrangements in order to measure the particle or the wave nature of a physical system. One of the most known representations of this principle is the single-pho
@PRL Experimental Estimate of a Classicality Witness via a Single Measurement
The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system’s state and numerical optimization procedures. Thus, it is natural to seek methods involving fewer measurements that indicate the nature of the correlations in a system. Here we propose a classicality witness that
@PRL Witnessing the quantumness of correlations in NMR systems
The quantification of quantum correlations (other than entanglement) usually entails labored numerical optimization procedures also demanding quantum state tomographic methods. Thus it is interesting to have a laboratory friendly witness for the nature of correlations. We report recently a direct experimental implementation of such a witness in a room temperature nuclear magnetic resonance (NMR) system. In our experiment the nature of correlations is revealed by performing on
Nonadiabatic quantum computation by dynamic invariants
We introduce an approach for quantum computing in continuous time based on the Lewis–Riesenfeld dynamic invariants. This approach allows, under certain conditions, for the design of quantum algorithms running on a nonadiabatic regime. We show that the relaxation of adiabaticity can be achieved by processing information in the eigenlevels of a time dependent observable, namely, the dynamic invariant operator. Moreover, we derive the conditions for which the computation can be
