IF - Artigos publicados em periódicoshttp://repositorio.bc.ufg.br//handle/ri/13592024-04-21T04:41:28Z2024-04-21T04:41:28Z6401Secure quantum communication using classical correlated channelhttp://repositorio.bc.ufg.br//handle/ri/245282024-03-19T13:32:16Z2016-01-01T00:00:00Zdc.title: Secure quantum communication using classical correlated channel
dc.description.abstract: We propose a secure protocol to send quantum information from one part to another without a quantum channel. In our protocol, which resembles quantum teleportation, a sender (Alice) and a receiver (Bob) share classical correlated states instead of EPR ones, with Alice performing measurements in two different bases and then communicating her results to Bob through a classical channel. Our secure quantum communication protocol requires the same amount of classical bits as the standard quantum teleportation protocol. In our scheme, as in the usual quantum teleportation protocol, once the classical channel is established in a secure way, a spy (Eve) will never be able to recover the information of the unknown quantum state, even if she is aware of Alice’s measurement results. Security, advantages, and limitations of our protocol are discussed and compared with the standard quantum teleportation protocol.
2016-01-01T00:00:00ZDoes “cooling by heating” protect quantum correlations?http://repositorio.bc.ufg.br//handle/ri/245272024-03-19T13:29:28Z2016-01-01T00:00:00Zdc.title: Does “cooling by heating” protect quantum correlations?
dc.description.abstract: The connection between nonequilibrium quantum correlations, such as entanglement and quantum discord, and cooling by heating is investigated for a system composed by two atoms interacting with a single electromagnetic mode of a lossy cavity. This Hamiltonian model is experimentally feasible in the quantum optics domain and presents the occurrence of both nonequilibrium quantum correlations and cooling by heating for a range of parameters. Since in the cooling by heating phenomenon the effective temperature of the system decreases even increasing the environments temperature, it could be expected that quantum correlations could be enhanced. Interestingly, for some parameters we show that, contrary to this expectation, in the case studied here the lowering of the system effective temperature leads to no enhancement in the quantum correlations. In addition, we found that at both zero and finite temperature, depending on the parameters used, quantum correlations can be enhanced even when increasing the damping rates, a somewhat counterintuitive result.
2016-01-01T00:00:00ZUnambiguous discrimination of nonorthogonal quantum states in cavity QEDhttp://repositorio.bc.ufg.br//handle/ri/245252024-03-19T13:26:13Z2017-01-01T00:00:00Zdc.title: Unambiguous discrimination of nonorthogonal quantum states in cavity QED
dc.description.abstract: We propose an oversimplified scheme to unambiguously discriminate nonorthogonal quantum field states inside high-Q cavities. Our scheme, which is based on positive operator-valued measures (POVM) technique, uses a single three-level atom interacting resonantly with a single mode of a cavity-field and selective atomic state detectors. While the single three-level atom takes the role of the ancilla, the single cavity mode field represents the system we want to obtain information. The efficiency of our proposal is analyzed considering the nowadays achievements in the context of cavity QED. We also analyze the effect of a thermal environment to discrimination of nonorthogonal states.
2017-01-01T00:00:00ZReconstruction of Bohmian trajectories via weak measurement for bipartite stateshttp://repositorio.bc.ufg.br//handle/ri/245242024-03-19T13:22:58Z2018-01-01T00:00:00Zdc.title: Reconstruction of Bohmian trajectories via weak measurement for bipartite states
dc.description.abstract: Here we propose a protocol to reconstruct Bohmian trajectories for bipartite states of massive particles moving in an arbitrary one-dimensional potential. The proposal employs weak measurements and generalizes recent proposals presented in the literature (Kocsis et al., 2011). Finally, our work opens perspectives to experimentally study quantum correlation (primary resource for quantum information tasks) using the hydrodynamic formulation of quantum mechanics as suggested by Madelung and Bohm.
2018-01-01T00:00:00ZUniversal two-level quantum Otto machine under a squeezed reservoirhttp://repositorio.bc.ufg.br//handle/ri/245232024-03-19T13:19:52Z2020-01-01T00:00:00Zdc.title: Universal two-level quantum Otto machine under a squeezed reservoir
dc.description.abstract: We study an Otto heat machine whose working substance is a single two-level system interacting with a cold thermal reservoir and with a squeezed hot thermal reservoir. By adjusting the squeezing or the adiabaticity parameter (the probability of transition) we show that our two-level system can function as a universal heat machine, either producing net work by consuming heat or consuming work that is used to cool or heat environments. Using our model we study the performance of these machine in the finite-time regime of the isentropic strokes, which is a regime that contributes to make them useful from a practical point of view.
2020-01-01T00:00:00ZEfficiency of a quantum Otto heat engine operating under a reservoir at effective negative temperatureshttp://repositorio.bc.ufg.br//handle/ri/245222024-03-19T13:16:22Z2019-01-01T00:00:00Zdc.title: Efficiency of a quantum Otto heat engine operating under a reservoir at effective negative temperatures
dc.description.abstract: We perform an experiment in which a quantum heat engine works under two reservoirs, one at a positive spin temperature and the other at an effective negative spin temperature, i.e., when the spin system presents population inversion. We show that the efficiency of this engine can be greater than that when both reservoirs are at positive temperatures. We also demonstrate the counterintuitive result that the Otto efficiency can be beaten only when the quantum engine is operating in the finite-time mode.
2019-01-01T00:00:00ZQuantum Otto thermal machines powered by Kerr nonlinearityhttp://repositorio.bc.ufg.br//handle/ri/245212024-03-19T13:11:49Z2021-01-01T00:00:00Zdc.title: Quantum Otto thermal machines powered by Kerr nonlinearity
dc.description.abstract: We study the effect of Kerr nonlinearity in quantum thermal machines having a Kerr-nonlinear oscillator as working substance and operating under the ideal quantum Otto cycle. We first investigate the efficiency of a Kerr-nonlinear heat engine and show that by varying the Kerr-nonlinear strength the efficiency surpasses in up to 2.5 times the efficiency of a quantum harmonic oscillator (QHO) Otto engine. Moreover, the Kerr-nonlinearity makes the coefficient of performance of the Kerr-nonlinear refrigerator to be as large as three times the performance of QHO Otto refrigerators. These results were obtained using realistic parameters from circuit quantum electrodynamics devices formed by superconducting circuits and operating in the microwave regime.
2021-01-01T00:00:00ZFeasible platform to study negative temperatureshttp://repositorio.bc.ufg.br//handle/ri/245202024-03-19T13:08:30Z2019-01-01T00:00:00Zdc.title: Feasible platform to study negative temperatures
dc.description.abstract: We afford an experimentally feasible platform to study Boltzmann negative temperatures. Our proposal takes advantage of well-known techniques of engineering Hamiltonian to achieve steady states with highly controllable population inversion. Our model is completely general and can be applied in a number of contexts, such as trapped ions, cavity-QED, quantum dots coupled to optical cavities, circuit-QED, and so on. To exemplify, we use Hamiltonian models currently used in optical cavities and trapped ions domain, where the level of precision achieved the control of the freedom degrees of a single atom inside a cavity as well as a single trapped ion. We show several interesting effects such as absence of thermalization between systems with inverted population and cooling by heating in these unconventional systems.
2019-01-01T00:00:00ZTwo-level quantum Otto heat engine operating with unit efficiency far from the quasi-static regime under a squeezed reservoirhttp://repositorio.bc.ufg.br//handle/ri/245192024-03-19T13:05:35Z2021-01-01T00:00:00Zdc.title: Two-level quantum Otto heat engine operating with unit efficiency far from the quasi-static regime under a squeezed reservoir
dc.description.abstract: Recent theoretical and experimental studies in quantum heat engines show that, in the quasi-static regime, it is possible to have higher efficiency than the limit imposed by Carnot, provided that engineered reservoirs are used. The quasi-static regime, however, is a strong limitation to the operation of heat engines, since an infinitely long time is required to complete a cycle. In this paper we propose a two-level model as the working substance to perform a quantum Otto heat engine surrounded by a cold thermal reservoir and a squeezed hot thermal reservoir. Taking advantage of this model we show a striking achievement, that is to attain unity efficiency even at non-null power.
2021-01-01T00:00:00ZEntanglement dynamics for a conditionally kicked harmonic oscillatorhttp://repositorio.bc.ufg.br//handle/ri/245182024-03-19T13:02:10Z2016-01-01T00:00:00Zdc.title: Entanglement dynamics for a conditionally kicked harmonic oscillator
dc.description.abstract: The time evolution of the quantum kicked harmonic oscillator (KHO) is described by the Floquet operator which maps the state of the system immediately before one kick onto the state at a time immediately after the next. Quantum KHO is characterized by three parameters: the coupling strength V0, the so-called Lamb–Dicke parameter η whose square is proportional to the effective Planck constant , and the ratio T of the natural frequency of the oscillator and the kick frequency. To a given coupling strength and depending on T being a natural or irrational number, the phase space of the classical kicked oscillator can display different behaviors, as for example, stochastic webs or quasicrystal structures, thus showing a chaotic or localized behavior that is mirrored in the quantum phase space. On the other hand, the classical limit is studied letting become negligible. In this paper we investigate how the ratio T, considered as integer, rational or irrational, influences the entanglement dynamics of the quantum KHO and study how the entanglement dynamics behaves when varying either V0 or parameters.
2016-01-01T00:00:00Z