Papers by Antonio Vidiella-Barranco
Arxiv preprint quant-ph/0312056, 2003
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reciprocation using three level atoms in a lambda configuration
Fundamental Problems in Quantum Physics, 1995
We consider a simple model of a photon detector which consists of a set of N three-level atoms. A... more We consider a simple model of a photon detector which consists of a set of N three-level atoms. Absorption takes place when a transition happens from the initial, metastable state |1〉 to the upper state |2〉. Irreversible amplification takes place when the atom spontaneously decays (from level |2〉) to a state |3〉 lower than |1〉. We show that the product of the dark rate with the dead time is bounded from below by a number which increases linearly with the frequency width (characteristic of the incoming beam) times the detector area.
Optik
We investigate the generation and transfer of entangled states between two coupled microtoroidal ... more We investigate the generation and transfer of entangled states between two coupled microtoroidal cavities considering two different types of couplings, namely i) via a bridge qubit and ii) via evanescent fields. The cavities support two counter-propagating whispering-gallery modes (WGMs) that may also interact with each other. We firstly show that it is possible to transfer, with high fidelity, a maximally entangled state between the two modes of the first cavity (cavity 1) to the two modes of the second cavity (cavity 2), independently of the type of coupling. Interesting differences, though, arise concerning the generation of entangled states from initial product states; if the cavities are coupled via a bridge qubit, we show that it is possible to generate a 4partite entangled state involving all four cavity modes. On the other hand, contrarily to what happens in the qubit coupling case, it is possible to generate bipartite maximally entangled states between modes of different cavities from initial separable states for cavities coupled by evanescent waves. Besides, we show that different entangled states between the propagating and counter-propagating modes of distinct cavities may be generated by tuning the interaction between modes belonging to the same cavity (intra-cavity couplings). Again, this is possible only for the couplings via evanescent waves. For the completion of our work, we discuss the effects of losses on the dynamics of the system.
Physics Letters A
In this work, we investigate the influence of a minimal, phase-sensitive environment on a system ... more In this work, we investigate the influence of a minimal, phase-sensitive environment on a system of two coupled qubits. The environment is constituted by a single-mode field initially prepared in a type of Schrödinger cat state, a quantum superposition of two squeezed coherent states. We present an analytical solution to the model and investigate the degradation of the quantum features of the system due to the action of the environment. In particular, we find that the time-averaged linear entropy for long times,ST , has approximately a linear dependence on Mandel's Q parameter as well as on the variance of theX quadrature of the initial state of the environment.
2022 IEEE Workshop on Complexity in Engineering (COMPENG)
We investigate some aspects of the dynamics and entanglement of bipartite quantum system (atom-qu... more We investigate some aspects of the dynamics and entanglement of bipartite quantum system (atom-quantized field), coupled to a third “external” subsystem (quantized field). We make use of the Raman coupled model; a three-level atom in a lambda configuration interacting with two modes of the quantized cavity field. We consider the far off resonance limit, which allows the derivation of an effective Hamiltonian of a two-level atom coupled to the fields. We also make a comparison with the situation in which one of the modes is treated classically rather than prepared in a quantum field (coherent state).
Physical Review A, 2021
We present a scheme of quantum state truncation in the Fock basis (quantum scissors), based on th... more We present a scheme of quantum state truncation in the Fock basis (quantum scissors), based on the combined action of a nondegenerate optical parametric amplifier and a beamsplitter. Differently from previously proposed linear-optics-based quantum scissors devices, which depend on reliable Fock states sources, our scheme requires only readily available Gaussian states, such as coherent states inputs (vacuum state included). A truncated state is generated after performing photodetections in the global state. We find that, depending on which output ports each of the two photodetectors is positioned, different types of truncated states may be produced: i) states having a maximum Fock number of N , or ii) states having a minimum Fock number N. In order to illustrate our method, we discuss an example having as input states a coherent state in the beamsplitter and vacuum states in the amplifier, and show that the resulting truncated states display nonclassical properties, such as sub-Poissonian statistics and squeezing. We quantify the nonclassicality degree of the generated states using the Wigner-Yanase skew information measure. For complementarity, we discuss the efficiency of the protocol, e.g., generation probability as well as the effects of imperfections such as the detector's quantum efficiency and dark counts rate.
A cavity QED generation scheme is suggested where atoms crossing the cavities act as quantum chan... more A cavity QED generation scheme is suggested where atoms crossing the cavities act as quantum channels capable of entangling the flelds. A suitable choice of the atom-cavity interactions and the realization of simple atomic measurements lead to the generation of cluster-type entangled coherent states (CTECS) describing nonlocal electromagnetic flelds of separate cavities. Multipartite entangled states are vital for the full exploration of quantum computation and communication protocols. A special kind of multipartite entangled states called cluster states (1) have attracted much attention due to their potential applications. Such states form the basis of the one-way quantum computing model (2), an alternative to the conventional circuit approach (3). Moreover, the use of cluster states has proven useful in linear optics quantum computing (4) where it seems to reduce the demand of resources as demonstrated in recent experiment (5). Conceptual foundations of quantum mechanics have also...
Journal of Optics B: Quantum and Semiclassical Optics, 2000
Latin America Optics and Photonics Conference, 2012
We present an interferometry-based scheme to entangle the quantum state of a moving mirror of an ... more We present an interferometry-based scheme to entangle the quantum state of a moving mirror of an optomechanical cavity with the vibrational state of a single ion trapped inside a second cavity.
We discuss a continuous variables method of quantum key distribution employing strongly polarized... more We discuss a continuous variables method of quantum key distribution employing strongly polarized coherent states of light. The key encoding is performed using the variables known as Stokes parameters, rather than the field quadratures. Their quantum counterpart, the Stokes operatorsŜi (i=1,2,3), constitute a set of non-commuting operators, being the precision of simultaneous measurements of a pair of them limited by an uncertainty-like relation. Alice transmits a conveniently modulated two-mode coherent state, and Bob randomly measures one of the Stokes parameters of the incoming beam. After performing reconciliation and privacy amplification procedures, it is possible to distill a secret common key. We also consider a non-ideal situation, in which coherent states with thermal noise, instead of pure coherent states, are used for encoding.
Physica A: Statistical Mechanics and its Applications, 2016
In this paper it is studied the influence of a minimal thermal environment on the dynamics of a q... more In this paper it is studied the influence of a minimal thermal environment on the dynamics of a quantum harmonic oscillator (labelled A), prepared in a coherent state. The environment itself consists of a second oscillator (labelled B), initially in a thermal state. Two types of interaction Hamiltonians are considered, and the time-evolution of the reduced density operator of oscillator A is compared to the one obtained from the usual master equation approach, i.e., assuming that oscillator A is coupled to a large reservoir. An analysis of the linear entropy evolution of oscillator A shows that simplified models may be able to describe important features related to the phenomenon of decoherence.
Coherence and Quantum Optics VII, 1996
The single mode binomial states of the quantized electromagnetic field are defined, in terms of t... more The single mode binomial states of the quantized electromagnetic field are defined, in terms of the number state basis In) as1: (1) where The probability of ocurrence of m photons, is a binomial distribution, Each photon has a probability p of being emitted, having M independent ways of doing it. It is interesting to note that if p → ∞ and M → such that pM = α constant, ∣p, M 〉 → ∣α〉 where ∣α〉 is a coherent state. If p → 1, then ∣p, M〉(number state having M photons). Therefore, the binomial states could allow a continuous interpolation betweeen fundamentally different quantum-mechanical states. Their generation could be in principle accomplished in a. system containing N 2 molecules mixed with CO 2 1 , as well as in a free electron laser2.
The European Physical Journal Plus
The combination of different quantum systems may allow the exploration of the distinctive feature... more The combination of different quantum systems may allow the exploration of the distinctive features of each system for the investigation of fundamental phenomena as well as for quantum technologies. In this work we consider a setup consisting of an atomic ensemble enclosed within a laser-driven optomechanical cavity, having the moving mirror further (capacitively) coupled to a low frequency LC circuit. This constitutes a four-partite optoelectromechanical quantum system containing three macroscopic quantum subsystems of a different nature, viz, the atomic ensemble, the massive mirror and the LC circuit. The quantized cavity field plays the role of an auxiliary system that allows the coupling of two other quantum subsystems. We show that for experimentally achievable parameters, it is possible to generate steady state bipartite Gaussian entanglement between pairs of macroscopic systems. In particular, we find under which conditions it is possible to obtain a reasonable amount of entanglement between the atomic ensemble and the LC circuit, systems that might be suitable for constituting a quantum memory and for quantum processing, respectively. For complementarity, we discuss the effect of the environmental temperature on quantum entanglement.
Optik, 2021
In this paper we present a study of the quantum phase estimation problem employing continuous-var... more In this paper we present a study of the quantum phase estimation problem employing continuous-variable, entangled squeezed coherent (quasi-Bell) states as probe states. We show that their inherent squeezing and entanglement properties might bring advantages, increasing the precision of phase estimation compared to protocols which employ other continuous variable states e.g., two-mode, entangled coherent states or single-mode, squeezed states. We also analyze the phase estimation process considering: i) a linear (unitary) perturbation, and ii) dissipation, and conclude that the use of entangled squeezed coherent states as probe states may still be advantageous even under non-ideal conditions.
Individual quantum systems may be interacting with surrounding environments having a small number... more Individual quantum systems may be interacting with surrounding environments having a small number of degrees of freedom. It is therefore relevant to understand the extent to which such small (but uncontrollable) environments could affect the quantum properties of the system of interest. Here we discuss a simple system-environment toy model, constituted by a two-level atom (atom 1) interacting with a single mode cavity field. The field is also assumed to be (weakly) coupled to an external noisy subsystem, the small environment, modeled as a second two-level atom (atom 2). We investigate the action of the minimal environment on the dynamics of the linear entropy (state purity) and the atomic dipole squeezing of atom 1, as well as the entanglement between atom 1 and the field. We also obtain the full analytical solution of the two atom Tavis-Cummings model for both arbitrary coupling strengths and frequency detunings, necessary to analyze the influence of the field-environment detuning...
In this work we present a quantum key distribution protocol using continuous-variable non-Gaussia... more In this work we present a quantum key distribution protocol using continuous-variable non-Gaussian states, homodyne detection and post-selection. The employed signal states are the Photon Added then Subtracted Coherent States (PASCS) in which one photon is added and subsequently one photon is subtracted. We analyze the performance of our protocol, compared to a coherent state based protocol, for two different attacks that could be carried out by the eavesdropper (Eve). We calculate the secret key rate transmission in a lossy line for a superior channel (beam-splitter) attack, and we show that we may increase the secret key generation rate by using the non-Gaussian PASCS rather than coherent states. We also consider the simultaneous quadrature measurement (intercept-resend) attack and we show that the efficiency of Eve's attack is substantially reduced if PASCS are used as signal states.
We present a scheme for cavity-assisted generation of hybrid entanglement between a moving mirror... more We present a scheme for cavity-assisted generation of hybrid entanglement between a moving mirror belonging to an optomechanical cavity and a single trapped ion located inside a second cavity. Due to radiation pressure, it is possible to entangle the moving mirror with one of the cavity fields. Also, by tuning the second cavity field with the internal degrees of freedom of the ion, an entangled state of the cavity field/ion can be independently generated. The fields leaking from each cavity are then combined in a beam-splitter, and following the detection of the outgoing photons by conveniently placed photodetectors, we show that it is possible to generate entangled states of the moving mirror and the single trapped ion subsystems. In our scheme the generated states are hybrid entangled states, in the sense that they are constituted by discrete (Fock) states and continuous variable (coherent) states.
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Papers by Antonio Vidiella-Barranco