# Daniel Felinto's research while affiliated with Federal University of Pernambuco and other places

## Publications (97)

Article
Full-text available
The COVID-19 pandemic was severely aggravated in Brazil due to its politicization by the country’s federal government. However, the impact of diffuse political forces on the fatality of an epidemic is notoriously difficult to quantify. Here we introduce a method to measure this effect in the Brazilian case, based on the inhomogeneous distribution t...
Article
In this work, we perform a detailed theoretical and experimental investigation of an atomic memory based on recoil-induced resonance in cold cesium atoms. We consider the interaction of nearly degenerate pump and probe beams with an ensemble of two-level atoms. A full theoretical density matrix calculation in the extended Hilbert space of the inter...
Article
We report the experimental verification of nonclassical correlations for an unfiltered spontaneous four-wave mixing process in an ensemble of cold two-level atoms, confirming theoretical predictions by Du et al. in 2007 for the violation of a Cauchy-Schwarz inequality in the system, and obtaining R=(1.98±0.03)≰1. Quantum correlations are observed i...
Preprint
Full-text available
The COVID-19 pandemic was severely aggravated in Brazil due to its politicization by the country’s central government. However, the impact of diffuse political forces on the fatality of an epidemic is commonly hard to quantify. Here we introduce a method to measure this effect in the Brazilian case, based on the inhomogeneous distribution throughou...
Conference Paper
By combining genetic algorithm and a spatial light modulator we demonstrate theoretically how to improve a two-photon cascade absorption in atomic ensembles using optimized phase masks. At low atomic densities, we compare the cases of sequential transitions with the two photons coming from the same pulse and from two different pulses. We achieved a...
Conference Paper
We report the experimental observation of nonclassical correlations for an unfiltered spontaneous four-wave mixing process in an ensemble of cold two-level atoms, confirming theoretical predictions for the violation of a Cauchy-Schwarz inequality. We obtain R = 1.98 ± 0.03 > 1.
Preprint
Full-text available
We report the experimental verification of nonclassical correlations for a four-wave-mixing process in an ensemble of cold two-level atoms, confirming theoretical predictions by Du et al. in 2007 for the violation of a Cauchy-Schwarz inequality in the system, and obtaining $R = (1.98\pm0.03) \nleq 1$. Quantum correlations are observed in a nano-sec...
Article
The bunching of light resulting from the spontaneous emission of an atomic ensemble is a well known effect, shared with various sources of thermal fields. It is, on the other hand, also an integral part of recently developed quantum memories for various applications. Here we theoretically and experimentally investigate the statistical correlations...
Article
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The storage of broadband single photons from a parametric-down-conversion source is a capability with the potential to foster significant development in the field of quantum information. A particular challenge to this problem, however, is the mismatch between the short-lived photon and the long-lived memories, which translates into quite different...
Article
In this work, we explore both the internal and external atomic degrees of freedom to demonstrate the observation of giant gain and parametric oscillation in multiple four-wave mixing (FWM) processes in a sample of cold cesium atoms. We employ a standard backward FWM beam configuration to achieve parametric probe-beam gains exceeding 2000. This gian...
Preprint
Full-text available
A simplified theory for the wavepackets of the photons emitted during the read process of a quantum memory formed by cold atoms is provided. We arrive at analytical expressions for the single- and double-photon emissions, evidencing superradiant features in both cases. In the two-photon case, both photons are emitted in the same spatiotemporal mode...
Article
In spite of recent conceptual and experimental advances, the ultimate nature of the wave function in quantum theory remains nebulous. Is it a mathematical device that describes our knowledge on a physical system or is it a physical field in any tenable sense? In this work we report on significant experimental steps toward a test on the reality of t...
Article
The present work explores new possibilities for the selective storage of optical information through higher-order nonlinearities in a sample of cold cesium atoms obtained from a magneto-optical trap. Particularly, we demonstrate the storage of a third-, fifth-, and seventh-order nonlinear atom–light interaction into the coherences and populations o...
Article
We report a new type of optical memory using a pure two-level system of cesium atoms cooled by the magnetically assisted Sisyphus effect. The optical information of a probe field is stored in the coherence between quantized vibrational levels of the atoms in the potential wells of a 1-D optical lattice. The retrieved pulse shows Rabi oscillations w...
Conference Paper
Full-text available
Article
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The two-photon transition 5S−5P−5D in rubidium vapor is investigated by detecting the fluorescence from the 6P3/2 state when the atomic system is excited by the combined action of a cw diode laser and a frequency comb. The cw laser plays a role as a velocity-selective filter and allows for sub-Doppler spectroscopy over a large spectral range includ...
Article
Superradiance in an ensemble of atoms leads to the collective enhancement of radiation in a particular mode shared by the atoms in their spontaneous decay from an excited state. The quantum aspects of this phenomenon are highlighted when such collective enhancement is observed in the emission of a single quantum of light. Here we report a further s...
Article
Full-text available
The two-photon transition $5S-5P-5D$ in rubidium vapor is investigated by detecting the fluorescence from the $6P_{3/2}$ state when the atomic system is excited by the combined action of a cw diode laser and a train of ultrashort pulses. The cw-laser plays a role as a velocity-selective filter and allows for a spectroscopy over a large spectral ran...
Conference Paper
An experimental test for the wave function collapse is realized. The experimental results reaffirms the epistemic interpretation for the state vector and opposes the ontic view.
Article
We report on the storage of light via the phenomenon of recoil-induced resonance in a pure two- level system of cold cesium atoms. We use a strong coupling beam and a weak probe beam to couple different external momentum states of the cesium atom via two-photon Raman interaction which leads to the storage of the optical information of the probe bea...
Article
We report on the amplification of an optical vortex beam carrying orbital angular momentum via induced narrow Raman gain in an ensemble of cold cesium atoms. A 20% single-pass Raman gain of a weak vortex signal field is observed with a spectral width of order of 1 MHz, much smaller than the natural width, demonstrating that the amplification proces...
Article
Full-text available
We report on the demonstration of a nonlinear optical memory (NOM) for storage and on-demand manipulation of orbital angular momentum (OAM) of light via higher-order nonlinear processes in cold cesium atoms. A spatially resolved phase-matching technique is used to select each order of the nonlinear susceptibility associated, respectively, with time...
Article
We characterize a polarization-entangled photon source based on femtosecond pulsed parametric downconversion in a periodically poled χ (2) medium. Employing a Sagnac interferometer, we prepared different quantum states aiming at future investigations in quantum information and on the foundations of quantum mechanics. In this work we demonstrate the...
Article
Full-text available
Broadband single photons are usually considered not to couple efficiently to atomic gases because of the large mismatch in bandwidth. Contrary to this intuitive picture, here we demonstrate that the interaction of ultrashort single photons with a dense resonant atomic sample deeply modifies the temporal shape of their wavepacket mode without degrad...
Conference Paper
We demonstrate that the interaction of ultrashort single photons with a dense resonant atomic sample deeply modifies the temporal shape of their wavepacket mode without degrading their non-classical character, and effectively generates zero-area single-photon pulses.
Article
We report the experimental observation of Coherent Population Oscillation (CPO) based light storage in thermal helium and cesium vapors.
Article
Full-text available
We report on the storage of light via the phenomenon of Coherent Population Oscillation (CPO) in an atomic cesium vapor at room temperature. In the experiment the optical information of a probe field is stored in the CPO of two ground states of a Lambda three-level system formed by the Zeeman sublevels of the hyperfine transition F = 3 - F' = 2 of...
Article
Full-text available
We report on the storage of orbital angu- lar momentum (OAM) of light of a Laguerre-Gaussian mode in an ensemble of cold cesium atoms and its re- trieval along an axis different from the incident light beam. We employed a time-delayed four-wave mixing configuration to demonstrate that at small angle (2o), after storage, the retrieved beam carries t...
Article
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The interaction of an ensemble of atoms with common vacuum modes may lead to an enhanced emission into these modes. This phenomenon, known as superradiance, highlights the coherent nature of spontaneous emission, resulting in macroscopic entangled states in mundane situations. The complexity of the typical observations of superradiance, however, ma...
Article
We report a detailed investigation on the properties of correlation spectra for cold atoms under the condition of Electromagnetically Induced Transparency (EIT). We describe the transition in the system from correlation to anti-correlation as the intensity of the fields increases. Such transition occurs for laser frequencies around the EIT resonanc...
Article
Full-text available
The mechanism of extraction of information stored in a quantum memory is studied here in detail. We consider memories containing a single excitation of a collective atomic state, which is mapped into a single photon during the reading process. A theory is developed for the wavepacket of the extracted photon, leading to a simple analytical expressio...
Conference Paper
Light beams carrying orbital angular momentum (OAM) have attracted a great interest owing to their several applications ranging from the mechanical manipulation of macroscopic particles to the encoding of quantum information [1]. A well-known family of these beams is constituted by Laguerre-Gaussian modes specified by a topological charge ℓ, which...
Article
The phenomenon called Electromagnetically Induced Transparency (EIT) may induce different types of correlation between two optical fields interacting with an ensemble of atoms. It is presently well known, for example, that in the vicinity of an EIT resonance the dominant correlations at low powers turn into anti-correlations as power increases. Suc...
Conference Paper
Full-text available
We use an ultrashort pulse train and a cw laser to investigate one- and two-photon transitions in Rb vapor. The action of the two lasers, combined with a 1 GHz repetition rate, allows a velocity selective spectroscopy of the hyperfine levels of the 5P and 5D states. Moreover, the experimental data are well described in the frequency domain picture.
Article
Full-text available
We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P_{3/2} state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D_{2} lin...
Article
We report a spectroscopic investigation of the reading process of a cold atomic ensemble coherently prepared in a superposition of its degenerate ground states. Specifically we measure the spectra of the generated signal for different frequencies of the reading laser pulse and for intensities below saturation. The spectra present a double-peaked st...
Article
We analyze the efficiency and scalability of the Duan-Lukin-Cirac-Zoller (DLCZ) protocol for quantum repeaters focusing on the behavior of the experimentally accessible measures of entanglement for the system, taking into account crucial imperfections of the stored entangled states. We calculate then the degradation of the final state of the quantu...
Article
Full-text available
Electromagnetically induced transparency (EIT) has led to several quantum optics effects such as lasing without inversion or squeezed light generation. More recently quantum memories based on EIT have been experimentally implemented in different systems such as alkali metal atoms. In this system the excited state of the optical transition splits in...
Article
Full-text available
We report on the observation of enhanced four-wave mixing via crossover resonance in a Doppler broadened cesium vapor. Using a single laser frequency, a resonant parametric process in a double-$\Lambda$ level configuration is directly excited for a specific velocity class. We investigate this process in different saturation regimes and demonstrate...
Article
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Electromagnetically induced transparency (EIT) has mainly been modeled for three-level systems. In particular, considerable interest has been dedicated to the Î configuration, with two ground states and one excited state. However, in the alkali-metal atoms, which are commonly used, the hyperfine interaction in the excited state introduces several l...
Conference Paper
We analyze the efficiency and scalability of the DLCZ protocol for quantum repeaters through experimentally accessible measures of entanglement (concurrence; CHSH inequality) providing a better time estimate to succeed in each step of the protocol.
Article
Full-text available
We report on the simultaneous observation, by delayed Bragg diffraction, of four- and six-wave mixing processes in a coherently prepared atomic ensemble consisting of cold cesium atoms. For each diffracted order, we observe different temporal pulse shapes and dependencies with the intensities of the exciting fields, evidencing the different mechani...
Article
Full-text available
We report a detailed investigation on the generation of pulse pairs during the readout of a coherence grating stored in a cold atomic ensemble. The pulse shapes and the split of the retrieved energy between the two pulses are studied as a function of the relative intensities of the two reading fields, and a minimum is observed for the total retriev...
Conference Paper
We present experimental results on the Two-Beam Coupling of femtosecond beams in atomic rubidium vapor. Propagation and accumulation effects due to the modelocked pulse train are investigated.
Conference Paper
We summarize recent developments in direct frequency-comb spectroscopy that allowed high-resolution, broad-bandwidth measurements of multiple atomic and molecular resonances using only a phase-stabilized femtosecond laser, opening the way for merging precision spectroscopy with coherent control.
Conference Paper
We investigate the generation of correlated light beams in a coherently prepared atomic system consisting of cold cesium atoms. Double Bragg diffraction into a Zeeman coherence grating is employed to conditionally extract the stored information.
Article
Full-text available
We investigate the evolution of a Zeeman coherence grating induced in a cold atomic cesium sample in the presence of an external magnetic field. The gratings are created in a three-beam light storage configuration using two quasi-collinear writing laser pulses and reading with a counterpropagating pulse after a variable time delay. The phase conjug...
Article
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We report on a detailed investigation of the coupling between a femtosecond-laser frequency comb and a cw diode laser interacting with an atomic medium of variable density. The comb is printed on a Doppler-broadened atomic transition and the frequency-dependent transmission of the cw laser is monitored as it is scanned over the inhomogenously broad...
Conference Paper
We introduce a theory for the interaction of multi-level atoms with well-stabilized pulse trains, which is general enough to take into account arbitrarily-shaped frequency combs. It is applied to the excitation of rubidium-87 atoms.
Conference Paper
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We investigate the transmission of a cw laser interacting with rubidium vapor and a frequency comb. The results reveal various regimes of competition and the importance of optical pumping and power broadening of the lasers.
Article
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Direct frequency-comb spectroscopy is a technique that employs a train of well-stabilized ultrashort pulses to study the spectral properties of atomic or molecular systems. In this way, it opens the possibility of incorporating various coherent-control techniques for such spectral investigations. Here we introduce a theory for the interaction of a...
Conference Paper
The paper reports on the storage of superposition of orbital angular momentum (OAM) states, as well as its manipulation through an applied transverse magnetic field. In the experiment , Zeeman sublevels of the degenerate two-level system is used. In another series of experiments,an external dc magnetic field is applied, nearly orthogonal to the pla...
Article
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We report on the storage of orbital angular momentum of light in a cold ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The stored information can be manipulated by an applied magnetic field and we were able to observe collapses and re...
Article
We report on the observation of collapse and revival of a spatial light grating stored into the Zeeman coherences of cold cesium atoms. Bragg diffraction is employed to probe the dynamic of the stored grating.
Conference Paper
Entanglement is generated by path-erasing detection of single photon emitted indistinguishably by two atomic ensembles. We characterize relationship of degree of entanglement to local dephasing. Parallel pairs of entanglement are distributed to polarization entanglement via conditional control. (C)2008 Optical Society of America
Article
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We report on a detailed investigation of the dynamics and the saturation of a light grating stored in a sample of cold cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The diffracted efficiency is studied as a function of the intensities of both wr...
Article
We demonstrated entanglement distribution between two remote quantum nodes located 3 meters apart. This distribution involves the asynchronous preparation of two pairs of atomic memories and the coherent mapping of stored atomic states into light fields in an effective state of near-maximum polarization entanglement. Entanglement is verified by way...
Conference Paper
Diode and Ti:Sapphire lasers were used to analyze the laser noise influence on an EIT resonance. In the first case phase-to-amplitude noise conversion dominates while atomic dipole fluctuations emerge in the latter.
Article
Full-text available
We present a protocol for performing entanglement connection between pairs of atomic ensembles in the single excitation regime. Two pairs are prepared in an asynchronous fashion and then connected via a Bell measurement. The resulting state of the two remaining ensembles is mapped to photonic modes and a reduced density matrix is then reconstructed...
Article
Quantum networks hold the promise for revolutionary advances in information processing with entanglement distributed over remote locations via quantum repeaters. We report two milestones in this direction: the conditional control of memories and the implementation of functional nodes.
Conference Paper
Quantum networks hold the promise for revolutionary advances in information processing with entanglement distributed over remote locations via quantum repeaters. We report two milestones in this direction: the conditional control of memories and the implementation of functional nodes.
Article
Full-text available
High degrees of intensity correlation between two independent lasers were observed after propagation through a rubidium vapor cell in which they generate Electromagnetically Induced Transparency (EIT). As the optical field intensities are increased, the correlation changes sign (becoming anti-correlation). The experiment was performed in a room tem...
Article
Full-text available
The ability to distribute quantum resources over long distances is a key element for the development of several practical applications in the field of quantum information. In this way, major efforts have been made in the past decade to extend the maximum distances for the observation of entanglement or for the realization of quantum cryptography. U...
Article
Quantum networks hold the promise for revolutionary advances in information processing with quantum resources distributed over remote locations via quantum-repeater architectures. Quantum networks are composed of nodes for storing and processing quantum states, and of channels for transmitting states between them. The scalability of such networks r...
Article
Violations of a Bell inequality are reported for an experiment where one of two entangled qubits is stored in a collective atomic memory for a user-defined time delay. The atomic qubit is found to preserve the violation of a Bell inequality for storage times up to 21 micros, 700 times longer than the duration of the excitation pulse that creates th...
Article
We report significant improvements in the retrieval efficiency of a single excitation stored in an atomic ensemble and in the subsequent generation of strongly correlated pairs of photons. A 50% probability of transforming the stored excitation into one photon in a well-defined spatio-temporal mode at the output of the ensemble is demonstrated. The...
Conference Paper
A critical requirement for diverse applications in quantum information science is the capability to disseminate quantum resources over complex quantum networks. For example, the coherent distribution of entangled quantum states together with quantum memory (for storing the states) can enable scalable architectures for quantum computation, communica...
Article
A critical requirement for diverse applications in Quantum Information Science is the capability to disseminate quantum resources over complex quantum networks. This requires deterministic or heralded storage of entanglement between remote locations. Atomic ensembles appear to be a promising candidate for this task . In this contribution we report...
Article
Full-text available
A critical requirement for diverse applications in quantum information science is the capability to disseminate quantum resources over complex quantum networks. For example, the coherent distribution of entangled quantum states together with quantum memory (for storing the states) can enable scalable architectures for quantum computation, communica...
Article
Full-text available
We investigate a time-resolved four-wave mixing when a two-photon resonance is involved. By varying the relative polarization of the pulse pairs, we are able to select the quatum pathways and distinguish optical and quantum interferences.
Article
Conditioned upon a photoelectric event, entanglement is created between two atomic ensembles separated by 2.8 m. The joint atomic state is transferred to two light modes and entanglement verified by quantum state tomography.
Article
Full-text available
Pairs of pulses from an incoherent source are used to investigate the time-resolved four-wave mixing response of atomic rubidium when a two-photon resonance is involved in the nonlinear process. By varying the relative polarization of the pulse pairs, we are able to select the quantum pathways and clearly distinguish optical and quantum interferenc...
Article
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We report an investigation to establish the physical mechanisms responsible for decoherence in the generation of photon pairs from atomic ensembles, via the protocol of Duan et. al for long distance quantum communication [Nature (London) 414, 413 (2001)] and present the experimental techniques necessary to properly control the process. We develop a...
Article
Full-text available
A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled 87Rb atoms. Absolute atomic transition frequencies, such as the 5S1/2 F=2-->7S1/2 F"=2 two-photon resonance measured at 788,794 768,921 (44) kHz, are determined wi...
Article
The development of phase stabilized modelocked lasers has enabled a revolution in the field of high precision spectroscopy. The light produced by such a broadband laser typically consists of millions of equally spaced modes spanning many tens of nanometers. Once the comb is referenced to a frequency standard the optical frequencies of the laser mod...
Article
Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applicati...
Article
Full-text available
The time dependence of nonclassical correlations is investigated for two fields (1,2) generated by an ensemble of cold cesium atoms via the protocol of Duan et al. [Nature (London) 414, 413 (2001)]]. The correlation function R(t1,t2) for the ratio of cross to autocorrelations for the (1,2) fields at times (t1,t2) is found to have a maximum value R(...
Article
Full-text available
We investigate coherent accumulation processes in three-level atoms excited by a train of ultrashort pulses in the case where the atomic relaxation times are greater than the laser repetition period. In this situation the resonances of the laser field with the atomic system are determined by the laser frequency comb rather than by the spectrum of a...