Marcelo Almeida | The University of Queensland, Australia (original) (raw)

Papers by Marcelo Almeida

Physical Review Letters, 2013

The key requirement for quantum networking is the distribution of entanglement between nodes. Sur... more The key requirement for quantum networking is the distribution of entanglement between nodes. Surprisingly, entanglement can be generated across a network without direct transfer-or communication-of entanglement. In contrast to information gain, which cannot exceed the communicated information, the entanglement gain is bounded by the communicated quantum discord, a more general measure of quantum correlation that includes but is not limited to entanglement. Here, we experimentally entangle two communicating parties sharing three initially separable photonic qubits by exchange of a carrier photon that is unentangled with either party at all times. We show that distributing entanglement with separable carriers is resilient to noise and in some cases becomes the only way of distributing entanglement through noisy environments.

Quantum information & computation

... A, 62, 052317. 52. Daniel Collins, Noah Linden and Sandu Popeseu (2001), Nonlocal content of ... more ... A, 62, 052317. 52. Daniel Collins, Noah Linden and Sandu Popeseu (2001), Nonlocal content of quantum operations,Phys. ... 55. JL O'Brien, GJ Pryde, AG White, TC Ralph, and D. Branning (2003), Demonstrationof an all-optical quantum controlled-NOT gate, Nature, 426, 264. ...

Abstract Quantum computation promises to solve fundamental, yet otherwise intractable, problems a... more Abstract Quantum computation promises to solve fundamental, yet otherwise intractable, problems across a range of active fields of research. Recently, universal quantum logic-gate sets—the elemental building blocks for a quantum computer—have been demonstrated in several physical architectures. A serious obstacle to a full-scale implementation is the large number of these gates required to build even small quantum circuits. Here, we present and demonstrate a general technique that harnesses multi-level information carriers to ...

Proceedings. Vol.1. Sixth Brazilian Symposium on Neural Networks, 2000

SVM-KM: speeding SVMs learning with a priori cluster selection and k-means Marcel0 Barros de Alme... more SVM-KM: speeding SVMs learning with a priori cluster selection and k-means Marcel0 Barros de Almeida, Antanio de Piidua Braga Jo50 Pedro Braga Universidade Federal de Minas Gerais Department of Electronics Engineering { barros,apbraga} @cpdee.ufmg.br Abstract ...

International Conference on Quantum Information, 2007

AG White, M. Pereira de Almeida, M. Barbieri, DN Biggerstaff, RB Dalton, A. Gilchrist, G. Gillett... more AG White, M. Pereira de Almeida, M. Barbieri, DN Biggerstaff, RB Dalton, A. Gilchrist, G. Gillett, DFV James†, NK Langford, BN Lanyon, KJ Resch‡, T. Weinhold ... Department of Physics and Centre for Quantum Computer Technology, University of Queensland, Brisbane, Australia †Department of Physics, University of Toronto, Ontario, Canada ‡Department of Physics and Institute for Quantum Computing, University of Waterloo, Ontario, Canada ... We demonstrate significantly compacted quantum algorithms and demonstrate a Fock-state filter by going ...

The Rochester Conferences on Coherence and Quantum Optics and the Quantum Information and Measurement meeting, 2013

We describe a coherent control technique for coupling electron spin states associated with semico... more We describe a coherent control technique for coupling electron spin states associated with semiconductor double-dot molecule to a microwave stripline resonator on a chip. We identify a novel regime of operation in which strong interaction between a molecule and a resonator can be achieved with minimal decoherence, reaching the so-called strong coupling regime of cavity QED. We describe potential applications of such a system, including low-noise coherent electrical control, fast QND measurements of spin states, and long-range spin coupling.

CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009

Abstract An essential requirement for any quantum computing architecture is the existence of a un... more Abstract An essential requirement for any quantum computing architecture is the existence of a universal set of quantum gates. Examples of such sets are the 2-qubit CNOT gate in combination with arbitrary 1-qubit gates, and the 3-qubit Toffoli gate together with the 1-qubit Hadamard. A third set, which has not been implemented so far, is Valiant's 2-qubit matchgate G (A, B) which is universal with the SWAP operation. This paper presents how symmetric Valiant gates are decomposed which are sufficient for universal quantum ...

Optics Express, 2011

We present a simple technique to reduce the emission rate of higher-order photon events from puls... more We present a simple technique to reduce the emission rate of higher-order photon events from pulsed spontaneous parametric down-conversion. The technique uses extra-cavity control over a mode locked ultrafast laser to simultaneously increase repetition rate and reduce the energy of each pulse from the pump beam. We apply our scheme to a photonic quantum gate, showing improvements in the non-classical interference visibility for 2-photon and 4-photon experiments, and in the quantum-gate fidelity and entangled state production in the 2-photon case.

Conference on Coherence and Quantum Optics, 2007

ABSTRACT Bell inequality is violated with transverse spatial variables of twin photons, through o... more ABSTRACT Bell inequality is violated with transverse spatial variables of twin photons, through optical implementation of Fractional Fourier Transforms. A q-bit can be constructed and manipulated in the same way, with promising applications to quantum information.

Noise and Fluctuations in Photonics, Quantum Optics, and Communications, 2007

We demonstrate the difference between local, single-particle dynamics and global dynamics of enta... more We demonstrate the difference between local, single-particle dynamics and global dynamics of entangled quantum systems coupled to independent environments. Using an all-optical experimental setup, we show that, while the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear. This "sudden death" constitutes yet another distinct and counter-intuitive trait of entanglement.

Conference on Coherence and Quantum Optics, 2007

... Marcelo P. Almeida1, Fernando de Melo2, Malena O. Hor-Meyll, Alejo Salles, Stephen P. Walborn... more ... Marcelo P. Almeida1, Fernando de Melo2, Malena O. Hor-Meyll, Alejo Salles, Stephen P. Walborn, Paulo Henrique Souto Ribeiro, and Luiz Davidovich ... 9. L. Davidovich, A. Maali, M. Brune, JM Raimond, and S. Haroche, “Quantum switches and nonlocal mi-crowave fields,” Phys ...

Chemical Speciation and Bioavailability, 2011

Page 1. Evaluation of the chromium bioavailability in tanned leather shavings using the SM&am... more Page 1. Evaluation of the chromium bioavailability in tanned leather shavings using the SM&T sequential extractions scheme Lılian Irene Dias da Silva, Fernanda Veronesi Marinho Pontes, Manuel Castro Carneiro, Maria Ineˆ ...

Water Research, 2004

Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were meas... more Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were measured in samples of majors tributaries of the Sepetiba Bay, SE Brazil (Itimirim, Itingu@u, Guarda, Guandu, S* ao Francisco and Ita rivers), in dry and rainy seasons. The average Hg concentrations found varied from 0.02 to 0.18 ng L À1 for dissolved gaseous Hg, from 0.1 to 18.1 ng L À1 for reactive Hg, from 0.1 to 66.6 ng L À1 for total dissolved Hg and from 0.3 to 250 ng L À1 for particulate Hg. During the rainy season, a decrease in the dissolved Hg concentrations and an increase in the particulate Hg concentrations was observed. Positive correlations were found between the reactive Hg and the total dissolved Hg concentrations ðr ¼ 0:99Þ; between the particulate Hg and TSS concentrations ðr ¼ 0:82Þ and between total Hg and particulate Hg concentrations ðr ¼ 0:95Þ: The instantaneous Hg fluxes varied among rivers from 0.02 to 412 mg s À1 for total dissolved Hg and from 0.03 to 12,572 mg s À1 for particulate Hg. The log K d varied from 3.76 to 6.43 and showed a significant increase in rainy season following an increase in particulate Hg and a decrease in dissolved Hg concentrations. These results suggest that erosion and runoff are the major pathways of Hg transport to rivers and eventually to Sepetiba Bay. r

Science, 2007

We demonstrate the difference between local, single-particle dynamics and global dynamics of enta... more We demonstrate the difference between local, single-particle dynamics and global dynamics of entangled quantum systems coupled to independent environments. Using an all-optical experimental setup, we showed that, even when the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear. This "sudden death" constitutes yet another distinct and counterintuitive trait of entanglement.

Proceedings of the National Academy of Sciences, 2011

By weakly measuring the polarization of a photon between two strong polarization measurements, we... more By weakly measuring the polarization of a photon between two strong polarization measurements, we experimentally investigate the correlation between the appearance of anomalous values in quantum weak measurements, and the violation of realism and non-intrusiveness of measurements. A quantitative formulation of the latter concept is expressed in terms of a Leggett-Garg inequality for the outcomes of subsequent measurements of an individual quantum system. We experimentally violate the Leggett-Garg inequality for several measurement strengths. Furthermore, we experimentally demonstrate that there is a one-to-one correlation between achieving strange weak values and violating the Leggett-Garg inequality.

Physical Review Letters, 2001

We observe experimentally the transfer of angular spectrum and image formation in the process of ... more We observe experimentally the transfer of angular spectrum and image formation in the process of stimulated parametric down-conversion. Images and interference patterns can be transferred either from the pump or the auxiliary laser beams to the stimulated down-converted one. The stimulated field propagates as the complex conjugate of the auxiliary laser. The phase conjugation is observed through intensity pattern measurements. 42.50.Ar, 42.25.Kb *

Physical Review Letters, 2010

A goal of the emerging field of quantum control is to develop methods for quantum technologies to... more A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of non-orthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.

Physical Review Letters, 2006

We present a proof of principle demonstration of a quantum key distribution scheme in higherorder... more We present a proof of principle demonstration of a quantum key distribution scheme in higherorder d-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.

Physical Review Letters, 2008

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation... more Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

Physical Review Letters, 2013

We demonstrate unambiguous entangling operation of a photonic quantum-logic gate driven by an ult... more We demonstrate unambiguous entangling operation of a photonic quantum-logic gate driven by an ultrabright solid-state single-photon source. Indistinguishable single photons emitted by a single semiconductor quantum dot in a micropillar optical cavity are used as target and control qubits. For a source brightness of 0.56 collected photons-per-pulse, the measured truth table has an overlap with the ideal case of 68.4±0.5%, increasing to 73.0±0.6% for a source brightness of 0.17 photonsper-pulse. The gate is entangling: at a source brightness of 0.48, the Bell-state fidelity is above the entangling threshold of 50%, and reaches 71.0±3.6% for a source brightness of 0.15.

Physical Review Letters, 2013

The key requirement for quantum networking is the distribution of entanglement between nodes. Sur... more The key requirement for quantum networking is the distribution of entanglement between nodes. Surprisingly, entanglement can be generated across a network without direct transfer-or communication-of entanglement. In contrast to information gain, which cannot exceed the communicated information, the entanglement gain is bounded by the communicated quantum discord, a more general measure of quantum correlation that includes but is not limited to entanglement. Here, we experimentally entangle two communicating parties sharing three initially separable photonic qubits by exchange of a carrier photon that is unentangled with either party at all times. We show that distributing entanglement with separable carriers is resilient to noise and in some cases becomes the only way of distributing entanglement through noisy environments.

Quantum information & computation

... A, 62, 052317. 52. Daniel Collins, Noah Linden and Sandu Popeseu (2001), Nonlocal content of ... more ... A, 62, 052317. 52. Daniel Collins, Noah Linden and Sandu Popeseu (2001), Nonlocal content of quantum operations,Phys. ... 55. JL O'Brien, GJ Pryde, AG White, TC Ralph, and D. Branning (2003), Demonstrationof an all-optical quantum controlled-NOT gate, Nature, 426, 264. ...

Abstract Quantum computation promises to solve fundamental, yet otherwise intractable, problems a... more Abstract Quantum computation promises to solve fundamental, yet otherwise intractable, problems across a range of active fields of research. Recently, universal quantum logic-gate sets—the elemental building blocks for a quantum computer—have been demonstrated in several physical architectures. A serious obstacle to a full-scale implementation is the large number of these gates required to build even small quantum circuits. Here, we present and demonstrate a general technique that harnesses multi-level information carriers to ...

Proceedings. Vol.1. Sixth Brazilian Symposium on Neural Networks, 2000

SVM-KM: speeding SVMs learning with a priori cluster selection and k-means Marcel0 Barros de Alme... more SVM-KM: speeding SVMs learning with a priori cluster selection and k-means Marcel0 Barros de Almeida, Antanio de Piidua Braga Jo50 Pedro Braga Universidade Federal de Minas Gerais Department of Electronics Engineering { barros,apbraga} @cpdee.ufmg.br Abstract ...

International Conference on Quantum Information, 2007

AG White, M. Pereira de Almeida, M. Barbieri, DN Biggerstaff, RB Dalton, A. Gilchrist, G. Gillett... more AG White, M. Pereira de Almeida, M. Barbieri, DN Biggerstaff, RB Dalton, A. Gilchrist, G. Gillett, DFV James†, NK Langford, BN Lanyon, KJ Resch‡, T. Weinhold ... Department of Physics and Centre for Quantum Computer Technology, University of Queensland, Brisbane, Australia †Department of Physics, University of Toronto, Ontario, Canada ‡Department of Physics and Institute for Quantum Computing, University of Waterloo, Ontario, Canada ... We demonstrate significantly compacted quantum algorithms and demonstrate a Fock-state filter by going ...

The Rochester Conferences on Coherence and Quantum Optics and the Quantum Information and Measurement meeting, 2013

We describe a coherent control technique for coupling electron spin states associated with semico... more We describe a coherent control technique for coupling electron spin states associated with semiconductor double-dot molecule to a microwave stripline resonator on a chip. We identify a novel regime of operation in which strong interaction between a molecule and a resonator can be achieved with minimal decoherence, reaching the so-called strong coupling regime of cavity QED. We describe potential applications of such a system, including low-noise coherent electrical control, fast QND measurements of spin states, and long-range spin coupling.

CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009

Abstract An essential requirement for any quantum computing architecture is the existence of a un... more Abstract An essential requirement for any quantum computing architecture is the existence of a universal set of quantum gates. Examples of such sets are the 2-qubit CNOT gate in combination with arbitrary 1-qubit gates, and the 3-qubit Toffoli gate together with the 1-qubit Hadamard. A third set, which has not been implemented so far, is Valiant's 2-qubit matchgate G (A, B) which is universal with the SWAP operation. This paper presents how symmetric Valiant gates are decomposed which are sufficient for universal quantum ...

Optics Express, 2011

We present a simple technique to reduce the emission rate of higher-order photon events from puls... more We present a simple technique to reduce the emission rate of higher-order photon events from pulsed spontaneous parametric down-conversion. The technique uses extra-cavity control over a mode locked ultrafast laser to simultaneously increase repetition rate and reduce the energy of each pulse from the pump beam. We apply our scheme to a photonic quantum gate, showing improvements in the non-classical interference visibility for 2-photon and 4-photon experiments, and in the quantum-gate fidelity and entangled state production in the 2-photon case.

Conference on Coherence and Quantum Optics, 2007

ABSTRACT Bell inequality is violated with transverse spatial variables of twin photons, through o... more ABSTRACT Bell inequality is violated with transverse spatial variables of twin photons, through optical implementation of Fractional Fourier Transforms. A q-bit can be constructed and manipulated in the same way, with promising applications to quantum information.

Noise and Fluctuations in Photonics, Quantum Optics, and Communications, 2007

We demonstrate the difference between local, single-particle dynamics and global dynamics of enta... more We demonstrate the difference between local, single-particle dynamics and global dynamics of entangled quantum systems coupled to independent environments. Using an all-optical experimental setup, we show that, while the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear. This "sudden death" constitutes yet another distinct and counter-intuitive trait of entanglement.

Conference on Coherence and Quantum Optics, 2007

... Marcelo P. Almeida1, Fernando de Melo2, Malena O. Hor-Meyll, Alejo Salles, Stephen P. Walborn... more ... Marcelo P. Almeida1, Fernando de Melo2, Malena O. Hor-Meyll, Alejo Salles, Stephen P. Walborn, Paulo Henrique Souto Ribeiro, and Luiz Davidovich ... 9. L. Davidovich, A. Maali, M. Brune, JM Raimond, and S. Haroche, “Quantum switches and nonlocal mi-crowave fields,” Phys ...

Chemical Speciation and Bioavailability, 2011

Page 1. Evaluation of the chromium bioavailability in tanned leather shavings using the SM&am... more Page 1. Evaluation of the chromium bioavailability in tanned leather shavings using the SM&T sequential extractions scheme Lılian Irene Dias da Silva, Fernanda Veronesi Marinho Pontes, Manuel Castro Carneiro, Maria Ineˆ ...

Water Research, 2004

Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were meas... more Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were measured in samples of majors tributaries of the Sepetiba Bay, SE Brazil (Itimirim, Itingu@u, Guarda, Guandu, S* ao Francisco and Ita rivers), in dry and rainy seasons. The average Hg concentrations found varied from 0.02 to 0.18 ng L À1 for dissolved gaseous Hg, from 0.1 to 18.1 ng L À1 for reactive Hg, from 0.1 to 66.6 ng L À1 for total dissolved Hg and from 0.3 to 250 ng L À1 for particulate Hg. During the rainy season, a decrease in the dissolved Hg concentrations and an increase in the particulate Hg concentrations was observed. Positive correlations were found between the reactive Hg and the total dissolved Hg concentrations ðr ¼ 0:99Þ; between the particulate Hg and TSS concentrations ðr ¼ 0:82Þ and between total Hg and particulate Hg concentrations ðr ¼ 0:95Þ: The instantaneous Hg fluxes varied among rivers from 0.02 to 412 mg s À1 for total dissolved Hg and from 0.03 to 12,572 mg s À1 for particulate Hg. The log K d varied from 3.76 to 6.43 and showed a significant increase in rainy season following an increase in particulate Hg and a decrease in dissolved Hg concentrations. These results suggest that erosion and runoff are the major pathways of Hg transport to rivers and eventually to Sepetiba Bay. r

Science, 2007

We demonstrate the difference between local, single-particle dynamics and global dynamics of enta... more We demonstrate the difference between local, single-particle dynamics and global dynamics of entangled quantum systems coupled to independent environments. Using an all-optical experimental setup, we showed that, even when the environment-induced decay of each system is asymptotic, quantum entanglement may suddenly disappear. This "sudden death" constitutes yet another distinct and counterintuitive trait of entanglement.

Proceedings of the National Academy of Sciences, 2011

By weakly measuring the polarization of a photon between two strong polarization measurements, we... more By weakly measuring the polarization of a photon between two strong polarization measurements, we experimentally investigate the correlation between the appearance of anomalous values in quantum weak measurements, and the violation of realism and non-intrusiveness of measurements. A quantitative formulation of the latter concept is expressed in terms of a Leggett-Garg inequality for the outcomes of subsequent measurements of an individual quantum system. We experimentally violate the Leggett-Garg inequality for several measurement strengths. Furthermore, we experimentally demonstrate that there is a one-to-one correlation between achieving strange weak values and violating the Leggett-Garg inequality.

Physical Review Letters, 2001

We observe experimentally the transfer of angular spectrum and image formation in the process of ... more We observe experimentally the transfer of angular spectrum and image formation in the process of stimulated parametric down-conversion. Images and interference patterns can be transferred either from the pump or the auxiliary laser beams to the stimulated down-converted one. The stimulated field propagates as the complex conjugate of the auxiliary laser. The phase conjugation is observed through intensity pattern measurements. 42.50.Ar, 42.25.Kb *

Physical Review Letters, 2010

A goal of the emerging field of quantum control is to develop methods for quantum technologies to... more A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of non-orthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.

Physical Review Letters, 2006

We present a proof of principle demonstration of a quantum key distribution scheme in higherorder... more We present a proof of principle demonstration of a quantum key distribution scheme in higherorder d-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.

Physical Review Letters, 2008

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation... more Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

Physical Review Letters, 2013

We demonstrate unambiguous entangling operation of a photonic quantum-logic gate driven by an ult... more We demonstrate unambiguous entangling operation of a photonic quantum-logic gate driven by an ultrabright solid-state single-photon source. Indistinguishable single photons emitted by a single semiconductor quantum dot in a micropillar optical cavity are used as target and control qubits. For a source brightness of 0.56 collected photons-per-pulse, the measured truth table has an overlap with the ideal case of 68.4±0.5%, increasing to 73.0±0.6% for a source brightness of 0.17 photonsper-pulse. The gate is entangling: at a source brightness of 0.48, the Bell-state fidelity is above the entangling threshold of 50%, and reaches 71.0±3.6% for a source brightness of 0.15.