Marco Barbieri

Publications (9)7.37 Total impact

• Source

  Available from: Holger F. Hofmann

  Article: Estimation of a quantum interaction parameter using weak measurements: Theory and experiment

  Holger F. Hofmann, Michael E. Goggin, Marcelo P. Almeida, Marco Barbieri
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  ABSTRACT: We investigate the estimation of a small interaction parameter from the outcomes of weak quantum measurements implemented by the interaction. The relation of weak values and sensitivity is explained and the different contributions of postselected results are identified using experimental data. The results show how weak values can be used to control the distribution of input state sensitivity between different postselected outcomes.
  07/2011;
• Source

  Available from: Matthew Broome

  Article: Hardy's paradox and violation of a state-independent Bell inequality in time.

  Alessandro Fedrizzi, Marcelo P Almeida, Matthew A Broome, Andrew G White, Marco Barbieri
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  ABSTRACT: Tests such as Bell's inequality and Hardy's paradox show that joint probabilities and correlations between distant particles in quantum mechanics are inconsistent with local realistic theories. Here we experimentally demonstrate these concepts in the time domain, using a photonic entangling gate to perform nondestructive measurements on a single photon at different times. We show that Hardy's paradox is much stronger in time and demonstrate the violation of a temporal Bell inequality independent of the quantum state, including for fully mixed states.
  Physical Review Letters 05/2011; 106(20):200402. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: Single-photon device requirements for operating linear optics quantum computing outside the post-selection basis

  Thomas Jennewein, Marco Barbieri, Andrew G. White
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  ABSTRACT: Photonics is a promising architecture for the realisation of quantum information processing, since the two-photon interaction, or non-linearity, necessary to build logical gates can efficiently be realised by the use of interference with ancillary photons and detection. Although single-photon sources and detectors are pivotal in realisations of such systems, clear guidelines for the required performance of realistic systems are yet to be defined. We present our detailed numerical simulation of several quantum optics circuits including sources and detectors all represented in multi-dimensional Fockspaces, which allows to obtain experimentally realistic performance bounds for for these devices. In addition, the single-photon source based on switched parametric down-conversion is studied, which in principle could reach the required performance. Three approaches for implementing the switching hierarchy of the photons are simulated, and their anticipated performance is obtained. Our results define the bar for the optical devices needed to achieve the first level of linear-optics quantum computing outside the coincidence basis.
  12/2010;
• Source

  Available from: Alán Aspuru-Guzik

  Article: Towards Quantum Chemistry on a Quantum Computer

  Benjamin P. Lanyon, James D. Whitfield, Geoff G. Gillet, Michael E. Goggin, Marcelo P. Almeida, Ivan Kassal, Jacob D. Biamonte, Masoud Mohseni, Ben J. Powell, Marco Barbieri, Alán Aspuru-Guzik, Andrew G. White
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  ABSTRACT: The fundamental problem faced in quantum chemistry is the calculation of molecular properties, which are of practical importance in fields ranging from materials science to biochemistry. Within chemical precision, the total energy of a molecule as well as most other properties, can be calculated by solving the Schrodinger equation. However, the computational resources required to obtain exact solutions on a conventional computer generally increase exponentially with the number of atoms involved. This renders such calculations intractable for all but the smallest of systems. Recently, an efficient algorithm has been proposed enabling a quantum computer to overcome this problem by achieving only a polynomial resource scaling with system size. Such a tool would therefore provide an extremely powerful tool for new science and technology. Here we present a photonic implementation for the smallest problem: obtaining the energies of H2, the hydrogen molecule in a minimal basis. We perform a key algorithmic step - the iterative phase estimation algorithm - in full, achieving a high level of precision and robustness to error. We implement other algorithmic steps with assistance from a classical computer and explain how this non-scalable approach could be avoided. Finally, we provide new theoretical results which lay the foundations for the next generation of simulation experiments using quantum computers. We have made early experimental progress towards the long-term goal of exploiting quantum information to speed up quantum chemistry calculations. Comment: 20 pages, 5 figures, corrected author affiliations
  05/2009;
• Source

  Available from: ArXiv

  Article: Anti-symmetrization reveals hidden entanglement

  Alessandro Fedrizzi, Thomas Herbst, Markus Aspelmeyer, Marco Barbieri, Thomas Jennewein, Anton Zeilinger
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  ABSTRACT: Two-photon anti-bunching at a beamsplitter is only possible if the photons are entangled in a specific state, anti-symmetric in the spatial modes. Thus, observation of anti-bunching is an indication of entanglement in a degree of freedom which might not be easily accessible in an experiment. We experimentally demonstrate this concept in the case of the interference of two frequency entangled photons with continuous frequency detunings. The principle of anti-symmetrisation of the spatial part of a wavefunction and subsequent detection of hidden entanglement via anti-bunching at a beamsplitter may facilitate the observation of entanglement in other systems, like atomic ensembles or Bose-Einstein condensates. The analogue for fermionic systems would be to observe bunching. Comment: Published version, 10 pages, 3 figures
  07/2008;
• Article: Complementarity in variable strength quantum non-demolition measurements

  Marco Barbieri, M. E. Goggin, M. P. Almeida, B. P. Lanyon, A. G. White
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  ABSTRACT: Using a linear optic quantum gate we perform a variable strength quantum non-demolition measurement, to elucidate the role of which-path knowledge in a complementarity experiment. Specifically, we demonstrate that the entanglement created by the measurement interaction prevents an exhaustive description in terms of complementary wave-like and particle-like behaviour of a single photon in an interferometer.
  New Journal of Physics.
• Article: Simplifying quantum logic using higher-dimensional Hilbert spaces

  Benjamin P. Lanyon, Marco Barbieri, Marcelo P. Almeida, Thomas Jennewein, Timothy C. Ralph, Kevin J. Resch, Geoff Pryde, Jeremy L. O'Brien, Alexei Gilchrist, Andrew G. White
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  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 significantly reduce this number, enabling the construction of key quantum circuits with existing technology. We present implementations of two key quantum circuits: the three-qubit Toffoli gate and the general two-qubit controlled-unitary gate. Although our experiment is carried out in a photonic architecture, the technique is independent of the particular physical encoding of quantum information, and has the potential for wider application. Yes Yes
• Article: Where is a photon when nobody looks? Realism and complementarity in weak measurements

  Marco Barbieri, M. P. Almeida, S. D. Bartlett, R. B. Dalton, G. G. Gillett, M. E. Goggin, B. P. Lanyon, Jeremy L. O'Brian, Geoff J. Pryde, A. G. White
  18th International Laser Physics Workshop.
• Source

  Available from: Andrew G White

  Article: Simplifying quantum logic using higher-dimensional Hilbert spaces

  Benjamin P. Lanyon, Marco Barbieri, Marco P. Almeida, Thomas Jennewein, Timothy C. Ralph, Kevin J. Resch, Geoff J. Pryde, Jeremy L. O'Brien, Alexei Gilchrist, Andrew G. White
  [show abstract] [hide abstract]
  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 significantly reduce this number, enabling the construction of key quantum circuits with existing technology. We present implementations of two key quantum circuits: the three-qubit Toffoli gate and the general two-qubit controlled-unitary gate. Although our experiment is carried out in a photonic architecture, the technique is independent of the particular physical encoding of quantum information, and has the potential for wider application.