Juan Pablo Paz

Publications (9)29.48 Total impact

• Article: Selective and Efficient Quantum State Tomography and its Application to Quantum Process Tomography

  Ariel Bendersky, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: We present a method for quantum state tomography that enables the efficient estimation, with fixed precision, of any of the matrix elements of the density matrix of a state, provided that the states from the basis in which the matrix is written can be efficiently prepared in a controlled manner. Furthermore, we show how this algorithm is well suited for quantum process tomography, enabling to perform selective and efficient quantum process tomography.
  11/2012;
• Article: Selective and efficient quantum process tomography without ancilla.

  Christian Tomás Schmiegelow, Ariel Bendersky, Miguel Antonio Larotonda, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: Several methods, known as quantum process tomography, are available to characterize the evolution of quantum systems, a task of crucial importance. However, their complexity dramatically increases with the size of the system. Here we present a new method for quantum process tomography. We describe a new algorithm that can be used to selectively estimate any parameter characterizing a quantum process. Unlike any of its predecessors this new quantum tomographer combines two virtues: it requires investing a number of physical resources scaling polynomially with the number of qubits and at the same time it does not require any ancillary resources. We present the results of the first implementation of this quantum device, characterizing quantum processes affecting two qubits encoded in heralded single photons. Even for this small system our method displays clear advantages over the other existing ones.
  Physical Review Letters 09/2011; 107(10):100502. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: Ancilla-less selective and efficient quantum process tomography

  Christian Tomás Schmiegelow, Ariel Bendersky, Miguel Antonio Larotonda, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: Several methods, known as Quantum Process Tomography, are available to characterize the evolution of quantum systems, a task of crucial importance. However, their complexity dramatically increases with the size of the system. Here we present the theory describing a new type of method for quantum process tomography. We describe an algorithm that can be used to selectively estimate any parameter characterizing a quantum process. Unlike any of its predecessors this new quantum tomographer combines two main virtues: it requires investing a number of physical resources scaling polynomially with the number of qubits and at the same time it does not require any ancillary resources. We present the results of the first photonic implementation of this quantum device, characterizing quantum processes affecting two qubits encoded in heralded single photons. Even for this small system our method displays clear advantages over the other existing ones.
  05/2011;
• Source

  Available from: ArXiv

  Article: Progress toward scalable tomography of quantum maps using twirling-based methods and information hierarchies

  Cecilia C. López, Ariel Bendersky, Juan Pablo Paz, David G. Cory
  [show abstract] [hide abstract]
  ABSTRACT: We present in a unified manner the existing methods for scalable partial quantum process tomography. We focus on two main approaches: the one presented in Bendersky et al. [Phys. Rev. Lett. 100, 190403 (2008)], and the ones described, respectively, in Emerson et al. [Science 317, 1893 (2007)] and L\'{o}pez et al. [Phys. Rev. A 79, 042328 (2009)], which can be combined together. The methods share an essential feature: They are based on the idea that the tomography of a quantum map can be efficiently performed by studying certain properties of a twirling of such a map. From this perspective, in this paper we present extensions, improvements and comparative analyses of the scalable methods for partial quantum process tomography. We also clarify the significance of the extracted information, and we introduce interesting and useful properties of the $\chi$-matrix representation of quantum maps that can be used to establish a clearer path toward achieving full tomography of quantum processes in a scalable way. Comment: Replaced with published version (only minor changes respect to the first version)
  03/2010;
• Source

  Available from: arxiv.org

  Article: Selective and efficient quantum process tomography with single photons.

  Christian Tomás Schmiegelow, Miguel Antonio Larotonda, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: We present the results of the first photonic implementation of a new method for quantum process tomography. The method {originally presented by A. Bendersky et al. [Phys. Rev. Lett. 100, 190403 (2008)10.1103/PhysRevLett.100.190403]} enables the estimation of any element of the chi-matrix that characterizes a quantum process using resources that scale polynomially with the number of qubits. It is based on the idea of mapping the estimation of any chi-matrix element onto the average fidelity of a quantum channel and estimating the latter by sampling randomly over a special set of states called a 2-design. With a heralded single photon source we fully implement such algorithm and perform process tomography on a number of channels affecting the polarization qubit. The method is compared with other existing ones, and its advantages are discussed.
  Physical Review Letters 03/2010; 104(12):123601. · 7.37 Impact Factor
• Source

  Available from: arxiv.org

  Article: General theory of measurement with two copies of a quantum state.

  Ariel Bendersky, Juan Pablo Paz, Marcelo Terra Cunha
  [show abstract] [hide abstract]
  ABSTRACT: We analyze the results of the most general measurement on two copies of a quantum state. We show that by using two copies of a quantum state it is possible to achieve an exponential improvement with respect to known methods for quantum state tomography. We demonstrate that mu can label a set of outcomes of a measurement on two copies if and only if there is a family of maps C_{micro} such that the probability Prob(micro) is the fidelity of each map, i.e., Prob(micro) = Tr[rhoC_{micro}(rho)]. Here, the map C_{micro} must be completely positive after being composed with the transposition (these are called completely copositive, or CCP, maps) and must add up to the fully depolarizing map. This implies that a positive operator valued measure on two copies induces a measure on the set of CCP maps (i.e., a CCP map valued measure).
  Physical Review Letters 08/2009; 103(4):040404. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: Selective and Efficient Quantum Process Tomography

  Ariel Bendersky, Fernando Pastawski, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: In this paper we describe in detail and generalize a method for quantum process tomography that was presented in [A. Bendersky, F. Pastawski, J. P. Paz, Physical Review Letters 100, 190403 (2008)]. The method enables the efficient estimation of any element of the $\chi$--matrix of a quantum process. Such elements are estimated as averages over experimental outcomes with a precision that is fixed by the number of repetitions of the experiment. Resources required to implement it scale polynomically with the number of qubits of the system. The estimation of all diagonal elements of the $\chi$--matrix can be efficiently done without any ancillary qubits. In turn, the estimation of all the off-diagonal elements requires an extra clean qubit. The key ideas of the method, that is based on efficient estimation by random sampling over a set of states forming a 2--design, are described in detail. Efficient methods for preparing and detecting such states are explicitly shown. Comment: 9 pages, 5 figures
  06/2009;
• Article: Selective and efficient estimation of parameters for quantum process tomography.

  Ariel Bendersky, Fernando Pastawski, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: We present a new method for quantum process tomography enabling the efficient estimation, with fixed precision, of any of the parameters characterizing a quantum channel. The estimation strategy depends upon the set of matrix elements one selects to estimate. Furthermore, we describe a way to efficiently gather all the information required to efficiently estimate any average survival probability of the channel (i.e., to measure any diagonal element of its chi matrix).
  Physical Review Letters 05/2008; 100(19):190403. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: Selective Efficient Quantum Process Tomography

  Ariel Bendersky, Fernando Pastawski, Juan Pablo Paz
  [show abstract] [hide abstract]
  ABSTRACT: We present a new method for quantum process tomography. The method enables us to efficiently estimate, with fixed precision, any of the parameters characterizing a quantum channel. It is selective since one can choose to estimate the value of any specific set of matrix elements of the super-operator describing the channel. Also, we show how to efficiently estimate all the average survival probabilities associated with the channel (i.e., all the diagonal elements of its $\chi$--matrix.
  02/2008;