27,202 research outputs found
Selective and Efficient Quantum Process Tomography
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 --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
--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 figure
Quantum Process Tomography: Resource Analysis of Different Strategies
Characterization of quantum dynamics is a fundamental problem in quantum
physics and quantum information science. Several methods are known which
achieve this goal, namely Standard Quantum Process Tomography (SQPT),
Ancilla-Assisted Process Tomography (AAPT), and the recently proposed scheme of
Direct Characterization of Quantum Dynamics (DCQD). Here, we review these
schemes and analyze them with respect to some of the physical resources they
require. Although a reliable figure-of-merit for process characterization is
not yet available, our analysis can provide a benchmark which is necessary for
choosing the scheme that is the most appropriate in a given situation, with
given resources. As a result, we conclude that for quantum systems where
two-body interactions are not naturally available, SQPT is the most efficient
scheme. However, for quantum systems with controllable two-body interactions,
the DCQD scheme is more efficient than other known QPT schemes in terms of the
total number of required elementary quantum operations.Comment: 15 pages, 5 figures, published versio
- …