TY  - JOUR
A1  - Hübener, Robert
A1  - Kruszynska, Caroline
A1  - Hartmann, Lorenz
A1  - Duer, Wolfgang
A1  - Verstraete, Frank
A1  - Eisert, Jens
A1  - Plenio, Martin B.
T1  - Renormalization algorithm with graph enhancement
N2  - We introduce a class of variational states to describe quantum many-body systems. This class generalizes matrix product states which underlie the density-matrix renormalization-group approach by combining them with weighted graph states. States within this class may (i) possess arbitrarily long-ranged two-point correlations, (ii) exhibit an arbitrary degree of block entanglement entropy up to a volume law, (iii) be taken translationally invariant, while at the same time (iv) local properties and two-point correlations can be computed efficiently. This variational class of states can be thought of as being prepared from matrix product states, followed by commuting unitaries on arbitrary constituents, hence truly generalizing both matrix product and weighted graph states. We use this class of states to formulate a renormalization algorithm with graph enhancement and present numerical examples, demonstrating that improvements over density-matrix renormalization-group simulations can be achieved in the simulation of ground states and quantum algorithms. Further generalizations, e.g., to higher spatial dimensions, are outlined.
Y1  - 2009
UR  - http://pra.aps.org/
U6  - https://doi.org/10.1103/Physreva.79.022317
SN  - 1050-2947
ER  - 
TY  - JOUR
A1  - Feito Boirac, Alvaro Felipe
A1  - Lundeen, Jeff S.
A1  - Coldenstrodt-Ronge, Hendrik
A1  - Eisert, Jens
A1  - Plenio, Martin B.
A1  - Walmsley, Ian A.
T1  - Measuring measurement : theory and practice
N2  - Recent efforts have applied quantum tomography techniques to the calibration and characterization of complex quantum detectors using minimal assumptions. In this work, we provide detail and insight concerning the formalism, the experimental and theoretical challenges and the scope of these tomographical tools. Our focus is on the detection of photons with avalanche photodiodes and photon-number resolving detectors and our approach is to fully characterize the quantum operators describing these detectors with a minimal set of well-specified assumptions. The formalism is completely general and can be applied to a wide range of detectors.
Y1  - 2009
UR  - http://iopscience.iop.org/1367-2630
U6  - https://doi.org/10.1088/1367-2630/11/9/093038
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - Feito, Alvaro
A1  - Lundeen, Jeff
A1  - Coldenstrodt-Ronge, Hendrik
A1  - Eisert, Jens
A1  - Plenio, Martin B.
A1  - Walmsley, Ian A.
T1  - Measuring measurement : theory and practice
N2  - Recent efforts have applied quantum tomography techniques to the calibration and characterization of complex quantum detectors using minimal assumptions. In this work, we provide detail and insight concerning the formalism, the experimental and theoretical challenges and the scope of these tomographical tools. Our focus is on the detection of photons with avalanche photodiodes and photon-number resolving detectors and our approach is to fully characterize the quantum operators describing these detectors with a minimal set of well-specified assumptions. The formalism is completely general and can be applied to a wide range of detectors.
Y1  - 2009
UR  - http://iopscience.iop.org/1367-2630
U6  - https://doi.org/10.1088/1367-2630/11/9/093038
SN  - 1367-2630
ER  -