David Branning

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The promise of tremendous computational power, coupled with the development of robust error-correcting schemes, has fuelled extensive efforts to build a quantum computer. The requirements for realizing such a device are confounding: scalable quantum bits (two-level quantum systems, or qubits) that can be well isolated from the environment, but also(More)
Complete and precise characterization of a quantum dynamical process can be achieved via the method of quantum process tomography. Using a source of correlated photons, we have implemented several methods, each investigating a wide range of processes, e.g., unitary, decohering, and polarizing. One of these methods, ancilla-assisted process tomography(More)
A method of calculating the characteristics of non-collinear phase-matching in both uniaxial and biaxial crystals is presented. Although significant work has been done to characterize collinear phase-matching and to present many of its applications, non-collinear phase-matching also has unique characteristics, leading to several useful applications. The(More)
We present a novel interferometric technique for suppressing distinguishing information in the spacetime component of the state vector of an entangled pair of photons by providing two indistinguishable ways for each photon to occupy any given space-time mode. We demonstrate this method by using spontaneous parametric down-conversion to generate a pair of(More)
We report on an experiment to determine both the group and phase delays experienced by orthogonally polarized photon pairs traveling through a birefringent medium. Both types of delay are determined from the same set of coincidence-counting data. The experiment is based on an interference technique using two-photon multipath indistinguishability to produce(More)
Using correlated photons from parametric down-conversion, we extend the boundaries of experimentally accessible two-qubit Hilbert space. Specifically, we have created and characterized maximally entangled mixed states that lie above the Werner boundary in the linear entropy-tangle plane. In addition, we demonstrate that such states can be efficiently(More)
Tzu-Chieh Wei, Joseph B. Altepeter, David Branning,* Paul M. Goldbart, D. F. V. James, Evan Jeffrey, Paul G. Kwiat, Swagatam Mukhopadhyay, and Nicholas A. Peters Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3080, USA Theoretical Division, T-4, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA(More)
It is a well-known and remarkable fact that in certain coincidence photon-counting experiments with cwpumped parametric down-converters, the effects of group-velocity dispersion arising from media interposed between source and detectors are completely canceled, even if the media physically affect only one of the photons of the pair. Recently Perina et al.(More)
We give a detailed account of a recently introduced technique to suppress distinguishing information in the space-time component of the state vector of a pair of photons. The method works by creating interference between two possible ways for each photon to occupy any given space-time mode. Under certain conditions, this technique also allows the(More)