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https://hdl.handle.net/2142/31905
Description
Title
Testing the limits of nonlocality
Author(s)
Altepeter, Joseph Benjamin
Issue Date
2006
Director of Research (if dissertation) or Advisor (if thesis)
Kwiat, Paul G.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
quantum information
polarization-entangled photon pairs
Language
en
Abstract
The nascent field of quantum information offers the promise of dramatic speed
increases for certain types of computation and logical protocols which are classically
impossible. The phenomenon of nonlocality is fundamental to this study,
and polarization-entangled photons o er a clean, bright, and stable system for
its experimental investigation. This thesis investigates, both experimentally
and theoretically, the creation, manipulation, and measurement of polarization-entangled
photon pairs.
Our entangled photon pairs are created through spontaneous parametric
down-conversion within a pair of adjacent, orthogonally oriented nonlinear crystals.
The quality and brightness of this source is then dramatically improved
through the use of birefringent crystals which compensate for an angle-dependent
phase shift. The use of these compensation crystals has allowed measured count
rates of two million pairs per second with 97.7% fidelity (with a maximally entangled
state) or alternately, ten thousand pairs per second with 99.5% fidelity.
By manipulating these entangled states, it is possible to study both how they
change and how they can be used. We discuss the theory of state manipulation
and the experimental implementation of extremely precise single-qubit operations.
To study the operations themselves, we use quantum process tomography
to characterize them and have successfully implemented the first experimental
realization of ancilla-assisted process tomography. To study decoherence, we
implemented the first experimental decoherence-free subspace. By using techniques
developed during these investigations, we are able to transform our source
of entangled photons into a source of any two-photon polarization state, mixed
or pure.
Developing new techniques for state creation and manipulation is possible
because of simultaneous development in state measurement. In addition to
detailing both a theoretical analysis and experimental instructions for state
tomography, we experimentally and theoretically compared state tomography
with tests of local realism (Bell inequalities) and entanglement witnesses (an
entanglement detection technique). In the process, we have measured the largest
violations of local realism to date, both statistical (over 2400-sigma) and absolute
(S = 2:826 ± 0:005 -- within 0:2% of a maximal violation).
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