Defense Intelligence Reference Document The Space Communication Implications Of Quantum Entanglement

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Coherent Superposition: The formation of a quantum mechanical state (for example,
right circular polarization) by adding components of other states (for example, left and
right polarization) with a definite complex phase between the added states.
Collapse: A quantum mechanical wave function is said to collapse to a particular basis
value when a measurement is made in that basis. For example, if a photon is emitted
isotropically (with equal probability in all directions), its wave function is distributed
uniformly over a sphere with a radius that grows at the speed of light until it is
detected. Upon detection, the photon's wave function is localized at the detection point
and disappears everywhere else.
Entangled: The separated parts of the same quantum system are said to be entangled
when each of the parts can be described only by referencing the state of other parts.
This is one of the most counterintuitive aspects of quantum mechanics, because,
classically, system parts out of "local" contact should be completely independent. Thus,
entanglement represents a kind of quantum "connectedness" in which measurements
on one isolated part of an entangled quantum system have nonclassical consequences
for the outcome of measurements performed on other (possibly very distant) parts of
the same system.
EPR Experiment: A class of experiments with entangled particles, usually photons,
that demonstrate quantum nonlocality. A gedankenexperiment of this kind was first
suggested in the famous 1936 paper by Einstein, Podolsky, and Rosen (Reference 4) in
which a set of criticisms of quantum mechanics were presented.
Hidden Variable Theories: A set of alternatives to quantum mechanics intended to
satisfy the objections of the EPR paper in which the uncertainty principle does not apply
and a quantum system can simultaneously have definite values of complementary
variables like position and momentum, provided one of these values is somehow
"hidden." Hidden variable theories are usually also "local" (see below) to deal with
Einstein's objection to the non locality of quantum mechanics.
Immaculate Conception Paradox: A type of back-in-time communication paradox in
which a completely consistent causal loop produces information with no known origin.
An example is the Book Paradox, in which an author receives a book in a message from
the future. He publishes it, and when the time comes, he transmits the manuscript to
himself in the past. The question then arises, Who wrote the book? In this case, no
inconsistent timelike loops are involved, and the arguments against bilking (see above)
do not apply in this case.
Locality: The assumption that the correlations between parts of a system can be
established only while the subsystems are in contact (or speed-of-light communication),
and that once out of such contact, no changes in such correlations are possible.
Nonlocality: The situation, apparently present in quantum mechanics, in which
correlations between parts of a system can be established independent of the
separation of the parts in time and space.
Retro-Causal: Situations in theory or in the real world where the effect precedes the
cause, in violation of the principle of causality.
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