The Heisenberg uncertainty principle is one of the most famous features of
quantum mechanics. However, the non-determinism implied by the Heisenberg
uncertainty principle --- together with other prominent aspects of quantum
mechanics such as superposition, entanglement, and nonlocality --- poses deep
puzzles about the underlying physical reality, even while these same features
are at the heart of exciting developments such as quantum cryptography,
algorithms, and computing. These puzzles might be resolved if the mathematical
structure of quantum mechanics were built up from physically interpretable
axioms, but it is not. We propose three physically-based axioms which together
characterize the simplest quantum system, namely the qubit. Our starting point
is the class of all no-signaling theories. Each such theory can be regarded as
a family of empirical models, and we proceed to associate entropies, i.e.,
measures of information, with these models. To do this, we move to phase space
and impose the condition that entropies are real-valued. This requirement,
which we call the Information Reality Principle, arises because in order to
represent all no-signaling theories (including quantum mechanics itself) in
phase space, it is necessary to allow negative probabilities (Wigner [1932]).
Our second and third principles take two important features of quantum
mechanics and turn them into deliberately chosen physical axioms. One axiom is
an Uncertainty Principle, stated in terms of entropy. The other axiom is an
Unbiasedness Principle, which requires that whenever there is complete
certainty about the outcome of a measurement in one of three mutually
orthogonal directions, there must be maximal uncertainty about the outcomes in
each of the two other directions.Comment: 8 pages, 3 figure