181 research outputs found
KLM quantum computation as a measurement based computation
We show that the Knill Laflamme Milburn method of quantum computation with
linear optics gates can be interpreted as a one-way, measurement based quantum
computation of the type introduced by Briegel and Rausendorf. We also show that
the permanent state of n n-dimensional systems is a universal state for quantum
computation.Comment: 4 pages 3 figure
How energy conservation limits our measurements
Observations in Quantum Mechanics are subject to complex restrictions arising
from the principle of energy conservation. Determining such restrictions,
however, has been so far an elusive task, and only partial results are known.
In this paper we discuss how constraints on the energy spectrum of a
measurement device translate into limitations on the measurements which we can
effect on a target system with non-trivial energy operator. We provide
efficient algorithms to characterize such limitations and we quantify them
exactly when the target is a two-level quantum system. Our work thus identifies
the boundaries between what is possible or impossible to measure, i.e., between
what we can see or not, when energy conservation is at stake.Comment: Better read the 5-page published version firs
Causality and Nonlocality as Axioms for Quantum Mechanics
Quantum mechanics permits nonlocality - both nonlocal correlations and
nonlocal equations of motion - while respecting relativistic causality. Is
quantum mechanics the unique theory that reconciles nonlocality and causality?
We consider two models, going beyond quantum mechanics, of nonlocality:
"superquantum" correlations, and nonlocal "jamming" of correlations. These
models are consistent with some definitions of nonlocality and causality.Comment: 9 pages, RevTeX; for the proceedings of the symposium on Causality
and Locality in Modern Physics and Astronomy: Open Questions and Possible
Solutions (York University, Toronto, August 25-29, 1997). This version
contains an additional affiliation and address for one autho
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