10,176 research outputs found
Universal quantum computation using only projective measurement, quantum memory, and preparation of the 0 state
What resources are universal for quantum computation? In the standard model,
a quantum computer consists of a sequence of unitary gates acting coherently on
the qubits making up the computer. This paper shows that a very different model
involving only projective measurements, quantum memory, and the ability to
prepare the |0> state is also universal for quantum computation. In particular,
no coherent unitary dynamics are involved in the computation.Comment: 4 page
Optical quantum computation using cluster states
We propose an approach to optical quantum computation in which a
deterministic entangling quantum gate may be performed using, on average, a few
hundred coherently interacting optical elements (beamsplitters, phase shifters,
single photon sources, and photodetectors with feedforward). This scheme
combines ideas from the optical quantum computing proposal of Knill, Laflamme
and Milburn [Nature 409 (6816), 46 (2001)], and the abstract cluster-state
model of quantum computation proposed by Raussendorf and Briegel [Phys. Rev.
Lett. 86, 5188 (2001)].Comment: 4 page
Another Approach to Consensus and Maximally Informed Opinions with Increasing Evidence
Merging of opinions results underwrite Bayesian rejoinders to complaints about the subjective nature of personal probability. Such results establish that sufficiently similar priors achieve consensus in the long run when fed the same increasing stream of evidence. Initial subjectivity, the line goes, is of mere transient significance, giving way to intersubjective agreement eventually. Here, we establish a merging result for sets of probability measures that are updated by Jeffrey conditioning. This generalizes a number of different merging results in the literature. We also show that such sets converge to a shared, maximally informed opinion. Convergence to a maximally informed opinion is a (weak) Jeffrey conditioning analogue of Bayesian “convergence to the truth” for conditional probabilities. Finally, we demonstrate the philosophical significance of our study by detailing applications to the topics of dynamic coherence, imprecise probabilities, and probabilistic opinion pooling
How robust is a quantum gate in the presence of noise?
We define several quantitative measures of the robustness of a quantum gate
against noise. Exact analytic expressions for the robustness against
depolarizing noise are obtained for all unitary quantum gates, and it is found
that the controlled-not is the most robust two-qubit quantum gate, in the sense
that it is the quantum gate which can tolerate the most depolarizing noise and
still generate entanglement. Our results enable us to place several analytic
upper bounds on the value of the threshold for quantum computation, with the
best bound in the most pessimistic error model being 0.5.Comment: 14 page
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