Dr. Wojciech Zurek
Los Alamos National Laboratory

Project Title

Quantum Darwinism

Project Summary

Classical states exist independently of measurements: We do not perturb a pendulum by watching it. But state of a quantum oscillator may be redefined by a measurement: Heisenberg's indeterminacy implies that its velocity would change if we determine its position too accurately. Yet, our universe is built from "quantum stuff". Hence, classicality - including measurement-resistant states - somehow emerges from "quantum stuff". However, quantum measurement models (following von Neumann) assume direct interaction between measured system and apparatus. Direct interaction inevitably endangers state of the system. Quantum Darwinism recognizes that such models misrepresent our indirect way of observing: For instance, readers of this text rely on photon environment - photons that already scattered from the print. Moreover, our eyes intercept only a tiny fraction of photons, yet they provide all our information. Therefore, there are many "copies" of the same information scattered throughout the environment, and the resulting states are in effect classical, as indicated by their objectivity, the hallmark of independent existence: Many can find out state of the system indirectly, without perturbing it. We shall study the number of its copies - the redundancy of information -- in realistic models of decoherence. Redundancy provides an observerindependent measure of objectivity.



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