The physics of 2-state systems
The physics of 2-state systems
The physics of 2-state systems
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Outline Symmetry Oscillations Density matrices Keywords and ReferencesQuantum Zeno EffectZeno’s Paradox: An arrow cannot move, Achilles cannot win a raceagainst a tortoise. False, because an accurate measurement <strong>of</strong>position does not mean that the velocity is zero. <strong>The</strong> meaning <strong>of</strong>derivatives not properly understood until Newton and hiscontemporaries.Quantum Zeno effect: Repeated measurements can prevent change<strong>of</strong> <strong>state</strong>. Prepare a 2-<strong>state</strong> system in a <strong>state</strong> |1〉. After time t its<strong>state</strong> changes to something else, the probability <strong>of</strong> finding it againin <strong>state</strong> t is given by P(t). Perform the measurement, and thenwait for another interval <strong>of</strong> time t. Now the probability <strong>of</strong> findingsystem in |1〉 is again P(t). However, if the <strong>state</strong> was not measuredat time t, then the probability is P(2t) ≠ P(t) in general.Sourendu Gupta Quantum Mechanics 1 2013: Lecture 5
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