Timeline for Continuous Measurement in Quantum Mechanics
Current License: CC BY-SA 3.0
5 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 2, 2011 at 15:08 | comment | added | Ron Maimon | Also, keep in mind that measurements can be pushed up to the level of psychology, the measurement can be thought to happen only at the last step, when you look at the measuring device. Then one can ask what physical reason allows a strong laser tuned to 0-2 transitions to prevent 1-0 transitions. The reason is that transition from 1-0 is accompanied by high frequency amplitudes for transitions to 2, which are entangled with incoming photon phases and therefore incoherent, so the down transition amplitudes get scrambled. The ground state in the presence of the photons is not stationary. | |
| Aug 2, 2011 at 14:48 | comment | added | Ron Maimon | It took me a little thinking to understand why people are saying that quantum zeno is limited by time-energy uncertainty, because it isn't at all. The wrong idea is that a measurement of energy to accuracy "delta" will have to take 1/delta seconds, so that the density of measurements can never exceed 1/delta. The first clause it true--- a measurement will have to take a long time, but the measurements can overlap, so that the density is unlimited. | |
| Aug 2, 2011 at 14:06 | comment | added | Ron Maimon | A measurement can be a failure of interaction. If you have an atom in its first excited state, it will decay to the ground state normally. You can apply an arbitrarily strong laser whose frequency is tuned to the energy difference between the ground state and the second excited state, and this measures when the atom transitioned to the ground state. This will prevent the atom from ever making the transition to the ground state, and there is no theoretical limit to the density of measurements from the uncertainty principle, because the different measurements are free photons. | |
| Aug 2, 2011 at 4:55 | comment | added | Alexander Moll | Thank you for your suggested steps towards a more subtle construction, and for pointing me to the "Quantum Zeno effect". I'm reluctant to accept your answer to my second question above: quoting from the Wikipedia entry for the Quantum Zeno effect, "It is still an open question how closely one can approach the limit of an infinite number of interrogations due to the Heisenberg uncertainty involved in shorter measurement times. In 2006, Streed et al. at MIT observed the dependence of the Zeno effect on measurement pulse characteristics.[29]" | |
| Aug 1, 2011 at 18:58 | history | answered | Ron Maimon | CC BY-SA 3.0 |