B Can an electron remain in an exited state forever with constant energy input?

[medammari]

TL;DR Summary

what will happend if I keep giving the same amount of energy, constant in time to an electron?
Will it stay at the excited state forever

what will happend if I keep giving the same amount of energy, constant in time to an electron? Will it stay at the exited state forever

 

[Drakkith]

If you're referring to electrons in their atomic/molecular orbitals, then no, an electron in an excited state will move to an even higher energy state if it absorbs energy. You could, however, make it jump to an excited state, wait for it to transition back down, and then make it jump back up to its excited state again. This is how several devices such as lasers and LED's work.

 

[PeroK]

TL;DR Summary: what will happend if I keep giving the same amount of energy, constant in time to an electron?

An electron bound to an atom or molecule can only increase its energy in discrete quanta. The classical notion of continuous energy input does not apply at the atomic or molecular level.

Will it stay at the excited state forever

There was a post recently about some clever idea to prevent radioactive decay by almost continuously resetting the quantum state of the object by repeated measurements - but I can't find the thread.

What you could ask is whether by a clever experimental set-up you could sustain an atom in an excited state almost indefinitely? I don't know the answer to that.

what will happend if I keep giving the same amount of energy, constant in time to an electron? Will it stay at the exited state forever

If you keep giving the electron more energy, then eventually you will ionise the atom or molecule.

 

[gentzen]

There was a post recently about some clever idea to prevent radioactive decay by almost continuously resetting the quantum state of the object by repeated measurements - but I can't find the thread.

I guess you mean the thread: Geiger counters and measurement. We certainly had fun. Just like this thread, it was a question from a first time poster. But were allowed to have fun and dive into those technical details, because the thread level was "I: intermediate".

You could, however, make it jump to an excited state, wait for it to transition back down, and then make it jump back up to its excited state again. This is how several devices such as lasers and LED's work.

Except that lasers have to work with more than one excited state, both for theoretical and practical reasons. And LED's just work like a waterfall, no need to bring the water back up to the higher level, new water at the higher level will keep floating in anyway.

what will happend if I keep giving the same amount of energy, constant in time to an electron

Giving the same amount of energy to the same electron is only possible in a thought experiment. In actual practical devices (and also in real experiments), more manipulations of details of quantum states of small systems like molecules, ions, electrons, or even photons are possible, compared to what a layman or even a physics freshman would believe. But still, there remain fundamental restrictions of which manipulations are possible ("for theoretical and practical reasons"), just like in the case of lasers.

 

[Hyperfine]

Rabi cycling

 

[f95toli]

Rabi cycling

Sure. but this still only work if the frequency matches that of the transition frequency between the ground and exitcted state.
Under "normal" situations (i.e. the field is not extremely strong) nothing will happens if that is not the case.

 

[Hyperfine]

Sure. but this still only work if the frequency matches that of the transition frequency between the ground and exitcted state.
Under "normal" situations (i.e. the field is not extremely strong) nothing will happens if that is not the case.

That is certainly true. Given the original question, I leapt to the conclusion that a resonant transition was a possibility, and certainly not totally irrelevant to the response provided by Drakkith.