detecting electrons with photons

[gib65]

They say that in order to measure or detect an electron, a photon must be fired at it. But can an electron be measured or detected if the detection device simply receives a photon it spontaneously emits?

 

I have a follow up question about this.

[swansont]

They say that in order to measure or detect an electron, a photon must be fired at it. But can an electron be measured or detected if the detection device simply receives a photon it spontaneously emits?

 

I have a follow up question about this.

 

You generally gear your experiment so that the target will emit a distinctive photon (wavelength, polarization) so that you can match it with whatever you are investigating.

[gib65]

So what happens in the double-slit experiment where they setup a detection device near one of the slits so that they can detect whether or not an electron passes through the slit? Does the decive attempt to fire photons at the electron or does it sit quietly waiting for the electron to fire a photon at it?

[Klaynos]

http://www.nature.com/nature/journal/v391/n6670/abs/391871a0.html

 

It seems to be quite complicated, I'm on my way home but if I get time will try and read the paper fully this weekend...

[gib65]

I might as well spell out my purpose in asking these questions. I'm wondering whether something needs to interact directly with the electron in the double-slit experiment in order to collapse its wave structure into the more streamline structure it takes on as it passes through only one slit. I always assumed that any detection device you setup at the slit can only detect the presence of the electron by interacting or disturbing it, but a thought occurred to me the other day that the electron could emit a photon and that photon could interact with the detection device, effectively causing it to detect the electron's presence. This photon could be emitted spontaneously (i.e. it wouldn't necessarily have to be fired at the electron), and although we'd have to be extremely lucky to detect it, it could happen in principle.

 

In that case, we'd be 'observing' the electron without actually interacting with it directly. They say that observation causes the electron to act like a particle, but in this case it seems almost 'magical' (or as they say 'spooky action at a distance'). I suppose you could invoke quantum entanglement to explain this - i.e. the electron is entangled with the photon it emits - and so for anything that happens to the photon (like interacting with the detection device), something will also happen to the electron (it will act like a particle).

 

Is this how it might happen in actuality. Is entanglement the way a physicist would typically explain it?

[Klaynos]

How would you get the electron into an excited energy state, whilst being in freespace?

 

As far as I'm aware you always have to interact with it, even it giving off a photon would be interaction of sorts. The probability of the photon being given off at the right time would be phenomenally low, even if you set up the lifetimes and distances as good as you could.

[gib65]

How would you get the electron into an excited energy state, whilst being in freespace?

 

Could it not hold a certain amount of energy at the beginning and release it later? Or is that not how it works?

 

As far as I'm aware you always have to interact with it' date=' even it giving off a photon would be interaction of sorts. The probability of the photon being given off at the right time would be phenomenally low, even if you set up the lifetimes and distances as good as you could.[/quote']

 

Yes, it's not too practical, but do you understand the deeper question I'm asking? I'm basically asking whether the commonly held notion that "observation causes the electron to act like a particle" can be interpreted to mean that there need not be any direct interaction between the observing mechanism and the observed electron. Sounds like you're saying this is the wrong interpretation.

[swansont]

Could it not hold a certain amount of energy at the beginning and release it later? Or is that not how it works?

 

 

Excited states imply a bound system, which are the ones with quantized energy levels — you need a negative potential energy (classically speaking) larger in magnitude than KE, which comes from an attractive force. A free electron can only have kinetic energy, and there's no place to "store it until later."