Re: New look for classic double-slit quantum-interference experiment

mmeron_at_cars3.uchicago.edu
Date: 03/08/05 

Date: Tue, 08 Mar 2005 22:04:09 GMT

In article <4flXd.21419$FM3.10069@fed1read02>, Mark Fergerson <nunya@biz.ness> writes:
>Quantum Mirror wrote:
>>> It's worse. Did you read the next-to-the-last paragraph? Note that
>>> there're two "positive" peaks in the laser pulses, but only one
>>> "negative" pulse. The negative pulses kick electrons out the other
>>> way and produce no interference pattern because there's no energy
>>> difference to create one. So in a sense, you simultaneously get
>>> complete and no "which-way" information about each electron that
>>> did produce the pattern
>>
>> They are saying that the two peaks act as the two slits. I can find
>> no preprint or paper describing the exact experiment. This is a
>> strange idea to me.
>
> Yup, neither can I, and me too.
>
>> The time must be so short it is much smaller than the wavelength of
>> the light. For this to act like a slit in the fashion they are
>> describing each peak would need to produce half of the electron.
>
> It's basically just photoionization, but with previously unachievable,
>nearly unbelievable control.
>
> The article includes a link to Paulus' webpage:
>
>http://faculty.physics.tamu.edu/ggp/
>
> where you'll find a "chatty" explanation of the experiment. He says
>there about the intensity of the fields:
>
> "The pulses can be focussed down to a spot size with a diameter
>comparable to the wavelength thus causing intensities of the order of
>10^20 W/cm^2. Such intensities are associated with tremendous field
>strengths. The electric part would have an amplitude of 20 TV/m..."
>
> Seems reasonable that such field strength should be adequate to yank
>an electron loose even on one peak.
>
> He says about the duration of the peaks:
>
> "Such pulses consist (full-width half-maximum) of less than two
>optical cycles only (few-cycle pulses). This means that the pulse
>envelope changes almost as fast as the field oscillates. Therefore, the
>temporal evolution of the field depends on the phase of the carrier wave
>with respect to the envelope."
>
> This is the "nearly unbelievable" part; that adequate field strength
>to free an electron can be turned on and off at a chosen location, in a
>preferred direction, pretty much at will.
>
>> Are they saying that because we can't know which peak created the
>> electron complementarity or uncertainty plays a part in the
>> interference?
>
> Apparently so. From the article:
>
> "The team registered the arrival times of the electrons at both
>detectors and then plotted the number of electrons as a function of
>energy. The researchers observed interference fringes at the first
>detector because it was impossible to know if an electron counted by the
>detector was produced during the first or second maximum."
>
>> Someone has misunderstood the details of this and I would like to see
>> the paper.
>
> I'm not sure why you say that, and so would I.
>
>> I think a alternative explanation for this would be the two peaks
>> produce two electrons which interfere with each other.
>
> If two electrons were produced it would be obvious from the ionization
>state of the remnant atoms (determinable from the recombination glow
>color, return current from the electron detectors etc). That isn't
>mentioned.
>
> If the experiment proves to show what they think it does, it puts a
>neat twist in the old quantum computing game. As I mentioned, we now
>simultaneously have total and zero "which-way" information about the
>interfering particles depending on which way you look at it, because
>this is basically the standard Young's Experiment "done sideways" so to
>speak.
>
> <I keep waiting for Mati or somebody to whack me upside the head for my
> miscomprehension, but nothing so far. Maybe he's stopped reading me.>
>
Nah. My "to read" list is rather short nowadays, but you're certainly
on it. Not much time to write, though, we've a run period coming.

Anyway, I didn't read the detailed description yet (see "time
shortage", above) but this is a real neat experiment. And as for
pulling out an electron, well, atomic fields (in the outer electron
region are of the order 0f 0.1-1 TV/m, so the field generated by the
laser is way more than adequate for the job.

Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"

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