Caltech Scientists Film Photons With Electrons

al0ha writes "Techniques recently invented by researchers at the California Institute of Technology which allow the real-time, real-space visualization of fleeting changes in the structure of nanoscale matter have been used to image the evanescent electrical fields produced by the interaction of electrons and photons, and to track changes in atomic-scale structures."

Moving pictures of the 4D microscope

[Silpher]

Can be seen here: http://ust.caltech.edu/movie_gallery/#paper3 [caltech.edu]

not really the same...

[slew]

The photo-electric effect is when electrons are released from a material when they absorb energy from photons. When the energy of the photons isn't above the threshold energy of the material, you get nothing. Also the energy of the emitted electrons doesn't depend on the intensity of the light.

This new technique called PINEM (photon-induced near-field electron microscopy), is used to image the "glow" (i.e., photon emissions) that is emitted by objects that have been excited by femto-second laser pulses using short pulses of electron beams. The image of the object glow is formed by measuring the energy of the scatterred short electron beam.

So in PINEM we are measuring a photons field using an electron pulse in a way where the electrons have a scatter function and different electron energies (think of this as an "analog" 4-d picture of the photon field), in the PE-effect, we are getting some number of electrons of a fixed energy which we can count (think of this like a "geiger counter" measurement of the incident photon field on the material).

Also since you are measuring a field and not the material, in the PE-effect, the material has to absorb the photon and emit (non-coherently) at it's electron work function energy. If the absorbtion ability and/or the energy disparity beween the photons and the work function is large, PE-effect doesn't even give you anything.

As a not very good analogy to think about, with PINEM, you can effectively take a "flash" picture (the flash is the femto-second laser pulse) of the photon emmission field which doesn't disturb the material that much. With any imaging technique that tried to use the PE effect, you'd have to illumiate the material with a photon field (over time and with different intensities) which wouldn't allow you to see anything. This would be like taking a picture with no shutter over a long period of time and imaging them with a binary threshold (kinda-like how old fax machines scanned pictures before dithering). Very blurry (because of the time averaging of the illumiation to get electrons emitted), and very uninteresting (because of the single energy level, uncorrelated nature of the electron emmission from the PE-effect). As another silly analogy, PE-effect is like hearing the alarm of water going above a dam, where PINEM is like looking at the a 3-d movie of the water-level behind the dam even if the water level didn't go above the dam.

Saying this is "old news" is like saying that the transistor was old news, because we discovered lightning a long time ago. ;^)

Interesting, but not for actual quantum computing

[Zorpheus]

As I understand the article, this technology works as follows: a short laser pulse excites the electrons of a sample material. After a short delay t, a short electron pulse hits the sample. The diffraction of the electron pulse is used to generate a picture of the electronic states in the sample at the time t after the excitation by the laser pulse. This is repeated several times, with different delays t. By combining these images, they can see how the electronic states develop over time. It is a combination of pump probe spectroscopy and electron microscopy, very interesting that this is possible. However the state of the electrons excited by the laser is destroyed every time an electron pulse hits the sample. You can only see the time development of electronic states by repeating the complete experiment, which is not what you want for a quantum computer. I think this is a fundamental principle of quantum mechanics described by Heisenberg's uncertainty equation. However this is not my field, and I don't know much about the details of quantum computing. Maybe this technology can help to understand what happens in a quantum computer though.