emarti

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	1,147 reputation	bio	website		visits	member for	10 months
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Jan 27	comment	Travel direction of lightning that's one of my favorite youtube videos.
Jan 26	comment	Have we managed to make a perfect vacuum? @user44430, UHV is mostly limited by H2, not N2 or O2. This is because (1) most pumps (turbopumps, ion pumps, etc.) preferentially pumps heavier molecules and (2) the hydrogen load is from the walls of the vacuum chamber. Air leaking into a vacuum chamber is negligible in most systems.
Jan 26	comment	Have we managed to make a perfect vacuum? In most UHV (ultra high vacuum) systems, including mine, the main component is by far hydrogen molecules (H2). They're light and very difficult to pump out. For that reason, many pumps in the UHV range focus solely on pumping hydrogen (e.g., titanium sublimation or non-evaporable getters).
Jan 21	answered	Non-destructive measurement of qbits
Jan 21	comment	What can the D-Wave quantum computer do? @Lagerbaer: I think D-wave has a fantastic PR department, for exactly the same reason. They make a lot of incorrect claims and hype their system, which is exactly what a PR department is supposed to do. As a scientist, I find the whole thing highly disturbing.
Jan 20	comment	Temperature in space Temperature is NOT a measure of kinetic energy. It is a measure of how much energy is required to change the energy of a system. Truth be told, temperature can be somewhat subtle in many situations, as the answers clearly demonstrate in this one.
Jan 20	answered	How were the crystal lattices of elements determined to perfection ? (Ex:- That of a copper is a cubic lattice )
Jan 13	comment	Can all quantum superpositions be realized experimentally? Beware of question like, "Can ... be realized experimentally?" Do you mean that, theoretically, can an experiment realize it? I would argue that's not the same as, "Can an experiment realize ..."? (More below on my answer.)
Jan 13	comment	Rutherford's Gold Foil Experiment As the older professors say: things are easy for us youngin' grad students. I can go to dinner while I acquire data, unlike poor Marsden and Geiger.
Jan 13	revised	Can all quantum superpositions be realized experimentally? added 512 characters in body
Jan 13	answered	Can all quantum superpositions be realized experimentally?
Jan 12	comment	Does a quantum phase transition have latent heat? Some do, some don't. Just like classical phase transitions, quantum ones can be first order (with latent heat) or second order (without) -- or something else. Most of the traditional examples that leap to my mind are second order.
Jan 12	answered	instrument that measures the distance from a point in space, through a material like bone, to a live wire carrying very low voltage current?
Jan 12	comment	Why are so many forces explainable using inverse squares when space is three dimensional? Feynman had an interesting comment: nature tends to be described by laws that can be understood or mathematically expressed in qualitatively different ways. Take a look at Ch. 8 of lecture 2 of the Messenger Series (research.microsoft.com/apps/tools/tuva/#data=3\|\|\|).
Jan 12	comment	Alkali atom in oscilating electromagnetic field The rotating wave approximation can be confusing. I originally learned it in the context of a spin-1/2 particle in a magnetic field, where the coordinates of the spin and real space match. It's a little more confusing in general problems, where the real space and spin space coordinate systems are nontrivially related.
Jan 11	awarded	Nice Answer
Jan 11	revised	Alkali atom in oscilating electromagnetic field added 181 characters in body
Jan 11	answered	Alkali atom in oscilating electromagnetic field
Jan 11	answered	Why is a critical system equal to a gapless system?
Jan 9	comment	Where does energy for high and low tides come from? This is why we always see the same face of the moon: there are no longer tides on the moon. Tidal forces lead to friction, which locks the precessional and rotational rates.