5,484 reputation
1334
bio website math.mit.edu/~shor
location Cambridge, MA
age
visits member for 3 years, 9 months
seen Aug 23 at 18:02

Aug
5
comment Why is the sun brighter in Australia compared to parts of Asia?
Less air pollution?
Aug
4
comment Theoretically, is there a way to hold a quantum entangled particle in a state by continuously observing it?
Once the spin of a particle has been measured, it is no longer entangled.
Aug
3
comment Why is there a difference between additive and subtractive trichromatic color theories?
This is the right idea, but it's not true that everything non-RED is GREEN. This is simplified too much.
Jul
28
comment How to simulate rotational instability?
The angular momentum of an object doesn't change when an object tumbles, but the actual orientation of the object with respect to the axis the object is rotating around does. I believe you have identified a problem with Unity's built-in physics engine.
Jul
28
comment Is this kids experiment a legitimate way to show that air has mass?
But why do you think that the air pressure inside the balloon is equal to the outside? Aren't you doing work when you blow up a balloon?
Jul
28
comment Evidence of why the Standard Model is a successful theory of particle physics
After the discovery of the Bullet cluster, hasn't it become quite hard to find theories that give DM a gravitational origin.
Jul
28
comment Output of a beamsplitter with photon number (Fock) state inputs
@M.B.M.: using the same idea as in the HOM effect, it's easy to calculate for one photon at each input, and an arbitrary beam splitter: 2 out of one output with probability $2\tau(1-\tau)$; one from each output with probability $(1-2\tau)^2$. It gets more complicated when you have larger input photon numbers. See this paper. Also this one. Available here with no pay wall.
Jul
27
comment Output of a beamsplitter with photon number (Fock) state inputs
It's the Hong-Ou-Mandel effect.
Jul
27
comment Output of a beamsplitter with photon number (Fock) state inputs
And if you put in one photon at each input for a 50-50 beam splitter, two come out of one output and none the other output.
Jul
20
comment What force counteracts friction when a block is pulled?
If there were no friction, there would be no forces acting on the gum, and the gum would not move. Thus, if there is only a small amount of friction acting on the gum, the gum won't move much. You don't need a counteracting force to make a body that stays at rest remain (largely) at rest.
Jul
20
comment Non-unqiue basis sets of reduced density matrix in quantum mechanics/decoherence
Presumably he gave the constraint $\langle s_1 | s_2 \rangle = \langle a_1 | a_2 \rangle = 0$, and you just left it out of the question. It's linear algebra. Here, $|s_1\rangle$ and $|s_2 \rangle$ are the eigenvectors of $\rho_S$, and this fact comes from the fact that Hermitian matrices with distinct eigenvalues have a unique set of eigenvectors.
Jun
26
comment Why doesn't a typical beam splitter cause a photon to decohere?
@Slaviks: you're right; probably all that's necessary is that the mirror is localized in space.
Jun
25
awarded  Necromancer
Jun
25
comment Why doesn't a typical beam splitter cause a photon to decohere?
None of the photons are absorbed (or rather, since the apparatus isn't perfect, a very small fraction; much less than 50%).
Jun
25
comment Why doesn't a typical beam splitter cause a photon to decohere?
There's no heat transferred ... the photon has the same energy after it passes through the mirror as before.
Jun
25
revised Why doesn't a typical beam splitter cause a photon to decohere?
added 264 characters in body
Jun
25
comment Why doesn't a typical beam splitter cause a photon to decohere?
If you know how close the phases are, it's straightforward to calculate how much of the interference you lose. But what I'd like to see done is: starting with the thermal state of a mirror, calculate how close these phases are for a given $\Delta p_\gamma$. I think I know how to do it, but it would take me quite a bit of time that I don't want to spare right now.
Jun
25
awarded  Revival
Jun
25
revised Why doesn't a typical beam splitter cause a photon to decohere?
added 15 characters in body
Jun
24
revised Why doesn't a typical beam splitter cause a photon to decohere?
added 99 characters in body