Reputation
12,081
Next privilege 15,000 Rep.
Protect questions
Badges
1 36 87
Impact
~568k people reached

1d
comment Is it possible to create an entangled pair of photons if they originate initially from operations at two separate sites?
You can't. Photons from different sources by definition have been "tagged" with statistically irreversible information, that being the two classical-physics sources. The best you can do is absorb pairs of photons from two sources into a single new quantum system. That is very doable, e.g. by using two lasers to stimulate two-photon transitions. You then emit new higher-energy photons. The newly emitted photons are source-entangled with only one classical system, so they can be split at the quantum level -- e.g. by that beam splitter you mentioned -- without endangering classical causality.
Apr
27
awarded  Nice Question
Apr
23
awarded  Famous Question
Apr
17
awarded  Nice Answer
Apr
12
awarded  Generalist
Mar
22
awarded  Nice Answer
Feb
14
awarded  Yearling
Jan
26
comment Can matter really fall through an event horizon?
Sounds pretty good to me!
Jan
19
comment Does momentum space have a speed limit?
Good point for consideration, thanks! I gave that one mostly because motion is such a tricky issue in momentum space, and that is one that has meaning. I am... genuinely unsure?... whether such a band drop, which is a quite high energy event (X-ray photon emission for silver) qualifies as a purely quantum event in momentum space, or instead has a kinematic component. I suspect the latter because those high energies which would not be typical of something falling under the auspices of time-energy uncertainty. But in any case, my intent was to give that only as an example, not the defining case.
Jan
18
comment Does momentum space have a speed limit?
Nice point, one that makes me think "I should have thought of that!" (Cool name BTW, apt for this question.) So my question is equivalent to "Is there a maximum acceleration regardless of the magnitude of the force applied?"... which sounds like the situation when approaching $c$... hmm!
Jan
18
asked Does momentum space have a speed limit?
Jan
12
answered visible light spectrum
Jan
5
comment Entangle more than two atoms?
Whoa! Entanglement is not gravity. Entanglement is arguably everywhere. That includes at astronomical distances, e.g. for two photons billions of light years apart after being created by an early electron/positron collision. But if entanglement was gravity, you would expect the strongest gravitational attraction to occur between the lightest, simplest particles, such as those two photons. That's not what we see, since gravity is strongest between the heaviest particles that are least likely to have detectably entangled states. Complex entanglement networks relate to entropy, not gravity.
Jan
5
comment Entangle more than two atoms?
@OlegSilkin yes, experimentally meaningful entanglement — the kind that is both detectable with real equipment and not explainable using speed-of-light constrained casualty — is a lot like a very tiny, rather precious resource that once created cannot be replicated, only divided up or spread around.
Jan
5
comment Entangle more than two atoms?
@igael, correct, it would have been more precise if I had said "entangled states of composite, multi-particle objects".
Jan
5
answered Entangle more than two atoms?
Dec
22
comment What allows us to assume spacetime is flat when no normal matter is present?
Ah, I see you have an answer. Hmm. Try reading his question again. Ask yourself "What is the core issue that is puzzling the writer? Does the writer have some kind of subtle misconception not about the precise mathematical formulation of how curved space works, but perhaps in how we interpret the experimental data gathered by telescopes?"
Dec
22
comment What allows us to assume spacetime is flat when no normal matter is present?
Heh! That's a delightfully odd way to get a minus one! Alas, I'dhave to think hard about how to make it sound more complicated, so I'll just pass... :)
Dec
22
comment Does laser light with less than the work function still ionise some atoms?
Two-photon absorption has even become a lively research and trcnology topic these days. Neural researchers use it to select and activate individual neurons, and if you search the web, you can find amazing micro-sculptures created by using two-photon transitions.
Dec
22
answered What allows us to assume spacetime is flat when no normal matter is present?