Much better. I am not sure what to make of fractional quantum states however, back when I took quantum mechanics fractional states were as impossible as having electrons at mid-energy levels.
Solid materials are much more complex than single atoms and support several types of multiple particle states. One
noteworthy example is the Cooper pairs that result in conventional superconductivity. Spin-liquid states are also multi particle states with the interesting property that they exhibit entanglement between the magnetic moments of the atoms, and it is this entanglement that makes them intersting for quantum informatics because it can be used fo form qbits.
An intersting feature of the Herbertsmitihe crystals that were used for the study is that have a geometric structure that frustrates the ordering of the magnetic moments (or spins) of the atoms. The magnetic moment will try to align in opposite directions but the crystal structure has three magnetic moments in each unit cell and therefore only two of them can allign in an energetically favorable state while the last one is unable to moove into a stable equlibrium. Since there is no distinction between the three magnetic moments per se, the frustration is spread across the whole solid structure and a "large" entangled stage is formed.
Because these states are not locallized they are not constrained by the atomic properties of the cryatal atoms and therefore they are allowed to accept excitations at a continous range of engergies rather than the discrete ones that we normally see. It is a little bit similar to free electrons in metals. They can also be excited by a continous range of energies because they are free to move within the material.
An important thing to note, however, is that these experiments were carried out at 1.6 K, where thermal fluctuations play a very small role compared to room temperature. Therefore it is not likely that this effect will be portable to regular electronics devices. More likely quantum informatics applications include massive server like facilities that has the infrastructure to cool the devices down to cryogenic temperatures and the best we can hope for in terms of avaliability is some kind of cloud service.
My vary limited understanding of that was it was closer to an emergent state on a surface vs. something that ever applied to an individual atom. Can you clarify what's going on?
They aren't excitations of individual electrons, but of the system as a whole. I'd assume they're some sort of quasi-particle, though this isn't really my field.
There is a good chance that MIT's press release was written , outlined, or edited by the actual scientists who did the research. I recall working in OpenAcess publishing and we would inform the author's when their paper was published so they could time the press release.
Thanks for this. It is a lot more informative and accurate than the Extremetech article while remaining greatly more accessible than the original Nature journal paper.
In particular, the fractional quantum states/excitations aspect was completely missing in the Extremetech article.
More informative indeed, but still with the unexplained "There is no theory that describes everything that we’re seeing." What are they seeing that no theory describes?
Most things below the atomic level occur in quantized form, meaning variables that hop between discrete states. For example, energy radiated by electrons falling into a lower orbit is exactly equal to the difference in energy between the two orbits. Or take sub-atomic particles that have properties like spin, this also occurs in discrete steps. What this means in the context of these new magnets though I'm not sure. I seem to recall a paper where fractionalized spin states where hypothesized but I can't find it right now.
Interesting how often scientific research links on HN seem to be to discoveries with Chinese names in American universities. As someone who didn't study in the US, are there particularly large numbers of Chinese students and professors in say MIT?
The top physics kids in the US tend to get picked up by financial (or some other industry) firms because they're really really sharp because making 200k sounds much better than making 30k. This means that the kids who go into physics are doing it because they truly love the subject but it also means that we have a much smaller percentage of kids going into graduate studies than otherwise. This, combined with the fact that many countries are rapidly industrializing and newly able to support an academic class means that lots of international students are applying to Harvard/MIT/Stanford/etc where some of the best science in the world is happening. Some of the foreign kids go back, some stay here. It really depends. As for makeup? probably 40%-50% of my entering cohort was foreign and probably 60% of the foreigners were asian. That's not really a bad thing though. They're brilliant scientists and it's truly a pleasure to collaborate with them and everyone else in my programme as well.
Disclaimer, I'm a physics PhD student at Harvard and go to seminars a lot with kids from MIT.
They don't go into details, but I assume the implications for communications are new ways to make entangled particles for quantum cryptography, not FTL communication or something else that's considered impossible. Right?
Well, from my read, it'd be theoretically possible to transmit at near-infinite bandwidth using quantum entanglement (since you just keep adding more entangled particles). There'd still be the latency of at least the speed of light though
Entanglement alone can't be used to transmit information. If this is the first time long-range entanglement has been possible then the communications advances they're talking about would include anything that requires parties to share entanglement over a distance. So quantum encryption, key exchange, superdense coding (is that even likely to be useful?) etc. Someone who knows what they're talking about want to weigh in here?
Entangled particles communicate instantaneously through space. That is to say, communication faster than the speed of light. This was actually one of the reasons that Einstein did not want to accept quantum theory. In fact, he proposed quantum entanglement as an argument against the validity of quantum theory. According to quantum theory, transfer of information faster than the speed of light should be possible (via quantum entanglement). Therefore, quantum theory was incorrect/incomplete- that was Einstein's reasoning.
There would still have to be an entanglement step. The photons need to be coupled. This is currently accomplished by a laser across long distances. I suppose that in this sense there is a latency at the speed of light to add new particles. But once the photons have been entangled they can communicate instantaneously.
No. Sorry to shatter the dream of FTL communication. You cannot achieve it with entangled particles. While it seems like there is some transfer of information going on its much better to think of two entangled photons as a pair of dice which will roll the same number wherever they are. Spooky, yes. Useful for cryptography, certainly. But sadly no FTL communication. At best its FTL transmission of complete noise.
Edit 2: If you say that the particles themselve are 'communicating' ftl, then you are perfeclty correct, yes. Unfortunatly one cannot use this behaviour to transmit arbitrary data.
I don't understand. If they can measure and compare the states of two entangled photons to determine that the states are identical, then couldn't they encode information in the intervals between state changes by measuring the photons at a previously agreed upon rate? Or is it simply impossible to impute a state transition on one of the entangled photons?
Comparison of the states of each entangled particle, to find the signal, requires communication (light-speed); so while there was information sent, you can't figure out what it is until you receive a signal from the source of the transmission, thus no causal violations.
This is also why it's interesting cryptographically, unless you have information on the movements of both particles you can't pull a signal from the movements.
Why would you need to compare the states of the particles if you know a priori that they are entangled? Doesn't the theory say that the states will always match? I still don't understand why one side couldn't just measure the interval between state changes and use that channel to read information.
Correct. But in theory a small classical signal could be sent to essentially say "measure/extract data from the entangled particles in this way", and then the bandwidth from this communication would be based on the amount of data extractable from the entangled particles, while the latency will still be capped at however long it takes to send the classical signal
Ah, that's too bad. I was about to imagine future hackers who would tap into a secret FTL communication with their own particles to steal entangled data :)
Actually, it is an open question. Delayed choice entanglement seems to be able to send messages back in time, but the experiment was unable to tell whether it was communication into the past or simply an after-the-fact relabelling of events.
"In Quantum entanglement, part of the transfer happens instantaneously. Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the sites of measurement" http://en.wikipedia.org/wiki/Quantum_entanglement
Yeah it occurs instantaneously but because you can't influence either particle without destroying the entanglement you can't use it to communicate faster than the speed of light.
http://curious.astro.cornell.edu/question.php?number=612
From wikipedia: "In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs.... The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation." http://en.wikipedia.org/wiki/Superconductivity#Zero_electric... So a new kind of magnetism that lets electrons flow like a liquid might be very useful to develop new superconductors.
There are so many properties of matter that the notion of "solid liquid gas" is about as ridiculous as the ancient notion of alchemy where matter/energy is a function of earth, wind and fire.
Cool something down and turns into to a solid, that is, until you cool it so much it becomes a liquid again, that climbs walls to fall out of cups. Matter is bizarre.
From the press release: "The QSL is a solid crystal, but its magnetic state is described as liquid: Unlike the other two kinds of magnetism, the magnetic orientations of the individual particles within it fluctuate constantly, resembling the constant motion of molecules within a true liquid." I'm not sure why the extremetech article calls it a new state of matter.
Catagorizing new matter/energy phemenon as a state of matter just confuses the understanding. If the particle is simultaneously exhibiting qualities of liquid and a solid, it means a shift in thinking is required.
Iron is solid, but that doesn't mean we should group it with other things that are hard. The other hard object might be hard for a completely different quantum mechanical reason.
The problem is there's a conflation here. "States of matter" which are solid/liquid/gas and "states of matter" which are quantum spin liquids are not the same thing. One is an English term, and one is a more precise physic/chemistry term.
Don't try to understand one in terms of the other. And your "shift in thinking" has loooong since occurred. It just isn't useful to conventional English, so it has not picked it up.
What constitutes a state of matter is very well defined, and in my opinion the Wikipedia article linked above explains it very well to a non-technical audience. The shift in thinking has happened more than 130 years ago, it was well established around 1870. See also: http://en.wikipedia.org/wiki/Statistical_mechanics
Its nuclei and inner electrons are solid. Its valence electrons are a gas, allowing it to conduct electricity. Different parts of the material can be in different states.
