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Physicists Claim First Observation of a Quantum Cheshire Cat
KentuckyFC writes "Last year, a group of theoretical physicists suggested a bizarre experiment based on a quantum phenomenon known as weak measurement. Unlike ordinary measurements that always change the state of a quantum object, a weak measurement extracts such a small amount of information that it leaves the quantum state intact. For example, a weak measurement can detect the presence of a photon by the deflection it causes when it bounces off a mirror. However, this does not change the photon's quantum state. The new idea was to make two weak measurements on a quantum system that is in a superposition of states, the goal being to separate the location of this quantum system from its properties, like a Cheshire cat. Now a group of experimentalists say they've observed a quantum Cheshire cat for the first time in an experiment involving neutrons. They passed a beam of neutrons through a magnetic field to align their spins and then sent them through an interferometer in which the neutrons pass down both arms of the experiment at the same time. They then used weak measurements to locate the neutrons in one arm while measuring their magnetic properties in the other. Voila! A quantum Cheshire cat."
Did they kill the cat, by looking?
Is it just me or does that sound a lot like a Heisenberg Compensator ?
Beam me up!
Why the acid trip Alice in wonderland analogy? Does it convey additional information about what they're doing, or is it just obfuscating what they're doing. I vote obfuscation, but it might just over my head right now. Stupid, grinning cat with no head.
and Curioser
"a weak measurement extracts such a small amount of information that it leaves the quantum state intact."
That's not correct description -- the quantum state is changed, albeit less than with projective measurement. The paper itself calls it in the abstract "minimal disturbing" measurement, not the "non-disturbing" measurement.
So this is abit hard to wrap my mind around.
Lets say you have two big tanks. In one tank you pour water down into. In the other you place a person.
What they have done is basically moving the state of the water into the empty tank so that the person would feel the water pressure and wetness eventhough the water itself isnt present.
Am i correct in this?
We must stop looking into things like this. Quantum physics is fairy magic. Let's leave it at that!
I'm going to toss this out there but I expect the answer to be "no."
Does this solve the issue with using quantum entanglement as a possible means of FTL communications? I'm under the impression that quantum entanglement can't be used for this because the act of looking at the particle would change the state. But this seems to be away around that.
So am I wrong here and why?
Supporting World Peace Through Nuclear Pacification
and the photon that leaves the cat isn't really the same photon that reflects off the mirror.
At issue is whether the result is really paradoxical or simply an ordinary consequence of the way the experiment is set up. For example, perhaps the experiment measures the properties of different neutrons in each of these places.
Personally i dont even understand why those guys are thinking they are measuring the properties of the same neutron.
It was a somewhat amusing reference to Shroedinger's cat, get over it.
sorry, the statement I was posting to disappeared.
Sounds like it was both observed and not observed ...
Here's a more familiar example of a weak measurement. QM says you can't measure the magnetic moment of a single particle along two perpendicular axes at the same time. And yet, you can easily measure the magnetic moment of a bar magnet along two perpendicular axes at the same time. How is that possible? The bar magnet's moment is just the sum of the ones from all the particles that make it up. So by measuring the total magnetic moment, aren't you measuring the moments of all the individual particles, and hence violating the uncertainty principle?
The answer is no. When you measure the total moment of a macroscopic magnet, you only need to interact very very weakly with any individual particle, so the experiment only has a tiny effect on the state of each one. The more particles you sum over, the less information you need about each one, so the less restrictive the uncertainty principle becomes.
But the mathematical details of the explanation are curious. Weak measurements were originally proposed based on time reversible interpretations of QM, in which the future can affect the past and it's basically arbitrary which direction you call "forward in time". It was later shown that other interpretations also predicted them - of course they must, since the interpretations are mathematically equivalent. But the explanations are very different. Other interpretations explain them through an incredibly complicated series of cancellations, whereas in time reversible QM the explanation is straightforward, almost obvious. So is this evidence that time reversible QM is correct? At the moment, that question is more philosophy than science, but it's interesting to think about.
"I'm too busy to research this and form an educated opinion, but I do have time to tell everyone my uninformed opinion."
...about this write-up was that there was NO mention of the nationality of the scientists ("group of experimentalists"?) who had performed this feat. Slashdot almost always prefaces this sort of news story with "Scientists at MIT..." or some such.
So I guessed that this meant they were not American. And I clicked on the reference to find out that I was right. They aren't. They aren't even in the US.
So why is this story even mentioned? Isn't it the case that nothing is true unless it happens here?
wrong cat buddy
-The wise argue that there are few absolutes, the fool argues that there are no probabilities.
It's a lot simpler. They had one neutron in two places and measured different properties of it in the different places.
The new thing is that it's a bit more "real" that it's the same particle in two places than has been done before. I'd guess it's theoretically impossible to measure the same thing in two places, but I really don't know that much about quantum mechanics.
Everything looks like fairy magic until you figure it out. If it works, it's worth researching it until you reach a dead end or come up with a better solution.
That said, I'm drawing the line if I have to wear a sparkly dress and dance under the moonlight.
Holy crap! I forgot to feed my cat! Being a physicist, I now have no idea whether he's alive or dead.
Or Schrodinger?
If we are going to use bad analogies, could we please stick to cars?
Have gnu, will travel.
I was gonna say, someone has been watching Alice and Wonderland too many times. lol
Why is it that 90% of the comments on this interesting subject are silly attempts to make a joke? /. left this place and I am stuck with the 4chan crowd?
Is it perhaps that the smart audience of
It used to be that these subjects generated a lot of interesting discussion. IANAP but I always learned something from them. Now I just went through 47 comments and only 4 are somewhat interesting. I feel like I am wasting my time.
The quantum world doesn't work that way. A photon passing through glass will exit the exact same point every time, based on the superposition of all interactions that it had the probability of transversing. You can't cheat. Your measurements are not accurate.
That's correct. Their observation is not accurate.
BINGO!
I am a fucking physicist and I have absolutely no idea what is happening in the experiment related to the Cheshire Cat. If this is some sort of sci-fi/fantasy lingo, it is not on the Wikipedia disambiguation page for Cheshire Cat, and it really bothers me when I see physics articles delivered to the general population that aren't even sensible to an expert in the field.
If Schrodinger had lab assistants I can imagine this dialogue:
"A box arrived for you today, Dr.Schrodinger. I took the liberty of opening it for you. Why did you order a dead cat?"
They haven't even ever quantum entangled something as large as a neutron.
...
They have quantum entangled photons. The amount of energy in a neutron compared to the run of the mill photon is off the scale.
I'm drawing a blank as to what the hell any of this article is supposed to mean, quite frankly
Priest: "Universe from nothing, no laws of physics, sped up time"+ huge discrepancies. Creationism? No. Big Bang Theory
What about entanglement? Does that means I can not entangle two particles, send one far away, change its state, and weak-read the state change on the first article so that entanglement is not lost and I can do it over and over?
Bash physics:
echo $0
quit
Only for the analogy to be correct, the script cannot have a name, location, an OS, or user running it. Now the object is to come up with a theory (as to what the hell $0 is) that's currently unable to be disqualified. GO!
Now you're doing (something just like) physics! And since this is the case, not only are there no people on this site able to "understand the topic", but neither are the folks on any other site. In my opinion, physicists are trying to count to zero, in the most intelligent way possible.
Politics; n. : A religion whereby man is god.
(theoretical physicists whiz kids waving hands really close in front of mr. Q's face)
"We're not touching you.... we're not touching you... we're not touching you.... haha hah haaha.. we're not touching you..."
Newsflash: Quantum Physicists Discover New Quantum State: ANNOYED - Story at 11.
small amount of information that it leaves the quantum state intact
OK, so I'm seeing a measurement technique that the final value is likely 0.123456789e-8 maybe 2 times then 0.123456788e-8 during t=0 to t=3.
Is the consistent measurement computer related (aka Chaos) or physical (the cat)? That is the question.
The splitter is functionally equivalent to taking a measurement, you may not be extracting the information, but it is an interaction, and it's the interaction part of "taking a measurement" that changes it, not the information extraction/conversion into another form.
We know the splitter changes it, because its velocity changes... it leaves along a different vector.
The revolution will not be televised... but it will have a page on Wikipedia
from the summary:
For example, a weak measurement can detect the presence of a photon by the deflection it causes when it bounces off a mirror. However, this does not change the photon's quantum state.
Cough.... say what? If the photon produces a measurable deflection of the mirror then it transferred energy to the mirror. Therefore the QM state of the photon was changed. This sounds like a bunch of rubbish.
Some drink at the fountain of knowledge. Others just gargle.
re: "Twas brillig, and the slithy toves. Did gyre and gimble in the wabe: All mimsy were the borogoves, And the mome raths outgrabe."
Awesome lesbian erotic poetry dude!
sorry, the statement I was posting to disappeared.
You were probably trying to reply to the thread just before this one: "Why a Cheshire Cat?"
But that question should be understood "Why a Cheshire Cat?" rather than "Why a Cheshire Cat?"
good point, thanks
Was the Cat dead or alive?
lots of info encoded in such a way as to form superpostions rather than having a 'sub-conscious' constantly expending energy.
weakly read superpostions of previously encoded scenery
we will have the tech to photocopy consciousness
We know the splitter changes it
I don't see how that's relevant. They're still measuring it.
Great spirits have always encountered violent opposition from mediocre minds -- Albert Einstein
...that Cheshire cat of SchrÃdinger's from the quantum cradle to the quantum grave, which may be side by side, or not!
- I can't help punning, I'm the product of a Jesuit Education. -
At issue is whether the result is really paradoxical or simply an ordinary consequence of the way the experiment is set up. For example, perhaps the experiment measures the properties of different neutrons in each of these places.
Uncertainty here kind of negates the credibility of the whole experiment, doesn't it?
No, I still see its smile
having the physical bits undisturbed in one place and having access to the info they encode in another
from the actual article:
"For example , it is possible to measure whether a photon has travelled down one arm of an interferometer by looking for the deflection it causes to a mirror it bounces off. That doesn’t significantly change the state of the photon because it produces only a small amount of information: whether the photon is present or not. This is known as a weak measurement."
but the actual experiment doesn't even use photons
from the paper:
Up to now most
experiments studying weak measurements were done with photonic setups [21].
To reveal the peculiarities of a quantum Cheshire Cat the use of non-zero mass
particles is most appealing, since no classical description is possible. Here, we
report an experiment using a neutron interferometer [22–25] to create and observe
a purely quantum mechanical Cheshire Cat. The experimental results suggest that
the system behaves as if the neutrons went through one beam path, while their
spin travelled along the other.
not only are there no people on this site able to "understand the topic", but neither are the folks on any other site. In my opinion, physicists are trying to count to zero, in the most intelligent way possible.
I will give you the benefit of the doubt and trust that you are actually aware that the doodad you used to post this comment does not work by magic, even though you seem to be implying that physics is pointless.