Macro Quantum Effect witnessed: Implies time travel? Multiple Universes?

Factual Questions
21

The original article is published in Nature, doi:10.1038/nature08967. I just read it (or, gave it a 60%-level skim). The paper is very detailed, if terse, and the experimental approach is complex, if clever, so I’ll give only a short summary.

The “drum” is piezoelectric, so it can be coupled to a circuit capacitively for readout and manipulation. That readout and manipulation is, in turn, provided by a qubit, which is a small two-state quantum system. The energy gap between the ground state and excited state of the qubit can be tuned inductively (i.e., magnetically).

The main “trick” of the experiment is that you can tune the qubit’s energy gap to be either close to or far from the lowest frequency mode of the drum (energy E=hf). When these match, they exhibit the usual coupled resonator phenomenon of sharing energy back and forth. (Think: classical weakly coupled pendula. The “trading” of energy here, though, is between two systems that have only two accessible states each.)

The first half of the paper describes multiple methods used to demonstrate that they can get the coupled system into its ground state. The actual, physical, measurement performed at any given instance is What state is the qubit in? This is a quantum mechanical question, so they repeat this “~1000” times when they ask it so that they can actually determine P(e)=What is the probability that the qubit is in the excited state?

That’s the crux of it. They proceed to plot P(e) under various configurations of: (1) the quality of “tune” between the qubit and the mechanical resonators, (2) how long they hold the pair in tune, (3) how long they keep them out of tune (to let the drum’s state evolve a bit before reading it out resonantly), (4) how long and hard they ping the drum through a separate excitation channel (a blast of microwaves).

They look at P(e) as a function of all these things, and they extract quantities such as the energy transfer time, the resonator relaxation time, etc. These data are in excellent agreement with the quantum mechanical expectations, demonstrating, among other things, that the drum and qubit indeed seem to become quantum mechanically entangled and seem to have quantum mechanically “uncertain” states.

22

So what it amounts to is that they took a bunch of repeated measurements of some kind which didn’t all come out the same, and then analyzed the statistics of this, repeating this process in various configurations as well. But it’s not any nonsense like “They took a single measurement, and got two different answers at the same time, in some crazy magic that uses the word ‘quantum’, take our word for it…”.

23

That is an accurate summary. (Although, I will note that even the authors play up the mystique a bit with their opening two words: “The bizarre […predictions of QM].” Really? For the Nature audience?)

24

Quantum mechanics is clearly-defined until it is observed by journalists.

Then it collapses into a superposition of nonsensical states, emitting only virtual factoids.

25

Well, to be fair even the scientists who work on QM call it bizarre. I forget who said it and the exact quote but one notable scientist said something like, “Anyone who is not deeply disturbed by Quantum Mechanics does not understand it.”

26

Do they? I agree it is reasonable to use such verbiage to help get the non-intuitiveness across to lay audiences, but in my experience, physicists these days do have some intuition about QM and don’t find it all that bizarre. (Sort of like the “spooky” 4D spacetime concept that nowadays is pretty mundane for those that use it day to day. Or, for a more extreme example, the Copernican model of the solar system, which was about as non-intuitive as a theory could get when it was new.)

I dunno, maybe it’s just me that thinks humanity (well, physicists at least) should direct their awe to some new initially-hard-to-intuit-but-after-nine-decades-really-isn’t-all-that-bad topic. These are folks that presumably have been exposed to QM since their formative undergraduate days.

(BTW - The quote you mention was from Bohr, who certainly meant what he said – in 1935 or whenever.)

27

Actually, it wouldn’t surprise me all that much that a professional scientist would consider his area of study to be wonky and cool. It’s their fascination with the subject that brought them there and kept them studying it to begin with.

28

One thing though, doesn’t verifiable macroscopic superposition potentially allow experiments into what exactly counts as an observer?

29

Perhaps from repeated exposure a physicist may become used to quantum weirdness and seem nonplussed but I doubt it ever really goes away.

How can anyone really find something being in two places at once, being “on”/“off” at the same time, being a wave and a particle at the same time not find it strange?

30

By not thinking of things as being a wave and a particle at the same time? We had this idea for how some things behaved, and called the concept a “particle”, and we had this other idea for how some things behaved, and called the concept a “wave”. But not everything has either particle-behavior or wave-behavior. Turns out, some things have a way of behaving which is different from both of those, even if there are similarities to each in certain ways. Finding this strange is like finding it strange that oranges have a thick bitter skin, like a banana, but fleshy juicy innards, like a peach. “How can something be a banana and a peach at the same time?”. But, of course, it’s not a banana, and it’s not a peach; it’s just an orange. Fretting on about some paradox of wave-particle duality is great for making things sound mystical and cool, but it’s antithetical to the kind of understanding one would expect after nearly a century of familiarity.

You play Mario long enough, you get comfortable with the rules of Mario. You play Tetris long enough, you get comfortable with the rules of Tetris. You play around in the details of our world long enough, and you should get comfortable with the rules of our world.

31

Yes, but the real question is does understanding the quantum world let me throw fire balls or help me rescue princesses from evil turtles? :wink:

I agree that studying QM should demystify the whole thing, but it still has a certain level of weirdness that, say, biology or even Newtonian physics doesn’t have. Common sense from our experience in the macro world makes things like superposition counterintuitive; here a cat is either alive or dead. Sure I can study it and learn how it fits in with other laws of nature, but it’s still a little weird.

To make a clumsy analogy, I can study India my whole life, but some aspects of the culture will always be a little foreign to me since all my experience is as a Westerner. Growing up in Newtonia, the customs and norms of Heisenbergistan will always be slightly foreign, no matter how long I live there.

32

Well, everyone talks about superposition like it’s the ultimate weirdness of quantum mechanics, but superposition in itself is perfectly cromulent even as a classical concept. If a coin is tossed and I have not yet observed the result, I can model my uncertainty probabilistically as 1/2|Head> + 1/2|Tail>. Applying various further nondeterministic processes (e.g., a machine which kills pets with various probabilities based on the coin flip results) will cause the superposition to evolve further, in a linear manner subject to natural constraints. Perhaps I eventually reach something like 1/6|the cat is dead and the dog is alive> + 1/3|the cat is dead and the dog is dead> + 1/4|the cat is alive and the dog is alive> + 1/4|the cat is alive and the dog is dead>. Then, I actually observe that the cat is dead, and, conditioning the probability distribution representing my knowledge upon this new information, it “collapses” into 1/3|the cat is dead and the dog is alive> + 2/3|the cat is dead and the dog is dead>. And so on and so on. The mere concept of superposition, in itself, is not an illustration of quantum phenomena (this blog post puts it nicely).

Rather, the interesting thing that happens in the quantum context which is different from mere classical superposition is that the weights involved aren’t restricted to being nonnegative reals (as in ordinary probability), but can in fact be turned 180 degrees around from this and be negative (or even turned by intermediate angles to be complex), thus allowing for “interference” of a kind not otherwise modellable. This is something new and interesting, but here mere idea of superposition is old hat.

33

Typo corrected in bold.

34

In the classical case, the assumption is that the system “really is” just in one state or the other, and the “superposition of states” reflects our knowledge of the system, not a fact about the system itself. But everything I’ve read about quantum physics (all of it firmly at the lay level of course) indicates that what’s “wierd” about quantum physics is that the superposition of states reflects a fact about the system itself, and not just our knowledge about the system.

Is this wrong, though?

35

I am the layest of laymen but I think this is correct. Once observed the superposition collapses to a definite state (as definite as possible; can’t know velocity and momentum both).

I think the comparison of classical “superposition” to quantum is just to create an analogy, and analogies are imperfect by their nature.

36

I feign no hypotheses as to what’s “really” going on; I don’t want to even pretend there is any meaning to this, beyond what is ultimately observable (and perhaps as inspiration for directions in which to generalize methods by which to make predictions about what is ultimately observable). I am not proposing that even in the classical case, we should think of the system being “really” in just one state, rather than the superposition. All I am saying is that the same calculus of superpositions can be harnessed to give reliable predictions in a similar way in that context, which is, for me, the most one can say about the truth of an abstract mathematical model of the world. But, anyway, let me ask, what kind of experimental data would support for you the answer being one way as opposed to another?

Incidentally, I’m curious if you read the link from this reply of mine to a post of yours from a thread we were recently in on similar matters. For me, it was very enlightening.

37

Heck, I don’t know, I’ve always wondered that myself. But it seems to be what all the books I’ve read insist on.

Yeah, I did read it, set it aside intending to read it again, and didn’t read it again.

I’ll get back to you, I hope.

Repeating that conversation again: Isn’t it supposed to be that the Bell’s Theorem stuff shows that the observational evidence is inconsistent with the idea that systems in a superposition are in some sense “actually” just in one of the component states or the other? I haven’t been able to understand how the observational evidence is supposed to be able to show that, but books by experts that I read seem to assure me that, somehow, the observational evidence does indeed accomplish that.

38

Maybe not. It looks like I’ve confused “hidden variable theories” with “local hidden variable theories,” and that Bell’s Theorem’s confirmation shows that local hidden variable theories can’t work, but says nothing about hidden variable theories in general. And if the article I linked to is right (which is not clear–there are a few red flags in the article that make me unsure about the authoritativeness of some of it) then hidden variable interpretations of QM can work. I guess as long as they’re not “local hidden variable” theories.

39

So when will I be able to buy my matter transporter, and how much will it cost*?
*Secretly, my plan is to buy it on credit and then transport all the gold out of Fort Knox to pay for it. Muahaha!

40

This has been discussed up-thread some but I think it bears being clarified.

I think many people have the sense that despite the Heisenberg Uncertainty Principle a particle has a definite position and a definite momentum. We may be blocked from knowing both with perfect precision but at the bottom of it all the particle is “there” and moving “that way” with a specific speed.

A superimposed state however turns that on its head. The particle is not “there”. It is, quite literally, “here” and “there” at the same time. This is most easily shown by the double-slit experiment. In a more complex fashion quantum computers have been built that exploit this feature.

I think this experiment is fascinating in that they took something we thought relegated to the ultra-tiny and brought it in to our “big” world. As mentioned up-thread what does it look like, now we can actually see it with our own eyes, to have something moving and not moving at the same time? Or, as mentioned, how does observing it collapse the wave-state so we only see one or the other? How does the object know the photon that bounced off it entered your eye and was “observed”?

Bringing this into the macro world, to me, re-opens these questions and highlights a point where science meets philosophy.