Yale researchers 'teleport' a quantum gate | Hacker News Reader

Yale researchers 'teleport' a quantum gate

news.yale.edu

171 pointsvtomole31 comments

The article mentions that quantum computers are “an order of magnitude” faster than traditional computing. My understanding is that at the moment, this is incorrect: (noise-free) quantum computers are better at certain specific tasks, and otherwise, are no better than classical computers.

The article:

> Fully useful quantum computers have the potential to reach computation speeds that are orders of magnitude faster than today’s supercomputers.

It's not talking about the present, where IIUC quantum computers are basically useless for anything but research, not performing as well as classical computers because of noise and shortage of qubits.

Your understanding is correct.

The "order of magnitude" statement is completely false.

If we're talking about algorithmic complexity: for some algorithms quantum computers won't be any better than classical ones; for others, the improvement will be exponential, not multiplicative, say from O(eⁿ) to O(n).

If we're talking about actual performance, we have no idea, because there is no general purpose quantum computer yet.

So the mention of "orders of magnitude" belies a complete ignorance of the topic.

Quantum computers will likely be hybridized with classical computers, meaning classical computers will just become really good at processing quantum algorithms as well. It really wouldn’t make sense to have a purely classical or purely quantum computer at the point where both technologies are available.

I can imagine that once (if?) the technology becomes miniaturised enough, we'd end up with a "quantum card" alongside our sound and graphics cards, for specialised processing.

They seem to be costly enough to keep within temperature constraints that what that might actually look like is a quantum room at AWS or whoever that costs $x/hr to access.

Just FYI you're misusing "belies". You use it like "reveals" but it's meaning is closer to the opposite, more like "misrepresents" or "contradicts".

Ooops. Thanks

can anyone ELI5 what's the impact of this research?

Quantum computers are difficult to scale because of noise. Applying a quantum gate to a qubit using teleportation is a protocol for performing fault-tolerant quantum computation.

I don't know what 5 year olds you hang out with, but I think this would have gone over their heads ;)

On Hacker News everybody's five year old kids:

1. Configure and run their own Minecraft Server

2. Are fully proficient with the linux commandline

3. Are skilled in basic safe cracking techniques such as auto-dialling, weak point drilling, scoping and the use of brute force methodologies including the use of thermal lances (having acquired relevant Health and Safety accreditations).

And besides that they are on their third startup, have a blog, will debate the finer points of faking it until you make it with gusto, and are proficient in LISP, Rust and Elixir.

And will explain monads to their parents

Which is why we got them in the first place! Failure to contain I mean.

So did any of these five year olds notice this sentence?

> Using a theoretical protocol developed in the 1990s, Yale researchers experimentally demonstrated a quantum operation, or “gate,” without relying on any direct interaction.

They're basically saying it's magic. But no 5 year olds I hang out with are any good at magic yet.

Quantum teleportation is the transmission of a quantum state using an entangled pair and two classical bits. No magic needed.

It's a huge step for building the next generation of computers. Imagine you want to listen to your favorite music in a very busy street with lots of cars and people without headphones. Not very enjoyable. These guys figured out a way to suppress all noise with a special headphone. They move the information from your phone directly to your ears. That's obvious for you I suppose, but it was really hard to do that on vert very small scales these computers operate on.

I'm looking forward to the first quantum computer with hundreds or thousands of qubits, to see how the Many Worlds deniers explain its existence.

EXPLAIN?

Sorry, I was being too brief.

Basically, the equations of quantum Physics are fixed, but there are many ways to "interpret" or give meaning to them. The classical one, called Copenhagen, asserts a "wavefunction collapse" that would happen on ill-defined conditions, and is problematic as we find experimentally larger and larger quantum systems.

Another interpretation, Many Worlds (or its more mathematically rigorous form, Decoherence) does not introduce any new concept other than the basic quantum physics equations and has no problem with large systems. In fact, under the Decoherence / Many World interpretation, the entire universe is a single quantum system that has been evolving according to the wave functions since the beginning of time.

I've written more about it above.

wavefunction collapse? My (layman's) understanding is that the Many Worlds theory is just an explanation for why quantum mechanics appear non-deterministic, (that they actually are deterministic, just that branching universes are created for each outcome and our experiential continuum is in only one of them) rather than the assertion that they are non-deterministic.

Mostly, yes.

But "wavefunction collapse" is an ill-defined, non mathematical concept that will not stand the test of bigger and bigger quantum systems. See my more elaborate comment above.

(Disclaimer: I am not a physicist)

Probably they would just explain it with the normal Copenhagen interpretation?

https://en.wikipedia.org/wiki/Copenhagen_interpretation

In terms of quantum theory, the behaviour of a quantum computer is not fundamentally any different to the behaviour of any small scale particle or collection of particles.

Even buckyballs have been shown to self-interfere in a double-slit experiment, and that doesn't _prove_ multi-worlds over the Copenhagen interpretation.

https://web.archive.org/web/20120331115055/http://www.quantu...

There might be other philosophical reasons to believe in many-worlds, and I am partial to it myself, but experimental observation of this form would not to my understanding contribute to that argument.

They've gotten it a little bit bigger than a buckyball

https://arxiv.org/abs/1310.8343

Also what's cool is that these things are visible under an electron microscope (so are buckyballs iirc).

Excuse me? Collapse theories have a problem with large quantum systems. Many-World is fine.

Exactly my point. Collapse theories, in addition to the shady concept of "measurement", have a problem scaling to large systems. Many Worlds, or Decoherence, makes perfectly sense with any sized system.

Oh, I'm sorry. I've misread your comment.

No prob. Also, I'd love to read your thoughts on my longer reply above.

Here's a more in-depth explanation of what I mean.

When the formulas for Quantum Physics were discovered a century ago, they made little sense. You could not think of a photon or an electron, for instance, as being a "little billiard ball" anymore, but neither it was a classical wave as in sound waves.

For instance, the well-known double slit experiment shown that every single electron passes through both slits (otherwise there wouldn't be an interference pattern on the other side) but confusingly, when we "measure" the electron's position—that is, when any kind of sensor interacts with it—we only find it in one position. The result of the measurement is not deterministic, meaning there is a probability distribution on where we will find the electron, and it "prunes" any other path that was not measured, changing the results of the experiment, with respect to not measuring its position. This puzzled the scientists for the longest time.

After a century of scientific inquiry, what seems to be the case (to many physicists and to me—although IANAP) is that what we call "electron" is only an emergent phenomenon. What really exists underneath is the wave of "amplitude" (for lack of a better term) propagating through spacetime. Moreover, what's really real is not a single wave of amplitude for a single electron, but an amplitude distribution in the exponentially huge space of all possible waves / particles in the entire universe ("configurations").

A single particle with a definite position and momentum is not "real", it's just a partial, approximate multiplicative factor in this amplitude distribution. That is, in the space of all configurations (a huge-dimensional mathematical space) the amplitude distribution may approximately factor (multiplicatively) into 1. a particle being here and moving this way, and 2. everything else. When that happens, then we see it as a particle being definitely there and we can call it "particle A". But A has no physical reality, it's just an aspect of the amplitude distribution, and so may "disappear" and reappear in other places as the complex amplitude distribution evolves over time.

This explanation (or "interpretation") that gives physical reality to the amplitude distribution is called Decoherence and is the modern take on Everett's Many Worlds. It explains almost all observables, without introducing ill-defined, non mathematical concepts like a waveform collapse—which incidentally will not stand the test of bigger and bigger quantum systems, hence my comment.

The only observable which is still not explained are the Born probabilities. But they are likely to be a byproduct of another emergent system, that which we call "consciousness".

For example, when the amplitude distribution does not factor anymore into A times everything else, but there is A_1 going left and A_2 going right, why do I find myself in one of those two sub-distributions with probability that depends on the sum of the squares of the amplitudes of each wave? Currently there is no physical explanation for it. The formulas don't event mention "you", obviously. It's possible that if/when we find out what consciousness is (what "you" is), it will also be apparent why the Born probabilities appear as they do.

If anybody is interested in more of this, or if my explanation was lacking (very likely), I highly recommend The Quantum Physics Sequence by Eliezer Yudkowsky:

https://www.lesswrong.com/posts/hc9Eg6erp6hk9bWhn/the-quantu...

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