Quantum Computer Works Better Shut Off

waimate writes "A New Scientist article relates how its possible to get answers from a quantum computer even when your program isn't running." From the article: "With the right set-up, the theory suggested, the computer would sometimes get an answer out of the computer even though the program did not run. And now researchers from the University of Illinois at Urbana-Champaign have improved on the original design and built a non-running quantum computer that really works."

Comments

Gee whiz

[JPamplin]

Wish I could do that with my "real" PC - save alot of power that way. Hard to see the screen though. ;-)

Re:Gee whiz

[flyingsquid]

I'll admidt I really don't understand what the article is talking about, but I'm pretty sure it has something to do with Heisenberg's Uncertainty...

This sounds like zen buddhist computer science. Either that or something cooked up after a little too much of the green stuff. Still, makes me wonder. What kind of software do you run... erm, not run... on a computer that isn't running? Non-existent programs, like Duke Nukem Forever?

Hrm. That would open up a whole new industry. That'd be a fun profession, full-time vaporware programmer... hell, I'm gonna start right now. I'm officially announcing VaporWorks, an integrated word processor, spreadsheet, calendar and presentation software suite, not running on your computer in the near future. If anyone needs me, I'll be on the beach in Cancun spending my startup money, not busy working 16 hour days to get it ready.

Re:Gee whiz

[radtea]

I'll admidt I really don't understand what the article is talking about,

Neither did whoever wrote the article.

It works like this:

1) Define some classical terms, like "running" and "actually"
2) Apply them incorrectly to quantum situations
3) ob. ????
4) Profit!

The components of the photon wavefunction that are "not actually running the program" become entangled with the components of the photon wavefunction that "are actully running the program", and therefore they carry information regarding the state of those components.

If we think about this in classical terms, where we incorrectly and falsely imagine that each component of the wavefunction represents a classical trajectory through the apparatus, we could incorrectly and falsely say that photons that have not followed classical trajectories through the part of the apparatus that does the quantum computation have not run the program.

But the clear contradiction of that statement makes the slippery bullshit marketing-speak of the article clear: of course a photon that has followed any classical trajectory whatsoever has not run the quantum program. And to claim that "a photon whose wavefunction is entangled with the program has not run the program" too obviously has the same epistemological and moral status as giving away "free" products that only require a "small" processing fee to claim.

One is motivated to ask, "Why doesn't entanglement with the program state count as 'really' running the program? What is this 'real' thing you keep talking about?" Admittedly, entangling things in this way is a different way of running the program, and is really rather clever, but to promote the results in this way is just attention-grabbing marketing, unworthy of the name of science.

This kind of abuse of language is similar to that of the "quantum teleportation" folks, whose deliberately misleading claims often make it sound like something other than the ontologically-problematic quantum state is being "teleported."

Re:Gee whiz

[waxigloo]

First of all: Profit? These are university physicists, not a company trying to trick you into buying something. The most they profit will be a pat on the back from the physics community.

Second: you clearly don't understand the experiment, so why accuse the authors of 'bullshit marketing-speak'? 'On and Off' are not necesarily classical notions; the method to implement on and off is quite simple -- you just use a beamsplitter.

You also seem to have the impression that just because two photons are entangled, that they somehow talk to one another nonlocally. Well, this does not happen in this experiment because there is only ever a single photon, which has an amplitude to go towards the computer ('on') or not towards it ('off'). There is no way for the amplitude for 'on' to communicate with the amplitude for 'off'.

The point of the experiment is that by having the computer not run you can still gain information about which element of the database is the marked element. This effect can be enhanced by utilizing the quantum Zeno effect, which they describe in the Nature article and the supplementary material -- though they don't seem to perform the experiment with the Zeno enhancement, which is a shame.

As for teleportation: you need words to describe the situation you produce. I think the word teleportation is a perfectly good word to describe the effect of transferring the quantum state of a photon instantaneously. I think it is wrong to assume the Star Trek definition of transportation is the correct one. If you are confused by what experiments are actually showing: read the article or ask a physicist.

Re:Gee whiz

[Wilson_6500]

Too late. I hold the patent on all non-running software. You either must pay the monthly licensing fees for not running my software, or purchase and run my software, which itself requires the additional purchase of monthly update packages.

It just sleeps on it.

[SomeoneGotMyNick]

I sometimes get better answers to my own questions simply by sleeping on it.

Better when shut off!

[Rob T Firefly]

Neat! It's an updated Sinclair ZX-81!

and...

[jcostantino]

in unrelated news, my refrigerator light bulb works better with the door closed.

Misleading

[karvind]

Running in quantum computers is doing "unitary transformations" and doing measurements on them. So as the article claimed, it is not that you are not doing anything. The only way not to run "it" is by putting it in eigenstate of the system (as well completely isolate it from any external perturbations). If you put it in a mixed state - yes it will evolve with time and then when you do the measurement it will give you "a" eigen state with certain probability. So yes in the end you are still doing measurement which is equally important and consitutes "running" the computer.

Does anyone know what is new here ?

Re:Misleading

[tbo]

Disclaimer: IAAQIS (I Am A Quantum Information Scientist).

The actual journal article that New Scientist is referring to was just published: Nature 439 949. I'm not sure if that link will work if you're not at an institution that has a subscription, but you'll probably at least get to see an abstract.

A few bits of background: New Scientist's coverage of quantum information is sometimes horrible. Therefore, it's not surprising that the New Scientist article makes no sense but contains lots of exciting fluff. That said, these guys do have something interesting.

I skimmed through the Nature article, and it looks interesting. It's especially nice that they have an experimental implementation. Nonetheless, the bit about the quantum computer being "off" is just silly.

Here's a summary of how it works, stripped of some hyperbole and converted into something more like plain english (note: qubit means quantum bit).

(1) Create a "control qubit" and some output qubits, with the control qubit initially set to 0, which we will take to mean off.

(2) "Rotate" the control qubit into a superposition of 1 (on) and 0 (off), with most of the "amplitude" being for the 0 state (the qubit is mostly off)

(3) Apply whatever algorithm to the data and the output qubits, conditional on the control bit being on. (Note: we don't actually measure anything here--this is entirely a unitary operation).

(4) Perform a weak measurement on the output qubits, which has the effect of reducing the amplitude of the output qubits being in something other than their initial state (which can only happen if the control qubit was on and the algorithm was applied), since the amplitude for that was small to begin with.

(5) Repeat (2) - (4) N times, such that, if the output bits are unmodified after each algorithm application, you end up with the control qubit in the 1 (on) state. Otherwise, you get the 0 (off) state.

(6) Profit!

This is the simple version, in which you only get to learn whether the application of the algorithm to the data gives you the default output or not. There's a more sophisticated version in which you learn more about the data.

There are a few catches here. One is that N has to be reasonably large, or the probability of an "error" in step 4 becomes an issue (by error, I mean that the weak measurement gives us the wrong outcome). Specifically, the probability of an error is 1 - cos^2N (pi / 2N), which scales as O(N^(1-4N)). Fortunately, that is exponential suppression of error, which is pretty good scaling. Another catch is that their particular experimental implementation used a non-scalable encoding. This isn't a major issue, but it means we should wait for an experiment using a scalable encoding before we really break out the champagne.

Laziness...

[bwcarty]

I may appear lazy, but on a quantum level, I'm really quite busy.

In related news....

[Lxy]

Microsoft reported earlier today that Windows performs better with your PC shut off.

Re:In related news....

[slashname3]

Microsoft reported earlier today that Windows performs better with your PC shut off.

Funny, most users report the same thing.

The Next Step

[the eric conspiracy]

I can just see the next article - "Quantum Software Works Better Without A Computer".

And the followup:

"Quantum Software Works Better Before Writing the Code Than After Writing the Code".

Re:So how do we...

[leonardluen]

So how do we overclock it?

buy more cats

Re:Oh Great: Ultimate in quantum malware

[timster]

Yeah, I can see it now:

"You imbecile! You let that virus infect our systems!"
"But I didn't open the file!"
"Yes, but there was a 2 percent chance that you would have, so two percent of our data was affected... and included in that two percent was your entry in the payroll database. So I'm not firing you, but you won't be paid anymore."
"This sucks! I'm going to commit Schroedinger's Seppuku! You'll regret this when I walk in that door with my guts both spilling out and in my body!"

Re:Deep Thought...

[Noryungi]

The computer says the answer is 42.

All we need to do now is program the question...

Duh. The question was: "An African, or a European Swallow?".

Think about THAT for a second. ;-)

Re:Black Magic

[MindStalker]

If you read the description its not actually as wrong headed as it sounds, the whole "its not running" thing is really inacurate. Basically they have a "program" that does a database search, this "program" is actually physical hardware that is run by optics. They "ran" it by shooting a photon at it, but then blocking the photon before it entered the program thus it "not running". The trick is that properties of the photon continued into the program and it worked. This really isn't new news for anyone who has every dealt with the slit experiment or any number of experiments that show that photons can be in multiple places at once.

Schrodinger's programmer

[LandKurt]

If anyone needs me, I'll be on the beach in Cancun spending my startup money, not busy working 16 hour days to get it ready.

No, here's what you do. You build a shielded, sound proofed room with your computer workstation, a nice entertainment center, bar and comfy recliner. Then you seal yourself in the room so no one can tell what you're doing. Either you have the computer turned on and are hard at work programming or you're kicked back doing nothing enjoying yourself. Call it Schrodinger's programmer.

Now, if your computer is hooked up to the Zeno effect device described in the article, it should be able to read the results of your work whether you actually did it or not. This should usher in a revolution in work environment for programmers everywhere.

Nature

[Anonymous Coward]

From an article in Nature:

http://www.nature.com/news/2006/060220/full/060220 -10.html#B1

http://www.nature.com/nature/journal/v439/n7079/ab s/nature04523.html

New Underpants business model for success

[saskboy]

New business model:
1. Buy super quantum computer
2. ???
3. Profit!

We now know step 2. Shut the computer off and go for a long weekend.

This is an old result

[Expert Determination]

I remember swapping a few emails with the author of a paper on this about ten years ago. Essentially you can get the result of the computation and yet the computer that runs destructively interferes with itself so that it essentially it remains unchanged at the end of the computation.

But this doesn't buy you anything. Quantum computers are reversible meaning they use no energy. And the computer has to spend just as long "doing nothing" as it would have spent doing the computation. And your computer is still tied up "doing nothing". So it's basically useless.

IANAP, but I'll try to explain...

[SirBruce]

I am not a physicist, but I did spend a couple years in college studying it with an intent to become one, and I still maintain a layman's interest in the subject. Unfortunately, the math is beyond me. In any case, a lot of people are confused how this "works", and so I thought I'd try to help.

Someone else already posted an useful background URL with is a good place to start:
http://en.wikipedia.org/wiki/Elitzur-Vaidman_bomb- testing_problem

Basically, what you have here is something called "interaction-free measurement". Because of the quantum mechanics work, a particle's wavefunction evolves in a certain way over time, which then "collapses" when you measure it to something specific. How it evolves is not deterministic, but probabillistic. Because of this, you can set up a quantum system whereby when you place a certain object in it at a certain place, you can change the whole system given the nature of what you add to it.

In this case, you have a quantum computer composed of mirrors that runs on photons. The mirrors are pre-set in a certain configuration to run a certain "program". No electricity is needed to "run" the program; you just inject photons into it and it spits out results when you measure it.

What they've done here is then place that computer in a certain location in an existing quantum mechanical system, the one which the photon comes from. This photon is associated with its own set of mirrors and detectors, and because of where and how the computer is placed into it, it effects the larger system.

Thanks to QM, you can then tweak the exterior system so that the chances of a photon ever actually getting to the quantum computer are infinitessimally small. But because there's still a small chance, the very nature of the computer in that location allows you to determine the results it would generate, even though a photon never actually gets into it to "run" it.

So, it's not to misleading to say the program never actually "runs". And you could say the computer isn't "on", but since it's just a mechanical-optical construct it's always "on". More importantly, though, is that exactly where the "computer" is becomes blurred; while it's true that it's particular programming is self-contained, by hooking it up to the external quantum system, you're sort-of making it a part of the computer as well. The "work" is being done by the photons outside the computer; remove them and you don't get anything.

Wow, reading the above, I didn't really do a good job of explaining this at all. But basically, even though the quantum program never actually executes, you still need to create it, and you still need to put it in a certain spot so that its quantum effect on the world around it can still be measured, and from that, you can infer what the program would actually do.

Bruce

Dammit Bill (was Re:Gee whiz)

[Aumaden]

Get your ass back to Redmond!