A "Photon Machine Gun" For Quantum Computers

An anonymous reader writes "Generating entangled photons in a reliable way is impossible right now, stalling the development of the optical quantum computers that would use entangled photons as quantum bits (qubits). Because entangled photons can only be produced at random — which takes time — the most powerful optical quantum computing device use only 6 qubits. UK and Israeli quantum physicists have designed a blueprint for a 'quantum machine gun' that fires out barrages of entangled photons on demand. They think within a few years this device will be built, and could lead to quantum computing using 20 to 30 qubits. Every additional qubit doubles the computing power, so these quantum computers could outperform any existing classical computer, the researchers say. The quantum machine gun is described as 'one of the most exciting theoretical proposals I've read in five years' by a leading quantum physicist." The research was published in Physical Review Letters earlier this month.

Comments

For certain problems.

[JorDan Clock]

Every additional qubit doubles the computing power, so these quantum computers could outperform any existing classical computer, the researchers say.

But only for probabilistic algorithms. It's not going to be faster at everything.

Re:For certain problems.

[Tablizer]

But only for probabilistic algorithms. It's not going to be faster at everything.

So Whpt if we occjsion?lly fl#p a fwe bits.
   

Qubit does not double power in traditional sense?

[religious freak]

Every additional qubit doubles the computing power, so these quantum computers could outperform any existing classical computer, the researchers say.

I thought that the "power doubling" was not in a traditional sense.. the qubit is fantastic at pattern matching and search functions, but no better than a classical computer for something like, say, a video game requiring finite mathematical calculations. I'd state this as a fact, because I've read this in at least a couple places, but seeing as how quantum physicists haunt this forum, I can't say I know as well as them. But this power is only useful in very specific circumstances, AFAIK.

Not particularly useful against an insurgency

[BadAnalogyGuy]

Israeli quantum physicists have designed a blueprint for a 'quantum machine gun'

In other news, Palestinian quantum physicists have designed shoulder-mounted quantum launchers and quantum vests in response.

Civilians are hopeful for peace and terrified for escalation of hostilities.

Re:Not particularly useful against an insurgency

[Shadow of Eternity]

Harmful harmful force? Dude i think you need to re-evaluate your worldview if you want to blame the group being constantly attacked and threatened with the explicit goal of genocide for everything wrong. The mere presence of jews in the middle east produces the reaction you see from Hamas and friends, whether or not Israel was officially a state would have fuck all to do with anything other than the success of those attempts at genocide.

Hell Hamas' own govt charter explicitly blames the jews (merchants of death) for everything from the french and russian revolutions to both world wars while outright demanding the death of every jew and anyone who refuses to participate in said genocide.

Re:Not particularly useful against an insurgency

[Shadow of Eternity]

So in other words you want them to do the exact opposite of the only thing keeping the number of rockets and mortars fired at Israeli (arab AND jew) civilian targets in the low to mid thousands rather than much higher.

What did we do with vietcong tunnels in vietnam? The ones used for moving and storing weapons and occasionally fired from. We demolished them. What does israel do with houses build on top of tunnels or used as weapons caches. They demolish them. If people don't want their house bulldozed all they need to do is say "No you cannot indiscriminately attack civilians from my house or store/transport the weapons you use to do that in/through my house."

As for the borders, wtf do you suggest they do? Just open them up for MORE weapons to get smuggled through?

The religious extremists in the region already HAVE a concrete and unarguable reason for doing what they do, it's called genocide. This has NOTHING to do with Israel as a state and everything to do with the fact that there are jews and christians (but mostly jews) over there that aren't dead yet. Read the Hamas charter sometime, the slaughter of all jews everywhere is listed as mandatory for the messiah to come in it. If you think anything Israel does has ANY bearing on anything the palestinians do you're delusional.

There's a palestinian couple living a few apartments away from me, do you know what he calls palestinians that don't want to kill all the jews? Israelis. Just like the million and a half arabs living in israel that are ALSO a target of palestinian violence because they don't join the genocidal crusade Hamas is currently leading.

no peeking

[RuBLed]

It's not going to be faster at everything.

It's going to be faster at everything.

Re:no peeking

[Anonymous Coward]

It's not going to be faster at everything.

It's going to be faster at everything.

It's going to be simultaneously faster and not faster at everything.

Re:no peeking

[Artifakt]

First, let's look at a fair attempt to explain why quantum indeterminacy is not just the same thing as classical indeterminacy (like your two particles, which by your question were presumably determinate in the classical model, at least until they became entangled). You seem to be reasoning much as the following note claims early quantum physicists tried to, when they first grappled with Heisenberg's uncertainty principle and the question of knowing the position and velocity of an electron simultaneously. I give you someone deliberately trying to put the concept in normal, natural language and not use any actual math:

http://www.uhh.hawaii.edu/~ronald/310/Quanta.htm

One point is, the interpretation that we can't know both position and velocity at the same instant, therefore the electron doesn't have both at the same instant, doesn't explain that thing you refer to as "with no regard to distance". This is what sometimes gets called "Spooky action" and is related to non-locality in general. Starting from the interpretation that it's not our not knowing that causes the indeterminacy but the indeterminacy which causes our not knowing turns out to be putting the horse back in front of the cart. Once people started working from the idea that the indeterminacy is fundamental and not like your example of the balls (where there is a definite color for each, and the observer just doesn't know it yet), they started making progress on figuring out how entanglement could be faster than light.

http://www.absoluteastronomy.com/topics/Quantum_indeterminacy

This is about what non-locality really means: One consequence is that we can't assign a local cause (such as: a localized observer hasn't looked yet) to explain why something on the quantum level is determinate, or we lose the ability to explain how the faster than light part happens.

Just as the original QM problem was about determining position and velocity, talking about "non-localizable" (position), and instantanious/faster than light (velocity) is two ends of the same stick. The more you prove that the action happens much faster than the limitation of light-speed, the more you can't claim the action is caused by anything in a particular locale.

ObCompJoke...

[Tastecicles]

imagine a Beowulf cluster of... NO! NONONO!

Re:Explain the hype, please?

[noundi]

Ok, so on this site bursting with intelligent, educated folk...

You lost me at "Ok".

Re:Explain the hype, please?

[maxwell demon]

Ok, I just wrote a lengthy reply, and then by accident hit "refresh", and all the text was gone :-(

Therefore here the short version:

• The speedup is basically because for quantum systems the dimension of the configuration space grows exponentially rather than linearly with the size of the system (i.e. number of qubits). The fact that we can't simply measure the complete state is actually a limitation, because it means we cannot directly access an arbitrary unknown state.
• You can do quantum computing by just doing measurements because every measurement modifies the measured system, and with entangled states, this change is non-local (i.e. you also modify parts of the system where you didn't just destroy any entanglement by your measurement). However you need special entangled states to do universal measurement-based quantum computing (i.e. to allow arbitrary transformations with measurement only); one state which works is the cluster state produced by this "photon machine gun"
• They didn't claim that qubits revolutionize storage, but that if emulating the 20 to 30 qubit quantum computer on a classical computer, it would not fit into computer storage. However I doubt that; storing the state of 30 qubits needs about 16 GB, which is large, but perfectly doable in todays computers (and may be actually standard by the time this photon gun is realized). The problem with simulating the quantum computer would not be storage, but time.

Re:Explain the hype, please?

[Anonymous Coward]

Bad analogy time.

The simplest way to factor a large number is to just try to divide it by 2, by 3, etc. Once you've divided it, you now have 2 smaller numbers to factor. Repeat until you get a prime. This takes a long time for a large number because you have to try it over and over again.

With a quantum computer you can do all of these computations in parallel, and then arrange for all of the non-factors to cancel each other out, meaning that you can only measure a legitimate factoring. (Getting all of the non-answers to cancel out is the trick in quantum computing, and it isn't a particularly easy one to pull off. These are not general purpose computers!) If it keeps giving you 1*n as your factoring, eventually you conclude it is prime. Otherwise the first time it gives you something else, you've broken the number down into 2 easier ones.

To break RSA you only have to factor one number. So everyone cites that as the classic problem. But you can't factor a number you can't put in. With 20-30 qbits you can only input 20-30 bit numbers so you can't factor anything bigger than that. By contrast a motivated person these days with a few PCs and a few months to devote to it can factor a general 600 bit number. Most people's codes are 1024 bits or longer.

Therefore this research is cool, but any claim of an immediate threat to cryptography is waaay overblown.

Dirty Erwin

[ciderVisor]

I know what you're thinking: "Did he flip six qbits or only five?" Well, to tell you the truth, in all this excitement I kind of lost track myself. But being as this is a Photon Machine Gun, the most powerful quantum entanglement source in the world, and would blow your head clean off, you've got to ask yourself one question: Is the cat dead or alive ? Well, is it, punk ?

Heh

[L4t3r4lu5]

The quantum machine gun is described as 'one of the most exciting theoretical proposals I've read in five years' by a leading quantum physicist.

The long winter nights must just fly by.