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Two-Photon Walk a Giant Leap For Quantum Computing
ElectricSteve writes "Research conducted at the University of Bristol means a number of quantum computing algorithms may soon be able to execute calculations of a complexity far beyond what today's computers allow us to do. The breakthrough involves the use of a specially designed optical chip to perform what's known as a 'quantum walk' with two particles ... and it suggests the era of quantum computing may be approaching faster than the scientific establishment had predicted. A random walk – a mathematical concept with useful applications in computer science – is the trajectory of an object taking successive steps in a random direction, be it over a line (with only two possible directions) or over a multi-dimensional space. A quantum walk is the same concept, but translated to the world of quantum computing, a field in which randomness plays a central role. Quantum walks form an essential part of many of the algorithms that make this new kind of computation so promising, including search algorithms that will perform exponentially faster than the ones we use today."
most software can't benefit from quantum logic...
Unless they perfect a neural interface.
I believe you mean until they perfect the neural interface. If the story is true, the neural interface seemed a lot closer to reality than practical quantum computing until about 3 mins ago.
I don't know how many years on this Earth I got left. I'm going to get real weird with it. - Frank Reynolds
But by looking you change where you are, so that doesn't work...
What does it mean a "one photon quantum walk"
Conceptually, no different from a "one-ball-in-the-maze random walk" - can have a single state.
...and what is the difference from any other kind of transformation that happens on a photon?
Again, no difference: the photons will random walk the maze independently (entanglement is not a requirement).
Also, what is the difference of "two-photon quantum walk" and normal interference?
a. Conceptual: while walking the maze (and solving your problem), the photons will be particles, thus interference is not an issue to consider.
b. The maze you make the photons walk through (instead of just two slits) should be programmable (model the system for which you want to compute the answer).
c. one may use interference at the end of "computation" to determine the probability of "maze exits" being chosen. This is why the extra requirement of "photons need to be identical" (when using them as waves to get the answer, one needs coherence).
Well, it may be a bit more complicated than that (i.e. one can have a single physical "exit" from the maze but different polarization states of the "balls"), but essentially the answer will come in "the experimentally determined superposition of quantum states after going through the quantum programmable maze").
Questions raise, answers kill. Raise questions to stay alive.
Because people always get it wrong every time a QC article hits slashdot, here's a link to my previous, highly-modded (upwards) post on QC:
http://slashdot.org/comments.pl?sid=1285849&cid=28520061
Quantum computers can do some cool things, but mostly solve problems no one cares much about (except a few of us mathematicians)
Summary is wrong. Quantum algorithms cannot provide "exponential" speedup of any problem. If they could, we would be able to [probably] solve NP-complete problems with quantum computers, and that hasn't been proven yet. The best they can do is "super-polynomial" speedup of classical algorithms.
Google "quantum algorithm zoo" to see all the known algorithms and their speedups (and how unexciting most of them are).
You can make general purpose quantum computers if you have a working set of "quantum gates" or similar -- much like you can make a general purpose classical computer if you have a working set of classical gates.
A quantum computer able to do useful classical computing (i.e., factoring large numbers) would have to have a large number of bits (512-1024, very far away by any metric). A quantum computer able to do simulations of quantum systems beyond what current supercomputers could do would have to have maybe 10 bits (maybe not too far away).
See the wikipedia link in the summary. It 'splains it.
Security is mostly a superstition... Avoiding danger is no safer in the long run than outright exposure. - Helen Keller
Come on, Scott Bakula was taking random quantum walks back in the late 80s, get with the times people!
Monstar L
Let me provide some context. This research group specializes in manufacturing arbitrary waveguide structures on chips, then coupling particular quantum states of light into them. The idea is to turn a large optical table worth of mirrors into a tiny chip. What they have done here, is allowed a two photon input state to interfere with itself in the waveguide structure.
While interesting technically, it isn't exactly a huge leap forward because the interaction is linear. What's needed for deterministic quantum computation with light is a very non-linear process. The waveguide structure can replace a large number of mirrors and compact the optics into a tiny space but, at the end of the day, mirrors aren't all that interesting for quantum computation. It is, however, worthwhile because of the impressive miniaturization and the technical challenge of working with quantum light in such tiny structures. A strong non-linear component will be needed for true optical quantum computation, but chips like these show a lot of promise for handling a lot of state preparation and measurement.
So if this is the future...where's my jet pack?