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Breakthrough for Quantum Measurement
said_captain_said_wo writes to tell us that PhysicsWeb is reporting that two teams of physicists have developed a new method for measuring the state of quantum bits in a quantum computer without disturbing the state. From the article: "In the future, the Josephson capacitance could be used for operations in a large-scale quantum computer," says Mika Sillanpaa of Helsinki University. "The Josephson inductance and Josephson capacitance together would also allow us to build new types of quantum 'band engineered' electronic devices, such as low-noise parametric amplifiers."
I'm not sure
> Wouldnt this violate the Heisenberg Uncertainty Principle?
Reading a qubit doesn't violate the Uncertainty Principle by itself; if qubits couldn't be read or written, they'd be worthless. The issue you are probably thinking of is that entanglements between qubits will be destroyed by the reading process (and there is no way to "read" such entanglements without destroying the individual qubit values).
I should clarify: reading the qubit will destroy all quantum effects (superposition as well as entanglement), effectively making the qubits look like ordinary bits (when you open the box, the cat's either dead or alive, not both). However, quantum computers are designed with this in mind; reading the output destroys any quantum properties it may have, but a computation can be repeated many times to get an idea of what uncertainty was present in the output.
Not to knock the discovery, which is very interesting, but it's a pity quantum computers have to be dragged into everything to justify research. I doubt that Tom's Hardware will be reviewing millikelvin coolers for your qubit box any time in the next 20 years (though I'd like to be proved wrong)
Pining for the fjords
Quantum computing is also good for solving problems in quantum mechanics. No, really.
In particular, something like rendering an environment in real-time won't be helped because there's an unpredictable input (the human).
Durring the 1/60th (or less) of a second that your system is rendering a single frame in that game, the state of the scene and all objects (as well as light positions, textures, and overlays) is very static. It just doesn't seem like it to you, because you are very slow compared to your computer.
There could be hundreds of applications of a Quantum Co-Processor in a game, from testing for occlusion in a 3D scene, to making AI decisions in computer controlled characters.
Quantum Computing may very well not be immediately useful in many traditional computation tasks ("While this value is true then do that") but it will open up whole new ways of tackling processes that are time consuming with today's methods ("do any of these things give us this, that, or something in between?").
Just thinking about it gives me that Fuzzy Logic Feeling...
"Everything you know is wrong. (And stupid.)"
Moderation Totals: Wrong=2, Stupid=3, Total=5.
They can do what they say, but it's a lot more trivial than measuring the entire quantum state of the system, which is, as others have suggested above, impossible.
The Heisenberg Unccertainty principle implies that measuring a quantity must add noise in the conjugate quantity. For example, measuring the momentum of an object spreads out the wavefunction. Another example, measuring the state of a qubit (whether it is a zero or a one) destroys the relative phase between the zero and the one.
So the "non-destructive" measurement they are talking about means that they aren't changing it from a zero to a one or vice-versa. But they are (and must) destroy the information about the phase of the qubit state during the measurement. For a more in-depth discussion, look up "quantum nondemolition measurements".
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Binaries may die but source code lives forever
I changed the article by reading it! Someone tell me what it says now...?
The uncertainty principle just states that you cannot know both ... in ... because you have interacted
... that IS its location ... or it is essentially .... you do not care.
... best I can do.
the position and momentum of a particle at the same time
other words you can know both but not precisely, if you know one
precisely you do not know the other
with it.
If you know that the particle is in a certain band, you do not need
to know its location
trapped
If you have your cow in a pasture, you do not care where it is, as
long as it is eating grass or hay in the pasture and how not escaped.
The statement without changing its value must refer to reading the value reliably. When reading the state of an individual subatomic particle it is extremely easy to have the result perturbed by noise. Given that there is a probability of reading an alternative value, then it is not normally possible to tell when the wrong value was read. It appears that this makes the process much more reliable.
IAAQP (I Am A Quantum Physicist). Though I could still learn a thing or two about subatomic physics.
presumably, given entanglement [wikipedia.org], measurement of qbit state allows potentially for instant communication ?
No, it doesn't. The closest you can come is instant synchronization of states, but you don't get to choose what state that is. For example, you can have two particles entangled to have the same (or opposite, as in the EPR thought experiment) spin orientation, but you can't send a signal from one to the other by choosing the orientation. Instead, it's random whether each one is spin up or spin down - the only guarantee is the relationship between the measurements. This would be great for things like cryptographic key exchange, since you can't have a man-in-the-middle attack if there is no middle, but it's useless for sending information. See: The No-Communication Theorem (warning: requires crazy math skills to avoid the MEGO effect)
nothing can travel faster than light.
I call bullshit. Relativity prohibits* local superluminal motion; non-locally, it's fair game. See, for example, the Alcubierre Warp Drive - the only question of whether it's possible or not (aside from new physics) rests on whether there's any local superluminal energy propagation at the edge of the spacetime bubble. Plus, QM allows for lots more in the way of non-local effects (even if you assume hidden variables, since Bell's Theorem rules out local hidden variables based on current experimental results), though, as I noted above, it still doesn't allow for superluminal communication (or teleportation, for that matter).
* Minor caveat: this is not counting tachyons, since nobody knows if they exist.
This is sqrt(not) a sig.