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Is D-Wave a Quantum Computer?

Critics charge its not a "real" QC
5/14/2015 08:52 PM EDT
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John K Sellers
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512 qubits...really?
John K Sellers   6/8/2015 4:32:08 PM
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If an entanglement has 512 qubits, then it has about 1.34 times 10 raised to the 154 power superimposed states.

The real trouble is that quanitative scaling like that implies a qualitative change as well.

let us make clear what I mean by example.  If you have one horse, a saddle will work just fine.  But if you have 4 horses, 4 saddles aren't going to help you pull a wagon.  You need something else altogether.  

So what are you going to do to handle our 512 entangled qubits?  This may be too complicated to ever be able to manage.  The properties of an entaglement are holistic and do not reside in each qubit, but exist only as a whole.  You can't just look at a qubit and check off the state of each of its bits else it would be pretty straight forward to read out an answer.  What you will probably (pun intended) have to do since our only tool is statistics is gather enough samples to precisely charactgerize what is going on.  And those samples will not be in the conext of a qubit or a particular state, but will be in the context of so many states that it is impossible to count them all much less comprehensively examine them. 

So let me ask you a question, how many statistical samples would you have to have to characterize over 10 raised to the 154 power superimposed states?  And how easy would this be to do even assuming we could somehow gather such samples when our entanglement colapses every time we look at it?

Personally I don't think we will ever be able to do it.

 

 

R_Colin_Johnson
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Re: quantum analog computers
R_Colin_Johnson   5/18/2015 4:55:44 PM
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traneus: You may be more right than your most optimistic prediction. Most researchers are going after a "universal" quantum computer that could replace conventional computers, but D-Wave's application-specific version may already be the end-game. If companies built more-and-more application-specific quantum computers like D-Wave's, but aimed at different difficult problems today (such as linear speedups of massively parallel computers) the quantum computer may end up being like the GPU--an add-on accelerator speeding up the problems at which the multi-core solution performs poorly.

traneus
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quantum analog computers
traneus   5/18/2015 4:37:46 PM
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Quantum computers are analog computers: They use physical analogs of the desired functions to find their results. As such, quantum computers are limited by noise, outside interference and other manifestations of physical reality. This makes building large quantum computers very difficult.

Fifty and more years ago, classical analog computers were discussed more than they are now. We still build analog computers, though we seldom use the term: Every time we use an opamp, we are building an analog computer: The term "operational amplifier" came from the analog-computer world.

Large, fast quantum computers would be useful for certain classes of problems: Those where finding solutions requires exhaustive search of large data spaces, but where checking potential solutions for correctness is fast and easy. One example is Shor's algorithm for rapidly factoring large integers using a large quantum computer.

Present-day quantum computers are useful to graduate students as topics for master's and doctoral theses.

R_Colin_Johnson
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Re: a couple of basic questions
R_Colin_Johnson   5/15/2015 3:27:59 PM
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The qubits precision cannot be specified in coventional terms, and you are right about the typo using variable twice, I'll fix that now :)

DCH0
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a couple of basic questions
DCH0   5/15/2015 3:03:28 PM
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Forgive a couple of basic questions, but I suspect I am not the only one who is a bit overwhelmed by qubits.

"D-Wave's current quantum processor has 512 qubits, allowing it to solve optimization problems with less than or equal to 512 variables in single machine cycle."  How many bits are in a variable?  Does it use a number of processors equal to the number of bits?

From Colin's response on neural networks "Most neural network models use linear equations, where the variables are the constants are the synaptic values and the variables are the inputs from the problem being solved."  Was this a typo with variables being used twice?

R_Colin_Johnson
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Re: machine cycle
R_Colin_Johnson   5/15/2015 12:07:32 PM
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Your are right. Most neural network models use linear equations, where the constants are the synaptic values and the variables are the inputs from the problem being solved. Its hard to understand why D-Wave did not concentrate on that application from the beginning, but they claim to be hot-on-the-trail of neural network solutions now that they have been popularized as "deep learning".

dt_hayden
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Re: machine cycle
dt_hayden   5/15/2015 11:39:59 AM
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Colin,  I found the following info in a paper* on D:Wave site:  the computer returns ... 10,000 answers in one second.

Aftr reading the paper, it strikes me A LOT as the same principle as "neural networks" but implmented in a parallel computing fashion rahter than sequential.   The issue I have with my understanding or neural networks is that the system only works if "trained" on all possible data sets.  Perhaps the fact that quantum computing can perform each analysis in parallel rather than sequential, this is no big deal.

This is an interesting topic I am looking forward to understanding better.

 

* http://www.dwavesys.com/sites/default/files/Map%20Coloring%20WP2.pdf

R_Colin_Johnson
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Re: machine cycle
R_Colin_Johnson   5/15/2015 10:58:53 AM
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dt_hayden: Thanks for your comment. A machine cycle for a D-Wave computer begins by loading its qubits with the weights (mutipliers) of the variables in the linear equation, which perturbs it from its ground-state (lowest energy state), then waiting for it to settle into a new ground state, then read-out the values of the variables.

dt_hayden
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machine cycle
dt_hayden   5/15/2015 10:31:59 AM
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"allowing it to solve optimization problems with less than or equal to 512 variables in single machine cycle."

So what constitutes a machine cycle?

 

This is certainly a paradigm shift in thinking.  All I can equate it to in my mind is an analog computing process along the lines of "artificial intelligence" or "expert systems" which were fads of the past.  Not to say this is a fad.

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