Is Quantum Computing Hype or Reality?

[FactChecker]

"today is frequent the understanding that the wave function signifies that the particle is in all places at the same time, and quantum theory would make possible the creation on a computer capable of realizing simultaneously infinite mathematical operations".

Quantum computers may be feasible, I do not know, my interests in Physics are other, but the machines frequently announciated by the lay press that could make infinite mathematical operations at the same time, that evidently is not possible.

As far as I can see, you are the only one here talking about infinite mathematical operations. IBM is allowing public access to a 5 qubit computer. D-Wave Systems has made a 1k+ qubit computer. (Many prefer to call it quantum annealing, not computing, but that is another discussion.) In any case, it is very possible to imagine the eventual development of a 100 qubit IBM-type computer. Suppose that computer can come to a single-step solution to a problem with 2¹⁰⁰ possible combinations to consider. That is not infinite. Far from it. Still, a conventional computer that can check 1 gig combinations per second would require 4 trillion years to try all combinations. With average random luck, it might find the solution in 2 trillion years.

 

[GTOM]

It is obvious when a message has been decrypted correctly. It turns into sentences. This is an example where finding the right solution is much, much harder than verifying that it is correct.

Obvious if there is something that reads it. Just because something can enumerate 2¹⁰⁰combinations in a second, that doesn't mean, that something can check all theese solutions.
Of course if there are local minimums in a function, so it is not just random, but rather like a n dimension gradient, i can imagine that those particles reach some ground level and stay there.

 

[FactChecker]

Obvious if there is something that reads it. Just because something can enumerate 2¹⁰⁰combinations in a second, that doesn't mean, that something can check all theese solutions.

No. Sorry if I was not clear. It picks one out of 2¹⁰⁰ possibilities as the solution. There is only one combination that has to be checked. And checking that one is easy.

Of course if there are local minimums in a function, so it is not just random, but rather like a n dimension gradient, i can imagine that those particles reach some ground level and stay there.

I assume you are talking about quantum annealing. Aren't local minimums at a high energy level less likely to be confused as a global minimum?

 

[GTOM]

As far as I can see, you are the only one here talking about infinite mathematical operations. IBM is allowing public access to a 5 qubit computer. D-Wave Systems has made a 1k+ qubit computer. (Many prefer to call it quantum annealing, not computing, but that is another discussion.) In any case, it is very possible to imagine the eventual development of a 100 qubit IBM-type computer. Suppose that computer can come to a single-step solution to a problem with 2¹⁰⁰ possible combinations to consider. That is not infinite. Far from it. Still, a conventional computer that can check 1 gig combinations per second would require 4 trillion years to try all combinations. With average random luck, it might find the solution in 2 trillion years.

That is not infinite, only practically infinite...
Ok it that can run through 2¹⁰⁰ combinations in a second. How do you tell the particles, stop when you found something meaningful to US, and don't proceed to a bad combination? Those particles only understand things like spin and ground energy level.

 

[FactChecker]

That is not infinite, only practically infinite...
Ok it that can run through 2¹⁰⁰ combinations in a second. How do you tell the particles, stop when you found something meaningful to US, and don't proceed to a bad combination? Those particles only understand things like spin and ground energy level.

The computer has to be programmed so that the state it settles into is the solution of the problem. It's not really "running through" the possible combinations. The program must be set up to influence the computer so that it will settle directly into the right solution out of all the 2¹⁰⁰ possibilities.

 

[Telemachus]

Can somebody explain the technical difficulties and what means that the program has to be runned in one step? I imagine it has to do with the collapse of the wave function, one need to has the superposition of entangled states to have the qbits running, is that right? and what about decoherence? that has to do with the life time of the wave function in the superposition state?

It is not clear to me neither this thing of the 'one step'. What I'm going to say is perhaps just stupid, but if you can make an algorithm that arrives at the solution on only one step, why do you need a quantum computer to run it? because of the volume of data in the input?

 

[.Scott]

Can somebody explain the technical difficulties and what means that the program has to be runned in one step? I imagine it has to do with the collapse of the wave function, one need to has the superposition of entangled states to have the qbits running, is that right? and what about decoherence? that has to do with the life time of the wave function in the superposition state?

It is not clear to me neither this thing of the 'one step'. What I'm going to say is perhaps just stupid, but if you can make an algorithm that arrives at the solution on only one step, why do you need a quantum computer to run it? because of the volume of data in the input?

I suppose it's "one step" in the sense that you only read the inputs once. But actually, you probably need to perform the quantum operations many times to get a significant result.
When the term "one step" was used in the previous posts, I think it refers to a superposition that is being processed - not just a "position".
In fact, even the simplest quantum algorithms require a setup and a read - two steps. More often it's dozens of steps to set up the entanglements and quantum state before the system of qubits is "measured". Then there are other steps before and after the quantum processing to get the data into and out of the form used to set up the quantum state.

 

[FactChecker]

I suppose it's "one step" in the sense that you only read the inputs once. But actually, you probably need to perform the quantum operations many times to get a significant result.
When the term "one step" was used in the previous posts, I think it refers to a superposition that is being processed - not just a "position".
In fact, even the simplest quantum algorithms require a setup and a read - two steps. More often it's dozens of steps to set up the entanglements and quantum state before the system of qubits is "measured". Then there are other steps before and after the quantum processing to get the data into and out of the form used to set up the quantum state.

When I used the term "one step", I mean that it is not iterating through 2¹⁰⁰ possible combinations. Even if the quantum process includes several phases that take hours, that is much different from the billions of years it would take to iterate through all the combinations. There is work going on to develop error correcting methods for quantum computers that may greatly reduce the need to repeat the process. Everything about quantum computers is in its infancy now.

 

[Quotidian]

Nevertheless, when we have a dice in hand before we throw it the possibility of each face falling upside is one to six. In the moment it falls upon the table and immobilize, to us it's clear one can no more speak of probabilities, as one of the faces was defined. Its obvious, there is nothing mysterious in it, as even Einstein and Niels Bohr concurred.

This post was made some time ago, but I hadn't re-visited the thread. However, I believe this comment is incorrect. In the case of dice, we know that even before they are thrown, the dice actually exist, it is a matter of simple probability which way they will land. It is precisely this which is in question with respect to sub-atomic particles (so-called). Before the measurement is taken, it is not as if they're in some place or other, but we don't know where they are until the measurement is taken. The point is, they're not anywhere before the measurement is taken. They are in what is described as a 'super-position', which is not a particular location, but which is described by the wave function. They're nowhere in particular, not in some place we don't know, but not anywhere. But when they are measured, there they are! It is very freaky and a major outstanding issue in philosophy of physics.

With respect to your claim that 'there is nothing mysterious in it', you would do well to recall Bohr's warning that 'those who have not been shocked by quantum mechanics have not understood it'.

Furthermore, Einstein and Bohr did not concur on the major points of interpretation of these findings. They had fundamental disagreements as to the meaning of 'uncertainty' and it is a testimony to their character and maturity that their friendship remained strong regardless.

See https://amzn.com/1400079969 , by David Lindley,
https://amzn.com/0393339882 by Manjit Kumar

 

[FactChecker]

This post was made some time ago, but I hadn't re-visited the thread. However, I believe this comment is incorrect. In the case of dice, we know that even before they are thrown, the dice actually exist, it is a matter of simple probability which way they will land. It is precisely this which is in question with respect to sub-atomic particles (so-called). Before the measurement is taken, it is not as if they're in some place or other, but we don't know where they are until the measurement is taken. The point is, they're not anywhere before the measurement is taken.

I like @Tollendal's use of an unthrown die to represent an entity in multiple states with a probability distribution. We can look at the unthrown die conceptually, not as it's current position, but rather as something with the potential of having state 1..6. The act of throwing the die is like observing the state of qubits and it results in a collapsed state of one number.

 

[FactChecker]

Can somebody explain the technical difficulties and what means that the program has to be runned in one step? I imagine it has to do with the collapse of the wave function, one need to has the superposition of entangled states to have the qbits running, is that right? and what about decoherence? that has to do with the life time of the wave function in the superposition state?

I know that I have been guilty of using the confusing term "one step" to describe one instance of collapsing the entangled states of many qubits into one state. I should have said one execution of that process (with several steps).

It is not clear to me neither this thing of the 'one step'. What I'm going to say is perhaps just stupid, but if you can make an algorithm that arrives at the solution on only one step, why do you need a quantum computer to run it? because of the volume of data in the input?

Not the volume of inputs, but rather the enormous number of possible combinations of a relatively small number of binary logicals. We can imagine a problem where a traditional computer algorithm takes inputs of 100 binary states and must test if that combination is the unique solution to a puzzle (e.g. the precise key to decode a message). That is not a lot of inputs but finding the solution might require iterating through the 2¹⁰⁰ > 10²⁹ possible combinations till a solution is found. It would require billions of years for the fastest traditional computer to do it. A quantum computer with 100 entangled qubits could conceivably represent all 2¹⁰⁰ possible states at once and collapse to the solution in one execution of the process. Even if that requires hours and several steps, it is still possible. Getting all that to work is going to be very difficult, but the potential is enormous.

 

[Quotidian]

I like @Tollendal's use of an unthrown die to represent an entity in multiple states with a probability distribution. We can look at the unthrown die conceptually, not as it's current position, but rather as something with the potential of having state 1..6. The act of throwing the die is like observing the state of qubits and it results in a collapsed state of one number.

The problem with the 'unthrown die' image is that it is too concrete. It is simply rationalising the problem so as to make sense out of the highly unintuitive reality of the situation. A proper analogy would be more like, a cloud of vapour that turns into a die when it has landed.

 

[FactChecker]

The problem with the 'unthrown die' image is that it is too concrete. It is simply rationalising the problem so as to make sense out of the highly unintuitive reality of the situation. A proper analogy would be more like, a cloud of vapour that turns into a die when it has landed.

Ha! That's right. I like that.