Comments on: Quantum computing for everyone http://michaelnielsen.org/blog/quantum-computing-for-everyone/ Mon, 07 May 2012 21:35:26 +0000 hourly 1 http://wordpress.org/?v=3.3 By: Ivo Rutten http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-36449 Ivo Rutten Mon, 30 Apr 2012 09:09:02 +0000 http://michaelnielsen.org/blog/?p=459#comment-36449 Further to the above, I spotted a few typo's that make things confusing, here is the text improved: ___________ Thank you for your courageous attempt to explain what a QC is like. I -however- got stuck with the following, and this nags me too much to be able to follow the rest: You state a 20-bit conventional ‘computer’ can be described in 20 numbers, and a 20-qubit QC needs 2^20 numbers to be fully described. ….but that is not right, is it? Even if the conventional (binary) computer were to consist of nothing more than 20 flipflops (which it doesn’t, it consists of millions of them), even then the group of 20 flipflops can be in any of 2^20 states. Of course these 2^20th states could each be given a number, and to do that one -indeed- needs 20 binary digits only. My point is: I do not get why this is different in a QC with -say- 20 of them berylium atoms? It would imply a single of these atoms can have two states, and if you bring two of them together the pair could have more than 4 states, where the proximity triggers the emergence of the extra ones, correct? If I try to follow your description, we would need 2^2=4 numbers to describe the state of two atoms….are those numbers not 00, 01, 10 and 11, then? Or do you mean to say that a single Qubit (a qubit in a group of 1 can have 2 states), and each qubit in a group of 2 can have 4 individual states, so that the group of two can have not 2^2 but 4^2 states?? If the latter is what you mean, an QC -unlike a binary cc, has a double exponential growth of states: an n-flipflop binary CC can be in any of 2^n states, and an n-qubit QC can then be in any of (2^n)^n states. Anyhow..I’m confused, as may be obvious from the above. Would love your clarification, thanks in advance. Ivo. Further to the above, I spotted a few typo’s that make things confusing, here is the text improved:
___________
Thank you for your courageous attempt to explain what a QC is like. I -however- got stuck with the following, and this nags me too much to be able to follow the rest:

You state a 20-bit conventional ‘computer’ can be described in 20 numbers, and a 20-qubit QC needs 2^20 numbers to be fully described.

….but that is not right, is it? Even if the conventional (binary) computer were to consist of nothing more than 20 flipflops (which it doesn’t, it consists of millions of them), even then the group of 20 flipflops can be in any of 2^20 states. Of course these 2^20th states could each be given a number, and to do that one -indeed- needs 20 binary digits only.

My point is: I do not get why this is different in a QC with -say- 20 of them berylium atoms? It would imply a single of these atoms can have two states, and if you bring two of them together the pair could have more than 4 states, where the proximity triggers the emergence of the extra ones, correct?

If I try to follow your description, we would need 2^2=4 numbers to describe the state of two atoms….are those numbers not 00, 01, 10 and 11, then? Or do you mean to say that a single Qubit (a qubit in a group of 1 can have 2 states), and each qubit in a group of 2 can have 4 individual states, so that the group of two can have not 2^2 but 4^2 states??

If the latter is what you mean, an QC -unlike a binary cc, has a double exponential growth of states: an n-flipflop binary CC can be in any of 2^n states, and an n-qubit QC can then be in any of (2^n)^n states.

Anyhow..I’m confused, as may be obvious from the above. Would love your clarification, thanks in advance.

Ivo.

]]> By: Ivo Rutten http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-36448 Ivo Rutten Mon, 30 Apr 2012 09:03:24 +0000 http://michaelnielsen.org/blog/?p=459#comment-36448 Dear Dr. Nielsen, Thank ou for your courageous attempt to explain what a QC is like. I -however- got stuck with the following, and this nags me too much to be able to follow the rest: You state a 20-bit conventional 'computer' can be described in 20 numbers, and a 20-qubit QC needs 2^20 numbers ....but that is not right, is it? Even if the conventional computer were to consist of nothing more than 20 flipflops (which it doesn't, it consists of millions of them), even then the group of 20 flipflops can be in any of 2^20 states. Of course these 2^20th states could each be given a number, and to do that one -indeed- needs 20 binary digits only. My point is: I do not get why this is different in a QC with -say- 20 of them berylium atoms? It would imply a single of these atoms can have two states, and if you bring two of them together the pair could have more than 4 states, where the proximity triggers the emergence of the extra ones. If I try to follow your description, we would need 2^2=4 numbers to describe the state of two atoms....are those numbers not 00, 01, 10 and 11, then?, or do you mean to say that each Qubit in a group of 1 can have 2 states, and each qubit in a group can have 4 individual states, so that the group of two can have not 2^2 but 4^2 states?? If the latter is what you mean, an QC -unlike a binary cc, has a duble exponential growth of states: a n flipflop binary CC can be in any of 2^n states, and an n-qubit QC can be in any of (2^n)n states. Anyhow..I'm confused, as may be obvious from the above. Would love your clarification, thanks in advance. Ivo. Dear Dr. Nielsen,

Thank ou for your courageous attempt to explain what a QC is like. I -however- got stuck with the following, and this nags me too much to be able to follow the rest:

You state a 20-bit conventional ‘computer’ can be described in 20 numbers, and a 20-qubit QC needs 2^20 numbers

….but that is not right, is it? Even if the conventional computer were to consist of nothing more than 20 flipflops (which it doesn’t, it consists of millions of them), even then the group of 20 flipflops can be in any of 2^20 states. Of course these 2^20th states could each be given a number, and to do that one -indeed- needs 20 binary digits only.

My point is: I do not get why this is different in a QC with -say- 20 of them berylium atoms? It would imply a single of these atoms can have two states, and if you bring two of them together the pair could have more than 4 states, where the proximity triggers the emergence of the extra ones.

If I try to follow your description, we would need 2^2=4 numbers to describe the state of two atoms….are those numbers not 00, 01, 10 and 11, then?, or do you mean to say that each Qubit in a group of 1 can have 2 states, and each qubit in a group can have 4 individual states, so that the group of two can have not 2^2 but 4^2 states??

If the latter is what you mean, an QC -unlike a binary cc, has a duble exponential growth of states: a n flipflop binary CC can be in any of 2^n states, and an n-qubit QC can be in any of (2^n)n states.

Anyhow..I’m confused, as may be obvious from the above. Would love your clarification, thanks in advance.

Ivo.

]]> By: Urock http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-36378 Urock Wed, 18 Apr 2012 16:32:53 +0000 http://michaelnielsen.org/blog/?p=459#comment-36378 Would a decent comparison be a vinyl record that uses natural mechanics and has no numerical values of sound compared to a cd with a digital, numerical representation of what used to be a smooth continuous sound wave? You can get pretty close with a cd, and using a higher bit and sample rate (aka, stronger computer) gives you a more refined version of the soundwave, but you can still zoom in and see jagged edges to the wave no matter how refined you go, whereas the analogue piece of vinyl is a pure wave which really represents what actually happened (or will happen) ... Still don't know how you would actually apply the quantum computer to a real life situation, it seems to be a tool to measure itself, like a magic 8 ball Would a decent comparison be a vinyl record that uses natural mechanics and has no numerical values of sound compared to a cd with a digital, numerical representation of what used to be a smooth continuous sound wave? You can get pretty close with a cd, and using a higher bit and sample rate (aka, stronger computer) gives you a more refined version of the soundwave, but you can still zoom in and see jagged edges to the wave no matter how refined you go, whereas the analogue piece of vinyl is a pure wave which really represents what actually happened (or will happen) …
Still don’t know how you would actually apply the quantum computer to a real life situation, it seems to be a tool to measure itself, like a magic 8 ball

]]> By: Michael Nielsen http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-36041 Michael Nielsen Wed, 07 Mar 2012 11:01:32 +0000 http://michaelnielsen.org/blog/?p=459#comment-36041 Thanks - turns out the superscript and subscript tags were there, but a bug in my Wordpress theme meant they did not display. I've fixed the bug. Thanks – turns out the superscript and subscript tags were there, but a bug in my WordPress theme meant they did not display. I’ve fixed the bug.

]]> By: rbrtw http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-35989 rbrtw Tue, 28 Feb 2012 08:26:44 +0000 http://michaelnielsen.org/blog/?p=459#comment-35989 <i>For example, when n = 300, 2n is larger than the number of atoms in the Universe</i> You really need a superscript tag or ^ here. For example, when n = 300, 2n is larger than the number of atoms in the Universe

You really need a superscript tag or ^ here.

]]> By: hamed.edalati http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-27068 hamed.edalati Tue, 21 Sep 2010 15:02:44 +0000 http://michaelnielsen.org/blog/?p=459#comment-27068 how can i get an quantum simulator? for example for simulation TSP in an quantum way. how can i get an quantum simulator?
for example for simulation TSP in an quantum way.

]]> By: Tor http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-27036 Tor Tue, 24 Aug 2010 23:49:30 +0000 http://michaelnielsen.org/blog/?p=459#comment-27036 Great post, and well written. I was looking for information on quantum computers on the net, and this article made things a bit clearer, and explained things I haven't found explained in the other articles or videos I found. Read some of your other posts, and they were interesting as well. Great post, and well written. I was looking for information on quantum computers on the net, and this article made things a bit clearer, and explained things I haven’t found explained in the other articles or videos I found. Read some of your other posts, and they were interesting as well.

]]> By: Alexander http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-26562 Alexander Wed, 16 Dec 2009 17:16:43 +0000 http://michaelnielsen.org/blog/?p=459#comment-26562 Do You know any application of quantum games or quantum random walks in finance ? Do You know any application of quantum games or quantum random walks in finance ?

]]> By: Ali Fasihi http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-26554 Ali Fasihi Sat, 12 Dec 2009 04:44:15 +0000 http://michaelnielsen.org/blog/?p=459#comment-26554 Dear Prof.Nielsen, Thanks a lot for your beutiful book. Please let me know do you have the solution for the problem of your book "Quantum information and quantum computation"? In case you have I would very appreciate if you possibly let me know how can I get it. Sincerely your, Fasihi Dear Prof.Nielsen,

Thanks a lot for your beutiful book.
Please let me know do you have the solution for the problem of your book “Quantum information and quantum computation”?
In case you have I would very appreciate if you possibly let me know how can I get it.

Sincerely your,
Fasihi

]]> By: Alexander http://michaelnielsen.org/blog/quantum-computing-for-everyone/comment-page-1/#comment-26503 Alexander Fri, 27 Nov 2009 23:50:34 +0000 http://michaelnielsen.org/blog/?p=459#comment-26503 May I ask do quantum games reflect the process of evoultion ? May I ask do quantum games reflect the process of evoultion ?

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