<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"
	xmlns:content="http://purl.org/rss/1.0/modules/content/"
	xmlns:dc="http://purl.org/dc/elements/1.1/"
	xmlns:atom="http://www.w3.org/2005/Atom"
	xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
		>
<channel>
	<title>Comments on: Quantum Computing: Sorry, no speedup in solving linear systems</title>
	<atom:link href="http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/feed/" rel="self" type="application/rss+xml" />
	<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/</link>
	<description>The Trajectory of Technology</description>
	<lastBuildDate>Thu, 02 Feb 2012 01:15:20 +0000</lastBuildDate>
	<sy:updatePeriod>hourly</sy:updatePeriod>
	<sy:updateFrequency>1</sy:updateFrequency>
	<generator>http://wordpress.org/?v=3.2.1</generator>
	<item>
		<title>By: Aram Harrow</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-4525</link>
		<dc:creator>Aram Harrow</dc:creator>
		<pubDate>Tue, 06 Dec 2011 05:58:32 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-4525</guid>
		<description>I just came across this post, somewhat after the discussion has died down.  One small point I want to mention is that our arxiv post has a link to my email address, and my coauthors and I would have been happy to respond to any questions or criticisms you had about our paper.

Contrary to your claims, I think the original title is accurate.  Our algorithm indeed &quot;solves&quot; linear systems of equations, although the answer is output in the form of the amplitudes of a quantum state, not in the form of a list of numbers.  This is similar to the way in which MCMC methods find stationary distributions: they don&#039;t output a list of numbers corresponding to a probability distribution, but they output a sample.  In both cases, people may find solutions of this form unsatisfactory answers, in which case, it is possible to use these samples to estimate scalar functions of the solution.

This is made totally clear in our paper, and anyone who understands that our algorithm runs in o(N)  time should understand that we&#039;re not outputting a list of numbers: how could N numbers be output in O(log(N)) time?  (As you point out, our algorithm is only interesting if the input is also created in o(N) time.)  But because we wanted to avoid a potentially misleading impression, we changed the title to be more vague, so that people will only know what exactly we do with linear systems of equations by reading further into the paper.

As for the popular summaries of the article, probably they should have mentioned that there are many technical restrictions on the algorithm (related not only to the output, as you mention, but also the encoding of the input), that classical linear systems solvers are getting pretty close to linear time (and so our algorithm is only interesting with large, implicitly specified inputs), and that our algorithm relies on quantum computers which don&#039;t exist yet.  Probably the scientific press should generally be less optimistic in its tone.  But your pessimism goes too far in the other direction.

If you want a better model of press coverage, this article does a really good job:
http://www.nature.com/nphys/journal/v5/n12/abs/nphys1473.html</description>
		<content:encoded><![CDATA[<p>I just came across this post, somewhat after the discussion has died down.  One small point I want to mention is that our arxiv post has a link to my email address, and my coauthors and I would have been happy to respond to any questions or criticisms you had about our paper.</p>
<p>Contrary to your claims, I think the original title is accurate.  Our algorithm indeed &#8220;solves&#8221; linear systems of equations, although the answer is output in the form of the amplitudes of a quantum state, not in the form of a list of numbers.  This is similar to the way in which MCMC methods find stationary distributions: they don&#8217;t output a list of numbers corresponding to a probability distribution, but they output a sample.  In both cases, people may find solutions of this form unsatisfactory answers, in which case, it is possible to use these samples to estimate scalar functions of the solution.</p>
<p>This is made totally clear in our paper, and anyone who understands that our algorithm runs in o(N)  time should understand that we&#8217;re not outputting a list of numbers: how could N numbers be output in O(log(N)) time?  (As you point out, our algorithm is only interesting if the input is also created in o(N) time.)  But because we wanted to avoid a potentially misleading impression, we changed the title to be more vague, so that people will only know what exactly we do with linear systems of equations by reading further into the paper.</p>
<p>As for the popular summaries of the article, probably they should have mentioned that there are many technical restrictions on the algorithm (related not only to the output, as you mention, but also the encoding of the input), that classical linear systems solvers are getting pretty close to linear time (and so our algorithm is only interesting with large, implicitly specified inputs), and that our algorithm relies on quantum computers which don&#8217;t exist yet.  Probably the scientific press should generally be less optimistic in its tone.  But your pessimism goes too far in the other direction.</p>
<p>If you want a better model of press coverage, this article does a really good job:<br />
<a href="http://www.nature.com/nphys/journal/v5/n12/abs/nphys1473.html" rel="nofollow">http://www.nature.com/nphys/journal/v5/n12/abs/nphys1473.html</a></p>
]]></content:encoded>
	</item>
	<item>
		<title>By: meitnerium109</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-3300</link>
		<dc:creator>meitnerium109</dc:creator>
		<pubDate>Sat, 10 Apr 2010 19:03:26 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-3300</guid>
		<description>Even though the algorithm provides only an expectation value of some operator on the solution set vector,  the authors prove(via complexity-theory) that you can&#039;t have a classical algorithm as fast as this one(or a quantum algorithm faster than this one)  even if you want only a summary statistic of the solution(as provided by this algorithm). 

But yes, I totally agree with the point you make about misrepresentation.</description>
		<content:encoded><![CDATA[<p>Even though the algorithm provides only an expectation value of some operator on the solution set vector,  the authors prove(via complexity-theory) that you can&#8217;t have a classical algorithm as fast as this one(or a quantum algorithm faster than this one)  even if you want only a summary statistic of the solution(as provided by this algorithm). </p>
<p>But yes, I totally agree with the point you make about misrepresentation.</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: A young researcher</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2602</link>
		<dc:creator>A young researcher</dc:creator>
		<pubDate>Sat, 16 Jan 2010 13:53:23 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2602</guid>
		<description>Thank You Dr. Drexler for highlighting the rampant practice of &quot;distorting&quot; the results of scientific investigations while publicizing to the layman.

To be honest, i am currently a Ph.D. in Electrical Engineering. I was inspired many such &quot;flawed&quot; articles in popular press and decided to pursue quantum computation when i was an undergrad. Being young and naive i thought i could come up with another exponenitally faster quantum alogrithm! In the end i came up with a much simpler result which was published at WorldComp 2009 (where you were one of the keynote speakers) and infact realized the potential limitations of QC to solve a simple image processing problem and decided to move to another field.

It is then I once again came across the &quot;fancy&quot; news articles about Nanoelectronics and I came to USA and spent(loaned) 35,000$ to do my MS at a Top 10 school and realized that i reached a dead-end. No one knows where the research in Nanotube,nanowire or Graphene transistors is going! Looks like the industry will be still using CMOS in the near future.After my MS in so called Nanoelectronics, i did not get even a single job offer!! 

Having burnt my fingers, i moved to more traditional ECE fields like Computer Architecure, Parallel Programming and Computational Intelligence during my Ph.D. studies and doing reasonably well.

A lot of people underestimate the harm caused by such frivolous reporting of scientific research.It can seriously mislead the young and naive aspiring researchers who will be the Scientists of tomorrow.

It is very unfortunate that it has become very fashionable to use the buzzwords &#039;quantum&#039; and &#039;nano&#039; very indiscriminately even by some of the scientific community as a means to attract funding and attention!

I always thought Science was an objective pursuit but unfortunately human beings are creatures of emotions rather than logic!</description>
		<content:encoded><![CDATA[<p>Thank You Dr. Drexler for highlighting the rampant practice of &#8220;distorting&#8221; the results of scientific investigations while publicizing to the layman.</p>
<p>To be honest, i am currently a Ph.D. in Electrical Engineering. I was inspired many such &#8220;flawed&#8221; articles in popular press and decided to pursue quantum computation when i was an undergrad. Being young and naive i thought i could come up with another exponenitally faster quantum alogrithm! In the end i came up with a much simpler result which was published at WorldComp 2009 (where you were one of the keynote speakers) and infact realized the potential limitations of QC to solve a simple image processing problem and decided to move to another field.</p>
<p>It is then I once again came across the &#8220;fancy&#8221; news articles about Nanoelectronics and I came to USA and spent(loaned) 35,000$ to do my MS at a Top 10 school and realized that i reached a dead-end. No one knows where the research in Nanotube,nanowire or Graphene transistors is going! Looks like the industry will be still using CMOS in the near future.After my MS in so called Nanoelectronics, i did not get even a single job offer!! </p>
<p>Having burnt my fingers, i moved to more traditional ECE fields like Computer Architecure, Parallel Programming and Computational Intelligence during my Ph.D. studies and doing reasonably well.</p>
<p>A lot of people underestimate the harm caused by such frivolous reporting of scientific research.It can seriously mislead the young and naive aspiring researchers who will be the Scientists of tomorrow.</p>
<p>It is very unfortunate that it has become very fashionable to use the buzzwords &#8216;quantum&#8217; and &#8216;nano&#8217; very indiscriminately even by some of the scientific community as a means to attract funding and attention!</p>
<p>I always thought Science was an objective pursuit but unfortunately human beings are creatures of emotions rather than logic!</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: rrtucci</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2110</link>
		<dc:creator>rrtucci</dc:creator>
		<pubDate>Thu, 19 Nov 2009 16:47:25 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2110</guid>
		<description>Chris Phoenix:  For a quantum computer,  a floating-point number is obtained by measuring N qubits. Say $latex x_i$ is the measurement of qubit i, and you have 3 qubits, and let $latex x=0.x_1 x_2 x_3 = x_1/2 + x_2/4 + x_3/8$ be your floating point answer. If your algorithm is a good one, the x_i come out the same most of the times you repeat the experiment, but because of quantum noise, there is a probability that they won&#039;t come out the same. This is what I am calling the statistical error, as opposed to the floating point error, which is the error produced by rounding-off.</description>
		<content:encoded><![CDATA[<p>Chris Phoenix:  For a quantum computer,  a floating-point number is obtained by measuring N qubits. Say $latex x_i$ is the measurement of qubit i, and you have 3 qubits, and let $latex x=0.x_1 x_2 x_3 = x_1/2 + x_2/4 + x_3/8$ be your floating point answer. If your algorithm is a good one, the x_i come out the same most of the times you repeat the experiment, but because of quantum noise, there is a probability that they won&#8217;t come out the same. This is what I am calling the statistical error, as opposed to the floating point error, which is the error produced by rounding-off.</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: Chris Phoenix</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2096</link>
		<dc:creator>Chris Phoenix</dc:creator>
		<pubDate>Wed, 18 Nov 2009 09:44:21 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2096</guid>
		<description>Hey, I think you guys talked past each other. Drexler was talking about how to read out a floating-point value from a single qubit. If I understood him correctly, you have to read it lots of times (re-doing the computation each time) and average the 0&#039;s and 1&#039;s. In fact, 10^2n times for 10^n precision. And this is if the system is working perfectly, noise-free! 

rrtucci&#039;s last message seems to be talking about the effects of noise on the system, saying that continuous/quantum problems are the worst in terms of noise.

Although these are both true, I think they are completely different, and it sounds like you both think you were talking about the same issue.</description>
		<content:encoded><![CDATA[<p>Hey, I think you guys talked past each other. Drexler was talking about how to read out a floating-point value from a single qubit. If I understood him correctly, you have to read it lots of times (re-doing the computation each time) and average the 0&#8242;s and 1&#8242;s. In fact, 10^2n times for 10^n precision. And this is if the system is working perfectly, noise-free! </p>
<p>rrtucci&#8217;s last message seems to be talking about the effects of noise on the system, saying that continuous/quantum problems are the worst in terms of noise.</p>
<p>Although these are both true, I think they are completely different, and it sounds like you both think you were talking about the same issue.</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: Followup discussion of quantum information and science hype</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2094</link>
		<dc:creator>Followup discussion of quantum information and science hype</dc:creator>
		<pubDate>Tue, 17 Nov 2009 22:42:13 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2094</guid>
		<description>[...] can read the discussion here.   &#160;&#160;  [...]</description>
		<content:encoded><![CDATA[<p>[...] can read the discussion here.   &nbsp;&nbsp;  [...]</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: Eric Drexler</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2092</link>
		<dc:creator>Eric Drexler</dc:creator>
		<pubDate>Tue, 17 Nov 2009 19:57:19 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2092</guid>
		<description>An advantage of the Bayesian-network representation is that it doesn’t imply a full, chronological order of gate operations, unless this is also implied by causality. Thinking in terms of a formal, system-wide state vector between each pair of operations (even if these are on disjoint sets of qubits) results in multiple not-&lt;i&gt;obviously&lt;/i&gt;-equivalent representations for a single set of causal relationships.</description>
		<content:encoded><![CDATA[<p>An advantage of the Bayesian-network representation is that it doesn’t imply a full, chronological order of gate operations, unless this is also implied by causality. Thinking in terms of a formal, system-wide state vector between each pair of operations (even if these are on disjoint sets of qubits) results in multiple not-<i>obviously</i>-equivalent representations for a single set of causal relationships.</p>
]]></content:encoded>
	</item>
	<item>
		<title>By: rrtucci</title>
		<link>http://metamodern.com/2009/11/10/quantum-computing-sorry-no-speedup-in-solving-linear-systems/comment-page-1/#comment-2087</link>
		<dc:creator>rrtucci</dc:creator>
		<pubDate>Tue, 17 Nov 2009 04:49:27 +0000</pubDate>
		<guid isPermaLink="false">http://metamodern.com/?p=5642#comment-2087</guid>
		<description>What I call quantum Bayesian networks is a simple generalization of the definition of classical Bayesian networks to quantum mechanics. I believe that quantum Bayesian networks are a rich and useful way of looking at quantum mechanics, in the same way that classical Bayesian networks are a rich and useful way of looking at classical probability theory. (By the way, Koller-Friedman have recently published their much awaited and wonderful textbook on classical Bayesian networks). Quantum computerists can think of quantum Bayesian networks as an &lt;a href=&quot;http://qbnets.wordpress.com/2008/10/04/quantum-computation-notation-propaganda/&quot; rel=&quot;nofollow&quot;&gt; alternative way of drawing quantum circuits.&lt;/a&gt; 

Besides quantum Bayesian networks and independently of them, I use my blog to advocate for the use of quantum computers to do MCMC (Markov Chain Monte Carlo)

Let me call discrete problems (continuous problems, respectively) those whose set of possible answers is the natural numbers (real numbers, resp.). I believe both quantum and classical computers can produce statistical errors in their answers for both discrete and continuous problems. (Shor&#039;s algorithm, though it solves a discrete problem, has a finite probability of failing, but there is a high probability of success after only a small number of repetitions of the experiment.) In the case of classical computers, we don&#039;t normally worry about statistical errors (unless it&#039;s a Monte Carlo algorithm) because current classical computers make such errors only extremely rarely. (If you operate then in a friendly environment, that is. You must, of course, worry about statistical errors if the environment is unfriendly; for instance, if your classical computer is operating at a very high temperature, or if it&#039;s in outer space and exposed to very high levels of cosmic radiation.) Compared with classical computers, quantum computers have to contend with an additional and hard to handle source of statistical errors, namely quantum mechanical noise. One worries less about statistical errors for discrete problems (because the discreteness tends to filter out some of the noise) than for continuous problems, and less for classical computers than for quantum ones. Hence, you are right in your intuition of singling out as the worse possible scenario for statistical errors, that of solving a continuous problem on a quantum computer.</description>
		<content:encoded><![CDATA[<p>What I call quantum Bayesian networks is a simple generalization of the definition of classical Bayesian networks to quantum mechanics. I believe that quantum Bayesian networks are a rich and useful way of looking at quantum mechanics, in the same way that classical Bayesian networks are a rich and useful way of looking at classical probability theory. (By the way, Koller-Friedman have recently published their much awaited and wonderful textbook on classical Bayesian networks). Quantum computerists can think of quantum Bayesian networks as an <a href="http://qbnets.wordpress.com/2008/10/04/quantum-computation-notation-propaganda/" rel="nofollow"> alternative way of drawing quantum circuits.</a> </p>
<p>Besides quantum Bayesian networks and independently of them, I use my blog to advocate for the use of quantum computers to do MCMC (Markov Chain Monte Carlo)</p>
<p>Let me call discrete problems (continuous problems, respectively) those whose set of possible answers is the natural numbers (real numbers, resp.). I believe both quantum and classical computers can produce statistical errors in their answers for both discrete and continuous problems. (Shor&#8217;s algorithm, though it solves a discrete problem, has a finite probability of failing, but there is a high probability of success after only a small number of repetitions of the experiment.) In the case of classical computers, we don&#8217;t normally worry about statistical errors (unless it&#8217;s a Monte Carlo algorithm) because current classical computers make such errors only extremely rarely. (If you operate then in a friendly environment, that is. You must, of course, worry about statistical errors if the environment is unfriendly; for instance, if your classical computer is operating at a very high temperature, or if it&#8217;s in outer space and exposed to very high levels of cosmic radiation.) Compared with classical computers, quantum computers have to contend with an additional and hard to handle source of statistical errors, namely quantum mechanical noise. One worries less about statistical errors for discrete problems (because the discreteness tends to filter out some of the noise) than for continuous problems, and less for classical computers than for quantum ones. Hence, you are right in your intuition of singling out as the worse possible scenario for statistical errors, that of solving a continuous problem on a quantum computer.</p>
]]></content:encoded>
	</item>
</channel>
</rss>

