{"id":1255,"date":"2013-02-04T09:14:32","date_gmt":"2013-02-04T14:14:32","guid":{"rendered":"https:\/\/scottaaronson.blog\/?p=1255"},"modified":"2016-12-10T04:57:36","modified_gmt":"2016-12-10T09:57:36","slug":"collaborative-refutation","status":"publish","type":"post","link":"https:\/\/scottaaronson.blog\/?p=1255","title":{"rendered":"Collaborative Refutation"},"content":{"rendered":"

At least eight people—journalists, colleagues, blog readers—have now asked my opinion of a recent paper<\/a> by Ross Anderson and Robert Brady, entitled “Why quantum computing is hard and quantum cryptography is not provably secure.”\u00a0 Where to begin?<\/p>\n

    \n
  1. Based on a “soliton” model—which seems to be almost<\/em> a local-hidden-variable model, though not quite—the paper advances the prediction that quantum computation will never be possible with more than 3 or 4 qubits.\u00a0 (Where “3 or 4” are not just convenient small numbers, but actually arise from the geometry of spacetime.)\u00a0 I wonder: before uploading their paper, did the authors check whether their prediction was, y’know, already falsified<\/em>?\u00a0 How do they reconcile their proposal with (for example) the 8-qubit entanglement<\/a> observed by Haffner et al. with trapped ions—not to mention the famous experiments with superconducting Josephson junctions, buckyballs, and so forth that have demonstrated the reality of entanglement among many thousands of particles (albeit not yet in a “controllable” form)?<\/li>\n
  2. The paper also predicts that, even with 3 qubits, general entanglement will only be possible if the qubits are not collinear; with 4 qubits, general entanglement will only be possible if the qubits are not coplanar.\u00a0 Are the authors aware that, in ion-trap experiments (like those of David Wineland that recently won<\/a> the Nobel Prize), the qubits generally are<\/em> arranged in a line?\u00a0 See for example this paper<\/a>, whose abstract reads in part: “Here we experimentally demonstrate quantum error correction using three beryllium atomic-ion qubits confined to a linear, multi-zone trap.”<\/li>\n
  3. Finally, the paper argues that, because entanglement might not be a real phenomenon, the security of quantum key distribution remains an open question.\u00a0 Again: are the authors aware that the most practical QKD schemes, like BB84<\/a>, never use entanglement at all?\u00a0 And that therefore, even if the paper’s quasi-local-hidden-variable model were viable (which it’s not), it still<\/em> wouldn’t justify the claim in the title that “…quantum cryptography is not provably secure”?<\/li>\n<\/ol>\n

    Yeah, this paper is pretty uninformed even by the usual standards of attempted quantum-mechanics-overthrowings.\u00a0 Let me now offer three more general thoughts.<\/p>\n

    First thought: it’s ironic that I’m increasingly seeing eye-to-eye with Lubos Motl—who once called me “the most corrupt piece of moral trash”—in his rantings against the world’s “anti-quantum-mechanical crackpots.”\u00a0 Let me put it this way: David Deutsch, Chris Fuchs, Sheldon Goldstein, and Roger Penrose hold views about quantum mechanics that are diametrically opposed to one another’s.\u00a0 Yet each of these very different physicists has earned my admiration, because each, in his own way, is trying<\/em> to listen to whatever quantum mechanics is saying about how the world works.\u00a0 However, there are also people all of whose “thoughts” about quantum mechanics are motivated by the urge to plug their ears and shut out<\/em> whatever quantum mechanics is saying—to show how whatever na\u00efve ideas they had before learning QM might still be right, and how all the experiments of the last century that seem to indicate otherwise might still be wiggled around.\u00a0 Like monarchists or segregationists, these people have been consistently<\/em> on the losing side of history for generations—so it’s surprising, to someone like me, that they continue to show up totally unfazed and itching for battle, like the knight from Monty Python and the Holy Grail<\/em> with his arms and legs hacked off.\u00a0 (“Bell’s Theorem?\u00a0 Just a flesh wound!”)<\/p>\n

    Like any physical theory, of course<\/em> quantum mechanics might someday be superseded by an even deeper theory.\u00a0 If and when that happens, it will rank alongside Newton’s apple, Einstein’s elevator, and the discovery of QM itself among the great turning points in the history of physics.\u00a0 But it’s crucial to understand that that’s not what we’re discussing here.\u00a0 Here we’re discussing the possibility that quantum mechanics is wrong, not for some deep reason, but for a trivial<\/em> reason that was somehow overlooked since the 1920s—that there’s some simple classical model that would make everyone exclaim,\u00a0 “oh!\u00a0 well, I guess that whole framework of exponentially-large Hilbert space was completely superfluous, then.\u00a0 why did anyone ever imagine it was needed?”\u00a0 And the probability of that<\/em> is comparable to the probability that the Moon is made of Gruy\u00e8re.\u00a0 If you’re a Bayesian with a sane prior, stuff like this shouldn’t even register.<\/p>\n

    Second thought: this paper illustrates, better than any other I’ve seen, how despite appearances, the “quantum computing will clearly be practical in a few years!” camp and the “quantum computing is clearly impossible!” camp aren’t actually<\/em> opposed to each other.\u00a0 Instead, they’re simply two sides of the same coin.\u00a0 Anderson and Brady start from the “puzzling” fact that, despite what they call “the investment of tremendous funding resources worldwide” over the last decade, quantum computing still<\/em> hasn’t progressed beyond a few qubits, and propose to overthrow quantum mechanics as a way to resolve the puzzle.\u00a0 To me, this is like arguing in 1835 that, since Charles Babbage still<\/em> hasn’t succeeded in building a scalable classical computer, we need to rewrite the laws of physics in order to explain why classical computing is impossible.\u00a0 I.e., it’s a form of argument that only makes sense if you’ve adopted what one might call the “Hype Axiom”: the axiom that any technology that’s possible sometime<\/em> in the future, must in fact be possible within the next few years.<\/p>\n

    Third thought: it’s worth noting that, if (for example) you found Michel Dyakonov’s arguments against QC<\/a> (discussed on this blog a month ago) persuasive, then you shouldn’t<\/em> find Anderson’s and Brady’s persuasive, and vice versa.\u00a0 Dyakonov agrees that scalable QC will never work, but he ridicules<\/em> the idea that we’d need to modify quantum mechanics itself to explain why.\u00a0 Anderson and Brady, by contrast, are so eager to modify QM that they don’t mind contradicting a mountain of existing experiments.\u00a0 Indeed, the question occurs to me of whether there’s any<\/em> pair of quantum computing skeptics whose arguments for why QC can’t work are compatible with one another’s.\u00a0 (Maybe Alicki and Dyakonov?)<\/p>\n

    But enough of this.\u00a0 The truth is that, at this point in my life, I find it infinitely more interesting to watch my two-week-old daughter Lily, as she discovers the wonderful world of shapes, colors, sounds, and smells, than to watch Anderson and Brady, as they fail to discover the wonderful world of many-particle quantum mechanics.\u00a0 So I’m issuing an appeal to the quantum computing and information community.\u00a0 Please<\/em>, in the comments section of this post, explain what you thought of the Anderson-Brady paper.\u00a0 Don’t leave me alone to respond to this stuff; I don’t have the time or the energy.\u00a0 If you get quantum probability, then stand up and be measured!<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

    At least eight people—journalists, colleagues, blog readers—have now asked my opinion of a recent paper by Ross Anderson and Robert Brady, entitled “Why quantum computing is hard and quantum cryptography is not provably secure.”\u00a0 Where to begin? Based on a “soliton” model—which seems to be almost a local-hidden-variable model, though not quite—the paper advances the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"_wpas_customize_per_network":false,"jetpack_post_was_ever_published":false},"categories":[33,4,16],"tags":[],"class_list":["post-1255","post","type-post","status-publish","format-standard","hentry","category-bells-theorem-but-a-flesh-wound","category-quantum","category-rage-against-doofosity"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/1255","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1255"}],"version-history":[{"count":6,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/1255\/revisions"}],"predecessor-version":[{"id":3039,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/1255\/revisions\/3039"}],"wp:attachment":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1255"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1255"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1255"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}