{"id":166509,"date":"2018-11-06T17:21:01","date_gmt":"2018-11-07T01:21:01","guid":{"rendered":"https:\/\/www.microsoft.com\/en-us\/research\/msr-research-item\/efficient-synthesis-of-universal-repeat-until-success-circuits\/"},"modified":"2018-11-06T17:21:01","modified_gmt":"2018-11-07T01:21:01","slug":"efficient-synthesis-of-universal-repeat-until-success-circuits","status":"publish","type":"msr-research-item","link":"https:\/\/www.microsoft.com\/en-us\/research\/publication\/efficient-synthesis-of-universal-repeat-until-success-circuits\/","title":{"rendered":"Efficient Synthesis of Universal Repeat-Until-Success Quantum Circuits"},"content":{"rendered":"<div class=\"asset-content\">\n<p>Recently it was shown that the resources required to implement unitary operations on a quantum computer can be reduced by using probabilistic quantum circuits called repeat-until-success (RUS) circuits. However, the previously best-known algorithm to synthesize a RUS circuit for a given target unitary requires exponential classical runtime. We present a probabilistically polynomial-time algorithm to synthesize a RUS circuit to approximate any given single-qubit unitary to precision <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-1-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-1\" class=\"math\"><span id=\"MathJax-Span-2\" class=\"mrow\"><span id=\"MathJax-Span-3\" class=\"mi\">\u03f5<\/span><\/span><\/span><\/span><\/span> over the <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-2-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-4\" class=\"math\"><span id=\"MathJax-Span-5\" class=\"mrow\"><span id=\"MathJax-Span-6\" class=\"mrow\"><span id=\"MathJax-Span-7\" class=\"mtext\">Clifford<\/span><span id=\"MathJax-Span-8\" class=\"mo\">+<\/span><span id=\"MathJax-Span-9\" class=\"mi\">T<\/span><\/span><\/span><\/span><\/span><\/span> basis. Surprisingly, the <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-3-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-10\" class=\"math\"><span id=\"MathJax-Span-11\" class=\"mrow\"><span id=\"MathJax-Span-12\" class=\"mi\">T<\/span><\/span><\/span><\/span><\/span> count of the synthesized RUS circuit surpasses the theoretical lower bound of <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-4-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-13\" class=\"math\"><span id=\"MathJax-Span-14\" class=\"mrow\"><span id=\"MathJax-Span-15\" class=\"mrow\"><span id=\"MathJax-Span-16\" class=\"mn\">3<\/span><span id=\"MathJax-Span-17\" class=\"mtext\">\u2009<\/span><span id=\"MathJax-Span-18\" class=\"msub\"><span id=\"MathJax-Span-19\" class=\"mrow\"><span id=\"MathJax-Span-20\" class=\"mi\">log<\/span><\/span><span id=\"MathJax-Span-21\" class=\"mrow\"><span id=\"MathJax-Span-22\" class=\"mn\">2<\/span><\/span><\/span><span id=\"MathJax-Span-23\" class=\"mo\">(<\/span><span id=\"MathJax-Span-24\" class=\"mn\">1<\/span><span id=\"MathJax-Span-25\" class=\"mo\">\/<\/span><span id=\"MathJax-Span-26\" class=\"mi\">\u03f5<\/span><span id=\"MathJax-Span-27\" class=\"mo\">)<\/span><\/span><\/span><\/span><\/span><\/span> that holds for purely unitary single-qubit circuit decomposition. By taking advantage of measurement and an ancilla qubit, RUS circuits achieve an expected <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-5-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-28\" class=\"math\"><span id=\"MathJax-Span-29\" class=\"mrow\"><span id=\"MathJax-Span-30\" class=\"mi\">T<\/span><\/span><\/span><\/span><\/span> count of <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-6-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-31\" class=\"math\"><span id=\"MathJax-Span-32\" class=\"mrow\"><span id=\"MathJax-Span-33\" class=\"mrow\"><span id=\"MathJax-Span-34\" class=\"mn\">1.15<\/span><span id=\"MathJax-Span-35\" class=\"mtext\">\u2009<\/span><span id=\"MathJax-Span-36\" class=\"msub\"><span id=\"MathJax-Span-37\" class=\"mrow\"><span id=\"MathJax-Span-38\" class=\"mi\">log<\/span><\/span><span id=\"MathJax-Span-39\" class=\"mrow\"><span id=\"MathJax-Span-40\" class=\"mn\">2<\/span><\/span><\/span><span id=\"MathJax-Span-41\" class=\"mo\">(<\/span><span id=\"MathJax-Span-42\" class=\"mn\">1<\/span><span id=\"MathJax-Span-43\" class=\"mo\">\/<\/span><span id=\"MathJax-Span-44\" class=\"mi\">\u03f5<\/span><span id=\"MathJax-Span-45\" class=\"mo\">)<\/span><\/span><\/span><\/span><\/span><\/span> for single-qubit <span class=\"aps-inline-formula\"><span id=\"MathJax-Element-7-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-46\" class=\"math\"><span id=\"MathJax-Span-47\" class=\"mrow\"><span id=\"MathJax-Span-48\" class=\"mi\">z<\/span><\/span><\/span><\/span><\/span> rotations. Our method leverages the fact that the set of unitaries implementable by RUS protocols has a higher density in the space of all unitaries compared to the density of purely unitary implementations.<\/p>\n<\/div>\n<p><!-- .asset-content --><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Recently it was shown that the resources required to implement unitary operations on a quantum computer can be reduced by using probabilistic quantum circuits called repeat-until-success (RUS) circuits. However, the previously best-known algorithm to synthesize a RUS circuit for a given target unitary requires exponential classical runtime. We present a probabilistically polynomial-time algorithm to synthesize [&hellip;]<\/p>\n","protected":false},"featured_media":0,"template":"","meta":{"msr-url-field":"","msr-podcast-episode":"","msrModifiedDate":"","msrModifiedDateEnabled":false,"ep_exclude_from_search":false,"_classifai_error":"","msr-author-ordering":null,"msr_publishername":"APS","msr_publisher_other":"","msr_booktitle":"","msr_chapter":"","msr_edition":"","msr_editors":"","msr_how_published":"","msr_isbn":"","msr_issue":"","msr_journal":"Physical Review Letters","msr_number":"","msr_organization":"","msr_pages_string":"080502","msr_page_range_start":"80502","msr_page_range_end":"","msr_series":"","msr_volume":"114","msr_copyright":"","msr_conference_name":"","msr_doi":"10.1103\/PhysRevLett.114.080502","msr_arxiv_id":"","msr_s2_paper_id":"","msr_mag_id":"","msr_pubmed_id":"","msr_other_authors":"Krysta M. 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