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        <title>A Quantum Approximate Optimization Algorithm</title>
        <author>Edward Farhi</author>
        <author>Jeffrey Goldstone</author>
        <author>Sam Gutmann</author>
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        <bibl>
          <title>A Quantum Approximate Optimization Algorithm</title>
          <date>2014</date>
          <publisher>arXiv</publisher>
          
          <idno type="arXiv">1411.4028</idno>
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        <label>method</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>approximate solutions to combinatorial optimization problems</label>
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        <label>mathematical-proof</label>
        <term>mathematical-proof</term>
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        <term>THE WHOLE ALGORITHM IS ONE INTEGER KNOB: the state is built by alternating two operators p times over a uniform starting superposition, and the paper&#x27;s claim is that the quality of the approximation improves as p is raised</term>
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        <term>the first operator is made diagonal in the computational basis, which buys two things at once - every term in the product COMMUTES, and each term&#x27;s locality is no worse than the locality of the clause it came from</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <term>THE PARAMETER RANGE IS DERIVED FROM A PROPERTY OF THE OBJECTIVE, NOT CHOSEN: because the objective has integer eigenvalues, one angle can be restricted to lie between 0 and 2 pi</term>
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        <term>MONOTONICITY IS STRUCTURAL RATHER THAN EMPIRICAL: the maximisation at p minus one IS a constrained maximisation at p, so the best value at each depth can never fall below the best value at the depth beneath it</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <term>the algorithm is used by repetition rather than by a single shot: measure in the computational basis, evaluate the objective on the string obtained, and repeat with the SAME angles - enough repetitions produce a string whose value is very near or above the expectation</term>
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        <term>the authors name the difficulty rather than presenting the method as complete - it is not obvious in advance how to pick good angles - and for p that does not grow with n they offer a search over a fine grid on the compact parameter set</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <term>the grid search is made tractable by a BOUND ON THE PARTIAL DERIVATIVES of the objective&#x27;s expectation, which is what turns a search over a continuous compact set into an efficient one</term>
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        <term>for fixed p and bounded clause participation the angles are found by an EFFICIENT CLASSICAL CALCULATION rather than by quantum search, and those angles are then used to run the quantum computer and produce the measured string</term>
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        <term>THE CONSTRAINT IS ENFORCED BY THE BASIS: for the independent-set variant the orthonormal basis consists only of strings that correspond to independent sets, so the space is exponentially large but smaller than the full 2^n, and is NOT a simple tensor product of qubits</term>
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        <term>the mixing operator is likewise restricted rather than penalised: it is the adjacency matrix of the hypercube confined to the legal strings, so the walk it generates can only ever move between independent sets</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>the classical preprocessing to choose the angles can require space doubly exponential in p</label>
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        <label>The authors state their headline result is beaten by classical methods already known.</label>
        <note>what this limits: the p = 1 performance reported here for 3-regular graphs: the authors state it</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>The next case up is analysed only partially, and the paper says so.</label>
        <note>what this limits: any extrapolation from p = 1 to larger p: the authors state the p = 2 case on 3-regular graphs is more complicated and that they show only partial results for it</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>The cost of the improvement is circuit depth, which grows with the same knob that buys the quality.</label>
        <note>what this limits: the claim that approximation quality improves with p: the depth of the circuit grows linearly with p times, at worst, the number of constraints, so the two move together</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>There is a property of the input the algorithm at p = 2 is stated to be unable to see at all.</label>
        <note>what this limits: results reported at p = 2 on 3-regular graphs: the authors state the algorithm at that depth cannot detect whether the graph is bipartite, that is, completely satisfiable</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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      <span xml:id="t18" type="concepts" ana="#concepts[4]" resp="#paper">
        <label>MaxCut</label>
        <term>MaxCut</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>QAOA</label>
        <term>QAOA</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>approximation ratio</label>
        <term>approximation ratio</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>classical algorithms</label>
        <term>classical algorithms</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>circuit depth</label>
        <term>circuit depth</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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      <span xml:id="t23" type="senses" ana="#senses[0]" resp="#tagger" cert="1.0">
        <label>the approximation ratio - AS OUTPUT OVER OPTIMUM: the quantity reported is the objective value at the algorithm&#x27;s own output divided by the true maximum, so it is a ratio against a quantity that must already be known to state it</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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      <span xml:id="t24" type="senses" ana="#senses[1]" resp="#tagger" cert="1.0">
        <label>the algorithm&#x27;s names - ITS OWN ACRONYM SURVIVED AND A SECOND NAME WAS ADDED LATER: the paper calls it the QAOA throughout - its expanded name survives only inside a damaged sentence - while the word the field now uses for its class, variational, appears nowhere in it</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>p - THE ONE KNOB, AND IT SETS BOTH SIDES OF THE TRADE: the paper introduces the algorithm as depending on an integer p, with quality improving as p rises and circuit depth rising with it, so a result quoted without its p is not a result about this algorithm</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>builds-on → the quantum adiabatic algorithm</label>
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        <label>QAOA —contrasted-with→ classical algorithms</label>
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        <term>classical algorithms</term>
        <note>strength of the relation: 1
Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but endpoint by anaphora: &#x27;This p = 1 result&#x27; = the QAOA&#x27;s result (previous sentence).</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>0.6924 — guaranteed approximation ratio for MaxCut on 3-regular graphs at p=1</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>2p — variational parameters (γ, β) defining the depth-p QAOA state</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>The approximation ratio can be made arbitrarily close to 1 by making p large enough, independent of n.</label>
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        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>For MaxCut on 3-regular graphs at p=1, QAOA guarantees a cut at least 0.6924x the optimum.</label>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>approximation ratio</label>
        <term>approximation ratio</term>
        <note>about this quote: QUOTE RECOVERED FROM THE PAPER&#x27;S OWN CHARACTERS. The recorded quote was LETTERS-ONLY IDENTICAL to this stretch of the staged text but not an exact substring of it - spaces, hyphens, ligature glyphs or mathematical operators differed, so it could never anchor. This is the file&#x27;s own text between the same two letters: not produced by a rule about the damage, copied out of the file. Round-trip checked (the recovered span is letters-only equal to the original) and length-checked. The text as originally recorded is kept in evidence as extracted.</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>combinatorial optimization problem</label>
        <term>combinatorial optimization problem</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>MaxCut</label>
        <term>MaxCut</term>
        <note>about this quote: QUOTE RECOVERED FROM THE PAPER&#x27;S OWN CHARACTERS. The recorded quote was LETTERS-ONLY IDENTICAL to this stretch of the staged text but not an exact substring of it - spaces, hyphens, ligature glyphs or mathematical operators differed, so it could never anchor. This is the file&#x27;s own text between the same two letters: not produced by a rule about the damage, copied out of the file. Round-trip checked (the recovered span is letters-only equal to the original) and length-checked. The text as originally recorded is kept in evidence as extracted.</note>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>mean</label>
        <term>mean</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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        <label>standard-deviation</label>
        <term>standard-deviation</term>
        <note type="quotation-withheld">Quotation withheld because this record is not cleared for redistribution.</note>
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