After quickly reading through the paper it seems that the algorithm they employ is very similar to Grover search [1], which provides a quadratic/square-root sp

After quickly reading through the paper it seems that the algorithm they employ is very similar to Grover search [1], which provides a quadratic/square-root speed-up for generic search problems, so O(2^m) -> O(2^(n/2)). Basically, they perform the following three steps: 1) Generate an even superposition of all possible solution states using a Hadamard transform (so go from |000000...> to 1/sqrt(N)*(|00000..0>+|000...1>+|1111...1>). This is pretty standard and used in almost all quantum algorithms. 2) Evaluate each clause of their Boolean E3-CNF function on the superposed input state and transfer the results to a register of control qubits, which yields an entangled state of the input state qubits with these control qubits (akin to the Oracle operator in the Grover search algorithm that performs the operation |x>|0> -> |x>|f(x)>, only here they use multiple Oracle functions and control qubits [which is fine of course]). This is a classical operation which we can implement in reversible computing btw, so no quantum magic involved here yet (apart from applying it to a superposed input state). 3) Increase the amplitude of the states that contain the solution to the search problem, very much akin to the rotation operator employed in Grover search that transfers amplitude from non-solution states to the solution state. <- The problem might be here. So where I have trouble understanding the algorithm is when they apply the operator M_x to increase "the amplitude of the truth vector of clauses with maximum number of satisfied clauses using a partial negation and iterative measurement technique" (page 6 ff.). They seem to want to repeatedly apply that operator to the same state in order to maximize the amplitude transfer to the correct solution states. However, there is a rather simple proof that shows that the maximum amount of amplitude which you can transfer from one component of a quantum state to another using a control qubit is fundamentally limited by the Unitarian nature of quantum operations. This also limits the efficiency of quantum search in the general case and is the reason that we cannot achieve arbitrary speed-up in the Grover algorithm (see e.g. my PhD thesis for a simple explanation [2] or Grover's original paper to get the full picture [3]). Basically this proof states that although we can generate the quantum information about the answer that we're looking for, we cannot get that information out of the quantum system in an (exponentially) efficient way. It would be very exciting if this algorithm was correct of course, I just can't imagine that someone would publish such an important finding on Arxiv.org without having it cross-checked and backed by some other people in the field first (which does not seem to be the case judging from the text). That being said, I think it should be not too difficult to simulate this algorithm and see if all of their transformations are actually unitary and possible to implement in reversible computing and if they correctly take into account the entanglement of individual control qubits and the corresponding wave function collapse due to the qubit measurements they perform. [1] Grover Search Algorithm - https://en.wikipedia.org/wiki/Grover%27s_algorithm https://en.wikipedia.org/wiki/Grover%27s_algorithm [2] My PhD thesis on an Experimental Realization of Grover's Algorithm - see page 136 ff. for a simple explanation of the effiency of quantum searching http://iramis.cea.fr/spec/Pres/Quantro/static/wp-content/uploads/2013/09/thesis_Dewes_web.pdf http://iramis.cea.fr/spec/Pres/Quantro/static/wp-content/upl... [3] Grover's Algorithm - Original Paper http://arxiv.org/abs/quant-ph/9605043 http://arxiv.org/abs/quant-ph/9605043 [4] The No-Cloning Theorem: https://en.wikipedia.org/wiki/No-cloning_theorem https://en.wikipedia.org/wiki/No-cloning_theorem