149 research outputs found
How Quantum Computers Fail: Quantum Codes, Correlations in Physical Systems, and Noise Accumulation
The feasibility of computationally superior quantum computers is one of the
most exciting and clear-cut scientific questions of our time. The question
touches on fundamental issues regarding probability, physics, and
computability, as well as on exciting problems in experimental physics,
engineering, computer science, and mathematics. We propose three related
directions towards a negative answer. The first is a conjecture about physical
realizations of quantum codes, the second has to do with correlations in
stochastic physical systems, and the third proposes a model for quantum
evolutions when noise accumulates. The paper is dedicated to the memory of
Itamar Pitowsky.Comment: 16 page
Three Puzzles on Mathematics, Computation, and Games
In this lecture I will talk about three mathematical puzzles involving
mathematics and computation that have preoccupied me over the years. The first
puzzle is to understand the amazing success of the simplex algorithm for linear
programming. The second puzzle is about errors made when votes are counted
during elections. The third puzzle is: are quantum computers possible?Comment: ICM 2018 plenary lecture, Rio de Janeiro, 36 pages, 7 Figure
Intersections of Leray complexes and regularity of monomial ideals
For a simplicial complex X and a field K, let h_i(X)=\dim \tilde{H}_i(X;K).
It is shown that if X,Y are complexes on the same vertex set, then for all k
h_{k-1}(X\cap Y) \leq \sum_{\sigma \in Y} \sum_{i+j=k} h_{i-1}(X[\sigma])\cdot
h_{j-1}(\lk(Y,\sigma)) . A simplicial complex X is d-Leray over K, if h_i(Y)=0
for all induced subcomplexes Y \subset X and i \geq d. Let L_K(X) denote the
minimal d such that X is d-Leray over K. The above theorem implies that if X,Y
are simplicial complexes on the same vertex set then L_K(X \cap Y) \leq L_K(X)
+L_K(Y). Reformulating this inequality in commutative algebra terms, we obtain
the following result conjectured by Terai: If I,J are square-free monomial
ideals in S=K[x_1,...,x_n], then reg(I+J) \leq reg(I)+reg(J)-1 where reg(I)
denotes the Castelnuovo-Mumford regularity of I.Comment: 9 page
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