Hi everyone, The Harvard Quantum Information Group Meeting will have a special guest this Thursday, April 13th at 4:30 pm in Jefferson 250. David Gosset, from the University of Waterloo and Perimeter Institute, will be speaking. Please see the title and abstract below. Title: How to simulate quantum measurement without computing marginals Abstract: In this work we provide new techniques for a fundamental and ubiquitous task: simulating measurement of a quantum state in the standard basis. Our algorithms reduce the sampling task to computing poly(n) amplitudes of n-qubit states; unlike previously known techniques they do not require computation of marginal probabilities. First we consider the case where the state of interest is the output state of an m-gate quantum circuit U. We propose an exact sampling algorithm which involves computing O(m) amplitudes of n-qubit states generated by subcircuits of U spanned by the first t=1,2,…,m gates. We show that our algorithm can significantly accelerate quantum circuit simulations based on tensor network contraction methods or low-rank stabilizer decompositions. Second, we consider the case in which ψ is the unique ground state of a local Hamiltonian with a spectral gap that is lower bounded by an inverse polynomial function of n. We prove convergence guarantees for a simple Metropolis-Hastings Markov Chain as well as a more involved continuous-time Markov chain that is related to the so-called fixed node Hamiltonian approach from the quantum Monte Carlo community. This talk is based on joint works arXiv:2112.08499 and arXiv:2207.07044 with Sergey Bravyi, Giuseppe Carleo, and Yinchen Liu. Hope to see you all there. Sincerely, Jordan Cotler