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Seth Lloyd from @MIT is visiting us at LIP6 and presents his work with András Gilyén (from @QuSoftAmsterdam ) and @ewintang (from @UW) on Quantum-inspired low-rank stochastic regression with logarithmic dependence on the dimension arXiv:1811.04909 arxiv.org/abs/1811.04909
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@MIT @QuSoftAmsterdam @ewintang @UW Seth Lloyd: presents the recommendation problem. For m users, n movies, a n×m matrix A encodes the movie preferences. The goal is to recommend movies a user likes, given their previous preferences.
A is assumed to be low rank (the rank is the effective number of genres).
#LTQI
@MIT @QuSoftAmsterdam @ewintang @UW Seth Lloyd: The @netflix way to solve this problem is through singular value decomposition of matrix A.

A=∑_l σ_l U^l V^l ^T
σ_l: singular values
U^l and V^l are left/right singular vectors
A V^l= σ_l U^l V^l
In short V^l^T b = p_l encodes weighted preference for genre l
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Read 19 tweets
Nows at #MCQS, Rafał Demkowicz-Dobrzański from (@UniWarsawski ) on the grand unified theory of quantum metrology.
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Rafał Demkowicz-Dobrzański seez quantum metrology as a channel estimation problem. The channel U_φ is given, one optimizes the state sent and the measurement.
#LTQI #MCQS
Rafał Demkowicz-Dobrzański: The Cramer-Rao bount gives limit on the variance Δ²φ≥1/F of an unbiased estimator., where F is the (Quantum or classical) Fisher information, defined in term of derivatives of probability/kets over φ
#LTQI #MCQS
Read 18 tweets
Now at #QuPa (at @InHenriPoincare), Bruno Laburthe-Tolra from @univ_paris13 on “Some aspects of quantum simulation using cold atoms”
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: works with quantum gases, with density 10¹²–10¹⁵ at/cm³, at nK or µK, with de Broglie wavelengths and inter-atomic distance > 100nm.
These systems (boson or fermions) are “clean” analogues of condensed matter systems.
#QuPa #LTQI
@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: Optical lattices are periodic (spin indeendent) potentials induced by stationary optical waves. This allows to make 1D, 2D and 3D potential, making 2D, 1D and strongly correlated spin gases.
#LTQI #QuPa
Read 16 tweets

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