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arXiv · 2409.18420

Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits

Hlér Kristjánsson·Tatsuki Odake·Satoshi Yoshida·Philip Taranto·Jessica Bavaresco·Marco Túlio Quintino·Mio Murao
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Abstract

Quantum theory is consistent with a computational model permitting black-box operations to be applied in an indefinite causal order, going beyond the standard circuit model of computation. The quantum switch -- the simplest such example -- has been shown to provide numerous information-processing advantages. Here, we prove that the action of the quantum switch on two $n$-qubit quantum channels cannot be simulated deterministically and exactly by any causally ordered quantum circuit that uses $M$ calls to one channel and one call to the other, if $M \leq \max(2, 2^n-1)$. This demonstrates an exponential separation in quantum query complexity of indefinite causal order compared to standard quantum circuits.

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Hlér Kristjánsson, Tatsuki Odake, Satoshi Yoshida, Philip Taranto, Jessica Bavaresco, Marco Túlio Quintino, Mio Murao. 2024-09-27. Exponential separation in quantum query complexity of the quantum switch with respect to simulations with standard quantum circuits. https://arxiv.org/abs/2409.18420

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