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arXiv · 2302.07895

Phase transition in Stabilizer Entropy and efficient purity estimation

Lorenzo Leone·Salvatore F. E. Oliviero·Gianluca Esposito·Alioscia Hamma
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Abstract

Stabilizer Entropy (SE) quantifies the spread of a state in the basis of Pauli operators. It is a computationally tractable measure of non-stabilizerness and thus a useful resource for quantum computation. SE can be moved around a quantum system, effectively purifying a subsystem from its complex features. We show that there is a phase transition in the residual subsystem SE as a function of the density of non-Clifford resources. This phase transition has important operational consequences: it marks the onset of a subsystem purity estimation protocol that requires $poly(n)exp(t)$ many queries to a circuit containing $t$ non-Clifford gates that prepares the state from a stabilizer state. Then, for $t=O(\log_2 n)$, it estimates the purity with polynomial resources and, for highly entangled states, attains an exponential speed-up over the known state-of-the-art algorithms.

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Lorenzo Leone, Salvatore F. E. Oliviero, Gianluca Esposito, Alioscia Hamma. 2023-02-15. Phase transition in Stabilizer Entropy and efficient purity estimation. https://doi.org/10.1103/physreva.109.032403

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