



@article {3256,
	title = {Error Mitigation Thresholds in Noisy Quantum Circuits},
	year = {2023},
	month = {2/8/2023},
	abstract = {<p>Extracting useful information from noisy near-term quantum simulations requires error mitigation strategies. A broad class of these strategies rely on precise characterization of the noise source. We study the performance of such strategies when the noise is imperfectly characterized. We adapt an Imry-Ma argument to predict the existence of an error mitigation threshold for random spatially local circuits in spatial dimensions D\&ge;2: characterization disorder below the threshold rate allows for error mitigation up to times that scale with the number of qubits. For one-dimensional circuits, by contrast, mitigation fails at an O(1) time for any imperfection in the characterization of disorder. We discuss implications for tests of quantum computational advantage, fault-tolerant probes of measurement-induced phase transitions, and quantum algorithms in near-term devices.</p>},
	url = {https://arxiv.org/abs/2302.04278},
	author = {Pradeep Niroula and Sarang Gopalakrishnan and Michael Gullans}
}
@article {2724,
	title = {Entanglement and purification transitions in non-Hermitian quantum mechanics},
	journal = {Phys. Rev. Lett., in press},
	year = {2021},
	month = {12/2/2020},
	abstract = {<p>A quantum system subject to continuous measurement and post-selection evolves according to a non-Hermitian Hamiltonian. We show that, as one increases the rate of post-selection, this non-Hermitian Hamiltonian undergoes a spectral phase transition. On one side of this phase transition (for weak post-selection) an initially mixed density matrix remains mixed at all times, and an initially unentangled state develops volume-law entanglement; on the other side, an arbitrary initial state approaches a unique pure state with low entanglement. We identify this transition with an exceptional point in the spectrum of the non-Hermitian Hamiltonian, at which PT symmetry is spontaneously broken. We characterize the transition as well as the nontrivial steady state that emerges at late times in the mixed phase using exact diagonalization and an approximate, analytically tractable mean-field theory; these methods yield consistent conclusions.</p>},
	url = {https://arxiv.org/abs/2012.01435},
	author = {Sarang Gopalakrishnan and Michael Gullans}
}
