Quantum natural gradient generalised to noisy and non-unitary circuits
Variational quantum algorithms are promising tools whose efficacy depends on their optimization method. For noise-free unitary circuits, the quantum generalization of natural gradient descent has been introduced and shown to be equivalent to imaginary time evolution: the approach is effective due to...
| Main Authors: | , |
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| Format: | Journal article |
| Language: | English |
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American Physical Society
2022
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| _version_ | 1797108442077331456 |
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| author | Koczor, B Benjami, SC |
| author_facet | Koczor, B Benjami, SC |
| author_sort | Koczor, B |
| collection | OXFORD |
| description | Variational quantum algorithms are promising tools whose efficacy depends on their optimization method. For noise-free unitary circuits, the quantum generalization of natural gradient descent has been introduced and shown to be equivalent to imaginary time evolution: the approach is effective due to a metric tensor reconciling the classical parameter space to the device's Hilbert space. Here we generalize quantum natural gradient to consider arbitrary quantum states (both mixed and pure) via completely positive maps; thus our circuits can incorporate both imperfect unitary gates and fundamentally nonunitary operations such as measurements. We employ the quantum Fisher information (QFI) as the core metric in the space of density operators. A modification of the error suppression by derangements (ESD) and virtual distillation (VD) techniques enables an accurate and experimentally efficient approximation of the QFI via the Hilbert-Schmidt metric tensor using prior results on the dominant eigenvector of noisy quantum states. Our rigorous proof also establishes the fundamental observation that the geometry of typical noisy quantum states is (approximately) identical in either the Hilbert-Schmidt metric or as characterized by the QFI. In numerical simulations of noisy quantum circuits we demonstrate the practicality of our approach and confirm it can significantly outperform other variational techniques. |
| first_indexed | 2024-03-07T07:29:17Z |
| format | Journal article |
| id | oxford-uuid:b2104e9f-d462-4815-bbf2-6c80ae9018a3 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T07:29:17Z |
| publishDate | 2022 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | oxford-uuid:b2104e9f-d462-4815-bbf2-6c80ae9018a32022-12-16T08:56:10ZQuantum natural gradient generalised to noisy and non-unitary circuitsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:b2104e9f-d462-4815-bbf2-6c80ae9018a3EnglishSymplectic ElementsAmerican Physical Society2022Koczor, BBenjami, SCVariational quantum algorithms are promising tools whose efficacy depends on their optimization method. For noise-free unitary circuits, the quantum generalization of natural gradient descent has been introduced and shown to be equivalent to imaginary time evolution: the approach is effective due to a metric tensor reconciling the classical parameter space to the device's Hilbert space. Here we generalize quantum natural gradient to consider arbitrary quantum states (both mixed and pure) via completely positive maps; thus our circuits can incorporate both imperfect unitary gates and fundamentally nonunitary operations such as measurements. We employ the quantum Fisher information (QFI) as the core metric in the space of density operators. A modification of the error suppression by derangements (ESD) and virtual distillation (VD) techniques enables an accurate and experimentally efficient approximation of the QFI via the Hilbert-Schmidt metric tensor using prior results on the dominant eigenvector of noisy quantum states. Our rigorous proof also establishes the fundamental observation that the geometry of typical noisy quantum states is (approximately) identical in either the Hilbert-Schmidt metric or as characterized by the QFI. In numerical simulations of noisy quantum circuits we demonstrate the practicality of our approach and confirm it can significantly outperform other variational techniques. |
| spellingShingle | Koczor, B Benjami, SC Quantum natural gradient generalised to noisy and non-unitary circuits |
| title | Quantum natural gradient generalised to noisy and non-unitary circuits |
| title_full | Quantum natural gradient generalised to noisy and non-unitary circuits |
| title_fullStr | Quantum natural gradient generalised to noisy and non-unitary circuits |
| title_full_unstemmed | Quantum natural gradient generalised to noisy and non-unitary circuits |
| title_short | Quantum natural gradient generalised to noisy and non-unitary circuits |
| title_sort | quantum natural gradient generalised to noisy and non unitary circuits |
| work_keys_str_mv | AT koczorb quantumnaturalgradientgeneralisedtonoisyandnonunitarycircuits AT benjamisc quantumnaturalgradientgeneralisedtonoisyandnonunitarycircuits |