Fast quantum state preparation and bath dynamics using non-Gaussian variational ansatz and quantum optimal control
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arXiv
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| Natura: | Preprint |
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2023
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| _version_ | 1866913414986596352 |
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| author | Bond, Liam J. Safavi-Naini, Arghavan Minář, Jiří |
| author_facet | Bond, Liam J. Safavi-Naini, Arghavan Minář, Jiří |
| contents | We combine quantum optimal control with a variational ansatz based on non-Gaussian states for fast, non-adiabatic preparation of quantum many-body states. We demonstrate this on the example of the spin-boson model, and use a multi-polaron ansatz to prepare near-critical ground states. For one mode, we achieve a reduction in infidelity of up to $\approx 60$ ($\approx 20$) times compared to linear (optimised local adiabatic) ramps respectively; for many modes we achieve a reduction in infidelity of up to $\approx 5$ times compared to non-adiabatic linear ramps. Further, we show that the typical control quantity, the leakage from the variational manifold, provides only a loose bound on the state's fidelity. Instead, in analogy to the bond dimension of matrix product states, we suggest a controlled convergence criterion based on the number of polarons. Finally, motivated by the possibility of realizations in trapped ions, we study the dynamics of a system with bath properties going beyond the paradigm of (sub/super) Ohmic couplings. We apply the ansatz to the study of the out-of-time-order-correlator (OTOC) of the bath modes in a non-perturbative regime. The scrambling time is found to be a robust feature only weakly dependent on the details of the coupling between the bath and the spin. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2306_01730 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Fast quantum state preparation and bath dynamics using non-Gaussian variational ansatz and quantum optimal control Bond, Liam J. Safavi-Naini, Arghavan Minář, Jiří Quantum Physics Mesoscale and Nanoscale Physics Quantum Gases Chaotic Dynamics We combine quantum optimal control with a variational ansatz based on non-Gaussian states for fast, non-adiabatic preparation of quantum many-body states. We demonstrate this on the example of the spin-boson model, and use a multi-polaron ansatz to prepare near-critical ground states. For one mode, we achieve a reduction in infidelity of up to $\approx 60$ ($\approx 20$) times compared to linear (optimised local adiabatic) ramps respectively; for many modes we achieve a reduction in infidelity of up to $\approx 5$ times compared to non-adiabatic linear ramps. Further, we show that the typical control quantity, the leakage from the variational manifold, provides only a loose bound on the state's fidelity. Instead, in analogy to the bond dimension of matrix product states, we suggest a controlled convergence criterion based on the number of polarons. Finally, motivated by the possibility of realizations in trapped ions, we study the dynamics of a system with bath properties going beyond the paradigm of (sub/super) Ohmic couplings. We apply the ansatz to the study of the out-of-time-order-correlator (OTOC) of the bath modes in a non-perturbative regime. The scrambling time is found to be a robust feature only weakly dependent on the details of the coupling between the bath and the spin. |
| title | Fast quantum state preparation and bath dynamics using non-Gaussian variational ansatz and quantum optimal control |
| topic | Quantum Physics Mesoscale and Nanoscale Physics Quantum Gases Chaotic Dynamics |
| url | https://arxiv.org/abs/2306.01730 |