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arXiv:2308.04183

Ultrafast and deterministic generation of Bell states in the ultrastrong coupling regime

Xin Xie, Junlong Tian, Peng, Jie

Published Aug 8, 2023• 0 citations
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Abstract

We have found the special dark state solutions of the anisotropic two-qubit quantum Rabi model (QRM), which has at most one photon, and constant eigenenergy in the whole coupling regime. Accordingly, we propose a scheme to deterministically generate two kinds of the two-qubit Bell states through adiabatic evolution along the dark states. With the assistance of the Stark shift, the generation time can be reduced to subnanosecond scales, proportional to the reverse of the resonator frequency, with fidelity reaching 99%. Furthermore, the other two kinds of Bell states can also be ultrafast generated.

DOI
10.48550/arxiv.2308.04183

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Abstract We study the two-qubit asymmetric quantum Rabi model (AQRM) and find its dark-state solution. Such solutions have at most one photon and constant eigenenergy in the whole coupling regime, causing level crossings in the spectrum, although there is no explicit conserved quantity except for energy. We find an operator in the eigenenergy basis to label all the degeneracies with its eigenvalues, and compare it with the well-known hidden symmetry which exists when bias parameter ϵ is a multiple of half of the resonator frequency ω . Extended to the multimode case, we find symmetries related with conserved bosonic number operators, which also cause level crossings. This paves the way for further symmetry studies on generalized Rabi models.
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\n We investigate how to deterministically generate symmetric Dicke states of many atomic qubits in a high-Q two-mode optical cavity via dark-state evolution. Our scheme is based on adiabatic evolution, which makes the relevant dynamics insensitive to randomness of the moderate fluctuations of experimental parameters. Assisted by the postselective process, our scheme could be of the fidelity of unity, and robust to imperfect factors such as dissipation, mismatch of cavity parameters, photon loss, and detector inefficiency.\n
We studied the two-qubit quantum Rabi model and found its dark state solutions with at most N photons. One peculiar case presents when N=3N=3N=3, which has constant eigenenergy in the whole coupling regime and leads to level crossings within the same parity subspace. We also discovered asymptotic solutions with at most N=2i+3N=2i+3N=2i+3 (i=1,2,3,… )(i=1,2,3,\dots)(i=1,2,3,…) photons, and constant eigenenergy NℏωN\hbar ωNℏω when coupling ggg becomes much larger than photon frequency ωωω. Although generally all photon number states are involved in the two-qubit quantum Rabi model, such NNN-photon solutions exist and may have applications in quantum information processing with ultrastrong couplings.