2020年8月18日

# Hamiltonian of a flux qubit-LC oscillator circuit in the deep-strong-coupling regime

• Fumiki Yoshihara
• ,
• Sahel Ashhab
• ,
• Tomoko Fuse
• ,
• Motoaki Bamba
• ,
• Kouichi Semba

We derive the Hamiltonian of a superconducting circuit that comprises a
single-Josephson-junction flux qubit and an LC oscillator. If we keep the
qubit's lowest two energy levels, the derived circuit Hamiltonian takes the
form of the quantum Rabi Hamiltonian, which describes a two-level system
coupled to a harmonic oscillator, regardless of the coupling strength. To
investigate contributions from the qubit's higher energy levels, we numerically
calculate the transition frequencies of the circuit Hamiltonian. We find that
the qubit's higher energy levels mainly cause an overall shift of the entire
spectrum, but the energy level structure up to the seventh excited states can
still be fitted well by the quantum Rabi Hamiltonian even in the case where the
coupling strength is larger than the frequencies of the qubit and the
oscillator, i.e., when the qubit-oscillator circuit is in the
deep-strong-coupling regime. We also confirm that some of the paradoxical
properties of the quantum Rabi Hamiltonian in the deep-strong-coupling regime,
e.g. the non-negligible number of photons and the nonzero expectation value of
the flux in the oscillator in the ground state, arise from the circuit
Hamiltonian as well.

リンク情報
arXiv
http://arxiv.org/abs/arXiv:2008.07708
URL
http://arxiv.org/abs/2008.07708 本文へのリンクあり

エクスポート