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. 2015 Jul 8;5:11818. doi: 10.1038/srep11818

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(a,b) Energy levels of the full model of Eq. (2) as a function of the ancilla frequency ω_a. We assume ħ = 1. For both (a,b), the USC qubit frequency is ω/ω_r = 0.8 and the ancilla-field cavity interaction strength is g_a/ω_r = 0.02. The USC qubit coupling is g/ω_r = 0.3 for (a) and g/ω_r = 0.6 for (b). Energies are rescaled in order to set the ground level to zero. The global parity of the corresponding eigenstates is identified, blue continuous line for odd and red dashed lines for even states. (c) Purity of the reduced density matrix of the ancillary qubit for different global system eigenstate, as a function of the ancilla frequency. For the ground state , is always unity.

Inline graphic — (a,b) Energy levels of the full model of Eq. (2) as a function of the ancilla frequency ω_a. We assume ħ = 1. For both (a,b), the USC qubit frequency is ω/ω_r = 0.8 and the ancilla-field cavity interaction strength is g_a/ω_r = 0.02. The USC qubit coupling is g/ω_r = 0.3 for (a) and g/ω_r = 0.6 for (b). Energies are rescaled in order to set the ground level to zero. The global parity of the corresponding eigenstates is identified, blue continuous line for odd and red dashed lines for even states. (c) Purity of the reduced density matrix of the ancillary qubit for different global system eigenstate, as a function of the ancilla frequency. For the ground state , is always unity.