Charge qubits can be created and manipulated in solid-state double-quantum-dot (DQD) platforms. Typically, these systems are strongly affected by quantum noise stemming from coupling to substrate phonons. This is usually assumed to lead to decoherence towards steady states that are diagonal in the energy eigenbasis. In this article, we show, to the contrary, that due to the presence of phonons the equilibrium steady state of the DQD charge qubit spontaneously exhibits coherence in the energy eigenbasis with high purity. The magnitude and phase of the coherence can be controlled by tuning the Hamiltonian parameters of the qubit. The coherence is also robust to the presence of fermionic leads. In addition, we show that this steady-state coherence can be used to drive an auxiliary cavity mode coupled to the DQD.

电荷量子位可以在固态双量子点（DQD）平台中创建和处理。通常，这些系统会受到耦合至基底声子的量子噪声的强烈影响。通常认为这会导致对能量本征基础中对角线的稳态产生退相干。相反，在本文中，我们表明，由于存在声子，DQD电荷量子位的平衡稳态自发地在能量本征基中表现出高纯的相干性。相干的大小和相位可以通过调整量子位的哈密顿参数来控制。相干性对于存在铁离子引线也很稳定。另外，我们表明，这种稳态相干性可用于驱动耦合到DQD的辅助腔模。