论文标题
四重奏线上的四个端子超导装置中的反演：ii。量子点和浮标理论
Inversion in a four terminal superconducting device on the quartet line: II. Quantum dot and Floquet theory
论文作者
论文摘要
在本文中，我们考虑了一个量子点，该量子点与四重奏线上相反电压的四个超导端子相连。接地的超导体包含由磁通量$φ$螺纹的环。我们为电压 - $ v $依赖性的Keldysh显微镜计算和物理图片。预计超导性在$φ/φ_0= 0 $的强度比$φ/φ_0= 1/2 $更强。 However, inversion $I_{q,c}(V,0)<I_{q,c}(V,1/2)$ is obtained in the critical current $I_{q,c}(V,Φ/Φ_0)$ on the quartet line in the voltage-$V$ ranges which match avoided crossings in the Floquet spectrum at $(V,Φ/Φ_0=0)$ but not在$（V，1/2）$。 $ i_ {q，c} $的减少出现在那些避免的交叉口的附近，其中Landau-Zener隧道会产生Andreevend Bound状态的动态量子机械叠加。此外，随着$ v $的进一步增加，$π$ - $ 0 $和$ 0 $ - $ - $ - $ - $π$交叉交叉在当前相关关系中出现。电压诱导的$π$缩影被解释为源自电压偏置产生的非平衡浮子种群。数值计算表明，反转对强的Landau-Zener隧道和量子点中的许多级别是可靠的。我们的理论提供了一种简单的``浮标水平和人口''机制，用于偏置电压$ v $调整的反转机制，该机制为最近观察到反转的最近的哈佛组实验铺平了更真实的模型。
In this paper, we consider a quantum dot connected to four superconducting terminals biased at opposite voltages on the quartet line. The grounded superconductor contains a loop threaded by the magnetic flux $Φ$. We provide Keldysh microscopic calculations and physical pictures for the voltage-$V$ dependence of the quartet current. Superconductivity is expected to be stronger at $Φ/Φ_0=0$ than at $Φ/Φ_0=1/2$. However, inversion $I_{q,c}(V,0)<I_{q,c}(V,1/2)$ is obtained in the critical current $I_{q,c}(V,Φ/Φ_0)$ on the quartet line in the voltage-$V$ ranges which match avoided crossings in the Floquet spectrum at $(V,Φ/Φ_0=0)$ but not at $(V,1/2)$. A reduction in $I_{q,c}$ appears in the vicinity of those avoided crossings, where Landau-Zener tunneling produces dynamical quantum mechanical superpositions of the Andreev bound states. In addition, $π$-$0$ and $0$-$π$ cross-overs emerge in the current-phase relations as $V$ is further increased. The voltage-induced $π$-shift is interpreted as originating from the nonequilibrium Floquet populations produced by voltage biasing. The numerical calculations reveal that the inversion is robust against strong Landau-Zener tunneling and many levels in the quantum dot. Our theory provides a simple ``Floquet level and population'' mechanism for inversion tuned by the bias voltage $V$, which paves the way towards more realistic models for the recent Harvard group experiment where the inversion is observed.
