AI 中文总结
研究通过超导传输子量子比特与两条传输线耦合，观察到功率流方向由量子比特叠加相位$\phi$控制，随$\cos\phi$变化，最大相干性时效率达$63\%$，接近理论界限，揭示了量子叠加相位对功率转移的独特控制作用。
AI 中文摘要
一个受驱动的量子比特与驱动它的传播模式交换能量。当两个空间分离的模式以相反幅度驱动单个量子比特时，它们对量子比特的净作用抵消。然而，量子比特仍可通过受激辐射将功率从一个模式转移到另一个模式。方向性源于进入每条线路的相反受激辐射功率。我们通过将超导传输子量子比特与两条传输线耦合实现了这种情况，并表明功率流的方向由量子比特基态和激发态之间叠加相位$\phi$设定，而非任何经典控制参数。通过对一条线路输出功率的时间分辨测量，我们观察到转移随$\cos\phi$变化，因此在$\phi = 0$和$\phi=\pi$之间改变方向。总功率流的方向性受反射驱动和自发发射的与相位无关贡献限制，我们测量了作为输入功率函数的路由效率。对于量子比特基态和激发态的等叠加（最大相干性），效率达到$63\%$，接近从测量的量子比特相干时间预期的$69\%$界限。
英文摘要
A driven qubit exchanges energy with the propagating modes that drive it. When two spatially separated modes drive a single qubit with opposite amplitudes, their net action on the qubit cancels. Yet the qubit can still transfer power from one mode to the other through stimulated emission. The directionality originates from opposite stimulated emission powers into each line. We realize this situation with a superconducting transmon qubit coupled to two transmission lines and show that the direction of the power flow is set by the phase $ϕ$ of the qubit superposition between its ground and excited states, rather than by any classical control parameter. From a time-resolved measurement of the output power in one line, we observe a transfer that varies as $\cosϕ$ and hence changes direction between $ϕ=0$ and $ϕ=π$. The directionality of the total power flow is limited by the phase independent contributions of the reflected drive and of spontaneous emission, which sets a routing efficiency that we measure as a function of the input power. For an equal superposition of ground and excited qubit states (maximal coherence), the efficiency reaches $63\%$, close to the bound of $69\%$ expected from the measured qubit coherence times.
