超导量子比特的西西弗斯冷却和放大
Sisyphus cooling and amplification by a superconducting qubit
摘要：
原子运动的激光冷却为量子光学和原子物理学领域的显著成就铺平了道路，包括玻色-爱因斯坦凝聚和光晶格中的原子捕获。最近，超导量子比特被证明可以充当人工二能级原子，显示拉比振荡，拉姆齐条纹和进一步的量子效应。将这样的量子比特耦合到谐振器，将超导电路带入了量子电动力学（电路QED）的领域。它开辟了使用超导量子位作为微冷却器或在量子位中创建粒子数反转以诱导谐振器的激光行为的前景。进一步的量子光学和超导系统之间的这些类比，我们在这里展示了西西弗斯冷却的低频LC振荡器耦合到近共振驱动的超导量子比特。在量子光学系统中，原子的机械自由度是通过激光驱动原子的电子自由度来冷却的。在这里，两个自由度的作用分别由LC电路和量子位的能级扮演。我们还展示了对应的西西弗斯冷却，即西西弗斯放大。平行的实验演示，我们从理论上分析系统，并找到定量的协议，这支持的解释，使我们能够估计系统参数。
英文摘要：
Laser cooling of the atomic motion paved the way for remarkable achievements in the fields of quantum optics and atomic physics, including Bose-Einstein condensation and the trapping of atoms in optical lattices. More recently superconducting qubits were shown to act as artificial two-level atoms, displaying Rabi oscillations, Ramsey fringes, and further quantum effects. Coupling such qubits to resonators brought the superconducting circuits into the realm of quantum electrodynamics (circuit QED). It opened the perspective to use superconducting qubits as micro-coolers or to create a population inversion in the qubit to induce lasing behavior of the resonator. Furthering these analogies between quantum optical and superconducting systems we demonstrate here Sisyphus cooling of a low frequency LC oscillator coupled to a near-resonantly driven superconducting qubit. In the quantum optics setup the mechanical degrees of freedom of an atom are cooled by laser driving the atom's electronic degrees of freedom. Here the roles of the two degrees of freedom are played by the LC circuit and the qubit's levels, respectively. We also demonstrate the counterpart of the Sisyphus cooling, namely Sisyphus amplification. Parallel to the experimental demonstration we analyze the system theoretically and find quantitative agreement, which supports the interpretation and allows us to estimate system parameters.
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