We study spectroscopy of artificial solid-state four-level quantum system. This system is formed by two coupled superconducting flux qubits. When multiple driving frequency of the applied microwaves matches the energy difference between any two levels, the transition to the upper level is induced. We demonstrate two types of the multi-photon transitions: direct transitions between two levels and ladder-type transitions via an intermediate level. For the latter transitions, in particular, the inverse population of the excited state with respect to the ground one is realized. These processes can be useful for the control of the level population for the multilevel scalable quantum systems.
Multiphoton up/down conversion in a transmon circuit, driven by a pair of microwaves tuned near and far off the qubit resonance, has been observed. The experimental realization of these high order non-linear processes is accomplished in the three-photon regime, when the transmon is coupled to weak bichromatic microwave fields with the same Rabi frequencies. A many-mode Floquet formalism, with longitudinal coupling, is used to simulate the quantum interferences in the absorption spectrum that manifest the multiphoton pumping processes in the transmon qubit. An intuitive graph theoretic approach…
Theory of quasiparticle generation by microwave drives in superconducting qubits
Research Laboratory of Electronics, Massachusetts Institute of Technology（麻省理工学院电子研究实验室）；Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology（麻省理工学院电气与计算机工程系）；MIT Lincoln Laboratory（麻省理工学院林肯实验室）
Sideband fingerprints of antibunched light in cascaded quantum wave mixing
Dukhov Research Institute of Automatics (VNIIA)（杜霍夫自动装置研究所）；Moscow Institute of Physics and Technology（莫斯科物理技术学院）；Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences（俄罗斯科学院理论与应用电动力学研究所）；Kotelnikov Institute of Radioengineering and Electronics, Russian Academy of Sciences（俄罗斯科学院科捷利尼科夫无线电工程与电子研究所）；Skolkovo Institute of Science and Technology（斯科尔科沃科学技术学院）
Distinguishing quantum from classical oscillations in a driven phase qubit
拉比振荡是量子二能级系统在共振微扰影响下的相干跃迁，其频率低得多，取决于微扰振幅。这是介观系统中量子相干演化的特征之一。最近，[N。Gronbech-Jensen和M. Cirillo，Phys. Rev. Lett. 95，067001（2005）]，在相位量子位（电流偏置的约瑟夫森结）中，这种效应可以通过由于有效势的非谐性而产生的经典振荡来模拟。然而，我们发现经典和量子效应之间的质的差异。首先，虽然量子拉比振荡可以由谐振频率的次谐波（多光子过程）产生，但当系统在泛频处被激发时，经典效应也存在。第二，在经典情况下，共振的形状是典型的不对称;而量子共振则由对称的洛伦兹方程描述。第三，势的非谐性导致了经典情形下谐振频率的负移，而量子情形下则相反。我们表明，在相关的参数范围内，这些功能可以自信地区分真正的拉比振荡从他们的经典Doppelganger。
