Multilevel effects in the Rabi oscillations of a Josephson phase qubit
S. K. Dutta, Frederick W. Strauch, R. M. Lewis, Kaushik Mitra, Hanhee Paik, T. A. Palomaki, Eite Tiesinga, J. R. Anderson, Alex J. Dragt, C. J. Lobb, F. C. Wellstood
备注:
14 pages, 9 figures; minor corrections, updated references
We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states.
We calculate the current-voltage (I-V) characteristic of a Josephson junction containing a resonant level in the weakly coupled regime (resonance width small compared to the superconducting gap). The phase $ϕ$ across the junction becomes time dependent in response to a DC current bias. Rabi oscillations in the Andreev levels produce a staircase I-V characteristic. The number of voltage steps counts the number of Rabi oscillations per $2π$ increment of $ϕ$, providing a way to probe the coherence of the qubit in the absence of any external AC driving. The phenomenology is the same as the "Majora…
We study the behavior of a topological Josephson junction in which two topological superconductors are coupled through a quantum dot. We focus on the case with the bulk superconducting gap being the largest energy scale. Two parameter regimes are investigated: a weak tunneling between the dot and the superconductors, with the dot near its charge degeneracy point, and a strong tunneling regime in which the transmission between the dot and the superconductors is nearly perfect. We show that in the former situation, the Andreev spectrum for each sector with fixed fermion parity consists of only t…
The basis for superconducting electronics can broadly be divided between two technologies: the Josephson junction and the superconducting nanowire. While the Josephson junction (JJ) remains the dominant technology due to its high speed and low power dissipation, recently proposed nanowire devices offer improvements such as gain, high fanout, and compatibility with CMOS circuits. Despite these benefits, nanowire-based electronics have largely been limited to binary operations, with devices switching between the superconducting state and a high-impedance resistive state dominated by uncontrolled…
We study the Berezinskii-Kosterlitz-Thouless (BKT) transition of two-component Bose mixtures in two spatial dimensions. When phases of both components are decoupled, half-quantized vortex-antivortex pairs of each component induce two-step BKT transitions. On the other hand, when phases of the both components are synchronized through the inter-component Josephson coupling, two species of vortices of each component are bind to form a molecule, and in this case, we find that there is only one BKT transition by molecule-antimolecule pairs. Our results can be tested by two weakly-connected Bose sys…
Dissipation in Josephson tunneling junctions at low temperatures
了解基于约瑟夫森结的量子比特的退相干机制是非常重要的。在低温下,由于准粒子浓度呈指数级变小,人们需要考虑从隧穿电子到其他自由度的能量转移,以发现约瑟夫森结中的耗散和量子位中的退相干。本文讨论了两能级系统的能量转移,即在绝缘层中由势垒隔开的两种不同构型的离子之间的跃迁。我们导出了两个超导电极之间相位差的一般运动方程,并发现了一个由于电磁机制引起的延迟耗散项和电子隧穿机制的贡献。利用运动方程,我们计算了由于二能级系统的存在而引起的拉比振荡的衰减和量子比特的频移。在长时间范围内,我们的结果与Martinis等人[J. M. Martinis等人物理修订信函95,210503(2005)]在费米黄金法则范围内接近数值因子。
We derive the Hamiltonian of a superconducting circuit that comprises a single-Josephson-junction flux qubit inductively coupled to an LC oscillator, and we compare the derived circuit Hamiltonian with the quantum Rabi Hamiltonian, which describes a two-level system coupled to a harmonic oscillator. We show that there is a simple, intuitive correspondence between the circuit Hamiltonian and the quantum Rabi Hamiltonian. While there is an overall shift of the entire spectrum, the energy level structure of the circuit Hamiltonian up to the seventh excited states can still be fitted well by the q…
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。