Vijay R, Devoret M H, Siddiqi I
Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA.
Rev Sci Instrum. 2009 Nov;80(11):111101. doi: 10.1063/1.3224703.
We review the theory, fabrication, and implementation of the Josephson bifurcation amplifier (JBA). At the core of the JBA is a nonlinear oscillator based on a reactively shunted Josephson junction. A weak input signal to the amplifier couples to the junction critical current I(0) and results in a dispersive shift in the resonator plasma frequency omega(p). This shift is enhanced by biasing the junction with a sufficiently strong microwave current I(rf) to access the nonlinear regime where omega(p) varies with I(rf). For a drive frequency omega(d) such that Omega=2Q(1-omega(d)/omega(p))>3, the oscillator enters the bistable regime where two nondissipative dynamical states O(L) and O(H), which differ in amplitude and phase, can exist. The sharp I(0) dependent transition from O(L) to O(H) forms the basis for a sensitive digital threshold amplifier. In the vicinity of the bistable regime (Omega<3), analog amplification of continuous signals is also possible. We present experimental data characterizing amplifier performance and discuss two specific applications--the readout of superconducting qubits (digital mode) and dispersive microwave magnetometry (analog mode).
我们回顾了约瑟夫森分岔放大器（JBA）的理论、制造和应用。JBA的核心是一个基于反应性分流约瑟夫森结的非线性振荡器。放大器的弱输入信号耦合到结临界电流I(0)，并导致谐振器等离子体频率ω(p)的色散偏移。通过用足够强的微波电流I(rf)对结进行偏置，以进入ω(p)随I(rf)变化的非线性区域，这种偏移会得到增强。对于驱动频率ω(d)，使得Ω=2Q(1 - ω(d)/ω(p))>3时，振荡器进入双稳态区域，在该区域中可以存在两个在幅度和相位上不同的非耗散动态状态O(L)和O(H)。从O(L)到O(H)的与I(0)相关的尖锐转变构成了灵敏数字阈值放大器的基础。在双稳态区域附近（Ω<3），连续信号的模拟放大也是可能的。我们展示了表征放大器性能的实验数据，并讨论了两个具体应用——超导量子比特的读出（数字模式）和色散微波磁力测量（模拟模式）。
