MEASUREMENTS OF QUANTUM NOISE IN RESISTIVELY SHUNTED JOSEPHSON-JUNCTIONS
MEASUREMENTS OF QUANTUM NOISE IN RESISTIVELY SHUNTED JOSEPHSON-JUNCTIONS
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DOI：
10.1103/physrevb.26.74
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发表时间：
1982-01-01
影响因子：
3.7
通讯作者：
CLARKE, J
中科院分区：
文献类型：
--
作者：
KOCH, RH;VANHARLINGEN, DJ;CLARKE, J
在从约瑟夫森频率 (ν J) 附近的频率混合到测量频率 (≪ ν J) 的噪声处于 h ν J> k B T 范围内的条件下，对电流偏置电阻分流约瑟夫森隧道结中的电压噪声的低频频谱密度进行了测量。在这种限制下，对混合噪声的量子校正非常重要。在电流-电压特性接近 Stewart-McCumber 模型的结点上测量的光谱密度与预测值非常一致，无需拟合参数。使用大范围偏置电压的混合噪声来推断频率 ν 下分流电阻器中电流噪声的频谱密度。在没有拟合参数的情况下，频率高达 500 GHz 时的谱密度与预测 (2 h ν R) coth (h ν 2 k B T) 非常一致。清楚地证明了频率 h ν > k B T 处零点项 2 h ν R 的存在。具有 β Leq 2 π L s I 0 Φ 0∼ 1 和 β Ceq 2 π I 0 R 2 C Φ 0≪ 1 的结的电流-电压特性，其中 I 0 是临界电流，C 是结电容，L s 是并联电感，显示了约瑟夫森频率接近 L s C 谐振频率的次谐波的电压下的结构。 I−V 特性的额外非线性导致约瑟夫森频率的高次谐波附近的噪声混合，从而大大增强了电压噪声。测量的噪声与计算机模拟预测的非常一致。
Measurements have been made of the low-frequency spectral density of the voltage noise in current-biased resistively shunted Josephson tunnel junctions under conditions in which the noise mixed-down from frequencies near the Josephson frequency (ν J) to the measurement frequency (≪ ν J) is in the regime h ν J> k B T. In this limit, quantum corrections to the mixed-down noise are important. The spectral densities measured on junctions with current-voltage characteristics close to the Stewart-McCumber model were in excellent agreement with the predicted values, with no fitted parameters. The mixed-down noise for a wide range of bias voltages was used to infer the spectral density of the current noise in the shunt resistor at frequency ν. With no fitted parameters, this spectral density at frequencies up to 500 GHz was in excellent agreement with the prediction (2 h ν R) coth (h ν 2 k B T). The presence of the zero-point term, 2 h ν R, at frequencies h ν> k B T was clearly demonstrated. The current-voltage characteristics of a junction with β L≡ 2 π L s I 0 Φ 0∼ 1 and β C≡ 2 π I 0 R 2 C Φ 0≪ 1, where I 0 is the critical current, C is the junction capacitance, and L s is the shunt inductance, showed structure at voltages where the Josephson frequency was near a subharmonic of the L s C resonant frequency. The additional nonlinearity of the I− V characteristic caused mixing down of noise near higher harmonics of the Josephson frequency, thereby greatly enhancing the voltage noise. The measured noise was in good agreement with that predicted by computer simulations.