Wideband Detection of the Third Moment of Shot Noise by a Hysteretic Josephson Junction

We use a hysteretic Josephson junction as an on-chip detector of the third moment of shot noise of a tunnel junction. The detectable bandwidth is determined by the plasma frequency of the detector, which is about 50 GHz in the present experiment. The third moment of shot noise results in a measurable change of the switching rate when reversing polarity of the current through the noise source. We analyze the observed asymmetry assuming adiabatic response of the detector.

Figure 1

Measurement scheme for on-chip detection of noise. A Josephson junction detects the current fluctuations arising from the noise source. Only heavily filtered dc lines (through cold resistors, line inductances, and thermocoax cables) connect the setup with the room temperature amplifiers and current sources. On top right we show the $IV$ characteristics of the detector junction taken with different values of average current ${\overline{I}}_N$ through the NIS noise source. The $IV$ of this NIS source is depicted in the lower right graph at small currents.

Figure 2

Escape characteristics of sample NIS. (a) Histograms taken with the four different polarity configurations of noise and pulse currents, and at several values of noise current: $|{\overline{I}}_N|=0\dots 3.8\mu \mathrm{A}$ from right to left. (b) Escape rates corresponding to $|{\overline{I}}_N|=2.2$, 2.4, and $2.6\mu \mathrm{A}$ from right to left displaying the splitting of data with $I^{++}$ and $I^{--}$ currents from those with $I^{+-}$ and $I^{-+}$ currents, respectively. (c) Escape rates with ${\overline{I}}_N=0$ in the MQT regime.

Figure 3

Results related to the second moment of shot noise. (a) Effective temperature extracted from measured escape histograms using Eq. (2) for $P=0.1$ (●), 0.5 (▵), and 0.9 (*). The solid line is obtained using Eq. (1) with $F=1$ and $Q=2.5$ determined from the bias current at which the underdamped phase diffusion sets in. This is shown by the arrow in (b), where width of the histogram has been plotted against ${\overline{I}}_N$. The dashed line is from the effective temperature model, ignoring phase diffusion.

Figure 4

Difference in switching currents of the threshold detector under reversal of the relative polarities of bias and noise currents. Data of sample NIS are shown by filled dots, of sample SIS by triangles and data of the reference sample, sample REF, by open dots. The solid lines are the result of the theoretical model for samples NIS and SIS. At currents ${\overline{I}}_N\le 0.2\mu \mathrm{A}$ the noise source of sample SIS is in the superconducting state, and the signal due to the third moment vanishes.