Contribution of Thermal Noise to the Line-Width of Josephson Radiation From Superconducting Point Contacts

Abstract

(Rccciwd I 4 J d y IF167)The line-width of the Josephson cscilhtions ol ; I voltapr-biased superc.olLduc-tiiig point contact has been measured k r w t c n I .4*K and IPK, with bias resistors H bctwnn I .7 X 10"' f l and 2.6 x IO-f n. Within the experimental accuracy the line-width is pruponicwral t o HT. and is coiisi*ttnl with the estimated theoretical value 8kTRPPI. where 4 b Boltzmann's constant and 4% is the Hux quantum. lim-widths below 0.1 l i z have been obscrvd at 4.PK for R = 1.7 x iO-" 0. pnwiding an experimental upper iimit io other noise sources and indicating that h i s is useful as a voltmeter and thermometer k k ; w I t P V and IO-+'K.It has been proposed' that a voluphiased superconducting point contactza might be used as a low temperature thermometer. This p r o p 1 was based on the assumption that the main contribution to the he-width of the Josephson radiation fmrn a superconducting point contact comes from the thermal noise voltage on the shunt mistor supply-* S u p p o d in part by NASA.ing the bias voltage. A simple argument t k n pdicts that the iine-width should be proportional to the shunt resistance R and absolute temperature T of this resistance. We report here an experimental verification of these predictions for values of T betwee9 1.4"K and 8°K and of R between 1.7 x IO-'' fl and 2.6 X 10-' 0.

Generation of Harmonics and Subharmonics of the Josephson Oscillation

“…The quantum number decreases with ie in full agreement with Eq. (14). Using the same resistance and inductance as above, we generated solutions for smaller ie which readily reproduce the results of Figs.…”

Linewidth measurement of millimeter wave radiation from a Josephson array source coupled to free space

“…The radiation linewidth of a single resistively shunted Josephson junction (RSJ) has been well studied [lo], [ll], and the predictions were verified experimentally [12], [13].…”

Resistive SQUID calorimetry at low temperatures

“…It can be shown 9 that the average value of the integral of v 2 over an interval of length tm is (Iot"Vn(t) 2 dt)= 2kTrt,~ (10) Hence the rms change in 0 brought about in a time t,, is…”