Browse Prior Art Database

DC Squid Vortex 0.1 Degree K Thermometer

IP.com Disclosure Number: IPCOM000050934D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Ketchen, M: AUTHOR [+2]

Abstract

Accurate temperature measurement in the 0.10K region is possible using a pair of inductively coupled non-hysteretic two-junction quantum interferometers (DC SQUIDs).

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DC Squid Vortex 0.1 Degree K Thermometer

Accurate temperature measurement in the 0.10K region is possible using a pair of inductively coupled non-hysteretic two-junction quantum interferometers (DC SQUIDs).

At the present time there are no universally accepted thermometers for use at temperatures below 0.10K degrees. Most thermometers presently in use for mK work rely on physical processes which are themselves poorly understood and/or suffer from other difficulties such as self heating. This thermometer circumvents many of the standard difficult ies and presents an attractive alternative to existing devices.

The device consists of a pair of inductively coupled non-hysteretic two-junction quantum interferometers (SQUIDS A and B in Fig. 1). SQUID A is biased below threshold with an applied flux theta approximately theta /2 + n theta (n=0+/-1 +/-2...). At this bias point, there are two non-dissipative (vortex) states with distinct values of screening current J accessible to the device (Fig. 2A). Thermally induced transitions between these states result in a random switching of the screening current around SQUID loop A. The transition probability is an exponential function of the barrier height delta U and the thermal energy K(B)T, P=C exp (- delta U/K(B)T).

The potential barrier is a function of the external DC bias current. The prefactor is a weak function of the bias point.

Successive transitions produce a switching of the circulating current as indicated in the figure. As a result, the flux linked into SQUID B is biased in the voltage state with a non-zero flux to voltage forward transfer function. As a result, switching is observed as a chain of voltage pulses at the output of SQUID
B...