P-A Colloquium: Development of Cryogenic Memory for Superconducting Computers
Speaker: Norman Birge, Michigan State University
Title: Development of Cryogenic Memory for Superconducting Computers
Refreshments at 3:30 pm in 1400 BPS.
Date: Thu, 02 Feb 2017, 4:10 pm - 5:10 pm
Location: 1415 BPS Bldg.
Large-scale computing facilities and data centers are using electrical power at an ever increasing rate. Current projections suggest that a future “exoscale” computer will require the power output of a typical nuclear power plant  – clearly an untenable situation. One approach to addressing this problem is to build a computer out of all superconducting elements, which dissipate very little power. Such a computer would have to be cooled to cryogenic temperatures, of course, so it must be extremely energy-efficient to justify the added complexity and cost associated with cooling.
Superconducting logic circuits based on manipulating single flux quanta have existed since 1991 ; what has been missing is a high-density, fast, and energy-efficient cryogenic memory. This talk will focus on proposals to use Josephson junctions containing ferromagnetic (F) materials as the basic memory element for such a memory . In our approach, a Josephson junction contains two ferromagnetic layers whose magnetization directions can be switched between being parallel or antiparallel to each other, just as in a conventional spin valve. We have recently demonstrated successful switching of such a junction between the “0” phase state and the “π” phase state, from measurements of two junctions in a SQUID geometry . If there is time, we will also discuss other possible types of Josephson junction memory elements, such as those that carry spin-triplet supercurrent rather than the conventional spin-singlet supercurrent.
 D.S. Holmes, A.L. Ripple, & M.A. Manheimer, IEEE Trans. Appl. Supercond. 23, 1701610 (2013).
 K.K. Likharev & V.K. Semenov, IEEE Trans. Appl. Supercond. 1, 3 (1991).
 A.Y. Herr & Q.P. Herr, US Patent 8,270,209 (2012).
 E. C. Gingrich, B. M. Niedzielski, J. A. Glick, Y. Wang, D. L. Miller, R. Loloee. W. P. Pratt Jr., and N. O. Birge, Nature Physics 12, 564 (2016), doi:10.1038/nphys3681.