P-A Colloquium: Development of Cryogenic Memory for Superconducting Computers

Speaker:  Norman Birge, Michigan State University

Title:  Development of Cryogenic Memory for Superconducting Computers

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Refreshments at 3:30 pm in 1400 BPS.

Date: Thu, 02 Feb 2017, 4:10 pm - 5:10 pm  

Type: Colloquium

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 [1] – 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 [2]; 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 [3]. 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 [4]. 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.

[1] D.S. Holmes, A.L. Ripple, & M.A. Manheimer, IEEE Trans. Appl. Supercond. 23, 1701610 (2013).
[2] K.K. Likharev & V.K. Semenov, IEEE Trans. Appl. Supercond. 1, 3 (1991).
[3] A.Y. Herr & Q.P. Herr, US Patent 8,270,209 (2012).
[4] 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.