Technical challenges I'd like to see more discussion on from IMEC:
- Superconductors are lossy with AC signals, is this loss not a big problem?
- Cooling things is very expensive, is this approach not simply transferring the costs to the cooling plant?
- I imagine that having a superconducting interconnect represents an impedance discontinuity, effects like the large kinetic inductances in superconducting materials have large ramifications on signal integrity. Any comments on how to deal with these problems? I worry when I see the words "top-down approach" towards this problem because from my experience it should be driven bottom-up. Superconducting circuits are not just: 'Oh it's lossless in DC, everything is great!' You have new limitations on trace dimensions because if you go too small or you drive too large a current you kill the superconducting state.
- NbTiN with amorphous Si as the barrier. How sensitive is the system to stray magnetic fields and stray radiation? If one of these structures switches into the normal state can it reset itself like sc photon detectors do or are the phonons trapped and the structure is latched in the normal state?
- Superconductors are lossy with AC signals, is this loss not a big problem?
In this logic style, data are represented with fluxons. One fluxon is the quantum unit of flux. You can't have "half a fluxon" in a superconducting loop. In that sense it's actually "more digital than" anything in commercial CMOS chips. The circuit can still malfunction of course -- the failure mode looks like a fluxon failing to move from one logic stage to the next.
The real worry is that cryocooler though. Cryocoolers that can do liquid helium temperatures have efficiency ratings around 1%, so that 500kW shoebox is going to need an entire cooling tower attached to its refrigerator.
There are a lot of ways to do helium recycling (common these days for MRI magnets), never 100% but close. Also there is a lot of helium wasted because it is not worth saving for the small amounts you could sell.
- Superconductors are lossy with AC signals, is this loss not a big problem?
- Cooling things is very expensive, is this approach not simply transferring the costs to the cooling plant?
- I imagine that having a superconducting interconnect represents an impedance discontinuity, effects like the large kinetic inductances in superconducting materials have large ramifications on signal integrity. Any comments on how to deal with these problems? I worry when I see the words "top-down approach" towards this problem because from my experience it should be driven bottom-up. Superconducting circuits are not just: 'Oh it's lossless in DC, everything is great!' You have new limitations on trace dimensions because if you go too small or you drive too large a current you kill the superconducting state.
- NbTiN with amorphous Si as the barrier. How sensitive is the system to stray magnetic fields and stray radiation? If one of these structures switches into the normal state can it reset itself like sc photon detectors do or are the phonons trapped and the structure is latched in the normal state?
It's nice to see people working on this.