[volt-nuts] Low-cost Josephson Junction Array

[acbern at gmx.de]

About two years ago I started an exercise to determine what it would take to build a kind of DIY JJ standard and also looked at certain detail technical aspects of designing/building what is reasonable doable. Baseline was 10V DC. It was clear that it would not be cheap, and I also looked at this as a personal challenge. So here in a nutshell: 
I did talk to a vendor of the JJA, and we finally agreed he would be supporting me with supplying a JJA and related waveguide with flange attached. Nothing else, to save costs. What would have remained is the 75Ghz RF source (including further waveguides with dewar interface and helium block, RF source, directional coupler and RF generator. Key is a source with low harmonics, so using a trippler and a 26.5GHz generator (locked to a gps-calibrated rubidium source) was a potential solution, but it was not clear if that would have been sufficienly clean overall, so quite some risk here having to go with another solution finally (Gunn...). Also the amplifier portion and transmission of the RF signal to the JJA without too much loss is not that simple, as the power needed is not that low. Lots of discussions with the vendor. Helium would have been obtained in a loaner dewar from a gas manufacturer, I did have a quotation at pretty reasonable cost, no need to go with a cryocooler (which can cause a lot of voltage noise potentialy, killing the DC signal). And some driving electronics of course, doable with reasonable effort. While I had some equipment such as e.g. the RF generator and reference clock, the shopping list was not that short. Also some test gear such as a 75GHz power head and so on was also on the shopping list. 
To make a long story short, I ended up with an estimate of 30 to 40 kUSD, with about 10k of additional risk, with the majority being the cost of the JJA. Quite some expense for an in the end academic exercise, so I finally decided to not further pursue this. I need to add that, being an EE, with no experience in cryo stuff, I would have got support by a fried who is physicist, otherwise I would not even have considered it (you cannot just put the JJA into the dewar...). There are some potential ways to cut the costs mentioned, e.g. by going with 1V instead, or having access to suitable 75GHz gear, but it is still a several 10k exercise.
Overall, at least from my perspective, it was just not worth it. Quite some risk and lots of time until it works. So I continue to send my references to a good lab with well below 1ppm of uncertainty, and I have an independent cal document, even though of course, it would certainly have been a lot of (quite expensive) fun.




> Gesendet: Donnerstag, 20. Oktober 2016 um 00:35 Uhr
> Von: "Ken Peek" <ken.peek at diligentminds.com>
> An: volt-nuts <volt-nuts at febo.com>
> Betreff: Re: [volt-nuts] Low-cost Josephson Junction Array
>
> @Vince:
> 
> Thank you for the link!  Very informative!  There is also a nice video
> showing some of the lab techniques, and some cautions working with
> cryogenic liquids.
> 
> I would also like to explore miniature cryocoolers-- as these might be able
> to support a small lower power array (1V) if it doesn't dissipate too much
> power...
> 
> There is already some progress in this area with a QHR made from graphene
> (at the NPL in the UK).  So, maybe the same cryocooler could be used also
> for the low-cost JJA ?
> 
> Having a 10V (fixed output) JJA and a 12K9 QHR would be the basis to
> calibrate all other electrical standards in a lab.  It would be nice to
> have these sitting in their cryocoolers cranking out volts and ohms
> practically indefinitely (or as long as you want)-- and if one has even a
> rubidium atomic clock, then no external signals or standards of any kind
> would be needed.  Well, that and a triple-point of water cell (which I
> have) for temperature calibrations.
> 
> -Ken
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