Home made Josephson Junction? - Page 1
Forum section: electronics / general

author: Amper
author_rank: Frequent Contributor
timestamp: May 01, 2018, 03:51:15 pm
content: Hello World!I hope, this first post will not already be a stupid one, but i have to ask someone ^^Over the last few years i have been doing a lot of dumpster diving at several institutes around my university and have accumulated a nice variety of instruments and machinery. Most notably a lot of vacuum equipment including two turbomolecular pumps plus accessories, a 10K CTI cryocooler, a HP3457a in perfect condition, HP3457a in perfect condition, HP5350 (20GHz counter) in perfect condition and a lot of other kethley meters. First obviously im bulding a Farnsworth fusor, because thats just what you have to do when you have high vacuum at hand.Though now i noticed that with this combination of material maybe i could actually build something more unique. If the cryocooler will reach the advertised "less than 10K" i would be able to get niobium to superconduct. With the vacuum equipment i have, basic thin film deposition should be possible quite easily, maybe even pulsed laser deposition with a small YAG. Photolithography can be done in a university lab and there i also would have access to SEM.How do you guys think, would this be in the range of possibilities, or is there some trick to J Junctions, that i dont know about?Cheers!Amp

author: ez24
author_rank: Super Contributor
timestamp: May 01, 2018, 07:20:05 pm
content: I am probably wrong but I think member Tin is (was) working on one or doing something like this with liquid nitrogen. Lets see if he finds this.

author: TiN
author_rank: Super Contributor
timestamp: May 01, 2018, 08:07:03 pm
content: I wish. LN2-cooled LTZ1000 stuff not even close. And buying 77K cryocooler does not count either. But I'd definately be remotely interested in the information about JJA system designs. After all , 10V JJA chip from NIST at 50K$ is "remotely affordable" for extreme volt-nut, given that all other hard stuff like cryostat, biasing source, shielding and housing, RF source and software to control it all is ready.Topic starter should clarify, if he interested in making Josephson effect (few junctions would be enough to see effect, even from HTS materials) or actual JJ array to generate somewhat usual voltages (hundred mV-V range).

author: Amper
author_rank: Frequent Contributor
timestamp: May 01, 2018, 08:22:07 pm
content: @zhtoor: Thank you very much, that looks like it will help!@TiN of cause im interested in making a 10V array, but obviously i think thats not even close to beeing possible with my stuff... Even if i did manage to make an array with enough cells to get to that voltage, its still pretty worthless without being able to verify the voltage exactly for calibrating anything. HTS is difficult sadly, i have tried making ybco, but so far it failed. Even ybco made by aldridge (thank you trashcan) is hard to get superconducting, because it still needs to be sintered and enriched with oxygen, not even talking about doing thin film stuff with these complex crystals.I guess i will need to check if i can get down to the necessary temperatures for the niobium. Maybe getting helium is possible here, but having to beg for stuff on every try would take a lot of fun out of it all.

author: ap
author_rank: Frequent Contributor
timestamp: May 01, 2018, 09:11:51 pm
content: I did a review some years ago about a DIY JJS. This however was based on buying an existing JJA and building the stuff arround it, which is complicated enough. The costs are considerable, even though the special costs of the JJA quoted was well below the 50k Tin mentioned above. Just the cost of a stable and powerfull 75GHz source (and related test gear) is 5 digits. I am not sure it is very realistic to build a JJA from scratch (in a realistic time/cost frame), given all the test issues (if it does not work, how do you make sure its not the DIY JJA). Even with a known good JJA, I decided its not worth it (at least for me allone). The cryocooler does not necessarily make things easier, its interferance is not to be underestimated.

author: TiN
author_rank: Super Contributor
timestamp: May 01, 2018, 09:34:45 pm
content: If one to go lower voltage amplitude, e.g. 1V or pulsed operation, then smaller (20ish GHz) frequency can also work, which is somewhat easier than 75.

author: Moon Winx
author_rank: Regular Contributor
timestamp: May 01, 2018, 11:28:23 pm
content: Quote from: ap on May 01, 2018, 09:11:51 pmYeah, these systems aren't exactly easy to use even with $400k worth of supporting equipment. The cryocooler just makes it harder, and good luck getting anything worthwhile @ 10 K. We have some chips that have sufficient critical current at around 8-9 K but it is unusable as a stable voltage at that temperature. You'll never rest on a single stable constant voltage step for any appreciable amount of time.

author: cellularmitosis
author_rank: Unknown
timestamp: May 02, 2018, 12:51:54 am
content: Quote from: Amper on May 01, 2018, 08:22:07 pmDid someone say ybco?https://youtu.be/sLFaa6RPJIU

author: Amper
author_rank: Frequent Contributor
timestamp: May 02, 2018, 05:27:40 am
content: @ap: What kind of interference ? The mechanical part can be shut down for a measurement, then it would just be a lump of metal. The "electronics" are in the compressor unit located several meters away.Thank you guys so far for the answers, these are exactly the kinds of problems i wanted to know about!My hope just was, that while making a real useful reference voltage supply is difficult, getting the basic effect would not be so much. Kind of like an electron microscope is several 100k and you can still build a small working one at home just sacrificing image quality.

author: ap
author_rank: Frequent Contributor
timestamp: May 02, 2018, 07:48:31 am
content: Overall the setup is very senstive to EMC, which may disturb the JJA function sufficiently to not work properly. Isolating it from the rest of the world is key.Also, all JJAs I am aware of are working at 75ish GHz, going down to 20GHz would make life considerably easier, however the RF tuning of commercially available JJAs will not allow that.

author: BU508A
author_rank: Super Contributor
timestamp: May 02, 2018, 08:42:26 am
content: I'd like you to point also to this website:https://www.ptb.de/cms/de/ptb/fachabteilungen/abt2/abt2-josephson.html(sorry, it is in german).There you can find some additional information about JJAs.If you really want to go this very stoney way and build your home-made JJA, then I wish you (in no particular order):- a lot of luck- a huge bag of money- stamina- endurance- lots of support- all the best- becoming a machinist-nut- becoming a RF-nut- becoming a time-nut- becoming a volt-nutImho.

author: Amper
author_rank: Frequent Contributor
timestamp: May 02, 2018, 10:09:41 am
content: @ap: Yes, reaching the usual 70GHz will be pretty much impossible with a home setup. Though the document zia posted in the first answer the used below 10GHz from a stabilized clystron. Their setup at the time was below 1ppm and was used as the Australian U standard even with only a single junction. I imagine i can update my HP5350 with an RB standard and use the output to fine tune the clystron in a feedback loop. This should give a pretty stable frequency. up to the 20GHz limit of the meter.The decoupling from the environment iss difficult, yes. i hope, that loosely mounting the assembly on the tip of the cooler sticking inside of the UHV chamber should be sufficient though. it has to be mounted somehow anyways, even in LHe it will not experience less vibration. Also the cooling will work a bit better without atmosphere. Also i could manufacture a new tip for the coldhead made from carbon fiber, further reducing the heat transfer to the outside. That could get the Temperature down by a bit more, though hopefully its not necessary.@BU508A: Thanks ^^ I think the nuttery is strong in me, about the rest we will seeObtaining equipment is some times easier than thought as a student. The most expensive things are usually left over in some place. Many scientists at universities are more than happy when they see someone who is actually interested in the stuff and not only doing it for some thesis. This leads to odd situations like having a cryocompressor and coldhead in working condition, but the helium lines to connect them are missing and cost me more time to obtain than all the really expensive stuff.about the PTB site i knew already, they are actually also referenced to in zias document, seems like ptb instructed the aussies how to do itI just found another Site, havent read it so far, but it looks to be promising:http://www.wikiwand.com/en/Josephson_voltage_standardIm curious how the RF is fed in and filtered later. The Australians used 6 twisted"pair" wires to get the dc measurement, probably the RF jis just not able to get through there.EDIT: These guys did it with a cryocooler and it actually seems to be the same as the one i havehttps://staff.aist.go.jp/h.yamamori/pjvs.html

author: saturnin
author_rank: Regular Contributor
timestamp: May 02, 2018, 05:00:41 pm
content: Some time ago, I found very nice demonstration video about Josephson Junction Effects (DC&AC). Professor Sumner Davis (University of California, Berkeley) presents basic theory and some experimental technics related to Josephson Junction Effects:https://archive.org/details/ucberkeley_webcast_Z9vBPQrG0U4Enjoy

author: Amper
author_rank: Frequent Contributor
timestamp: May 02, 2018, 06:35:55 pm
content: Thats a very nice video! Sadly no data on the frequency and amplification equipment, but its nice to see, how simple the setup can be. Seems to be a nice first step!

author: saturnin
author_rank: Regular Contributor
timestamp: May 02, 2018, 07:25:03 pm
content: I was also surprised you can basically create Josephson Junction on you own at home - just for observation of the Josephson effect though (due to low output voltage of a single JJ which impractical any real use).They used HP8350B with frequency range from 9 to 13 GHz. Its output was sent to a frequency doubler, so they got 18-26 GHz. The whole experimental setup is described in following pdf:http://experimentationlab.berkeley.edu/sites/default/files/writeups/JOS.pdf(~10 MB)

author: RoGeorge
author_rank: Super Contributor
timestamp: May 02, 2018, 09:01:17 pm
content: Thanks for the video, never thought the Josephson effect could be seen using such low tech and manual adjustmentYet, I wouldn't expect to see all that oscilloscope wiggling either, not from an intrinsic voltage standard