{wiki}

Unit of <electric current>.

Affected by the <ampere in the 2019 redefinition of the SI base units>.


Ampere

* the basis for the most promising 2019 <quantum computing> implementation: <superconducting quantum computer>
* <Josephson voltage standard>: the most practical/precise <Volt> standard, which motivated the definition of the <ampere in the 2019 redefinition of the SI base units>
* <SQUID devices>, which are:
  * very precise <magnetometer>
  * the basis for <superconducting quantum computers>


Applications of Josephson Junctions

{c}
{title2=JVS}
{wiki}

The most practical/precise volt standard.

It motivated the definition of the <ampere in the 2019 redefinition of the SI base units>

Good <NIST> articles about it:
* https://www.nist.gov/news-events/news/2013/04/primary-voltage-standard-whole-world[A Primary Voltage Standard for the Whole World]
   (2013)
 (https://web.archive.org/web/20190410011041/https://www.nist.gov/news-events/news/2013/04/primary-voltage-standard-whole-world[archive])
* https://www.nist.gov/pml/history-nist-quantum-voltage-standards[History of NIST Quantum Voltage Standards (2011-2022)]

The wiki page https://en.wikipedia.org/wiki/Josephson_voltage_standard contains amazing schematics of the device, apparently made by the <US Government>.

\Image[https://upload.wikimedia.org/wikipedia/commons/2/2b/Layout_and_Schematic_of_JVS_Chip.jpg]
{title=Schematic of a typical <Josephson voltage standard> chip}
{height=600}

\Image[https://web.archive.org/web/20241201074611im_/https://www.nist.gov/sites/default/files/styles/480_x_480_limit/public/images/pml/div686/devices/sam-switch900.png?itok=OyCJl26y]
{title=Sam Benz demonstrating the equipment required the voltage standard}
{height=600}
{source=https://www.nist.gov/news-events/news/2013/04/primary-voltage-standard-whole-world}

\Video[https://www.youtube.com/watch?v=VoRab8U2eS0]
{title=The evolution of voltage metrology to the latest generation of JVSs by Alain Rüfenacht}
{description=
Talk given in 2023. The speaker is from <NIST>, and the talk was hosted by the <BIPM>. Fantastic talk.
* https://youtu.be/VoRab8U2eS0?t=354 the desired output voltage is 10V
* https://youtu.be/VoRab8U2eS0?t=475 lists the three most commonly used 10V implementations currently:
  * <Japanese> one by <AIST>
  * <American> one by <NIST>
  * <German> one by <PTB>
}

\Video[https://www.youtube.com/watch?v=VoRab8U2eS0]
{title=Technical aspects of realizing the DC volt in the laboratory with a JVS by Stéphane Solve}
{description=
Talk given in 2023. The speaker is from <BIPM>, and the talk was hosted by the <BIPM>. Fantastic talk.
* https://youtu.be/6pgGNJby1lw?t=296 gives the experimental setup used to compare two different references. Notably it involves a <nanovoltmeter>
}


Josephson voltage standard

{tag=Hall effect}
{tag=Physics experiment without a decent modern video}
{title2=theorized 1975}
{title2=observed 1978}
{wiki}

Quantum version of the <Hall effect>.

As you increase the <magnetic field>, you can see the <Hall resistance> increase, but it does so in discrete steps.

\Image[https://upload.wikimedia.org/wikipedia/commons/3/38/Rhoxy.jpg]
{title=<Hall resistance> as a function of the applied <magnetic field> showing the <Quantum Hall effect>}
{description=As we can see, the blue line of the <Hall resistance>  TODO material, temperature, etc. It is unclear if this is just }

Gotta understand this because the name sounds cool. Maybe also because it is used to define the <fucking> <ampere in the 2019 redefinition of the SI base units>.

At least the experiment description itself is easy to understand. The hard part is the physical theory behind.

TODO <videos of all key physics experiments>[experiment video].

The effect can be separated into two modes:
* <Integer quantum Hall effect>: easier to explain from first principles
* <Fractional quantum Hall effect>: harder to explain from first principles
  * <Fractional quantum Hall effect for \nu = 1 m>: <1998 Nobel Prize in Physics>
  * <Fractional quantum Hall effect for \nu \ne 1 m>: one of the most important <unsolved physics problems> as of 2023

\Video[https://www.youtube.com/watch?v=UNyNjZeG1wc]
{title=Integer and fractional quantum Hall effects by Matthew A. Grayson}
{description=Presented 2015. This dude did good.}


Ciro Santilli @cirosantilli 35

 Incoming links: Ampere in the 2019 redefinition of the SI base units