* 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}
{wiki}

The voltage changes perpendicular to the current when magnetic field is applied.

\Image[https://upload.wikimedia.org/wikipedia/commons/1/19/Hall_Effect_Measurement_Setup_for_Electrons.png]
{title=<Hall effect> experimental diagram}
{description=The <Hall effect> refers to the produced voltage $V_H$, AKA $V_y$ on this setup.}

An intuitive video is:

\Video[https://upload.wikimedia.org/wikipedia/commons/transcoded/7/77/Hall_Sensor.webm/Hall_Sensor.webm.480p.vp9.webm]

The key formula for it is:
$$
V_{H} = \frac{I_x B_z}{n t e}
$$
where:
* $I_x$: current on x direction, which we can control by changing the voltage $V_x$
* $B_z$: strength of transversal <magnetic field> applied
* $n$: <charge carrier density>, a property of the material used
* $t$: height of the plate
* $e$: <electron charge>

Applications:
* the direction of the effect proves that electric currents in common electrical conductors are made up of negative charged particles
* <magnetometer>[measure magnetic fields], TODO vs other methods

Other more precise non-classical versions:
* <quantum Hall effect>

Bibliography:
* http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/Hall.html


Hall effect

{c}
{tag=Electronic component}
{tag=Magnetometer}
{wiki=SQUID}

Can be used as a very precise <magnetometer>.

There are high temperature <yttrium barium copper oxide> ones that work on <liquid nitrogen>.

\Video[https://www.youtube.com/watch?v=d_vrhzX3VcE]
{title=Superconducting Quantum Interference Device by Felipe Contipelli (2019)}
{description=Good intuiotionistic video. Some points deserved a bit more detail.}

\Video[https://www.youtube.com/watch?v=0kl3ucjh2Uw]
{title=Mishmash of SQUID interviews and talks by Bartek Glowaki}
{description=
The videos come from: https://www.ascg.msm.cam.ac.uk/lectures/[]. Vintage.

Mentions that the <SQUID device> is analogous to a <double-slit experiment>.

One of the segments is by John Clarke.
}

\Video[https://www.youtube.com/watch?v=ql2Yo5LgU8M]
{title=Superconducting Quantum Interference Devices by <UNSW> Physics (2020)}
{description=
An experimental lab video for <COVID-19> lockdown. Thanks, <COVID-19>. Presented by a cute and awkward Adam Stewart.

Uses a <SQUID device> and control system made by <STAR Cryoelectronics>. We can see <Mr. SQUID> EB-03 written on the probe and control box, that is their educational product.

As mentioned on the Mr. SQUID specs, it is a <high-temperature superconductor>, so <liquid nitrogen> is used.

He then measures the <I-V curve> on an <Agilent Technologies oscilloscope>.

Unfortunately, the video doesn't explain very well what is happening behind the scenes, e.g. with a <circuit diagram>. That is the curse of university laboratory videos: some of them assume that students will have material from other internal sources.

* https://youtu.be/ql2Yo5LgU8M?t=211 shows the classic voltage oscillations, presumably on a magnetic field sweep, and then he puts a <magnet> next to the device from outside the <Dewar>
* https://youtu.be/ql2Yo5LgU8M?t=253 demonstrates the formation of <Shapiro steps>. Inserts a <Rohde & Schwarz> signal generator into the Dewar to vary the flux. The result is not amazing, but they are visible somewhat.
}

\Video[https://www.youtube.com/watch?v=7PJguB3Y8L8]
{title=The Ubiquitous <SQUID device>[SQUID] by John Clarke (2018)}


Ciro Santilli @cirosantilli 37

 Incoming links: Magnetometer