Josephson Junction: Perpetual Motion System?

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In summary, the Josephson junction is a device which can allegedly create "supercurrent" which flows indefinitely without any voltage applied. Although this concept is not perpetual motion in the usual sense, it is still an interesting device which has some unusual properties.
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Fizica7
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Isn't the Josephson junction in effect a perpetual motion system ?
 
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Whats the reasoning behind this? There's no energy lost in the tunnelling of a cooper pair across the junction, as that's the essence of quantum mechanical tunnelling, the probability of tunnelling across the junction is just resonant with the barrier height ##E_j##, that being if the energy of the cooper pair is an integer multiple of ##E_j## then the tunnelling probability is greatest.
 
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Well it seems like one of those "Did you know that..." type thingy... As I see it it's motion, of electricity, without any end in sight... Sure it's not scalable or of any real use but it is like a very rare thing which laughs in the face of the notion that there is no such thing as a perpetual system... It's like a very rare gem.
I mean if you create one and trow it into deep space, I'll reach the other side of the galaxy and still hold its tiny charge, no?
 
  • #5
drvrm said:
pl. look up the following and point out at which stage of the working of the J Junction you felt like "a perpetual motion system "?

https://www.ph.tum.de/academics/org/labs/fopra/docs/userguide-16.en.pdf

I'm not going to read that cause it's above my pay grade(shhh-education).
I initially found out about the Josephson junction while browsing Wikipedia where it says :
" The Josephson effect is the phenomenon ofsupercurrent—i.e. a current that flows indefinitely long without any voltage applied—across a device known as a Josephson junction (JJ), ".
So i imagined it as a tiny loop of electricity that never stops going around the loop... isn't it so? Or maybe the wiki article needs better wording?
 
  • #6
First of all, you seem to be confusing a Josephson junction -which is a type of device which is typically made from an insulating layer sandwiched between two superconducting electrons - with the phenomenon of supercurrent which has to do with current flowing "without resistance" in a superconductor.
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Now, if you make a loop of a superconducting material (no Josephson junction needed) and somehow induce a current (there are are various ways of doing this) in it, he current will indeed -ideally- flow forever since a perfect superconductor will have no dissipation at DC. This is how superconducting magnets are used when in "persistent" mode.

However, this is not perpetual motion in the usual sense (which tends to refer to phenomena which "creates" energy). If you try to use the energy "stored" in this flowing current (the inductive energy) for anything it will decrease and eventually stop flowing altogether.

Hence, it is no more perpetual motion than the Earth circling the sun; you can store energy in such a system but it can't create "new" energy.
 
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Yeah I might be mixing the 2 a little bit cause when I first heard that notion ( nothing lasts forever, there's no perpetual motion) it was at a very small age, maybe 5, and it stuck with me in the sense that it was like the definition of unachievable... Like just the notion itself, that it would be impossible to create something, place it on a table, give it a "go" and it would last forever..it was just so fascinating to read about the possibility that there is something than can be man made and will last forever. In my mind it never required to do any "work" or to have any practical use to qualify as a perpetual motion... just it's existence alone.
 

1. What is a Josephson Junction?

A Josephson Junction is a device made of two superconducting materials separated by an insulating layer. It allows for the flow of supercurrent, which is the current that flows without any resistance.

2. How does a Josephson Junction work?

The Josephson Junction works by exploiting a quantum mechanical effect known as the Josephson effect. This effect allows for the flow of supercurrent between the two superconducting materials, as long as they are at a specific temperature and have a specific voltage applied to them.

3. Can a Josephson Junction be used for perpetual motion?

No, a Josephson Junction cannot be used for perpetual motion. While it does allow for the flow of supercurrent without resistance, it still requires energy to function and cannot create an infinite amount of energy.

4. What is the potential application of a Josephson Junction?

Josephson Junctions have potential applications in quantum computing, precision measurements, and high-speed signal processing. They are also used in devices such as superconducting quantum interference devices (SQUIDs) and superconducting quantum bits (qubits).

5. Are there any limitations to the use of Josephson Junctions?

Yes, there are limitations to the use of Josephson Junctions. They require extremely low temperatures and precise voltage control to function, which can be challenging and expensive to achieve. Additionally, they are sensitive to external magnetic fields, which can interfere with their operation.

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