B Is superconductivity something usual or weird?

[Spathi]

TL;DR

Maybe an experiment with superconductors can be invented, which illustrates something weird, like Elitzur–Vaidman bomb test?

Wikipedia says that superconductivity is a phenomenon which can only be explained by quantum mechanics. Maybe there is a close relation between the connection of superconductor parts and quantum entanglement? If yes, a question arises: what is the speed of electric current flowing through the superconductor? Is it equal to the speed of light, or maybe tachyonic? Please forgive me for this question, of course I understand that the quantum entanglement does not allow to transfer information; but this stupid question gives birth to an idea – maybe an experiment with superconductors can be invented, which illustrates something weird, like Elitzur–Vaidman bomb test?

 

[vanhees71]

Quantum theory is not weird but the most successful theory we have to describe Nature.

 

[topsquark]

TL;DR Summary: Maybe an experiment with superconductors can be invented, which illustrates something weird, like Elitzur–Vaidman bomb test?

Wikipedia says that superconductivity is a phenomenon which can only be explained by quantum mechanics. Maybe there is a close relation between the connection of superconductor parts and quantum entanglement? If yes, a question arises: what is the speed of electric current flowing through the superconductor? Is it equal to the speed of light, or maybe tachyonic? Please forgive me for this question, of course I understand that the quantum entanglement does not allow to transfer information; but this stupid question gives birth to an idea – maybe an experiment with superconductors can be invented, which illustrates something weird, like Elitzur–Vaidman bomb test?

The current in a superconductor is by Cooper pairs rather than single electrons. But the main principle is the same: the Cooper pairs are bonded electrons and electrons are physical particles that cannot travel faster than the speed of light. According to Wikipedia, the drift velocity of electrons in a 2mm diameter copper wire is around 8 cm/h. Cooper pairs probably don't move much faster than that.

(Changes in electric potential travel at close to the speed of light in a material. The electrons really don't move around that much.)

-Dan

 

[Drakkith]

If yes, a question arises: what is the speed of electric current flowing through the superconductor?

That's a rather complicated question to answer, as 'speed' of the current isn't very well defined. Electrons in a conductor are always moving throughout the material in random directions at various speeds. The so-called 'drift velocity' is the average velocity of all these electrons, which, for zero current flow, averages out to zero.

Once an electric potential (voltage) is applied each electron gains a slight amount of velocity in the direction opposite of the electric field. They still move about randomly, it's just that the average velocity of the whole group is no longer zero. This average velocity is called the drift velocity and is typically very small, on the order of a few centimeters per hour. This is in stark contrast with the Fermi velocity of around 1500 km/s, which, in a simplified explanation, is around how fast each electron will be moving inside the conductor at room temperature.

Is it equal to the speed of light, or maybe tachyonic?

No, not even close. Even extremely high current flows in a conductor (or superconductor) only represent a small increase in average velocity for the charges. This is because of the huge number of charges available. When you have on the order of 10²² charges per meter of wire, even a small increase in average velocity leads to a large increase in current flow. A drift velocity of 23 micrometers/second still puts 10¹⁶ charges across a cross sectional plane of the wire. Or, in other words, this small drift velocity of around 8.2 cm/h is still 1 amp of current in a 2mm diameter wire. A ludicrous 1,000 amps in the same wire would still only be a drift velocity of 23 mm/s, which is a tiny fraction of the 1500 km/s (1,500,000,000 mm/s) that individual electrons were already moving before the application of a voltage.