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CrazyisNSFW t1_jbskbhe wrote

Reply to comment by SwitchingtoUbuntu in How do impurities affect superconductivity? by Infferno122

Curious question: does superconductor have absolutely nil resistance or the resistance is just too low to measure with available techs?

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SwitchingtoUbuntu t1_jbskuge wrote

It depends! There is often a difference between bulk and thin film superconductors, and it will depend on loads of details relating to fabrication and the frequency of signals present.

For example, a resonator made of thin film Nb has zero DC resistance but will have dielectrics and other contaminants that give it some loss tangent when in the presence of microwave fields.

We usually talk about "Quality factor" which is sort of a way of saying how many times can a microwave photon bounce back and forth in the circuit before it leaves due to some loss mechanism.

Qs of tens of millions are achievable.

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ChemicalRain5513 t1_jbsveml wrote

How can you prove anything is zero? Even for the photon mass the best we have is an upper limit of 10^-18 ev/c^2.

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SwitchingtoUbuntu t1_jbtgdx4 wrote

Yeah I mean technically we can't say anything is actually zero but the lower bound is pretty low.

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luckyluke193 t1_jbuu6ht wrote

The superconducting coils that generate the magnetic fields for MRI and NMR spectroscopy systems have zero DC resistance.

They usually operate in persistent mode, meaning that there is no power supply attached to them. As long as you keep them superconducting, you can have hundreds of amps circulating in the coils without any change in the current over several years.

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