Quantized Majorana conductance

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shpalman
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Quantized Majorana conductance

Post by shpalman » Tue Mar 09, 2021 1:40 pm

... is not a thing: https://www.nature.com/articles/s41586-021-03373-x

Or at least, that paper which claimed to have demonstrated it turns out to have been very shonky indeed.

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Re: Quantized Majorana conductance

Post by jimbob » Tue Mar 09, 2021 2:19 pm

shpalman wrote:
Tue Mar 09, 2021 1:40 pm
... is not a thing: https://www.nature.com/articles/s41586-021-03373-x

Or at least, that paper which claimed to have demonstrated it turns out to have been very shonky indeed.

the Register;

full scientific takedown.

report from independent experts.

"there is no future if we don't learn from this"
Shades of the Bell Labs retractions from quite a few years ago
Have you considered stupidity as an explanation

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Re: Quantized Majorana conductance

Post by shpalman » Tue Mar 09, 2021 2:46 pm

Also at wired.

Das Sarma, who is one of the coauthors, was "convinced that these strange particles exist in these nanowires" but was not fooled at all into thinking that Majorana modes have been seen in 2018.

https://twitter.com/condensed_the/statu ... 2931175427
CMTC, director: Das Sarma wrote:What do people want to hear about during the CMTC APS talk on March 15? CMTC has total command over all aspects of Majorana, but the allotted time is 30 minutes. Experiments will be discussed, emphasizing how to find Majorana. They exist, but have not yet been seen in the labs
https://twitter.com/VincentMourik/statu ... 1386303493
one of the authors of the pdf presentation takedown wrote:Could you please explain the theory supporting the now retracted nature 2018 paper on which you are a senior PI? Since the experimental plateau is proven to be non-existent why didn't your theory intercept that? How is it wrong? Explanation much appreciated.
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Re: Quantized Majorana conductance

Post by Brightonian » Tue Mar 09, 2021 3:06 pm

At the risk of drifting from this Nerd Lab topic, I'd not heard of 'Majorana' before. 'Conductance' sounds like a word, and of course there's it's all 'quantized' so I get it, it's about a high bus worker with a machine made by Sir Clive Sinclair. Mods, do slap me down if you want, it won't hurt as I'm on my third glass of wine now.

The Wikipedia page for Majorana says Fermi suggested he was on a par with Galileo and Newton, but I'd never heard of him. Also suggests he "escaped" to South America, but what he was escaping from, we don't know (himself, it sounds like, as he'd become of a bit of a hermit).

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Re: Quantized Majorana conductance

Post by shpalman » Tue Mar 09, 2021 3:23 pm

He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
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Re: Quantized Majorana conductance

Post by dyqik » Tue Mar 09, 2021 6:02 pm

shpalman wrote:
Tue Mar 09, 2021 3:23 pm
He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".

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Re: Quantized Majorana conductance

Post by shpalman » Tue Mar 09, 2021 6:07 pm

dyqik wrote:
Tue Mar 09, 2021 6:02 pm
shpalman wrote:
Tue Mar 09, 2021 3:23 pm
He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Feel free to explain to Brightonian what a fermion is.
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Re: Quantized Majorana conductance

Post by dyqik » Tue Mar 09, 2021 6:10 pm

shpalman wrote:
Tue Mar 09, 2021 6:07 pm
dyqik wrote:
Tue Mar 09, 2021 6:02 pm
shpalman wrote:
Tue Mar 09, 2021 3:23 pm
He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Feel free to explain to Brightonian what a fermion is.
It's a particular type of particle that can't be its own antiparticle in standard particle physics.

:P

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Re: Quantized Majorana conductance

Post by shpalman » Wed Mar 10, 2021 10:44 pm

https://www.bbc.com/news/technology-56328980

Not that it really adds anything.
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Re: Quantized Majorana conductance

Post by shpalman » Thu Mar 11, 2021 8:52 am

dyqik wrote:
Tue Mar 09, 2021 6:02 pm
shpalman wrote:
Tue Mar 09, 2021 3:23 pm
He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Photons, Z bosons, and the Higgs aren't particles, they're waves. And the neutral pion isn't a particle, it's two particles.

There was a review article, New directions in the pursuit of Majorana fermions in solid state systems (well, they were new 9-10 years ago) but the abstract starts with "The 1937 theoretical discovery of Majorana fermions..."

A theoretical "discovery" isn't a discovery of anything.

Majorana's last paper was something about The value of statistical laws in physics and social sciences which I think is finally available here.
The deterministic conception of nature implies in itself a real cause of weakness in the irremediable contradiction that it faces with the most certain data of our consciousness. G. SOREL attempted to compose this disagreement with the distinction between artificial nature and natural nature (this last acausal), but in this way he denied the unity of science. On the other hand, the formal analogy between the statistical laws of physics and the ones of social sciences credited the opinion that human facts also undergo a rigid determinism. It is therefore important that quantum mechanics principles have brought to recognize the statistical character of basic laws of elementary processes, in addition to a certain absence of objectiveness in the description of phenomena. This conclusion has made essential the analogy between physics and social sciences, between which it turned out an identity of value and method.
Hm.
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Re: Quantized Majorana conductance

Post by Martin Y » Thu Mar 11, 2021 9:57 am

shpalman wrote:
Wed Mar 10, 2021 10:44 pm
https://www.bbc.com/news/technology-56328980

Not that it really adds anything.
Well, it has the handy guide "Quantum computing explained in 20 seconds" which only takes 20 seconds, has clever people saying some things about quantum computing and doesn't explain quantum computing at all.

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Re: Quantized Majorana conductance

Post by shpalman » Thu Mar 11, 2021 10:18 am

Martin Y wrote:
Thu Mar 11, 2021 9:57 am
shpalman wrote:
Wed Mar 10, 2021 10:44 pm
https://www.bbc.com/news/technology-56328980

Not that it really adds anything.
Well, it has the handy guide "Quantum computing explained in 20 seconds" which only takes 20 seconds, has clever people saying some things about quantum computing and doesn't explain quantum computing at all.
I've managed to get myself signed up for a course which will be two hours a week from now until June, explaining how to do quantum computing (with qiskit) via IBM's platform.

The BBC link also describes the Majorana as a "subatomic particle" which it wouldn't be in this context. It would be the behaviour of lots of electrons* making it look as if there was a Majorana.

(* - Even in a metal, for example, it's convenient to think of it being full of electrons running around conducting electricity, but it's wrong, because the electrons fill up the metal like water filling up a glass of water and their movement through the metal needs to vibe with the arrangement of atoms in the metal like walking on the pavement without stepping on the cracks; anyone with some experience in solid state physics and quantum mechanics generally will look at the necessary equations and immediately think f.ck that sh.t let's just pretend they're electrons running around and if necessary we'll just tweak their properties to fit what we measure. "Quasiparticles" in solid state physics - semiconductors and superconductors especially - are basically physicists saying f.ck that sh.t we're going to pretend these weird arrangements and interactions of electrons in here are just behaving as if it were some new particle, and then we can just play with those particles as if they're a thing. Majoranas in this case would be a particular kind of quasiparticle, except they aren't because nobody has seen any evidence for them yet.)
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Re: Quantized Majorana conductance

Post by jimbob » Thu Mar 11, 2021 10:30 am

shpalman wrote:
Thu Mar 11, 2021 10:18 am
Martin Y wrote:
Thu Mar 11, 2021 9:57 am
shpalman wrote:
Wed Mar 10, 2021 10:44 pm
https://www.bbc.com/news/technology-56328980

Not that it really adds anything.
Well, it has the handy guide "Quantum computing explained in 20 seconds" which only takes 20 seconds, has clever people saying some things about quantum computing and doesn't explain quantum computing at all.
I've managed to get myself signed up for a course which will be two hours a week from now until June, explaining how to do quantum computing (with qiskit) via IBM's platform.

The BBC link also describes the Majorana as a "subatomic particle" which it wouldn't be in this context. It would be the behaviour of lots of electrons* making it look as if there was a Majorana.

(* - Even in a metal, for example, it's convenient to think of it being full of electrons running around conducting electricity, but it's wrong, because the electrons fill up the metal like water filling up a glass of water and their movement through the metal needs to vibe with the arrangement of atoms in the metal like walking on the pavement without stepping on the cracks; anyone with some experience in solid state physics and quantum mechanics generally will look at the necessary equations and immediately think f.ck that sh.t let's just pretend they're electrons running around and if necessary we'll just tweak their properties to fit what we measure. "Quasiparticles" in solid state physics - semiconductors and superconductors especially - are basically physicists saying f.ck that sh.t we're going to pretend these weird arrangements and interactions of electrons in here are just behaving as if it were some new particle, and then we can just play with those particles as if they're a thing. Majoranas in this case would be a particular kind of quasiparticle, except they aren't because nobody has seen any evidence for them yet.)
A colleague and our former boss spent about 15 years that I know of arguing whether the concept of holes was useful. In fact they probably still are.
Have you considered stupidity as an explanation

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Re: Quantized Majorana conductance

Post by shpalman » Thu Mar 11, 2021 10:34 am

I wonder if holes should be considered as having the electron's (negative) charge and a negative mass, rather than a positive charge (equal but opposite to the electron) and a positive mass.

(Both electrons and holes in a semiconductor tend to have a mass which is somewhat less than the mass of an electron in free space, in terms of how much electric force is necessary to get them to move or rather the relationship between their momentum* and energy).
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Re: Quantized Majorana conductance

Post by dyqik » Thu Mar 11, 2021 11:16 am

shpalman wrote:
Thu Mar 11, 2021 8:52 am
dyqik wrote:
Tue Mar 09, 2021 6:02 pm
shpalman wrote:
Tue Mar 09, 2021 3:23 pm
He suggested you could have a particle which was its own antiparticle, which all known particles are not.*

But you might apparently get something happening in a superconductor which behaves like that, except that you don't.
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Photons, Z bosons, and the Higgs aren't particles, they're waves. And the neutral pion isn't a particle, it's two particles.
Er, no.

They are all particles, to the same extent that anything else is a particle.

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Re: Quantized Majorana conductance

Post by monkey » Thu Mar 11, 2021 3:58 pm

dyqik wrote:
Thu Mar 11, 2021 11:16 am
shpalman wrote:
Thu Mar 11, 2021 8:52 am
dyqik wrote:
Tue Mar 09, 2021 6:02 pm


*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Photons, Z bosons, and the Higgs aren't particles, they're waves. And the neutral pion isn't a particle, it's two particles.
Er, no.

They are all particles, to the same extent that anything else is a particle.
But they are also all waves, to the the same extent that anything else is a wave :P

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Re: Quantized Majorana conductance

Post by jimbob » Thu Mar 11, 2021 4:42 pm

monkey wrote:
Thu Mar 11, 2021 3:58 pm
dyqik wrote:
Thu Mar 11, 2021 11:16 am
shpalman wrote:
Thu Mar 11, 2021 8:52 am

Photons, Z bosons, and the Higgs aren't particles, they're waves. And the neutral pion isn't a particle, it's two particles.
Er, no.

They are all particles, to the same extent that anything else is a particle.
But they are also all waves, to the the same extent that anything else is a wave :P
Otherwise diffraction really wouldn't work on them.
Have you considered stupidity as an explanation

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Re: Quantized Majorana conductance

Post by shpalman » Thu Jul 22, 2021 8:21 pm

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Re: Quantized Majorana conductance

Post by IvanV » Fri Jul 23, 2021 10:40 am

dyqik wrote:
Tue Mar 09, 2021 6:10 pm
shpalman wrote:
Tue Mar 09, 2021 6:07 pm
dyqik wrote:
Tue Mar 09, 2021 6:02 pm
*except photons. And Z bosons. And the Higgs. And the neutral pion. I think you mean "fermion which is its own antiparticle".
Feel free to explain to Brightonian what a fermion is.
It's a particular type of particle that can't be its own antiparticle in standard particle physics.
When one is being careful about it, that's the definition of a Dirac fermion, to contrast it with a Majorana fermion, which is the hypothesized "fermion which is its own antiparticle".

There is one known class of fermions where we are not sure if they are Dirac fermions or or Majorana fermions. That's the neutrinos. We are not sure if the antineutrino is different from the neutrino. Work remains on-going to try and find out. See Wikipedia: Antineutrinos

I just happen to be reading Segré's biography of Fermi atmo, and just a couple of days ago read the where Majorana makes a major contribution to neutron physics, relevant to neutron flux in reactors and bombs, and Fermi wants to present it to a conference he is going to. But he refuses to let Fermi talk about it, unless Fermi attributes it to a colleague who isn't even a physicist, because he didn't consider it sufficiently worked through. Naturally the third pary refuses to allow his name to be used in this way. So it remained unpublished until rediscovered by others a few years later. Though Fermi probably made use of it in his own work on these matters at Chicago and Los Alamos.

Segré is also a leading Italian nuclear physicist and colleague of Fermi from early days. So there is rather more in the way of discussion of physics than in other science biographies I have read. Though much less of a good read than Farmelo's biography of Dirac.

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Re: Quantized Majorana conductance

Post by dyqik » Fri Jul 23, 2021 10:54 am

IvanV wrote:
Fri Jul 23, 2021 10:40 am
dyqik wrote:
Tue Mar 09, 2021 6:10 pm
shpalman wrote:
Tue Mar 09, 2021 6:07 pm

Feel free to explain to Brightonian what a fermion is.
It's a particular type of particle that can't be its own antiparticle in standard particle physics.
When one is being careful about it, that's the definition of a Dirac fermion, to contrast it with a Majorana fermion, which is the hypothesized "fermion which is its own antiparticle".
Which is why I wrote what I did.

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Re: Quantized Majorana conductance

Post by shpalman » Fri Jul 30, 2021 6:41 am

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Re: Quantized Majorana conductance

Post by shpalman » Fri Jul 30, 2021 7:59 am

IvanV wrote:
Fri Jul 23, 2021 10:40 am
There is one known class of fermions where we are not sure if they are Dirac fermions or or Majorana fermions. That's the neutrinos. We are not sure if the antineutrino is different from the neutrino. Work remains on-going to try and find out. See Wikipedia: Antineutrinos
We don't know enough about the neutrino to rule out that it's a Majorana fermion, but then neutrinoless double beta decay has never been seen.
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Re: Quantized Majorana conductance

Post by nezumi » Mon Aug 16, 2021 8:08 am

I know nothing about the subject and this comment adds nothing to the discussion but... I keep reading the thread title as marijuana and it's very distracting.
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Re: Quantized Majorana conductance

Post by dyqik » Mon Aug 16, 2021 12:08 pm

nezumi wrote:
Mon Aug 16, 2021 8:08 am
I know nothing about the subject and this comment adds nothing to the discussion but... I keep reading the thread title as marijuana and it's very distracting.
Hmm, maybe spin can come in units of 'teenths.

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Re: Quantized Majorana conductance

Post by shpalman » Thu Aug 19, 2021 7:04 pm

nezumi wrote:
Mon Aug 16, 2021 8:08 am
I know nothing about the subject and this comment adds nothing to the discussion but... I keep reading the thread title as marijuana and it's very distracting.
At least one very senior and respected professor calls them that.

Meanwhile here's some nonsense about how quantum is magic which will solve everyone's problems

https://thenextweb.com/news/optimists-g ... h-paradise

"But this isn’t a philosophy article."

Well it's certainly not a science article.
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