Quantized Majorana conductance

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Re: Quantized Majorana conductance

Post by shpalman » Thu Dec 15, 2022 8:34 pm

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Spin qubits in germanium work though.
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Re: Quantized Majorana conductance

Post by shpalman » Thu Feb 16, 2023 4:36 pm

NISQ Is Dead, a Dying Dead End, With No Prospects for a Brighter Future or Practical Quantum Computing

You just need "near-perfect qubits" instead. Well ok then why didn't you say.
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Re: Quantized Majorana conductance

Post by shpalman » Fri Mar 03, 2023 11:58 am

In addition to not existing as quasiparticles in solid state systems, Majorana fermions also do not exist as fundamental particles.

"The fact that we didn't detect anything demonstrates the feasibility of spending a whole bunch more money to not detect anything on a much bigger scale" said a particle physicist, again.
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Re: Quantized Majorana conductance

Post by shpalman » Wed Jun 21, 2023 9:44 pm

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Re: Quantized Majorana conductance

Post by IvanV » Thu Jun 22, 2023 10:27 am

shpalman wrote:
Fri Mar 03, 2023 11:58 am
In addition to not existing as quasiparticles in solid state systems, Majorana fermions also do not exist as fundamental particles.

"The fact that we didn't detect anything demonstrates the feasibility of spending a whole bunch more money to not detect anything on a much bigger scale" said a particle physicist, again.
Only just got around to looking at this. At some point it says, "While neutrinos have already been found to have a mass..."

I think to say that a neutrino has a mass, you have to demonstrate a non-zero lower bound for it. That does not seem to have been achieved.

It seems the justification for the above statement is neutrino oscillations. By some well-established theory, that can only happen if they have a mass. But whilst our well-established are excellent in their core zones, they are rather less reliable outside their known reliable areas of application, to the extent of appearing to be completely inconsistent with major facts. So I'm not convinced by this demonstration by a theory that has not been proven to be correct in relation to neutrinos.

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Re: Quantized Majorana conductance

Post by shpalman » Thu Jun 22, 2023 10:33 am

IvanV wrote:
Thu Jun 22, 2023 10:27 am
shpalman wrote:
Fri Mar 03, 2023 11:58 am
In addition to not existing as quasiparticles in solid state systems, Majorana fermions also do not exist as fundamental particles.

"The fact that we didn't detect anything demonstrates the feasibility of spending a whole bunch more money to not detect anything on a much bigger scale" said a particle physicist, again.
Only just got around to looking at this. At some point it says, "While neutrinos have already been found to have a mass..."

I think to say that a neutrino has a mass, you have to demonstrate a non-zero lower bound for it. That does not seem to have been achieved.

It seems the justification for the above statement is neutrino oscillations. By some well-established theory, that can only happen if they have a mass. But whilst our well-established are excellent in their core zones, they are rather less reliable outside their known reliable areas of application, to the extent of appearing to be completely inconsistent with major facts. So I'm not convinced by this demonstration by a theory that has not been proven to be correct in relation to neutrinos.
The neutrino has to have mass otherwise it would travel at the speed of light, and at the speed of light time would not evolve for it in our frame. So to be able to oscillate, time must be passing in its frame. Special relativity is simple and fundamental enough that for it to be wrong would be a major upset.
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Re: Quantized Majorana conductance

Post by IvanV » Fri Jun 23, 2023 2:07 pm

shpalman wrote:
Thu Jun 22, 2023 10:33 am
The neutrino has to have mass otherwise it would travel at the speed of light, and at the speed of light time would not evolve for it in our frame. So to be able to oscillate, time must be passing in its frame. Special relativity is simple and fundamental enough that for it to be wrong would be a major upset.
Yet several measurements of neutrino speed have been unable to distinguish it from the speed of light.

To me, the neutrino mass is in the same box as supersymmetric particles.

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Re: Quantized Majorana conductance

Post by dyqik » Fri Jun 23, 2023 2:17 pm

IvanV wrote:
Fri Jun 23, 2023 2:07 pm
shpalman wrote:
Thu Jun 22, 2023 10:33 am
The neutrino has to have mass otherwise it would travel at the speed of light, and at the speed of light time would not evolve for it in our frame. So to be able to oscillate, time must be passing in its frame. Special relativity is simple and fundamental enough that for it to be wrong would be a major upset.
Yet several measurements of neutrino speed have been unable to distinguish it from the speed of light.

To me, the neutrino mass is in the same box as supersymmetric particles.
Then you're an idiot who doesn't know what you're talking about.

Neutrinos have mass. We know that because they oscillate, which they could not do if they traveled at the speed of light.

If they don't have mass, then special relativity, quantum mechanics and general relativity are wrong.

I'm building a $660 million experiment to determine that mass.

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Re: Quantized Majorana conductance

Post by IvanV » Fri Jun 23, 2023 2:57 pm

dyqik wrote:
Fri Jun 23, 2023 2:17 pm
Then you're an idiot who doesn't know what you're talking about.

Neutrinos have mass. We know that because they oscillate, which they could not do if they traveled at the speed of light.

If they don't have mass, then special relativity, quantum mechanics and general relativity are wrong.

I'm building a $660 million experiment to determine that mass.
And I hope that you show they do have a mass, because we learn something from positive findings, whereas negative findings leave us still unsure.

A few years ago, some very clever people who seemingly utterly believed in super-symmetry used similar language against the doubters, and stated seemingly for certain that the LHC would vindicate them. Clearly super-symmetry isn't disproved, but there is a much narrower window of possibility for it to be true, and such people are less combative about it these days. Likewise, the failure of your experiment wouldn't disprove neutrino mass, we still wouldn't know either way, but it would be looking less likely. And it might be more difficult to get funding for an even more expensive experiment that might put an even lower upper limit on it.

I think we already know that some of these famous theories have to be wrong, but in the positive way that Newton's Laws are wrong - they have a range of application, and you need to know something else at the edges where they start to contradict each other, or where we have physical knowledge that is hard to make sense of. That kind of "wrong theory" is much more useful and insightful than those that are not even wrong.

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Re: Quantized Majorana conductance

Post by dyqik » Fri Jun 23, 2023 3:05 pm

Again, you are clearly showing that you don't know what you are talking about.

Supersymmetry has never had a direct evidence base. Meanwhile, special relativity and electroweak theory are proven by huge amounts of evidence.

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Re: Quantized Majorana conductance

Post by Gfamily » Sun Jun 25, 2023 2:05 pm

An interesting suggestion that there will be a joint announcement next week from
- a team attempting to detect GW waves through the measurement of deviations to the timing Pulsar signals
- a team using the Ice Cube Neutrino Observatory in Antarctica.

This may allow us to determine the speed at which neutrinos travel relative to the speed of light.
So far, we know (in part following the neutrino burst detected a few hours before* the gamma ray burst for the SN1987A supernova) that if there's a difference between the speed of neutrinos and light, it's only a few parts per billion, It'll be interesting to see if the announcement helps to narrow it down.

* neutrinos arrive first as they are created as the core collapses, and escape almost immediately, whereas the gamma rays emitted have to battle through the outer layers of the collapsing star before they are emitted.
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Re: Quantized Majorana conductance

Post by IvanV » Sun Jun 25, 2023 3:18 pm

I did a bit more reading and see I was ignorant, my apologies.

I thought this was going to be an unbounded game where we could just keep pushing it down a few more orders of magnitude, and never come to an end, but I see that is wrong. I also found it a bit hard to believe in a lepton with a positive mass at least 6 orders of magnitude less than an electron.

But now I see there are good reasons to believe the heaviest neutrino should have a mass around about 6 orders of magnitude less than electron. And if it is is excluded from having a mass in that range, then that shows there's something wrong with the theory.

I read the theory of neutrino oscillation depends upon differences in the square of the masses of neutrino flavours. We can estimate the difference of the sum of squares from the the oscillation characteristics. So that implies the heaviest flavour of neutrino should have a mass of at least 0.05eV/c2. But clearly the other flavours could weigh rather less.

Meanwhile, considerations from cosmology are suggesting an upper limit of 0.11eV/c2 - possibly that's an average of the flavours.

So there is a fairly narrow window to aim for, at least in terms of the mass of the heaviest neutrino. And you'll know something is wrong if they are strongly excluded from that window.

But maybe you don't have experimental methods of making measurements on all 3 neutrino flavours, so you can't necessarily determine the mass or speed of the heaviest type?

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Re: Quantized Majorana conductance

Post by bjn » Mon Jun 26, 2023 9:11 pm

AIUI neutrinos are in a superposition of three flavours and depending on when you observe one you get to see one of those three. But each of the three flavours have a different mass. What happens to conservation of mass? If you see it as an tau neutrino then later on as an electron neutrino, what happens to the missing mass? Same when it goes the other way, where does it get the mass from? Or does quantum mechanics manage to ignore that because quantum magic gets to over rule classical nonsense and involves maths way beyond what I’m now capable of?

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Re: Quantized Majorana conductance

Post by dyqik » Mon Jun 26, 2023 9:23 pm

bjn wrote:
Mon Jun 26, 2023 9:11 pm
AIUI neutrinos are in a superposition of three flavours and depending on when you observe one you get to see one of those three. But each of the three flavours have a different mass. What happens to conservation of mass? If you see it as an tau neutrino then later on as an electron neutrino, what happens to the missing mass? Same when it goes the other way, where does it get the mass from? Or does quantum mechanics manage to ignore that because quantum magic gets to over rule classical nonsense and involves maths way beyond what I’m now capable of?
Mass can be exchanged for energy.

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Re: Quantized Majorana conductance

Post by bjn » Mon Jun 26, 2023 9:57 pm

dyqik wrote:
Mon Jun 26, 2023 9:23 pm
bjn wrote:
Mon Jun 26, 2023 9:11 pm
AIUI neutrinos are in a superposition of three flavours and depending on when you observe one you get to see one of those three. But each of the three flavours have a different mass. What happens to conservation of mass? If you see it as an tau neutrino then later on as an electron neutrino, what happens to the missing mass? Same when it goes the other way, where does it get the mass from? Or does quantum mechanics manage to ignore that because quantum magic gets to over rule classical nonsense and involves maths way beyond what I’m now capable of?
Mass can be exchanged for energy.
I know that, so do they radiate/absorb energy or speed up/slow down when they flip between flavours? Or something else?

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Re: Quantized Majorana conductance

Post by dyqik » Mon Jun 26, 2023 10:51 pm

bjn wrote:
Mon Jun 26, 2023 9:57 pm
dyqik wrote:
Mon Jun 26, 2023 9:23 pm
bjn wrote:
Mon Jun 26, 2023 9:11 pm
AIUI neutrinos are in a superposition of three flavours and depending on when you observe one you get to see one of those three. But each of the three flavours have a different mass. What happens to conservation of mass? If you see it as an tau neutrino then later on as an electron neutrino, what happens to the missing mass? Same when it goes the other way, where does it get the mass from? Or does quantum mechanics manage to ignore that because quantum magic gets to over rule classical nonsense and involves maths way beyond what I’m now capable of?
Mass can be exchanged for energy.
I know that, so do they radiate/absorb energy or speed up/slow down when they flip between flavours? Or something else?
They don't flip between flavors as they travel - they travel as a superposition of the flavors, which has a well defined mass/energy (and thus momentum). But the mass eigenstates aren't the same as the flavor eigenstates, so when a weak interaction with a neutrino happens, the mass eigenstate is reduced to a flavor eigenstate, with different probabilities for each flavor.

The probability of a particular flavor eigenstate being the outcome of an interaction fluctuates as the phases of the flavor elements of the wavefunction of a mass eigenstate change with respect to one another.

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Re: Quantized Majorana conductance

Post by IvanV » Tue Jun 27, 2023 12:04 pm

bjn wrote:
Mon Jun 26, 2023 9:11 pm
AIUI neutrinos are in a superposition of three flavours and depending on when you observe one you get to see one of those three.
I read that a solar neutrino oscillates on average about once per 1250m. So unless you are detecting neutrinos from rather close to their source, it would seem "when" ceases to be a practical issue, as after a fairly short distance they will become fully randomised. Though maybe at higher energies the oscillation occurs over longer distances, due to greater time dilation, (he hand-waves in his ignorance). The 730km from Geneva to Gran Sasso seems to be enough for the muon-neutrinos emitted at CERN to oscillate to tau-neutrinos in detectable quantities.

The detection of tau-neutrinos in small numbers at Gran Sasso was news, so detecting these other flavours is possible but apparently not easy.

But we have just learned with thanks to dyqik that mass eigenstates are not aligned with flavour eigenstates. So that is implying we can straightforwardly detect the heavier/slower neutrinos in an experiment, because a fraction of the heavier mass eigenstates will interact as each of the flavours?

So is the sensitivity of this new experiment sufficient to close the window on neutrino mass?

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Re: Quantized Majorana conductance

Post by shpalman » Thu Jul 27, 2023 8:19 am

There's a Pinned thread from CMTC about topological quantum computing, which is of course moot as long as the quasi particles they need to be able to do it don't exist.

Meanwhile there's work to induce superconductivity in semiconductors by putting them very close to metallic superconductors.
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Re: Quantized Majorana conductance

Post by shpalman » Wed Mar 20, 2024 12:41 pm

I'll bump this because there are posts relevant to the Q day thing, amongst the neutrinos.
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Re: Quantized Majorana conductance

Post by shpalman » Mon May 13, 2024 2:46 pm

A NEW Kind of Quantum Computer - The Map of Topological Quantum Computing is a somewhat uncritical video on this, from @domainofscience.

I note that Microsoft Quantum wanted to comment on a paper* which explained that you could think you had the signature of Majoranas from some relatively trivial effects, but their comment was nonsense.

* - Trivial Andreev Band Mimicking Topological Bulk Gap Reopening in the Nonlocal Conductance of Long Rashba Nanowires https://arxiv.org/abs/2210.03507

tl;dr just because Microsoft think their devices pass the "topological gap protocol" doesn't mean there are really Majorana zero modes in there.

https://twitter.com/PhysicsHenry/status ... 2013060357
To summarise: Microsoft Quantum put a comment on our paper claiming that our mechanism would not cause false positives in their topological gap protocol.

1. Our mechanism can quite easily cause TGP false positives.

2. MSFT's comment was based on a demonstrably false figure.
I also note that the International Conference on Reproducibility in Condensed Matter Physics just happened. Calling it "reproducibility" is a bit of a euphemism... nobody could reproduce Jan Hendrik Schön's results because they were fabricated.
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