Re: Quantized Majorana conductance
Posted: Thu Dec 15, 2022 8:34 pm
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Only just got around to looking at this. At some point it says, "While neutrinos have already been found to have a mass..."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.
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.IvanV wrote: Thu Jun 22, 2023 10:27 amOnly just got around to looking at this. At some point it says, "While neutrinos have already been found to have a mass..."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.
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.
Yet several measurements of neutrino speed have been unable to distinguish it from the speed of light.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.
Then you're an idiot who doesn't know what you're talking about.IvanV wrote: Fri Jun 23, 2023 2:07 pmYet several measurements of neutrino speed have been unable to distinguish it from the speed of light.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.
To me, the neutrino mass is in the same box as supersymmetric particles.
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.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.
Mass can be exchanged for energy.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?
I know that, so do they radiate/absorb energy or speed up/slow down when they flip between flavours? Or something else?dyqik wrote: Mon Jun 26, 2023 9:23 pmMass can be exchanged for energy.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?
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.bjn wrote: Mon Jun 26, 2023 9:57 pmI know that, so do they radiate/absorb energy or speed up/slow down when they flip between flavours? Or something else?dyqik wrote: Mon Jun 26, 2023 9:23 pmMass can be exchanged for energy.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?
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.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.
A NEW Kind of Quantum Computer - The Map of Topological Quantum Computing is a somewhat uncritical video on this, from @domainofscience.
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.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.
The same referee, on reading the revised version, then commented:After a thorough analysis of the data and comparison with simulations, the main conclusion is that the results are consistent
with a measurement of the fermion parity encoded in a pair of Majorana zero modes in a long topological nanowire.
In my opinion, these experiments are very interesting and certainly relevant for the condensed matter community working on
topological superconductors and Majorana states. What I do NOT like is the way the article is written which, sometimes
subtly and sometimes more crudely, uses a language and wording that at all times leads the reader to think that we are
dealing with a measurement that demonstrates parity in a topological qubit based on Majorana states. The examples are
many and here I highlight only a few:
Page 1: lines 52 and 53 "albeit in a regime that does not allow qubit readout". Here the authors seem to imply that in this
manuscript a qubit (and its parity readout) is demonstrated which is not true.
Page 1: “In this paper we demonstrate an interferometric measurement of the parity of a near-zero-energy state in a 1D
Nanowire, thereby validating a necessary ingredient of topological quantum computation” How is this demonstrated? How
do the authors know that this is a 1D system? Etc.
Page 1: lines 62-68 "By itself, this measurement does not unequivocally distinguish between MZMs in the topological phase
and fine-tuned low-energy Andreev bound states in the trivial phase, but it does require the low-energy state to be supported
at both ends of the wire and very weakly coupled to other low- energy states". This is an interesting sentence, of course I
fully agree with it given its importance, but then the authors cite a series of papers related to Andreev qubit physics [49–53]
but not THE relevant references concerning the trivial Andreev versus Majorana controversy. These papers , which are cited
later in the paper, Refs [98-103] should be cited and highlighted in this important introductory paragraph. Moreover, the
Nature Review Physics discussing in great detail such controversy, Nature Reviews Physics 2, 575 (2020), should be cited.
-Page 1 section2:
Already the title of the section is misleading “Topological qubit…” There is no definitive proof of topology or qubit…
-Line 76: “in this work we introduce a topological qubit design…” the same as above.
-Line 80-82: “The first component is a nanowire, sections of which can be tuned into a 1DTS state, leading to topological
degeneracy of the many-body ground state…”
Page 2:
-Line 104, line 111: “To form a qubit…” “ a full qubit device therefore consists of…” again the same wording which implies
that the authors demonstrate a qubit.
-Line 118: “ we focus on the left topological section…”
I could continue since the text is plagued with such misleading and ambiguous wording where theoretical prediction, device
design and actual proof in experiment/data is mixed in a rather careless manner….
The tl;dr is that there's no qubits and no Majoranas in this paper.I stand by my previous report and, in fact, I must now be harsher since after one round of evaluation the authors have had the
opportunity to rewrite the article carefully and avoiding the continuous mixing of objective facts with interpretation
(sometimes bordering on a strong bias towards a priori conclusions on the part of the authors) but have largely ignored my
suggestion (and also that of other referees).