What is the significance of a propagating Majorana mode in topological qubits?

[smodak]

http://www.independent.co.uk/news/s...rd-university-california-irvine-a7851661.html

 

[fresh_42]

A bit better sources are:
http://news.stanford.edu/2017/07/20/evidence-particle-antiparticle/
https://phys.org/news/2017-07-evidence-majorana-fermion-particle-antiparticle.html
The article itself can be found here:
http://science.sciencemag.org/content/357/6348/294
but except the summary it's behind a paywall.

A propagating Majorana mode
Although Majorana fermions remain elusive as elementary particles, their solid-state analogs have been observed in hybrid semiconductor-superconductor nanowires. In a nanowire setting, the Majorana states are localized at the ends of the wire. He et al. built a two-dimensional heterostructure in which a one-dimensional Majorana mode is predicted to run along the sample edge (see the Perspective by Pribiag). The heterostructure consisted of a quantum anomalous Hall insulator (QAHI) bar contacted by a superconductor. The authors used an external magnetic field as a “knob” to tune into a regime where a Majorana mode was propagating along the edge of the QAHI bar covered by the superconductor. A signature of this propagation—half-quantized conductance—was then observed in transport experiments.

Abstract
Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing.

Science, this issue p. 294; see also p. 252

 

[DrChinese]

I couldn't locate an arxiv version. What little reference I could find did not sync well with the referenced article. Maybe someone else can find a useful link.

EDIT: Thanks to fresh_42, was able to find this (no pay wall):

https://arxiv.org/abs/1606.05712

 

[atyy]

Free version of the article

https://arxiv.org/abs/1606.05712
Chiral Majorana edge state in a quantum anomalous Hall insulator-superconductor structure
Qing Lin He, Lei Pan, Alexander L. Stern, Edward Burks, Xiaoyu Che, Gen Yin, Jing Wang, Biao Lian, Quan Zhou, Eun Sang Choi, Koichi Murata, Xufeng Kou, Tianxiao Nie, Qiming Shao, Yabin Fan, Shou-Cheng Zhang, Kai Liu, Jing Xia, Kang L. Wang
(Submitted on 18 Jun 2016)
After the recognition of the possibility to implement Majorana fermions using the building blocks of solid-state matters, the detection of this peculiar particle has been an intense focus of research. Here we experimentally demonstrate a collection of Majorana fermions living in a one-dimensional transport channel at the boundary of a superconducting quantum anomalous Hall insulator thin film. A series of topological phase changes are controlled by the reversal of the magnetization, where a half-integer quantized conductance plateau (0.5e2/h) is observed as a clear signature of the Majorana phase. This transport signature can be well repeated during many magnetic reversal sweeps, and can be tracked at different temperatures, providing a promising evidence of the chiral Majorana edge modes in the system.

 

[mfb]

Didn't the authors learn anything from the "God particle"? Do we really need this crap again?
At least the arXiv version doesn't contain "angel" (apart from one author affiliation, Los Angeles...).

Majorana fermions in superconductors have been seen as early as 1960. This study found a new type of quasiparticle. Great, and certainly amazing for the specific field they are working on. But on a global scale: Add it to the big pile of known quasiparticles.

 

[atyy]

Majorana fermions in superconductors have been seen as early as 1960. This study found a new type of quasiparticle. Great, and certainly amazing for the specific field they are working on. But on a global scale: Add it to the big pile of known quasiparticles.

I think they were still unobserved and the big deal is that they might help to implement topological quantum computing: http://www.physics.upenn.edu/~kane/pedagogical/WindsorLec3.pdf

 

[mfb]

They are new in topological superconductors only as far as I know.

 

[Demystifier]

Didn't the authors learn anything from the "God particle"? Do we really need this crap again?

Never underestimate the power of PR.

Now we need the devil particle. Any candidate?

 

[atyy]

Hmmm, they are not sure (bolding mine):

We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes.

 

[atyy]

Never underestimate the power of PR.

Now we need the devil particle. Any candidate?

If they are correct, this is the devil particle too, well or at least it's the demon particle.

 

[atyy]

They are new in topological superconductors only as far as I know.

Could you give a reference for the old stuff? My understanding is they are still not definitely observed. The closest before this was measurements by Leo Kouwenhoven https://www.newscientist.com/articl...-to-see-the-man-who-made-a-majorana-particle/, but that was not definitive.

 

[Vanadium 50]

>> So what do you guys think about the 'Angel' particle?

Hype, hype, hype and more hype.

 

[DrChinese]

>> So what do you guys think about the 'Angel' particle?

Hype, hype, hype and more hype.

I'm not sure where you stand on this. Could you elucidate?

 

[radium]

In solid state there quite a few experimental configurations that supposedly lead to Majorana bound states. I don't know if there are any other experiments claiming to see propagating Majorana fermions though. Either way, the claims made in this paper are definitely a lot stronger than many other scientists would ever make.

 

[ZapperZ]

Just to be clear, evidence for Majorana fermions in topological superconductors have been made as far back as 2012:

V. Mourik et al., Science v.336, p.1003 (2012)

And as with many people, I wish they didn't have to resort to calling this the "angel particle". I mean, what does that even mean?

BTW, I think this thread is more suited in the HEP forum than in the QP forum.

Zz.

 

[mfb]

Could you give a reference for the old stuff? My understanding is they are still not definitely observed. The closest before this was measurements by Leo Kouwenhoven https://www.newscientist.com/articl...-to-see-the-man-who-made-a-majorana-particle/, but that was not definitive.

I don't find a reference now, but with ZZ's post we have an even better one.

BTW, I think this thread is more suited in the HEP forum than in the QP forum.

I don't think superconductors count as high-energy or particle physics.

Edit: Moved to solid-state physics.

 

[ZapperZ]

I don't find a reference now, but with ZZ's post we have an even better one.
I don't think superconductors count as high-energy or particle physics.

OK, condensed matter then. After all, this is a solid-state system.

Zz.

 

[ZapperZ]

I don't find a reference now, but with ZZ's post we have an even better one.

In addition to the one I've given, there's also another one during the same year:

https://arxiv.org/abs/1204.4212

Zz.

 

[atyy]

I don't find a reference now, but with ZZ's post we have an even better one.

ZapperZ's post are all about recent work, not the 1960s (which is what you wrote in post #5). Also both of ZapperZ's references are about topological superconductors (which is different from what you wrote in post #7).

As many other posts above have indicated, there has been evidence for Majorana fermions more recently (since around 2012), but those are not watertight, which is why this paper is significant if it does indeed provide more compelling evidence.

 

[rootone]

I think people who associate subatomic particles with mythical religious creatures need to ask themselves why they do that.

 

[Fred Wright]

Never underestimate the power of PR.

Now we need the devil particle. Any candidate?

I think they should call it the Janus particle because it's creation operator is equal to its destruction operator and the end of the wire is topologically connected to it's beginning. But "Janus" would have little emotional appeal to the viewing public.

 

[atyy]

Brief mention of the paper of the OP by Doug Natelson on his blog: http://nanoscale.blogspot.sg/2017/07/several-items.html

 

[atyy]

Quantum Frontiers blog post on topological qubits by Ryan Mishmash and Jason Alicea: https://quantumfrontiers.com/2017/08/16/topological-qubits-arriving-in-2018/