[HN Gopher] Physicists measure quantum geometry for first time
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Physicists measure quantum geometry for first time
Author : pseudolus
Score : 53 points
Date : 2024-12-23 11:09 UTC (1 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| codethief wrote:
| Is "quantum geometry" a common way to say "shape of the wave
| function" in solid-state physics?
|
| Here I was, thinking the article would be about a topic at the
| intersection of quantum mechanics and relativity...
| gus_massa wrote:
| "quamtum geometry" appears in the title of the article in
| Nature Physics, it's not an invention of the press article.
|
| (I've seen a lot of horrible titles in other press articles,
| but this is not the case.)
| codethief wrote:
| Yes, I noticed that. Hence my question :)
| stronglikedan wrote:
| My take is that they have directly observed the quantum
| geometry of the physical electrons for the first time, and it
| matches the geometry theorized by the wave function. The shape
| of the wave function theoretically describes what we expect the
| physical geometry of the electrons to be in the quantum
| setting, and now they have been able to confirm that through
| direct observation. A small distinction, but a distinction
| nonetheless.
| quantumtwist wrote:
| Alright, this one is pretty interesting but, as usual, it needs
| some amount of background to appreciate it properly. Let me try
| to make an elementary summary.
|
| Electrons in a crystal are partially governed by a "quantum
| metric" on the "Brillouin zone manifold" [1]. Metric tensors on
| manifolds famously appear in general relativity, and are a
| central object in differential geometry (hence the accurate
| moniker "quantum geometry"). "Quantum geometry" is a hot topic in
| condensed matter physics in the last few years, and governs or is
| connected to many important quantities. For instance, the
| integral of the quantum metric is proportional to the
| conductivity (in the disorder-free regime) [2]. This paper makes
| a more-or-less direct measurement of the quantum metric in the
| material CoSn.
|
| [1] https://doi.org/10.1007/BF02193559 [2]
| https://doi.org/10.1103/PhysRev.133.A171,
| https://doi.org/10.1103/PhysRevB.62.1666
| codethief wrote:
| Thanks, that was quite insightful!
| ziofill wrote:
| As usual, journalists write clickbait titles. The quantum
| geometric tensor has not been measured for the _first time_.
| Perhaps it's a novel way to measure it in a crystal, but
| certainly it's a very well known concept in quantum physics. I've
| worked with it too to perform natural gradient descent on the
| space of quantum states.
| PittleyDunkin wrote:
| > As usual, journalists write clickbait titles.
|
| That's typically the editor's responsibility.
| gus_massa wrote:
| The article says "first" in the first paregraph, so don't
| blame only the editor.
|
| @GP: Have you used experimental values or values calculated
| theoreticaly with DFT or something?
| ziofill wrote:
| No, in my case it was a theoretical work, but others have
| measured it e.g.
| https://www.nature.com/articles/s41586-020-1989-2
| dallasg3 wrote:
| I'm imagining a mashup of a 50's boiler room except with lab
| coats. These scientific papers aren't going to sell
| themselves, boys. Gimme somethin' that sizzles.
| mmooss wrote:
| The paper itself:
|
| https://www.nature.com/articles/s41567-024-02678-8
|
| Why not link to the papers themselves on HN? They usually are not
| hard to read, at least the abstract, introduction, etc. And the
| papers provide excellent background, references, etc. For
| example,
|
| _Understanding the geometric properties of quantum states and
| their implications in fundamental physical phenomena is a core
| aspect of contemporary physics. The quantum geometric tensor
| (QGT) is a central physical object in this regard, encoding
| complete information about the geometry of the quantum state. The
| imaginary part of the QGT is the well-known Berry curvature,
| which plays an integral role in the topological magnetoelectric
| and optoelectronic phenomena. The real part of the QGT is the
| quantum metric, whose importance has come to prominence recently,
| giving rise to a new set of quantum geometric phenomena such as
| anomalous Landau levels, flat band superfluidity, excitonic Lamb
| shifts and nonlinear Hall effect. Despite the central importance
| of the QGT, its experimental measurements have been restricted
| only to artificial two-level systems. Here, we develop a
| framework to measure the QGT in crystalline solids using
| polarization-, spin- and angle-resolved photoemission
| spectroscopy. Using this framework, we demonstrate the effective
| reconstruction of the QGT in the kagome metal CoSn, which hosts
| topological flat bands. Establishing this momentum- and energy-
| resolved spectroscopic probe of the QGT is poised to
| significantly advance our understanding of quantum geometric
| responses in a wide range of crystalline systems._
| mmooss wrote:
| Some interesting commentary from the lead researcher:
|
| _Kang stresses that the new ability to measure the quantum
| geometry of materials "comes from the close cooperation between
| theorists and experimentalists."
|
| The COVID pandemic, too, had an impact. Kang, who is from South
| Korea, was based in that country during the pandemic. "That
| facilitated a collaboration with theorists in South Korea," says
| Kang, an experimentalist.
|
| The pandemic also led to an unusual opportunity for Comin. He
| traveled to Italy to help run the ARPES experiments at the
| Italian Light Source Elettra, a national laboratory. The lab was
| closed during the pandemic, but was starting to reopen when Comin
| arrived.
|
| He found himself alone, however, when Kang tested positive for
| COVID and couldn't join him. So he inadvertently ran the
| experiments himself with the support of local scientists.
|
| "As a professor, I lead projects but students and postdocs
| actually carry out the work. So this is basically the last study
| where I actually contributed to the experiments themselves," he
| says._
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