Cargo cult science

Feynman coined the term "cargo cult science" during a commencement address. This term describing research that is aimed at confirming an assumed hypothesis became more widely known after the address was incorporated into the final chapter of his book Surely You're Joking, Mr. Feynman! Methods which superficially seem scientific will ultimately fail to deliver if researchers lack "utter honesty" - not just avoiding falsehoods, but bending over backwards to state all the possible flaws in your research. The latter is scientific integrity, the former is advertising.

Feynman argued adamantly against fooling the layman when talking about your research. He gives an example of an astronomer friend who asked what applications of his work he should mention in a radio interview. Feynman retorted "there aren't any" and the friend was dismayed because saying that would not attract continued funding support for his research.

This message remains relevant today, especially with increasing competition for grant funding and faculty positions, high impact journals with strict length limits, and big conferences with short talks. Even when we agree with being honest and discussing flaws in our research in principle, excuses inevitably come up:

"I don't have time to discuss limitations - I only have 10 minutes including questions."

"My peers who publish in Top Journal all start their papers this way - it's the only way to make it past the editor." 

"Unless I frame my proposal in terms of this Grand Challenge it will not be funded."

"I have to play this game until I get tenure, and then I will be free to do honest old-fashioned research."

"I just need this grant so I can extend my postdoc's contract..."

The end result: Paper introductions and grant applications written by large language models, because they can sell the science in a more exciting way (weasel words can be inserted to smooth over overt factual errors). Seminars where the speaker boldly claims application X in the introduction, only to backtrack when questioned after the talk (lucky there was an expert present to point out a key flaw known by specialists in the topic). Researchers wasting months on ideas that were already tried and didn't work (no rewards for publishing negative results).

It doesn't need to be this way.

 

If you think there is not enough scientific integrity nowadays, you can help by participating in peer review and questioning unsubstantiated claims and excessive hype in the right way.

You should be curious and respectful, not belligerent and dismissive. Recommending rejection on the basis of how the broader context of the results are sold (rather than the results themselves) rarely leads to a constructive outcome - either the authors will ask for your opinion to be dismissed, or they will publish the offending claims unaltered in another venue. Instead you could ask the authors to explain in more detail how approach X is expected to help goal Y and possible flaws to better put the work in context. 

The same approach is also useful for Q&A sessions after talks. Often, the speaker is well aware of certain gaps in the logic of the presentation but didn't have the time to elaborate on them.  Questions in this vein help them to better convey the important unanswered questions in their research topic and are valuable to both the speaker and the audience.

The system has too much inertia to change immediately, but by putting the broader context and salesmanship behind the research under closer scrutiny you can help to diminish the influence of cargo cult science.

International Workshop on Polaritons in Emerging Materials

Last week I had the pleasure of attending an IBS PCS International Workshop on Polaritons in Emerging Materials held in Daejeon, Korea. Smaller workshops such a this one (~40 participants) with a more relaxed schedule (40 minutes per speaker and generous coffee/lunch breaks) are great for getting a more in-depth and candid picture of an unfamiliar research field!

One of the hot topics was polaritons in transition metal dichalcogenides - a rapidly-maturing family of two-dimensional graphene-inspired materials. Prof. Myung-Ki Kim from Korea University talked about plasmon resonances in multi-layer TMDs, Prof. Deep Jariwala from the University of Pennsylvania presented experiments with cavity-free polaritonic structures. The high refractive index of 2D materials such as molybdenum disulphide means that they can already exhibit strong light-matter coupling without requiring embedding in a microcavity. Thanks to the different localization of the photonic and electronic degrees of freedom one can form ultra-thin multilayer structures either as thin sheets of the 2D material (with the thickness controlling the electronic band structure), or as lattices formed by multiple non-interacting single sheets. Prof. Su-Hyun Gong (Korea University) presented waveguides based on multilayer tungsten disulphide can achieve tight (nanoscale) light confinement with lower losses compared to conventional plasonic materials such as gold. Expect to see many more works in this area as high-quality and large-area samples of these exotic materials start to become commercially available.

Another active area was optically-driven rotation and localization of exciton-polariton condensates. Dr. Michael Fraser (RIKEN) presented experiments in which a condensate is stirred via incoherent pumping with two slightly-detuned Laguerre-Gaussian layer beams, leading to an asymmetric reservoir density that undergoes a rotation, producing condensates with vortices. Theoretical analyses of vortex generation and turbulence in stirred exciton-polaritons were presented by Dr. Alexey Yulin (ITMO) and Dr. Helgi Sigurðsson (Warsaw), and Dr. Sergei Koniakhin (IBS PCS). Prof. Alberto Amo (Lille) showed that the dynamics of resonantly-driven condensates in lossy lattices can be remarkably counterintuitive - the strongest localization occurs between the pumped sites, not at them!

While not the main theme of the workshop, topological photonics was represented in talks by Profs. Sven Höfling, Sebastian Klembt (both from Würzburg University), Dr. Xingran Xu (NTU), who focused on lasing and non-Hermitian topological phenomena, and Dr. Alexander Cerjan (Sandia National Labs), who showed how real-space topological markers can be used to quantify the robustness of nonlinear topological edge states.

Prof. Fabrice Laussey (Wolverhampton) gave a captivating talk on quantum light and the importance of taking detector bandwidth into account when modelling quantum light sources. Since quantum light is so weak, signals measured using a finite bandwidth filter will inevitably be dominated by the tails of the much stronger pump beam unless homodyne detection is used. Look for quantum correlations in the spectral minima, not the dips! In related talks, Prof. Andrey Moskalenko (KAIST) analyzed entanglement between cavities generated by coherent optical driving, and Prof. Hyang-Tag Lim (KIST) covered experimental generation of multi-mode N00N states.

Most of the talks should become available to watch on the PCS Youtube account at some point.

What I've been reading lately

Continuity Equation for the Flow of Fisher Information in Wave Scattering

We can get an intuitive understanding of a wide variety of wave systems ranging including photonics, acoustics, and electronic condensed matter by visualizing the flow of intensity, energy, or probability density through them. These flows are useful for understanding the behaviour of conserved quantities, since they can be decomposed into sources, sinks, and solenoidal components. This paper shows that the Fisher information, a measure which bounds the precision with which parameters of interest can be measured, similarly obeys a conservation law enabling its visualization in terms of information flow. Remarkably, the Fisher information flow gives distinct insights into wave propagation in complex media and is complementary to more standard analysis methods based on the energy flow. This work raises many interesting questions and opens new possibilities!

Energy and Power requirements for alteration of the refractive index

This is another paper in a series of perspectives on estimating the capabilities and potential limits to the performance of photonic devices using relatively simple classical oscillator models and sharp physical insights. The take home message is that the power required to achieve a given level of optical modulation depends primarily on the interaction time, which depends on the device geometry (e.g. resonator vs travelling wave), without substantial variation among different materials. This suggests that improvements in power efficiency are more likely to come from improvements in fabrication methods and device design, rather than the discovery of some new material with substantially better physical properties.

Quantum Algorithm for Computing Distances Between Subspaces

There's growing evidence that the best place to look for a quantum advantage for classical machine learning will be geometrical or topological problems that have a natural connection to quantum systems. One example is the Betti number problem, which maps to computing the ground state of supersymmetric many-body Hamiltonians. This work shows that computing distances between k-dimensional subspaces of an n-dimensional space can be done exponentially faster using a fault-tolerant quantum computer. The algorithm exploits the ability to efficiently encode subspaces into quantum states combined with quantum signal processing. Subspace distances have to large scale machine learning and computer vision problems, suggesting the asymptotic exponential advantage promised by a fault-tolerant quantum computer could lead to practical speedups.