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Marek GluzaHere's an <a href="https://mathstodon.xyz/tags/introduction" class="mention hashtag" rel="tag">#introduction</a> of <a href="https://qubit-social.xyz/@frederikhahn" class="u-url mention">@frederikhahn</a> as part of my agenda that <a href="https://mathstodon.xyz/tags/nice" class="mention hashtag" rel="tag">#nice</a> should be a characteristic demanded of academics.In the past few years Freddy has been gently cracking his head on how to remove bottlenecks in a <a href="https://mathstodon.xyz/tags/quantumNetwork" class="mention hashtag" rel="tag">#quantumNetwork</a>. He focused on relevant <a href="https://mathstodon.xyz/tags/quantum" class="mention hashtag" rel="tag">#quantum</a> states and tweaked their parts like he tweaks parts in his bike to make it run seamlessly <a href="https://arxiv.org/abs/1805.04559" target="_blank" rel="nofollow noopener noreferrer" translate="no">https://arxiv.org/abs/1805.04559</a> (Local complementations interest me for <a href="https://mathstodon.xyz/tags/quantumCompiling" class="mention hashtag" rel="tag">#quantumCompiling</a>: the unitary encoding the repetition code can be turned into a gate between any two qubits because one can distill Bell pairs out of <a href="https://mathstodon.xyz/tags/GHZ" class="mention hashtag" rel="tag">#GHZ</a> states.)Rick came from Berlin to the <a href="https://mathstodon.xyz/tags/quantumInformation" class="mention hashtag" rel="tag">#quantumInformation</a> <a href="https://mathstodon.xyz/tags/workshop" class="mention hashtag" rel="tag">#workshop</a> in <a href="https://mathstodon.xyz/tags/benasque" class="mention hashtag" rel="tag">#benasque</a> by train. His tap water canister was half empty: he realized that meh whatev he can travel half Europe and not eat if the food is not what he wants provided he has water to last him even more than 24 hs.Frederik is a scientist who leads by example, is sustainably concerned about the <a href="https://mathstodon.xyz/tags/climateCrisis" class="mention hashtag" rel="tag">#climateCrisis</a> but look at him shining. His <a href="https://mathstodon.xyz/tags/intermittentFasting" class="mention hashtag" rel="tag">#intermittentFasting</a> skills allowed him to be chilled after a strainous long distance travel but I learn from him that being nice and chilled is a muscle we can all train. His integrity at work reminds me that it's not impossible to keep our humanity first and also excell at research. I wish we had an equivalent of <a href="https://mathstodon.xyz/tags/citationMetrics" class="mention hashtag" rel="tag">#citationMetrics</a> for acts of kindness in academia.These photos were taken on a Friday, on Monday that week he defended his thesis. In style, which is his style. For his <a href="https://mathstodon.xyz/tags/phd" class="mention hashtag" rel="tag">#phd</a> hat I'd add a phone charger, his daily cycling suffices to top up the battery. I don't know how to symbolize my thanks for having made my local science world wholesome, one <a href="https://mathstodon.xyz/tags/introvert" class="mention hashtag" rel="tag">#introvert</a> thought at a time, but: thank you for caring, Dr Hahn!

Marek GluzaAdrián Pérez-Salinas coordinated a <a href="https://mathstodon.xyz/tags/benasque" class="mention hashtag" rel="tag">#benasque</a> session on variational <a href="https://mathstodon.xyz/tags/quantum" class="mention hashtag" rel="tag">#quantum</a> algorithms. Here's the story what I think I learned :)People now say various things about the state of the field. It was clear to me from the very beginning that there will be trainability issues and you can verify it because I haven't written a single paper involving brute force training of circuits. But.While, I have been avoiding reading papers on VQAs (until I needed to cite variational diagonalization in context of my proposal to use double-bracket flows for diagonalization on quantum computers), now that the field has reached a milestone, here's a few insights I really like and claim will matter down the line: - statements about <a href="https://mathstodon.xyz/tags/barrenPlateaus" class="mention hashtag" rel="tag">#barrenPlateaus</a> are quantitative - appearance of barren plateaus is implied by presence of <a href="https://mathstodon.xyz/tags/t" class="mention hashtag" rel="tag">#t</a>-design properties <a href="https://arxiv.org/abs/2101.02138" target="_blank" rel="nofollow noopener noreferrer" translate="no">https://arxiv.org/abs/2101.02138</a> - plateaus result from high dimensionality of the training parameter set.To paraphrase grandmaster Bronstein, it's not about what but how. We now know very, very well how VQAs go wrong. Early on it was only clear what the problem will be.Each of the points above can guide better <a href="https://mathstodon.xyz/tags/ansatzae" class="mention hashtag" rel="tag">#ansatzae</a>: - they need to operate on clumped circuits to reduce the dimensionality - they shouldn't rotate back and forth but use physics equations to guide the <a href="https://mathstodon.xyz/tags/quantumCompiling" class="mention hashtag" rel="tag">#quantumCompiling</a> - a restricted ansatz with justified expressibility can be quantitatively tested using the average+variance criteria of regular barren plateaus.What the field achieved is to inform a large group of people how to recognize what a good variational ansatz will be once we will encounter it. And that it will not be naive? Come on, easy would have been boring.

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