pikovski

Associate professor in theoretical physics. Quantum information theory // quantum foundations // probing gravity-quantum interface

[pikovski @PikovskiQuantum]

Gravitons were thought to be impossible to detect. But our result shows that this was incorrect, a graviton detector is realistic: https://t.co/sJLqIjuByR

[pikovski @PikovskiQuantum]

@Amir_Safavi_N Yes great to discuss further! I'll get in touch with more details

[pikovski @PikovskiQuantum]

@Amir_Safavi_N I don't agree. It is such a profound disagreement about experimental input on fundamental physics that probably best to discuss in person. Hope we get this opportunity soon!

[pikovski @PikovskiQuantum]

My argument is model independent. If E=hf is extracted from the wave, that is a graviton. One can test if it follows all the quantum predictions. If a quantum of energy is not extracted from the wave, then energy conservation is violated. You can have only those two. I would be happy to collaborate and study what your model predicts

[pikovski @PikovskiQuantum]

@postquantum @quantum_geoff @Amir_Safavi_N But this is about graviton clicks, not standard GW detection. To reproduce them in a semiclassical model, energy conservation must break. Otherwise your theory contains gravitons and is no longer semiclassical.

[pikovski @PikovskiQuantum]

Ah, i see, yes this question is of course important. It would give direct access to the *single* particles predicted by linearized quantum gravity. Even if they were extracted from a coherent or other highly occupied state. Yes, by consistency we expect everything to align nicely. But this would give real and direct experimental access to probe all possible single graviton properties (spin 2? Massless? Maybe other surprises?). It's going from mathematical consistency to direct experimental observation of single gravitons and their properties. And as mentioned elsewhere, the counting statistics would be a great new window into GWs and their sources

[pikovski @PikovskiQuantum]

Graviton detection has only one definition, and our detector is a full bona fide graviton detector, no different than any other particle detector. Of course it is a single quantum of the field that is detected. The fact that some semiclassical model might also explain the result through violation of energy conservation is not the benchmark for particle detection.

In contrast, the "entanglement through mediators" is an ambiguous interpretation of GIE which only holds in one specific gauge, but has no meaning in another gauge. Feynman-wheeler is only one alternative option, another is simply the transverse gauge that doesnt include mediators in the GIE setup at all. My student and I provided a clear picture on this already in 2022: https://t.co/vUqxYfAn8V.

[pikovski @PikovskiQuantum]

No it wouldn't be, because there is always an underlying (crazy) classical model. For example, squeezed states can be fully described by a positive Wigner function, i.e. a classical distribution. The mediated entanglement also doesn't directly probe the gravitational degrees of freedom. Unless you violate a bell inequality loophole free, there is no "certainty". However, I will say that our graviton detector is also able to detect the full counting statistics in GWs, and thus also any possible non-classical state, if it exists (shown recently by Wilczek and our group)

[pikovski @PikovskiQuantum]

Yes I fully agree! But that's always true, and is unrelated to particle detection itself. It's just a collection of many (diffferent) experimental inputs that could establish firmly the quantum theory. But every experiment has some classical explanation in principle, just not standard classical physics but some artificial model. Similarly, graviton detection is not consistent with standard wave physics. But it can be explained through a semiclassical model that violates energy conservation (which we could rule out with other experiments). In short: particle detection and proving quantumness are different goals.

[pikovski @PikovskiQuantum]

@elonmusk @DavidDeutschOxf There is a lot of real advancement now beyond colliders, building on quantum technology instead. For example, we can directly detect gravitons in the near future: https://t.co/QzOApPybin

[pikovski @PikovskiQuantum]

@postquantum @Amir_Safavi_N @newscientist @carlorovelli @quantum_geoff @IvetteFuentesGu That's incorrect.

[pikovski @PikovskiQuantum]

@Briankeating It is absolutely possible to directly detect gravitons, and in fact tealistic in the near future. I explain this result in simple terms here: https://t.co/QzOApPybin

[pikovski @PikovskiQuantum]

Detecting gravitons was thought to be impossible. But it turns out it can be achieved, as we showed in 2024. In a write-up for Physics Today, I explain why graviton detection is now a realistic target for quantum technology, and how the conventional wisdom is overturned. https://t.co/okzOcd07Vp

[Henry Yuen @henryquantum]

3. Now, to the math. In 2016 I proved a polynomial-decay theorem; the exponential-decay theorem was left open and has since remained one of my favorite problems. I always intended to come back to it. Actually, a month ago I tried to set GPT 5.5 on it, and it didn't make very much progress.

A couple days ago Lijie Chen (@wjmzbmr1) sent me and a couple others a writeup. Life was busy so I didn't get a chance to look, but I guess now the cat's out of the bag so I probably should opine a bit.

I presume the proof is correct (there's supposedly a Lean formalization, after all), but it will take me some time to digest it. I am gratified that it starts from where my paper left off, but goes beyond the limitations of my proof strategy by using some tricks and techniques that are probably known, in some collective fashion, to operator theorists and functional analysts. The reasoning document furnished by OpenAI is interesting but opaque: it states the problem, and then there's a leap of intuition on how to find the right purification using the "resolvent", and then does some exotic matrix entropy calculations to show that it works out.

I don't understand it yet. Maybe it'll take me an afternoon to check all the calculations, but what would still be missing is _why_ this was an approach that would've made sense in the first place. Is there some broader context or theory within which this would've been the obvious thing to do? What other results can be proven using these techniques? What is it telling us about quantum information or operator theory? I have no idea. I spent about an hour this morning asking ChatGPT these questions, but it's somewhat frustrating because it speaks with a mishmash of physicist, operator algebraist, quantum information theorist-lingo, plus the usual LLM breezy lilt that annoys everybody.

I would love to hear from experts who find these calculations familiar. I might write about this again when I understand better.

[pikovski @PikovskiQuantum]

This is the correct, sober view. AI is impressive at solving some technical challenges, unclear yet if it can generate new science

[Sabine Hossenfelder @skdh]

solving a maths-only problem is one thing. developing a mathematical theory for a real world problem is another thing entirely. confusing the first with the second is the very reason why physicists got stuck in the foundations, it's not a trivial step.

https://t.co/aoNiCWjdEb

[pikovski @PikovskiQuantum]

Nice to see coverage by @skdh on our work. We show that superpositions of time should exist and could soon be measured with single-ion clocks (in @APSphysics https://t.co/S3dAHBQulP).

After graviton detection and quantum networks on curved space-time, that's the 3rd time her channel covers our results in recent months. Great to see the interest in our research!

[Sabine Hossenfelder @skdh]

In general relativity, the time an object experiences depends on its acceleration. But time in quantum physics is a universal parameter. Physicists say they want to use a special type of clock to test the difference.
https://t.co/8PyUcPYNeO

[pikovski @PikovskiQuantum]

@forallcurious That's our group's research, explained here: https://t.co/rg7axTjWex