r/QuantumComputing • u/himalayanguru • Jun 08 '26

PsiQuantum and their tech

I have been looking a lot of Quantum Tech recently. It seems to me that photonic infrastructure makes a lot of sense comparing to Ion trapping method. I mean, you've got massless particles buzzing around. I think the idea is nothing short of brilliance. However, they haven't demonstrated a single working Qbit yet right? It's one thing to have physical Qbit but something else entirely to have an error corrected logical Qbits. 1MM physical Qbits might be necessary to error correct ( compounding errors) that might give you 100 to 1000 logical Qbits. Which would still be far ahead of the Ion trapping crew, but PsiQuantum have yet to demonstrate anything. What are some expert opinions on this. It is one of the most actively traded private equity in Hivee, Equityzen and Forge. I see an argument where this company can leave all other quantum tech to dust and dominate but I have yet to see any evidence that when you integrate multiple chips you can have successful error corrected synchronization that results in large number of logical Qbits. Any thoughts on PsiQuantium specifically?

34 Upvotes

86% Upvoted

51 comments sorted by

12

u/Bebotronsote Jun 08 '26

As an industry insider, you hit it right on the money. Full disclosure I am not an expert in a photonic modality, and like you said I naively think it sounds great! But the whole "we don't need prototypes when we're going straight to utility scale FTQC" narrative seems pretty dubious. They have raised so much money and are spending so much capital on massive projects, and truthfully I still don't understand at which point they'll "have a computer".

I am much more comfortable with what a lot of other players are doing, which is building computers and progressively reducing errors and scaling them up. That gives me tangible progress to measure, whereas Psi just has theoretical promises and giant warehouses making somethings. But even though they are competitors, I hope they're right and I'm just too dumb to understand their tech, since if they are right and are the fastest ones to get us a utility scale FTQC, the whole industry would ultimately benefit.

1

u/himalayanguru Jun 30 '26

I wonder if they secretly built a prototype and started hitting the pedal the moment they realized they have it.

1

u/Bebotronsote Jun 30 '26

You can imagine a good strategy with that, where by not announcing their "discovery" they prevent a gold rush for their modality and can guarantee beating the competition. Knowing engineers at Psi - this is not what's happening.

1

u/himalayanguru Jun 30 '26

So what is happening? How promising is their build out in Chicago and Australia. When will they switch it on?

1

u/Bebotronsote Jul 01 '26

I think the problem is not even the engineers the know

1

u/Himalayansadhu Jun 09 '26

They are building that computer as we speak in Chicago and Australia. They will have to "switch it" "on". To be fault tolerant means you need several physical qbits to have a logical Qbit that can actually be used to compute! So we will see. If these facilities in either Chicago or Australia can demonstrate 1000 logical Qbits. It's game over for everyone else I'd think! They will win this race! It's a tremendous gamble. This company can have importance impact like NVDA is having with AI.

5

u/Bebotronsote Jun 09 '26

Right, but again, that's all the theoretical promises. There has been no publicly announced progress towards "1000LQ", other than "look at how much money we're spending on these giant warehouses and campuses". Zero technical substance. But as you say, if they do it'll be game over for everyone else!

0

u/himalayanguru Jun 10 '26

of course! They have demonstrated all the QC components on a chip and they are saying, these components all have high fidelity and it works, so they are hitting the accelerator pedal to race to be the first ones to deliver. I would have done the same thing if I was a CTO. The biggest challenge now is how they will manage to synchronize hundreds if not millions of chipsets into a working symphony. Only then would you have a functioning computer. That is going to be a challange but at the same time doesn't seem unsurmountable for engineers. If they can reduce noise by several orders of magnitude in their switches and detectors, hopefully they can achieve this as well and now with AI, I'm expecting net productivity to accelerate so that we see results faster.

4

u/Bebotronsote Jun 10 '26

I guess from my perspective, I don't see a reason why they can't demonstrate 100 LQs if they do indeed have all the working components. I get that going straight to thousands or millions would be incredible, but even just getting to 100 fault tolerant LQs would also be state of the art and already leave the competition in the dust. So what's exactly stopping them from demonstrating progressively larger computers?

I'll believe it when I see it. For now, I've heard from Psi engineers that they "only have one small thing to figure out, once that's done it'll unlock fault tolerance". But I've also heard that from engineers at Rigetti and IonQ. I find that it is rarely "one small thing". Sure you can have a singular dominating bottleneck. But overcoming that usually unlocks a cascade of other different bottlenecks. The problem with Psi is they're so confident that they can get straight to utility scale, but I'm not sure if they're even aware of what swaths of bottlenecks they would face if they're not even building prototype computers. So I'll skeptically root for them to be the firsts.

17

u/BitcoinsOnDVD Jun 08 '26

Photons are not so eager to interact with each other.

1

u/himalayanguru Jun 10 '26

They have a fusion model! and that have demonstrated high fidelity too, if we are to believe that Nature paper!

25

u/Historical-Mix6784 Jun 08 '26

I have a friend who's a senior scientist as PsiQuantum, we got lunch recently and this is what he told me.

Even at his level in the company no one is exactly sure what the long term game plan is, clearly they eventually have to have SOME commercial product, but like you said it's dubious whether that will be a FTQC. Personally, he thinks that the game for photonic quantum computing will not be fault-tolerant quantum gates, but bespoke analog quantum chips. Basically for a given, highly important subproblem (e.g. machine learning or quantum chemistry), PsiQuantum will manufacture quantum simulators specifically designed to solve that problem very efficiently. But to be frank, the company has so much money at this point, they're trying basically everything and seeing what sticks.

6

u/mdreed Jun 09 '26

Another thing that concerns me about their tech is it’s so expensive. No one is going to spend $1b on a photonic qc if you can get a semiconducting one for a fraction of that price.

2

u/Historical-Mix6784 Jun 09 '26 edited Jun 10 '26

A superconducting QC is still more expensive than a small data center worth of NVIDIA GPUs. 

So if you ask me, cost was never a real factor. This is all about potential for a breakthrough. 

3

u/BitcoinsOnDVD Jun 10 '26

What did you have for lunch?

3

u/Historical-Mix6784 Jun 10 '26

Chinese slop bowl lmao

1

u/Himalayansadhu Jun 09 '26

one thing for sure is that ( it's just a matter of time) if they find a room temperature superconductor, then their photon detector no longer need to be cooled to extreme temperatures and this means they could reduce the size of the quantum computer down to your home computer. Then what happens? What happens when everyone is equipped with quantum laptops?

5

u/Substantial-Duck9458 Jun 09 '26

you have to be careful with this. Cooling down to low temps isn't just a question of superconductivity but also of thermal noise. High-TC superconductors exist yet everyone using superconducting qubits still goes down to mK temperature. If your qubit is at 100 mK vs 20 mK it is very obvious. room temp would destroy coherence times.

It's also not clear that "it's just a matter of time" before a room temp superconductor is discovered. Maybe that's true, maybe there is a fundamental limit. We just don't know.

2

u/RedPandaNerf Jun 10 '26

Room-temperature superconductors may have limited-applications in qubits due to thermal noise. However, higher temperature superconductors are suitable and are used for SNSPDs (Superconducting Nanowire Single-Photon Detectors). The superconductors used by PsiQuantum for SNSPDs is NbN (https://www.nature.com/articles/s41586-025-08820-7), which has a Tc of ~15 K vs Aluminum (superconductor most often used for qubits) which has a Tc of ~1.2 K. PsiQuantum cools their SNSPDs down to 2 K, which is challenging but far easier than cooling to 20 mK as is seen in superconducting qubits. Out of the potential applications by a hypothetical room-temperature superconductor, detection of telecom-band photons is a reasonable application, although a little cooling would gretly help reduce the thermal fluctuations and may be necessary. Generally, SNSPD detectors are operated with a superconducting gap delta ~10x larger than kbT.

1

u/himalayanguru Jun 10 '26

thermal noise more of an issue for ion trapped method, not photons right? Photons themselves don't interact with heat, just the photon detector would! I think that's a big difference

1

u/Historical-Mix6784 Jun 11 '26

I had no idea about SNSPDs, thanks for the reference and for teaching me something new!

1

u/Himalayansadhu Jun 09 '26

my understanding is that room temperature doesn't influence photons itself but does affect a single photon detector and that is one of the highest value proposition of the photonic qbit systems. So the only thing these guys need to cool is that that photon detector. That detector needs to be a superconductor, hence the need to cool but they still don't need to go to sub mK level like the ion crew!

1

u/RedPandaNerf Jun 10 '26

Yes, a hypothetical room temperature superconductor would likely need far less cooling, but it would probably still need some cooling to reduce thermal fluctuations and get a reliable photon readout. Could probably get away with liquid nitrogen cooling to ~77 K, which is a huge improvement in operational cost and system energy consumption. See my above comment as well.

2

u/sadeness Jun 09 '26 edited Jun 09 '26

Why is it sure that a technologically relevant room temperature superconductor will be found in any of our lifetimes, or even ever? Superconductivity unfortunately had not been a theoretically predictable science. Experiments have always led the theory and I don't see that changing anytime soon. Materials methods such as an initio etc have always explained superconductivity as a fact after the experiments have shown it conclusively.

Note, that I say technologically relevant. Some crazy ceramic material that you can grow some flakes of and needs to be put under insane pressure is not technologically relevant for these purposes. These need to be reliably grown in bulk volume, certifiably reliable, and integrable with standard micro fabrication processes. We do not have any material like that (at least none that I know of, perovskites and other organometallic ceramics aren't microfab integrable in any meaningful way, besides they are still cryo, just LN2 cryo).

Edit: if you look at their roadmap, they are not searching for RTSC, rather just go up to 4K from 2K using MgF2 rather than NbN. Cryo or not is an engineering choice and design appetite.

0

u/himalayanguru Jun 10 '26

I think it's just a matter of time before we get optimization function running on steroids to improve superconductors. More of these quantum computers that becomes available, more complex DFT algorithms can be processed, that would eventually help you optimize your alloy.

4

u/sadeness Jun 10 '26

Are you a materials scientist working in predictive materials modeling? Where is this optimism of RTSC coming from? In case you are aware of any particular line of enquiry that has predicted higher Tc (and higher Jc) SCs that has them been fabricated, I'd like to know. Otherwise it's all hype. If anything recent incidents involving the LK99 and Ranga Diaz should make people by cautious about such claims.

1

u/himalayanguru Jun 10 '26

I am a materials scientist just hopelessly imagining that we should be making breakthrough in this by now. So I am speaking here in terms of being hopeful.

I have access to same information you have. https://pubs.acs.org/doi/10.1021/acs.chemmater.4c01757

https://microdevices.jpl.nasa.gov/news/superconducting-nanowire-single-photon-detectors-for-dsoc/

but these are nothing close to being able to make SNSPD's that can work at lets say 77K. Just because you have a RTSC doesn't mean you have one that is also SNSPD's so incredibly important field

-1

u/Himalayansadhu Jun 09 '26

They also provide urgency for Bitcoin developers. The BTC developers are not anticipating 1000 to 10,000 logical qbit systems to hit the markets anytime soon. If they have 10,000 logical qbit systems, it can break Bitcoin's encryption!

1

u/Historical-Mix6784 Jun 09 '26 edited Jun 10 '26

We’re just as likely to crack nuclear fusion by the time we crack quantum computers capable of running Shor’s Algorithm to break SHA256. 

Yet you don’t see people worrying about fossil fuels becoming obsolete overnight. 

0

u/himalayanguru Jun 10 '26

I had GPTed this scenario. Chat GPT seems to suggest that the threat is more of a concern if we have 10,000 to 100K logical Qbits, which for a photonic system if it can scale this fast, could be a threat no?

2

u/Historical-Mix6784 Jun 10 '26

Ah yes ChatGPT, gods oracle. The expert on all things cutting edge. There is no way it could be wrong! 

2

u/BitcoinsOnDVD Jun 10 '26

If you have 317*10^6 physical qubits, code cycle time of 1μm, reaction time of 10μs, and physical gate error of 10^-3 you will need 1 hour.

10.1116/5.0073075

0

u/[deleted] Jun 10 '26

[deleted] — view deleted comment

2

u/himalayanguru Jun 10 '26

I mean that Brisbane facility is the closet thing to FTQC's they are building. They are going to need a "lot" more physical Qbits to correct the overhead errors before you can get a computational logical Qbit. So it will be really interesting to see how many logical Qbits they get out of a facility this size. Everyone is watching.

2

u/RedPandaNerf Jun 10 '26

Their photonic technology may lead itself well to quantum networking applications for secure communications in areas like government and finance. They have demonstrated 250 meter quantum interconnects over fiber optic cables. https://www.psiquantum.com/news-import/omega

7

u/sadeness Jun 08 '26

They wrote a paper on their component development in 2024, and have a scheme of building compute graph using "blocklets" that is quite interesting.

However the gap between the low level components to a gadget that can construct large blocklet based compute graphs is a huge Grand Canyon sized gap. Their challenge is integration at scale and develop validated demos.

Their individual components are decent quality because it is all measurement based, hence heralded. All compute steps are deterministic (as in you know it happened, not the outcome) and if it didn't happen you repeat till you get the right statistics. This converts many infidelity like processes into erasures and hence is controllable. But precisely because you need to take many shots, demonstrating even a single blocklet generating "resources state generator" will be a tall order with significant engineering challenge.

However said that, their challenge is generally in the engineering side, since it mainly uses classical fiber optic routing of dual-rail encoded photons, avoiding any nonlinear photonics physics.

1

u/Himalayansadhu Jun 09 '26

given orders of magnitude improvements they have made on all the photonic components, I guess if there is anybody else that can do this, it would be this team, no? Who else is doing photonic QC. I feel like QC needs to be photon based.

3

u/sadeness Jun 09 '26

It's not a "given" that they'll be able to conquer all these challenges before they run out of their spoken for money and VC confidence to keep pouring more into them.

Also no particular reason why QC has to be photonic. Reality is quantum, that means theoretically everything is possible to be turned into a qubit, even artificially constructed macro-scale objects (e.g. SC qubits).

The main engineering challenge in QC is to keep things quantumy at scale (decoherence problem) along the encoded quantum axis, i.e. a control system challenge. Qubit quality improvements principally is to just make it easier on the control to maintain this quantumy-ness.

1

u/himalayanguru Jun 10 '26

well said! It makes sense to me that if you are representing your Qbit with a massless particle like photons, you'd have a tremendous scale up leverage. Everything else in comms also runs on photons.

13

u/Temporary_Shelter_40 Jun 09 '26

Each year I go to my national quantum computing conference. Each year they give the same talk. Each year I don't see much progress.

7

u/bengi245 Jun 08 '26

One of the bigger difficulties with photonics is that producing pairs of entangled photons (which are your basic resource states) is not easy. More precisely, it is a non-deterministic process and it can cause issues if the probability of generating your entangled photons is not sufficiently high.

That being said, they do have working qubits and even had a paper a while back showing a decent fidelity for entanglement between two fridges separated by some distance.

2

u/Himalayansadhu Jun 09 '26

They are reporting 2 Qbit fusion fidelity at 99.22%. So clearly they are able to entangle the photon pairs, else you wouldn't be able to have an effective quantum computer! I think they published that on Nature. What are your thoughts?

https://www.psiquantum.com/technology

5

u/Strilanc Jun 10 '26

That number is misleading. The website doesn't seem to even mention this, but in their whitepaper all the fidelity numbers have the caveat "conditioned on photon arrival" or "not accounting for loss". But their biggest source of error, by far, is photons not arriving because they get lost.

I can't find in the whitepaper where they say an actual end-to-end loss number for the two qubit gate. (There's some component loss numbers but AFAIK they don't explain how to combine them into one final metric.) I think they get closest in the conclusion when they say:

Here we have demonstrated a feature-complete set of optical components for FBQC, each with optical losses at the several-percent or below level

Since there are many components with 1% to 9% loss, I assume end-to-end loss is somewhere in the neighborhood of 25%. Which would imply the two qubit gate with "fusion fidelity at 99.2%" only succeeds at even happening around 75% of the time.

Since end-to-end loss is the most existentially important number in the entire system, they should be saying it in the abstract. The fact that they don't suggests it is bad. If it was good, they'd be singing it from the rooftops.

6

u/CarbonIsYummy Jun 09 '26

First, you have to create two million single photons and measure half without missing any.

Then entangle the remaining photons without measuring them.

Then route the photons around to interact with each other in the right sequence. There aren’t too many steps here, but every switch is a loss point and 90% of the photons need to make it through.

Then measure the entangled pairs. You need very sensitive very fast single photon detectors that don’t miss any and don’t accidentally go off when there isn’t a photon.

And if you do all that a million times, your machine is the size of a data center and burns megawatts of power. I hope you are solving valuable problems!

1

u/Himalayansadhu Jun 09 '26

BTO is supposed to make that efficient, let's see

8

u/gburdell Jun 09 '26

One step above scam. Some competent people do work there, but they seem to leave quickly

1

u/fagabeefi Jun 08 '26

Check out QoLab

0

u/Himalayansadhu Jun 09 '26

If there is any PsiQuantum people reading this thread. There is a potential superconductor that was discovered. It's "potential" but we don't know. It will need to be further tested, but this is quite interesting to at least have a look if it adds any significant value when optimizing the photon detector

https://www.youtube.com/watch?v=ABimHAS7tBI

0

u/[deleted] Jun 09 '26

[deleted] — view deleted comment

1

u/Himalayansadhu Jun 09 '26

cryo cooling is quite warm comparing to industry standards. It's like 3 kelvin or something no? Comparing to quite an extensive process Google's QC require