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Joyful Hanukkah! I’m returning to Austin from a Bay Space journey that included the annual Q2B (Quantum 2 Enterprise) convention. This 12 months, for the primary time, I opened the convention, with a chat on “The Way forward for Quantum Supremacy Experiments,” slightly than closing it with my regular ask-me-anything session.
The largest speak at Q2B this 12 months was yesterday’s announcement, by a Harvard/MIT/QuEra crew led by Misha Lukin and Vlad Vuletic, to have demonstrated “helpful” quantum error-correction, for some definition of “helpful,” in impartial atoms (see right here for the Nature paper). To drill down a bit into what they did:
- They ran experiments with as much as 280 bodily qubits, which simulated as much as 48 logical qubits.
- They demonstrated floor codes of various sizes in addition to coloration codes.
- They carried out over 200 two-qubit transversal gates on their encoded logical qubits.
- They did a pair demonstrations, together with the creation and verification of an encoded GHZ state and (extra impressively) an encoded IQP circuit, whose outputs have been validated utilizing the Linear Cross-Entropy Benchmark (LXEB).
- Crucially, they confirmed that of their system, the usage of logically encoded qubits produced a modest “web achieve” in success chance in comparison with not utilizing encoding, in keeping with theoretical expectations (although see beneath for the caveats). With a 48-qubit encoded IQP circuit with just a few hundred gates, for instance, they achieved an LXEB rating of 1.1, in comparison with a document of ~1.01 for unencoded bodily qubits.
- At the least with their GHZ demonstration and with a selected decoding technique (about which extra later), they confirmed that their success chance improves with growing code dimension.
Listed below are what I at present perceive to be the restrictions of the work:
- They didn’t instantly reveal making use of a common set of 2- or 3-qubit gates to their logical qubits. It is because they have been restricted to transversal gates, and the Eastin-Knill Theorem reveals that transversal gates can’t be common. Alternatively, they have been in a position to simulate as much as 48 CCZ gates, which do yield universality, through the use of magic preliminary states.
- They didn’t reveal the “full error-correction cycle” on encoded qubits, the place you’d first appropriate errors after which proceed to use extra logical gates to the corrected qubits. For now it’s principally simply: put together encoded qubits, then apply transversal gates, then measure, and use the encoding to take care of any errors.
- With their GHZ demonstration, they wanted to make use of what they name “correlated decoding,” the place the code blocks are decoded at the side of one another slightly than individually, in an effort to get good outcomes.
- With their IQP demonstration, they wanted to postselect on the occasion that no errors occurred (!!), which occurred about 0.1% of the time with their largest circuits. This simply additional underscores that they haven’t but demonstrated a full error-correction cycle.
- They don’t declare to have demonstrated quantum supremacy with their logical qubits—i.e., nothing that’s too arduous to simulate utilizing a classical pc. (Alternatively, if they will actually do 48-qubit encoded IQP circuits with a whole lot of gates, then a convincing demonstration of encoded quantum supremacy looks as if it ought to comply with in brief order.)
As all the time, specialists are strongly urged to appropriate something I acquired unsuitable.
I ought to point out that this may not be the primary experiment to get a web achieve from the usage of a quantum error-correcting code: Google may or won’t have gotten one in an experiment that they reported in a Nature paper from February of this 12 months (for dialogue, see a remark by Robin). In any case, although, the Google experiment simply encoded the qubits and measured them, slightly than making use of a whole lot of logical gates to the encoded qubits. Quantinuum additionally beforehand reported an experiment that at any fee acquired very near web achieve (once more see the feedback for dialogue).
Assuming the outcome stands, I believe it’s plausibly the highest experimental quantum computing advance of 2023 (coming in just below the deadline!). We clearly nonetheless have a protracted technique to go till “truly helpful” fault-tolerant QC, which could require hundreds of logical qubits and tens of millions of logical gates. However that is already past what I anticipated to be carried out this 12 months, and (to make use of the AI doomers’ lingo) it “strikes my timelines ahead” for quantum fault-tolerance. It ought to now be doable, amongst different milestones, to carry out the primary demonstrations of Shor’s factoring algorithm with logically encoded qubits (although nonetheless to issue tiny numbers, after all). I’m barely curious to see how Gil Kalai and the opposite quantum computing skeptics wiggle their means out now, although I’m completely sure they’ll discover a means! Anyway, big congratulations to the Harvard/MIT/QuEra crew for his or her achievement.
In different QC information, IBM acquired lots of press for saying a 1000-qubit superconducting chip just a few days in the past, though I don’t but know what two-qubit gate fidelities they’re in a position to obtain. Anybody with extra particulars is inspired to chime in.
Sure, I’m well-aware that 60 Minutes not too long ago ran a phase on quantum computing, that includes the often-in-error-but-never-in-doubt Michio Kaku. I wasn’t planning to look at it until occasions drive me to.
Do any of you may have sturdy opinions on whether or not, as soon as my present contract with OpenAI is over, I ought to focus my analysis efforts extra on quantum computing or on AI security?
On the one hand: I’m now utterly satisfied that AI will rework civilization and each day life in a a lot deeper means and on a shorter timescale than QC will — and that’s assuming full fault-tolerant QCs ultimately get constructed, which I’m truly considerably optimistic about (a bit greater than I used to be final week!). I’d prefer to contribute if I can to serving to the transition to an AI-centric world go effectively for humanity.
Alternatively: in quantum computing, I really feel like I’ve by some means been in a position to appropriate the factual misconceptions of 99.99999% of individuals, and it is a central supply of self-confidence in regards to the worth I can contribute to the world. In AI, against this, I really feel like no less than a thousand occasions extra individuals perceive the whole lot I do, and this causes critical self-doubt in regards to the worth and uniqueness of no matter I can contribute.
Replace (Dec. 8): A unique speak on the Harvard/MIT/QuEra work—not the one I missed at Q2B—is now on YouTube.
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