Pone-versjon: [[A question of when (Pone version)]] Bloggversjon: [[A question of when]] #### Outline - Kvantedatamaskiner er på vei - Men når kommer de? - Hva trenger Shor's algoritme? - Fysiske vs logiske qubits - Moore's lov - Figuren - Nye utviklinger: Regev's algoritme, bedre feilkorrigering, bedre qubits - Hvilke mulige utviklinger kunne kommet som ville snudd opp-ned på hele bildet? - Topologiske qubits - Uventede gjennombrudd i kvanteinformasjonsteori - Nye og uventede kvantealgoritmer? (Vel, trenger minst antall qubits til å laste opp en RSA-modulus da.) #### Recent advances - [Neutral atoms](https://www.quantamagazine.org/the-best-qubits-for-quantum-computing-might-just-be-atoms-20240325/) - In December, these researchers [reported](https://www.nature.com/articles/s41586-023-06927-3) that they created programmable quantum circuits with hundreds of neutral-atom qubits and had performed quantum computations and error correction with them. And this month, a team at the California Institute of Technology [reported](https://arxiv.org/abs/2403.12021) that they made an array of 6,100 atomic qubits. (…) Indeed, in their recent work, the team at Caltech created an optical-tweezer array of about 6,100 neutral cesium atoms, although they haven’t yet performed any quantum computations with them. These qubits also had coherence times of a whopping 12.6 seconds, a record so far for this qubit type. - Veldig interessant: In 2004, a team at the University of Connecticut [demonstrated](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.063001) a Rydberg blockade between rubidium atoms, trapped and cooled to just 100 microkelvins above absolute zero. They cooled the atoms by using lasers to “suck out” the atoms’ thermal energy. The approach means that, unlike superconducting qubits, neutral atoms require no cryogenic cooling and no cumbersome refrigerants. These systems can therefore be made very compact. “The apparatus as a whole is at room temperature,” Saffman said. “One centimeter away from these super cold atoms, you have a room-temperature window.” - Fin formulering: «The key to quantum computing is that the qubits’ states are left undetermined until the final result is read out. If you try to measure those states before that point, you terminate the computation.» - «Error-corrected logical qubits have been demonstrated with superconducting and trapped-ion qubits, but until recently it hasn’t been clear if they can be made from neutral atoms. That changed in December, when the Harvard-led team unveiled arrays of several hundred trapped rubidium atoms and ran algorithms on 48 logical qubits, each made from seven or eight physical atoms. The researchers used the system to conduct a simple logical operation called a controlled NOT gate (…)» (men ikke en error-corrected cnot?) - «The Harvard-led team demonstrated error-correction techniques for some simple logical-qubit algorithms, although for the largest ones, with 48 logical qubits, they merely achieved error detection.» - «Other, more efficient proposed error-correcting codes (than the surface code) require longer-range interactions between qubits, not just nearest-neighbor pairings. Practitioners of neutral-atom quantum computing think long-range Rydberg interactions should be up to the task. “I am extremely optimistic that experiments over the next two to three years will show us that the overhead need not be as bad as people thought,” Lukin said.» (!) - «Though there’s still more to be done, Steane considers the Harvard work “a step change in the degree to which error-correction protocols have been realized in the laboratory.”» (The community agrees.) - «Advances like these have Rydberg-atom qubits drawing even with their competitors. “The combination of **high-fidelity gates, the large numbers of qubits, high-accuracy measurements and flexible connectivity** allows us to deem the Rydberg-atom array as a real competitor to the superconducting and trapped-ion qubits,” Steane said.» - “Doing scalable error correction with neutral-atom qubits is definitely possible,” Thompson said. “**I think 10,000 neutral-atom qubits is clearly possible within a few years.**” Beyond that, he thinks that practical limitations on laser power and resolution will necessitate [modular designs](https://arxiv.org/abs/2401.04075) in which several distinct atom arrays are linked together. - [Regev’s factoring algorithm](https://www.quantamagazine.org/an-easy-sounding-problem-yields-numbers-too-big-for-our-universe-20231204/) - - [Error-correction of 2-qubit gates](https://blogs.microsoft.com/blog/2024/04/03/advancing-science-microsoft-and-quantinuum-demonstrate-the-most-reliable-logical-qubits-on-record-with-an-error-rate-800x-better-than-physical-qubits/) (se [Scotts post](https://scottaaronson.blog/?p=7916))