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    Quantum computing in 2026: a crash course

    Quantum computers store information in qubits that use superposition, entanglement and interference, which in theory lets them simulate matter and break some encryption that ordinary computers cannot.[1][2][3] As of October 2026 the field has shown error correction that improves as machines grow, and DARPA's benchmarking programme has six teams in its final hardware-validation stage, but useful advantage claims are still contested.[4][5][6]

    Editor reviewedUpdated Quantum computingComputingPhysics

    Why quantum computing matters

    Ordinary computers work with bits that are either 0 or 1. A quantum computer uses qubits, which can also be in a blend of both at once.[1] By linking qubits together (entanglement) and steering their possibilities so that wrong answers cancel out (interference), a quantum computer can attack some problems in a completely different way.[7][8]

    Two reasons people care. First, nature is quantum, so a quantum computer could in principle simulate molecules and materials that classical computers cannot.[2] Second, a large enough quantum computer could break encryption that protects much of today’s internet traffic, which is why governments are already moving to new “post-quantum” codes.[3]

    The computational resource is entangled superposition, exploited through interference that concentrates probability on useful outcomes rather than through raw parallelism.[7][8] The two applications with the strongest theoretical footing are simulation of quantum many-body systems and Shor-type cryptanalysis.[2][3] Resource estimates for the latter keep falling: a 2025 estimate for 2048-bit RSA dropped from 20 million to under a million noisy qubits, and a March 2026 Google estimate put 256-bit elliptic-curve cryptography at under 1,200 logical qubits.[9][10][11]

    The map of the field

    The field divides into three layers. The first is hardware: competing ways to build a qubit, each with its own trade-offs. Superconducting circuits (Google, IBM, USTC in China) are fast and made with chip-fabrication methods.[12][13][14] Trapped ions (Quantinuum, IonQ) have the highest reported gate fidelities.[15][16] Neutral atoms (QuEra, Atom Computing, Infleqtion) scale to thousands of qubits held by laser tweezers.[17] Topological qubits (Microsoft) remain unproven, and DARPA’s programme also covers silicon spin qubits and photonics.[18][19]

    The second layer is error correction: grouping many noisy physical qubits into fewer, more reliable logical qubits, using codes such as the surface-code or IBM’s qLDPC codes.[20][21] The third is algorithms and applications, where the open question is whether a quantum computer can do something both useful and provably beyond classical machines.[22]

    Key ideas in one paragraph each

    Decoherence. Qubits lose their quantum state through any disturbance from the environment, which is why they are kept in vacuum, near absolute zero, or both.[23][24]

    Threshold. If physical error rates are low enough, adding more qubits to a code lowers the logical error rate. Google’s Willow chip showed this in 2024, halving logical errors each time the code grew.[4]

    Quantum advantage. A quantum computer finishing a task that classical computers cannot do in practical time. It was first claimed in 2019, but many claims are later matched by better classical algorithms.[25][6]

    Who the main players are

    • Google Quantum AI builds superconducting chips and reported the first below-threshold surface code and a “verifiable” advantage result, Quantum Echoes.[26][27]
    • IBM runs the largest public cloud fleet and targets the fault-tolerant Starling machine by 2029.[28]
    • Quantinuum sells the 98-qubit Helios trapped-ion system.[29]
    • IonQ bought Oxford Ionics for $1.075 billion and reported 99.99% two-qubit fidelity.[30][16]
    • Harvard, MIT and QuEra demonstrated a 448-atom fault-tolerant architecture.[31]
    • Microsoft and PsiQuantum pursue topological and photonic qubits respectively.[32]
    • DARPA’s Quantum Benchmarking Initiative acts as the field’s referee, testing whether any approach can reach utility scale by 2033.[33]

    Where the frontier is in October 2026

    Logical qubits now number in the dozens: Quantinuum reported 48 error-corrected logical qubits, and Infleqtion reported 30 entangled logical qubits on a neutral-atom machine in September 2026.[34][35] In July 2026 IBM and partners claimed quantum advantage on several problems, but a preprint posted on 13 August reproduced one of them classically on 256 GPUs in 37 minutes.[36][6] On 7 October 2026 DARPA moved Atom Computing, Diraq, IBM and IonQ into QBI’s final Stage C, alongside Microsoft and PsiQuantum.[5]

    The big open questions are which modality scales first, whether advantage claims survive classical challenge, and how soon a machine could threaten encryption. The analysis page on the quantum advantage debate and the frontier tracker follow these questions as they develop.[37]

    Questions readers ask

    What is a qubit?

    A qubit can store a zero or a one like a normal bit, but it can also hold a weighted combination of both at once, called superposition.[1]

    Has anyone built an error-corrected quantum computer yet?

    Not at useful scale. Google showed in 2024 that logical error rates fall as its surface code grows, and Quantinuum reported 48 error-corrected logical qubits on Helios, but those experiments were not yet fully fault-tolerant machines.[4][38][39]

    When might a useful quantum computer exist?

    Nobody knows. DARPA is testing whether any approach can reach utility scale by 2033, and IBM targets a 200-logical-qubit fault-tolerant machine by 2029.[33][28]

    Could quantum computers break today's encryption?

    A large enough one could. A 2025 Google estimate put 2048-bit RSA within reach of fewer than a million noisy qubits running for under a week, far beyond any machine that exists today.[10][3]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      A qubit can act like a classical bit, storing a zero or a one, but it can also exist in a weighted combination of both at once (superposition). confirmedas of 2026-10-10

    2. [2]

      NIST describes quantum computers as a new kind of machine that can, in theory, simulate the quantum nature of matter and tackle certain problems that are currently unsolvable. confirmedas of 2026-10-10

    3. [3]

      NIST leads development of post-quantum cryptography to protect data from future quantum computers that could break widely used encryption. confirmedas of 2026-10-10

    4. [4]

      Google reported that as it scaled Willow's encoded qubit grids from 3x3 to 5x5 to 7x7, the logical error rate halved at each step, which it called the first below-threshold error correction. confirmedas of 2024-12-09

    5. [5]

      On 7 October 2026 DARPA advanced Atom Computing, Diraq, IBM and IonQ to QBI Stage C, joining Microsoft and PsiQuantum, which entered from the US2QC pilot. confirmedas of 2026-10-07

    6. [6]

      An August 2026 preprint reported classically reproducing all 2,051 amplitude batches of IBM's 70-qubit doped Clifford sampling experiment in 37.3 minutes on 256 NVIDIA H100 GPUs, with results compatible with IBM's fidelity bound. reportedas of 2026-08-13

    7. [7]

      Entanglement is the ability of qubits to correlate their state with other qubits, so that measuring one tells you something about the others. confirmedas of 2026-10-10

    8. [8]

      Interference, in which quantum amplitudes reinforce some outcomes and cancel others, is described by IBM as the engine of quantum computing. confirmedas of 2026-10-10

    9. [9]

      A 2019 estimate co-published by the same author put the requirement at 20 million noisy qubits running for eight hours to factor 2048-bit RSA. confirmedas of 2025-05-21

    10. [10]

      A May 2025 Google preprint estimated that a 2048-bit RSA integer could be factored in less than a week by a quantum computer with fewer than a million noisy qubits. confirmedas of 2025-05-21

    11. [11]

      In March 2026 Google researchers, in work framed around safeguarding cryptocurrency, estimated that 256-bit elliptic-curve cryptography could be broken with fewer than 1,200 logical qubits and 90 million Toffoli gates, or fewer than 500,000 physical superconducting qubits running for a few minutes, under standard hardware assumptions. confirmedas of 2026-03-31

    12. [12]

      Willow was fabricated in Google's dedicated quantum chip fabrication facility in Santa Barbara, California. confirmedas of 2024-12-09

    13. [13]

      IBM moved primary quantum chip fabrication to a 300 mm wafer facility at the Albany NanoTech Complex in New York. confirmedas of 2025-11-12

    14. [14]

      The University of Science and Technology of China reported in Physical Review Letters in March 2025 that its 105-qubit Zuchongzhi 3.0 superconducting processor ran an 83-qubit, 32-layer random circuit sampling task it estimated at 10^15 times faster than the most powerful supercomputer. confirmedas of 2025-03-06

    15. [15]

      Quantinuum reports Helios two-qubit gate fidelity of 99.921% and single-qubit gate fidelity of 99.9975%, with all 98 qubits fully connected. confirmedas of 2026-10-10

    16. [16]

      In October 2025 IonQ reported 99.99% two-qubit gate fidelity using its Electronic Qubit Control technology, which drives qubits with precision electronics instead of lasers. confirmedas of 2025-10-21

    17. [17]

      In September 2025 a Caltech team reported in Nature an array of 6,100 cesium-atom qubits held by optical tweezers (one laser split into 12,000 tweezers), with superposition lasting about 13 seconds and 99.98% accuracy in manipulating individual qubits; entangling the qubits for full computations was the stated next step. confirmedas of 2025-09-24

    18. [18]

      The Nature peer-review file for Microsoft's 2025 paper stated that its results do not represent evidence for Majorana zero modes, and the paper itself did not claim a topological qubit. confirmedas of 2025-02-25

    19. [19]

      DARPA lists the QBI Stage B approaches as neutral atoms (Atom Computing, QuEra), trapped ions (IonQ, Quantinuum), superconducting circuits (IBM, and Nord Quantique with bosonic error correction), silicon spin or atom qubits (Diraq, Photonic, Quantum Motion, Silicon Quantum Computing) and photonics (Xanadu). confirmedas of 2025-11-06

    20. [20]

      In the surface code, data qubits and measure qubits are interleaved on a square lattice; repeated measurements flag physical errors without disturbing the stored logical information. confirmedas of 2026-01-13

    21. [21]

      IBM's fault-tolerance plan uses quantum low-density parity check (qLDPC) codes, which it says cut error-correction overhead by about 90 percent compared with other leading codes. confirmedas of 2025-06-10

    22. [22]

      Google's stated next goal is a first useful, beyond-classical computation relevant to a real-world application, citing areas such as drug discovery, battery design and energy research. confirmedas of 2024-12-09

    23. [23]

      Decoherence is the process by which a quantum state collapses into a non-quantum state, through measurement or disturbance from the environment, causing qubits to fail. confirmedas of 2026-10-10

    24. [24]

      IBM put the first quantum computer on the cloud on 4 May 2016, a five-qubit superconducting device kept in a dilution refrigerator at roughly 15 to 20 millikelvin. confirmedas of 2021-05-04

    25. [25]

      Quantum computational advantage was first claimed in 2019, and later experiments have reinforced the claim. confirmedas of 2026-09-08

    26. [26]

      Google's below-threshold experiment, published in Nature in 2025, ran a 101-qubit distance-7 surface code with 0.143% logical error per cycle, with errors suppressed by a factor of 2.14 each time the code distance grew by two. confirmedas of 2025-02-01

    27. [27]

      On 22 October 2025 Google reported in Nature that its Quantum Echoes (out-of-time-order correlator) algorithm ran on Willow in about two hours, a task it estimated would take 13,000 times longer on the Frontier supercomputer. confirmedas of 2025-10-22

    28. [28]

      In June 2025 IBM said it would build IBM Quantum Starling, a fault-tolerant quantum computer with 200 logical qubits able to run 100 million quantum operations, in Poughkeepsie, New York, by 2029. confirmedas of 2025-06-10

    29. [29]

      Quantinuum launched its Helios trapped-ion computer commercially on 5 November 2025; it uses 98 barium-ion qubits. confirmedas of 2025-11-05

    30. [30]

      IonQ agreed on 9 June 2025 to acquire Oxford Ionics, a UK trapped-ion company that builds ion traps on standard semiconductor chips, for $1.075 billion, mostly in IonQ stock. confirmedas of 2025-06-09

    31. [31]

      In November 2025 Harvard, MIT and QuEra researchers reported in Nature an architecture using up to 448 rubidium-atom qubits that combined the essential elements of scalable error-corrected computation and suppressed errors below the threshold. confirmedas of 2025-11-12

    32. [32]

      In February 2025 DARPA selected Microsoft (topological qubits) and PsiQuantum (photonic qubits) for the final phase of its US2QC programme, evaluating whether each could build a utility-scale, error-corrected quantum computer. confirmedas of 2025-02-06

    33. [33]

      DARPA's Quantum Benchmarking Initiative aims to determine whether any quantum computing approach can reach utility-scale operation - computational value exceeding cost - by 2033. confirmedas of 2026-10-07

    34. [34]

      In March 2026 Quantinuum researchers reported computations with up to 94 error-detected and 48 error-corrected logical qubits on Helios, using iceberg and concatenated codes, with logical gate errors around one in ten thousand - better than the physical gates. confirmedas of 2026-03-10

    35. [35]

      On 24 September 2026 Infleqtion reported entangling 30 logical qubits encoded in 80 physical neutral-atom qubits on its Sqale system, in a circuit of about 1,000 physical operations, and said it targets 100 logical qubits by 2028. reportedas of 2026-09-24

    36. [36]

      Also on 30 July 2026 IBM and the University of Chicago claimed quantum advantage using an error-detecting encoded circuit on 70 logical qubits, run in about 15 minutes, with effective logical error rates 10 times lower than physical error rates. confirmedas of 2026-07-30

    37. [37]

      The same perspective proposes three milestones for the coming 100-logical-qubit era - fault-tolerant advantage, efficiently verifiable advantage, and classically verifiable advantage with applications such as certified randomness. confirmedas of 2026-09-08

    38. [38]

      At launch Quantinuum reported 94 error-detected logical qubits and 48 error-corrected logical qubits on Helios, the latter performing better than the physical qubits. confirmedas of 2025-11-05

    39. [39]

      The March 2026 Quantinuum results were described as partially rather than fully fault-tolerant computation. confirmedas of 2026-03-10

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    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

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    "Quantum computing in 2026: a crash course." ContentLora, updated Oct 10, 2026. https://contentlora.com/explain/quantum-computing

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