An educational reference
Quantum computing, and the cryptography built to outlast it
A plain-language look at what quantum computers can actually do today, the categories of problems they're suited to, and the mathematics now being deployed worldwide to protect data before large-scale quantum machines arrive. No products, no pitch — just the current state of the field, in numbers.
- $1.4BGlobal quantum computing market, 2025QED-C
- 4,158Qubits IBM is targeting with its Kookaburra multi-chip processor
- <1MPhysical qubits now estimated to factor RSA-2048, down from ~20M in 2021
- 3Post-quantum cryptography standards finalized by NIST, August 2024
Part One
Quantum computing
Classical computers store information as bits — 0 or 1. Quantum computers use qubits, which can exist in a superposition of both states at once and can be entangled with one another so their states become correlated regardless of distance. That difference doesn't make quantum computers faster at everything — it makes them differently suited to a narrow but important set of problem structures, described below.
State of quantum computing, 2026
Market size, government and venture funding, gate fidelity, verified logical qubits, and the quantum skills gap.
Read more →Problem classes
Optimization, chemistry, factoring, machine learning, and finance: where quantum computers are suited and where advantage is still unproven.
Read more →Hardware landscape
Superconducting, neutral-atom, and photonic systems compared, from Google Willow to PsiQuantum Omega.
Read more →Part Two
Post-quantum cryptography
Post-quantum cryptography (PQC) refers to cryptographic algorithms designed to run on today's classical computers while resisting attacks from both classical and quantum computers. Unlike quantum key distribution, PQC requires no special hardware — it's a software and standards migration, and it's already underway.
What is post-quantum cryptography?
Why harvest-now, decrypt-later makes the migration urgent, and where PQC has already shipped.
Read more →RSA-2048 qubit estimates
How the qubit estimate fell from about 20 million physical qubits to under one million.
Read more →NIST standards
ML-KEM, ML-DSA, SLH-DSA, HQC, and FN-DSA, and the three mathematical foundations behind them.
Read more →Migration timeline
Milestones from 2024 to 2035, including CNSA 2.0 and the 2030 RSA-2048 deprecation.
Read more →Frequently asked questions
What is “harvest now, decrypt later”?
An adversary intercepts and stores encrypted traffic today, intending to decrypt it once a cryptographically relevant quantum computer exists. Data with a long confidentiality lifetime is therefore already exposed under this model, which is why post-quantum cryptography is being deployed now.
Which post-quantum standards has NIST finalized?
In August 2024 NIST finalized FIPS 203 (ML-KEM), FIPS 204 (ML-DSA), and FIPS 205 (SLH-DSA). HQC was selected as a backup key-encapsulation mechanism in 2025, and FIPS 206 (FN-DSA) is expected in 2026–2027.
How many qubits would it take to break RSA-2048?
Estimates have fallen sharply: about 20 million physical qubits in 2021 (Gidney & Ekerå) to fewer than one million physical qubits in 2025 (Gidney, Google). Chevignard et al. estimated about 1,730 logical qubits in 2024. All remain far beyond current hardware.
When will RSA-2048 and ECC P-256 be deprecated?
Under NIST's transition plan (NIST IR 8547), RSA-2048 and ECC P-256 are set to be deprecated in 2030, and quantum-vulnerable algorithms are to be removed from NIST standards entirely by 2035.
What problems are quantum computers suited to?
Combinatorial optimization (QAOA), quantum chemistry and materials simulation (VQE), integer factorization and discrete logarithms (Shor's algorithm), quantum machine learning, and Monte Carlo-heavy finance modeling (quantum amplitude estimation). Their advantage is concentrated in specific problem structures, not across the board.
Reference & further reading
Every figure on this site is labeled with its approximate source. See the full list of sources and further reading, including the NIST Post-Quantum Cryptography Project.