QCryptWatch

Learn

Quantum computing modalities

There is more than one way to build a quantum computer. Each approach has different scaling, accuracy and runtime tradeoffs for attacks on public-key cryptography.

Q-Watch NetworkQSense Watch tracks a sourced threat projection with uncertainty. QCrypt Watch explores migration timing against an assumed horizon.Q-Day projection on QSense Watch

The threat

Shor's algorithm on a large, error-corrected quantum computer breaks RSA and elliptic-curve cryptography.

The variable

How many physical qubits, how accurate, and how fast. Modality drives all three.

The takeaway

No modality has to win for the risk to be real. Data captured today can be decrypted later, so migrate now.

Trapped ions

Individual charged atoms are held in place by electromagnetic fields inside a vacuum chamber. Lasers or microwaves set and read each atom's quantum state.

Strengths

  • Among the highest two-qubit gate fidelities reported by any modality
  • Every qubit can interact with every other qubit in a trap
  • Identical atoms, so qubits do not vary from chip to chip

Limits

  • Gate operations are slow compared with superconducting circuits
  • Scaling past one trap requires moving ions or linking modules

Why it matters for cryptography

High accuracy means fewer physical qubits per error-corrected logical qubit. Slow gates stretch the run time of Shor's algorithm. Watch for modular, networked systems: they remove the main scaling ceiling.

Leading players: Quantinuum, IonQ

Quantinuum hardware

Superconducting circuits

Tiny electrical circuits cooled to near absolute zero behave as qubits. Microwave pulses control them on a chip made with semiconductor-style fabrication.

Strengths

  • Very fast gates (tens of nanoseconds)
  • Builds on mature chip manufacturing
  • First modality to show error rates dropping as error-correcting codes grew

Limits

  • Short coherence times
  • Large cryogenic and wiring overhead as qubit counts grow

Why it matters for cryptography

This is the modality used in the best-known published estimates for breaking RSA-2048. Fast gates mean an attack, once the hardware exists, could finish in days rather than months.

Leading players: Google Quantum AI, IBM, Rigetti

Gidney 2025: RSA-2048 with under a million noisy qubits

Neutral atoms

Uncharged atoms are trapped in grids by focused laser beams (optical tweezers) and made to interact by exciting them to high-energy Rydberg states.

Strengths

  • Large arrays of hundreds to thousands of atoms
  • Atoms can be rearranged during a computation
  • Fast progress in logical-qubit demonstrations

Limits

  • Atoms can be lost and must be reloaded
  • Gate fidelity still catching up with ions and superconductors

Why it matters for cryptography

The fastest-growing qubit counts in the field. If fidelity keeps improving, this is the modality most likely to surprise forecasts on scale.

Leading players: QuEra, Atom Computing, Pasqal, Infleqtion

QuEra technology

Photonic

Particles of light carry the quantum information. Computation is done with optical components on chips and measurement of photons.

Strengths

  • Runs largely at or near room temperature for the photonics
  • Natural fit with fiber networking
  • Targets standard semiconductor foundries

Limits

  • Photon loss is the dominant error
  • Large-scale fault-tolerant demonstrations are still ahead

Why it matters for cryptography

Companies are aiming directly at a million-qubit fault-tolerant machine rather than incremental steps. Progress may arrive in large jumps, which makes it harder to time.

Leading players: PsiQuantum, Xanadu, Quandela

PsiQuantum approach

Spin qubits (silicon)

The spin of a single electron, trapped in a structure similar to a transistor, stores the qubit. Built in silicon with conventional chip processes.

Strengths

  • Very small qubits, so potentially millions on a chip
  • Compatible with existing silicon fabs

Limits

  • Small device counts so far
  • Uniformity across devices is hard

Why it matters for cryptography

A long-term scaling bet. Not a near-term threat driver, but the modality with the most direct path to massive qubit density.

Leading players: Intel, Diraq, Quantum Motion

Intel quantum research

Topological

Encodes information in exotic quasiparticle states that are, in theory, protected from local noise by their physics.

Strengths

  • Built-in error resistance could sharply cut error-correction overhead

Limits

  • Earliest stage of any modality
  • Scientific claims are still debated in the research community

Why it matters for cryptography

If it works as hoped, it would compress the timeline more than any other approach. Treat announcements as signals to monitor, not proof of capability.

Leading players: Microsoft

Microsoft Majorana 1 announcement

What to tell leadership

  • Several hardware approaches are advancing in parallel. Progress may change resource estimates, but does not establish an attack date.
  • Published RSA-2048 resource estimates include about 20 million noisy qubits (2019) and under one million (2025), with different runtime and error-correction assumptions. These are modeled requirements, not demonstrated attacks.
  • Federal deadlines do not wait for a winner. Inventory and migration plans are due regardless of which modality leads.