There are four leading approaches to building a quantum computer, each with fundamentally different physics, engineering tradeoffs, and paths to fault tolerance. Superconducting qubits (IBM, Google) dominate in deployment and gate speed. Trapped ions (Quantinuum, IonQ) lead in fidelity and connectivity. Photonic systems (PsiQuantum, Xanadu) offer room-temperature operation and networking potential. Neutral atoms (Atom Computing, QuEra) achieve the largest qubit arrays with reconfigurable geometry. This page provides a complete technical comparison of all four approaches across every metric that matters for building a fault-tolerant quantum computer.
| Spec | Superconducting | Trapped Ion | Photonic | Neutral Atom |
|---|---|---|---|---|
| Key Companies | IBM, Google, Rigetti | Quantinuum, IonQ, AQT | PsiQuantum, Xanadu, ORCA | Atom Computing, QuEra, Pasqal |
| Qubit Type | Transmon (Josephson junction) | Individual atoms (Yb-171, Ba-133) | Photons (squeezed states / single photons) | Individual atoms (Rb, Cs) in optical tweezers |
| Max Qubits (2026) | 1,121 (IBM Condor) | 56 (Quantinuum H2) | Variable (PsiQuantum targets 1M) | 1,180 (Atom Computing) |
| Best 2Q Gate Fidelity | ~99.7% 2Q (Google Willow) | 99.9975% 2Q (Quantinuum H2) | Lower (photon loss dominant error) | ~99.5% 2Q (improving rapidly) |
| Coherence Time | 50-300 microseconds | Seconds to minutes | N/A (photons do not decohere) | Seconds |
| Gate Speed | 10-100 nanoseconds | 1-100 microseconds | Picoseconds (speed of light) | ~1 microsecond (Rydberg gates) |
| Qubit Connectivity | Nearest-neighbor (fixed lattice) | All-to-all (any qubit to any qubit) | Reconfigurable via optical routing | Reconfigurable (atoms can be moved) |
| Operating Temperature | ~15 millikelvin | Room temperature (UHV chamber) | Room temperature (detectors may need cooling) | Near room temp (laser cooling) |
| Scaling Path | Modular chip-to-chip interconnects | Shuttle-based, multi-zone traps, photonic links | Semiconductor foundry fabrication (GlobalFoundries) | Larger tweezer arrays, 3D architectures |
| Error Correction Status | Below-threshold demonstrated (Google Willow) | Demonstrated logical qubits with record fidelity | Fusion-based error correction (theoretical) | Demonstrated with Harvard/QuEra (48 logical qubits) |
| Cloud Access | IBM Quantum (100+ systems), limited Google access | Azure Quantum, AWS Braket, Google Cloud | Xanadu Cloud (limited) | Amazon Braket (QuEra), limited direct access |
| Key Advantage | Fastest gates, mature fabrication, most deployed | Highest fidelity, all-to-all connectivity, long coherence | Room temp, networkable, foundry-compatible fabrication | Largest arrays, reconfigurable, mid-range coherence |
| Key Challenge | Short coherence, extreme cooling, limited connectivity | Slow gates, scaling past ~100 ions, complex laser systems | Photon loss, non-deterministic gates, detection limits | Lower fidelity than ions, Rydberg crosstalk, less mature |
Artificial atoms made from aluminum circuits on silicon chips, cooled to 15 millikelvin in dilution refrigerators. Quantum states are encoded in the energy levels of a Josephson junction — a thin insulating barrier between two superconductors. Microwave pulses manipulate qubit states and perform gate operations. The dominant commercial approach with the largest install base and most mature fabrication.
Individual atoms stripped of one electron (ionized) and suspended in electromagnetic traps in ultra-high vacuum. Quantum states are encoded in the electronic energy levels of the ion, and manipulated with precisely tuned laser beams. Entangling gates are performed through shared motional modes — the ions' collective vibration in the trap. The highest-fidelity approach with natural qubit-to-qubit uniformity.
Information is encoded in properties of photons — typically polarization, path, or squeezed-state amplitude. Optical components (beam splitters, phase shifters, single-photon detectors) perform quantum operations. PsiQuantum uses a fusion-based approach with silicon photonic chips manufactured at GlobalFoundries. Xanadu uses Gaussian boson sampling with squeezed light states.
Individual neutral atoms (rubidium or cesium) are trapped in arrays of focused laser beams called optical tweezers. Atoms can be physically rearranged by moving the tweezer beams, enabling reconfigurable connectivity. Entangling operations are performed by exciting atoms to highly energetic Rydberg states, where their electron clouds become extremely large and interact strongly with nearby atoms.
No single approach has won. The race to fault tolerance is genuinely open.
Superconducting qubits lead in commercial deployment and gate speed. Trapped ions lead in gate fidelity and connectivity. Neutral atoms lead in qubit count and reconfigurability. Photonic systems offer unique advantages in room-temperature operation and networking. Each approach has a credible path to fault-tolerant quantum computing, and the winner may ultimately depend on which team solves their respective engineering challenges fastest.
For investors and researchers, the safest assumption is that multiple modalities will coexist, serving different use cases. The quantum computing market is large enough for several approaches to succeed commercially.