Platforms
A zoological classification of quantum computing hardware — how platforms branch, compete, and evolve from common ancestors.
Phylogenetic Tree
Platform Comparison
Superconducting
The qubit is a tiny circuit made of superconducting metal (typically aluminum on silicon), cooled to ~15 mK in a dilution refrigerator. Quantum information is stored in the quantized energy levels of a nonlinear oscillator (transmon, fluxonium, or bosonic mode in a microwave cavity). Cat qubit variants encode information in superpositions of coherent states for built-in bit-flip protection.
Temperature
15 mK
Best fidelity
99.5%
Qubits
1,000+
- +Most mature — largest ecosystem of tools, cloud access, and talent
- +Fast gate speeds (~10–100 ns)
- +Established fabrication leveraging semiconductor lithography
- +Multiple companies already at cloud-access or production stage
- −Requires dilution refrigerators (~15 mK), expensive and hard to scale
- −Short coherence times relative to trapped ions
- −Each qubit slightly different (fabrication variability)
- −Wiring bottleneck limits scaling beyond ~1,000 qubits
Trapped Ion
The qubit is a single charged atom (typically ytterbium-171 or barium-133) suspended in vacuum by oscillating electric fields. Quantum information is stored in two hyperfine or optical energy levels of the ion. Two-qubit gates work by coupling ions through their shared motional modes — the ions' mutual Coulomb repulsion lets them "talk" to each other.
Temperature
Room temp (vacuum)
Best fidelity
99.9%
Qubits
~50
- +Highest gate fidelities achieved (>99.9%)
- +All qubits are identical (same atomic species)
- +Long coherence times (seconds to minutes)
- +All-to-all connectivity within a trap
- −Slow gate speeds (~1–100 µs) vs superconducting
- −Scaling past ~50 ions in a single trap is challenging
- −Complex laser and vacuum systems
- −Photonic interconnects for multi-trap scaling still maturing
Neutral Atom
The qubit is a single neutral atom (typically rubidium-87 or cesium-133) held in place by a focused laser beam (optical tweezer). Quantum information is stored in the atom's hyperfine ground states. Two-qubit gates work by exciting atoms to high-energy Rydberg states where they interact strongly over micron-scale distances. Arrays of hundreds of atoms can be rearranged in real time.
Temperature
~µK (laser-cooled)
Best fidelity
99.5%
Qubits
1,000+
- +Rapidly scaling — 1,000+ qubit arrays demonstrated
- +Identical qubits (same atomic species)
- +Reconfigurable connectivity via atom shuttling
- +Native multi-qubit gates (e.g., CCZ) via Rydberg interactions
- −Atom loss during computation limits circuit depth
- −Gate fidelities still trailing trapped ions
- −Mid-circuit measurement and feed-forward still developing
- −Relatively young platform with fewer deployed systems
Photonic
The qubit is a single photon — quantum information is encoded in its polarization, path, or time-bin. Photons are generated by single-photon sources (quantum dots or parametric down-conversion), manipulated with beam splitters and phase shifters on silicon photonic chips, and measured by single-photon detectors. Two-qubit entanglement relies on measurement-based schemes (fusion gates) rather than direct interaction.
Temperature
Room temp
Best fidelity
~99%
Qubits
N/A (measurement-based)
- +Room-temperature operation — no cryogenics needed
- +Natural for quantum networking and communication
- +Photons don’t decohere easily
- +Compatible with existing telecom fiber infrastructure
- −Photon loss is a major challenge
- −Deterministic two-photon gates are extremely difficult
- −Measurement-based approach requires massive resource overhead
- −No leading demonstration of computational advantage yet
Silicon Spin
The qubit is the spin (up or down) of a single electron confined in a nanoscale potential well (quantum dot) etched into a silicon chip. Gate voltages define the dot and tune interactions. Two-qubit gates use the exchange interaction between neighboring electron spins. The key appeal: these devices can be fabricated in the same foundries that make classical processors.
Temperature
~100 mK
Best fidelity
99.3%
Qubits
~12
- +Leverages existing CMOS semiconductor manufacturing
- +Extremely small qubits — potential for high density
- +Long coherence times in isotopically purified silicon
- +Industry giants (Intel) investing in scalable fabrication
- −Two-qubit gate fidelities still lagging leaders
- −Requires precise placement of individual atoms or dots
- −Cryogenic operation (~100 mK) still needed
- −Crosstalk between densely packed qubits is challenging