Quantum Hardware — How It's Actually Built

There's no consensus yet on which physical qubit technology will win. The main contenders: SUPERCONDUCTING QUBITS (IBM, Google): Tiny circuits cooled to near absolute zero (15 millikelvin — colder than space). Fast gate times (~10-100 ns). Short coherence times (~100 microseconds). Requires huge dilution refrigerators. IBM has the most qubits (1000+). Google's Willow chip uses this approach. TRAPPED ION QUBITS (IonQ, Quantinuum): Individual ions suspended in electromagnetic fields. Slower gate times (~1-10 ms) but much longer coherence. Higher gate fidelity. More accurate per qubit. Easier to build at small scales, harder to scale up. PHOTONIC QUBITS (PsiQuantum, Xanadu): Uses photons as qubits. Room temperature operation possible. Hard to make qubits interact.

Today's quantum computers are 'noisy' — errors accumulate rapidly. A qubit might only stay coherent for microseconds before environmental interference corrupts it. QUANTUM ERROR CORRECTION: Encode one logical qubit across many physical qubits to detect and correct errors. The surface code (most promising approach) needs roughly 1,000 physical qubits per logical qubit. SCALE NEEDED: Shor's algorithm for 2048-bit RSA needs ~4,000 logical qubits = ~4 million physical qubits. Current best: ~1,000 physical qubits. The gap is enormous — and closing. GOOGLE'S WILLOW BREAKTHROUGH: The chip demonstrated that adding more qubits reduces errors (exponentially). This is the threshold proof that fault-tolerant quantum computing is physically achievable.