1The Noise Floor
On current NISQ devices, every gate adds a small amount of noise. If a circuit is too deep, the final result will be indistinguishable from random noise.
2The Coldest Places
To keep superconducting qubits alive, they must be cooled to 10-20 milli-Kelvin, colder than interstellar space. This requires massive dilution refrigerators.
3Step-by-Step Breakdown
Quantum Fragility. Quantum states are extremely sensitive to their environment.
T1 Relaxation. Energy loss causes a qubit to fall from |1> back to |0>.
T2 Dephasing. The relative phase between |0> and |1> is lost, destroying superposition.
Gate Errors. Applying a gate is never 100% perfect. Errors accumulate.
Qubit Connectivity. Not all qubits can talk to each other directly on a physical chip.
Error Correction. Using multiple physical qubits to build one 'logical' qubit that is error-free.
Check. What is the term for energy loss in a qubit?
- →T1 Relaxation
- →T2 Dephasing
Scaling Up. Going from hundreds to millions of qubits is a massive engineering challenge.
Quantum Advantage. We need 'Logical Qubits' to achieve reliable advantage for most algorithms.
End. Challenges understood.
Model Real Quantum Decoherence. Finish computing how fidelity decays over time due to decoherence.
