A QPU (Quantum Processing Unit) is the quantum hardware equivalent of a CPU. It is the physical device that stores qubits and executes quantum gate operations. Current QPU technologies include superconducting qubits (IBM, Google, Rigetti), trapped-ion qubits (IonQ, Quantinuum), photonic qubits (PsiQuantum, Xanadu), and neutral atoms (QuEra, Pasqal). Each technology has different tradeoffs in qubit count, gate fidelity, connectivity, and coherence times. QPUs operate at cryogenic temperatures (superconducting) or in vacuum (trapped ions). Access is typically provided through cloud APIs. Running circuits on a real QPU always involves noise, transpilation overhead, and queue waiting times compared to simulators.
Related Terms
Qubit
FundamentalsThe fundamental unit of quantum information — the quantum analog of a classical bit.
NISQ
HardwareNoisy Intermediate-Scale Quantum — devices with 50–1000 qubits without full error correction.
T1 / T2 Time
HardwareT1 is the qubit energy relaxation time; T2 is the coherence (dephasing) time. Both limit circuit duration.
Fidelity
MetricsA measure (0 to 1) of how close an actual quantum operation or state is to the ideal target.
Transpilation
HardwareThe process of compiling a quantum circuit into the native gate set and qubit connectivity of a specific device.