Quantum Volume (QV) is a hardware-agnostic benchmark developed by IBM Research to measure the overall capability of a quantum computer. QV is defined as 2^d, where d is the largest square random circuit (d qubits, d layers) that a device can run with >2/3 success probability (i.e., the heavy output generation problem). QV captures qubit count, connectivity, gate fidelity, measurement error, and circuit compilation quality all in one number. A QV of 64 means d=6 (2^6=64). Higher is better. IBM's systems have reached QV values of 512+. Limitations: QV focuses on small square circuits and may not reflect performance on larger specialized circuits. Competitors like IonQ use alternative metrics such as #AQ (Algorithmic Qubits). Quantum Volume was influential but is now supplemented by application-specific benchmarks.
Related Terms
Fidelity
MetricsA measure (0 to 1) of how close an actual quantum operation or state is to the ideal target.
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.
QPU
HardwareQuantum Processing Unit — the physical hardware chip that executes quantum circuits.