Multi-qubit states on a sphere. Basis states are placed by Hamming weight: |00...0⟩ at the north pole, |11...1⟩ at the south pole. Dot size = amplitude, dot color = phase.
The Q-sphere extends the Bloch sphere to multi-qubit systems. Each computational basis state is placed on a sphere, with layers organized by Hamming weight — states with zero 1-bits at the top (|000⟩), states with all 1-bits at the bottom (|111⟩), and states with mixed bits in between.
Node size indicates measurement probability: larger nodes are more likely to be observed. Color encodes the complex phase of each amplitude, making interference and entanglement patterns visible at a glance. This representation was introduced by IBM Research as a way to visualize multi-qubit states that the single-qubit Bloch sphere cannot capture.