Bloch Sphere

An interactive Bloch sphere in your browser: click a gate, watch the qubit move. It is the quickest way to build intuition for what quantum gates actually do to a single qubit.

Grok Bloch Demo Interface

Needs: a display · Start it with: rq_demo_run.sh grok-bloch

Run it

Double-click the Grok Bloch icon on the desktop, and it opens in your browser.

It is also under Applications → RasQberry → Grok Bloch, or in sudo raspi-config → 0 RasQberry → Quantum Computing Demos.

Reading the sphere

Every pure state of one qubit is a point on the sphere:

  • North pole — |0⟩, south pole — |1⟩
  • Equator — superpositions with an equal chance of either
  • X axis — |+⟩ and |−⟩ (the Hadamard basis)
  • Y axis — |+i⟩ and |−i⟩ (the circular basis)

The state equation is shown at the top, and the probability of measuring |0⟩ alongside it. Click gates and watch the vector swing: X, Y and Z turn the state half a revolution about their axis, H takes the poles to the equator (|0⟩ → (|0⟩ + |1⟩)/√2), and Rx/Ry/Rz rotate by an angle you choose (θ = π/8 or π/12).

Start with X, Z and H before the rotation gates — the effect is easier to see. Then try reaching a state you pick in advance.

What it cannot show

Worth knowing, because it is the honest limit of the picture:

  • One qubit only. There is no Bloch sphere for two entangled qubits — the whole point of entanglement is that neither qubit has a state of its own.
  • Pure states only. No mixed states, so no decoherence or noise.

Credits and links

Built by James Weaver (JavaFXpert) — JavaFXpert/grok-bloch.

See the Demo List for everything else on the image.

Edit this page on GitHub