W/S or Arrow keys to move your paddle. F to activate your quantum zone. Q to toggle phase dial, E to rotate it. ESC to pause.
First to reach the score limit wins. A ball passing your paddle scores a point for your opponent.
Glowing zones at the top and bottom of the field split balls automatically. You also have a personal quantum zone in the center. Press F to activate it and split balls on demand. Activation costs 1 energy; you earn energy back each time your paddle hits a ball.
Each ball displays its chance of being real. When a ball scores, it's measured. If it turns out to be a ghost, no point is awarded.
Toggle phase dials (Q to activate, E to rotate) to apply quantum rotations. This biases which ball in an entangled pair is more likely to be real.
The phase dial does more than bias probabilities — it gives entangled balls a kind of quantum spin. Choose a mode in settings:
Bounce (default) — Spin changes how balls deflect off paddles and walls. A ball with phase spin will kick up or down when it bounces, letting you curve shots around your opponent.
Zones — Glowing spin-Hall zones appear in front of each paddle. Inside these zones, entangled balls feel a transverse force that curves their path. Outside the zones, balls travel straight. Use the phase dial to control the curve direction.
Drag on the playing field to move your paddle. Tap the center zone to activate it. Tap the phase dial to toggle it; hold to rotate.
First to reach the score limit wins. A ball passing your paddle scores a point for your opponent.
Glowing zones at the edges of the field split balls automatically. You also have a personal quantum zone in the center. Tap it to activate and split balls on demand. Activation costs 1 energy; you earn energy back each time your paddle hits a ball.
Each ball displays its chance of being real. When a ball scores, it's measured. If it turns out to be a ghost, no point is awarded.
Tap the phase dial (bottom-left) to toggle it on. Hold the dial to rotate and apply quantum rotations. This biases which ball in an entangled pair is more likely to be real.
The phase dial gives entangled balls quantum spin. Choose a mode in settings:
Bounce (default) — Spin changes how balls deflect off paddles and walls, letting you curve shots.
Zones — Spin-Hall zones near each paddle curve entangled balls as they pass through. Use the phase dial to control the direction.
Everything quantum in this game is computed by an actual quantum simulator (Quantum Forge). The qubits, entanglement, density matrices, and measurements are genuine quantum mechanics, not random numbers pretending to be quantum.
Each ball is a qubit: |1⟩ = exists, |0⟩ = ghost. When a ball enters a quantum zone, a √iSWAP gate entangles it with a new partner, producing the state (|10⟩ + i|01⟩)/√2. The system lives in the single-excitation subspace: exactly one ball is "real" at a time, but which one is undetermined until measurement.
The off-diagonal element ρ[i,j] of the reduced density matrix captures the coherence between balls i and j, their quantum phase relationship. The real part is the symmetric component. The imaginary part is the antisymmetric component. Only the antisymmetric part breaks left-right symmetry.
Real qubits don't have spatial trajectories, so we invented a mapping: the quantum phase between entangled balls plays the role of spin. The phase dial applies a Z-rotation to a ball's qubit, rotating the off-diagonal coherence ρ[i,j] in the complex plane: ρ[i,j] → eiθ·ρ[i,j]. After a split, Im(ρ) = −0.5, giving balls immediate spin. Rotating by π/2 zeroes the spin. Rotating by π reverses it.
In Bounce mode (the default), spin manifests as a deflection when a ball hits a paddle or wall — a quantum Magnus effect. The deflection is proportional to sin(ϕ), where ϕ is the ball's relative phase. Positive spin kicks the ball one way; negative spin kicks it the other. This lets you use the phase dial to put "english" on your shots, curving them around your opponent.
In Zones mode, spin creates a continuous transverse force — but only inside the spin-Hall effect zones, the glowing regions in front of each paddle. Inside a zone, Im(ρ[i,j]) drives an acceleration perpendicular to the ball's velocity and toward its entangled partner, curving its path. Outside the zones, balls travel in straight lines. This is inspired by the real spin-Hall effect, where particles with intrinsic spin experience a transverse deflection in specific regions of a material. Here, the zones are those regions, and quantum phase is the spin.
Built with Quantum Forge.
All sound effects from Kenney.nl (CC0 public domain).
"Cyberpunk Moonlight Sonata" by Joth (CC0)
"ICE temple" by HoliznaCC0 (CC0)
"Observing The Star" by yd (CC0)
"Rising Hero" by HoliznaCC0 (CC0)
"Synthwave Ambient" — source unconfirmed (CC0)
"Synthwave Type" — source unconfirmed (CC0)