Project Showcase: Superposition Sequencer

Superposition Sequencer is a web-based quantum music tool that turns superposition and entanglement into something you can hear.

It looks like a normal sequencer, with drums, percussion, chords, and melodies. But the notes are not programmed directly. They are generated by running quantum circuits live on IonQ hardware, with a simulator as a fallback. You design a circuit in a visual editor, and its measured output drives the pattern: pitch, rhythm, velocity, timbre.

It is a featured project from Qollab's Spring Creative Challenge, and one of the clearest answers yet to a question the challenge keeps asking: what does quantum computing feel like when it stops being a science experiment and becomes a creative tool?

I don't work with quantum regularly, but every few years I go back to it, study it a little, and get my mind blown. Then I forget about it, come back, and it happens again.

An instrument, not an experiment

Francisco's way in wasn't physics, it was history. The early days of computing and electronics, he points out, came with a wave of musical exploration that opened entirely new ways to make sound, with outsized cultural influence. He thinks quantum is in a similar moment, and that the way to meet it is to make it less intimidating, which is why, of all his quantum-and-music ideas, a sequencer felt like the most approachable first step.

Most quantum demos are random-number generators in a costume. This one flips that: the composer builds the circuit, and the quantum hardware is the instrument. The real twist is what is actually being computed.

We are not trying to compute the sequence. The sequence is the measurement. What we are computing is the relationship between instruments and effects. It is a systemic approach to musical sequencing.

It also leans into something most engineers spend their time trying to eliminate.

In sound design, people are always looking for ways to make things sound a little imperfect. That little bit of noise is also a characteristic of quantum computers, so it could bring a new personality to the sound itself.

It is also built to last, not to be a one-off demo. Circuits and the patterns they generate can be exported, saved, loaded, and reused, so you build up a personal library of quantum musical ideas, much like a hardware synth's patch memory. A downloadable library of pre-executed sequences even lets musicians use the output without their own hardware access.

How Francisco built it

Francisco's first prototype looked nothing like a sequencer. It was a rotating sphere whose cursor struck different notes as it turned, leaning on the geometric way we usually picture quantum states. It didn't fit the metaphors he was after, so he went back to something more familiar: a step sequencer where each track line is a single shot of the circuit.

Under the hood, Qiskit builds the circuits and each run, on IonQ or the local simulator, produces probability distributions or entangled measurement outcomes that map onto musical parameters: pitch selection, rhythm, velocity, timbre. The circuits are fully parameterized, so you can modify them without a full recompile and explore how each change reshapes the sound.

Each line is one shot of the circuit. It's that randomness and change between shots that creates the beat.

On the audio side, Tone.js handles sample-accurate scheduling, synthesis, and effects, all fed by the quantum-generated modulations. The app is fully serverless: a SvelteKit front end (with Threlte and Three.js driving the live Bloch spheres) talks to a stateless FastAPI service running Qiskit, which builds the circuit, extracts each qubit's Bloch vector layer by layer, and samples outcomes from the full statevector. Qiskit Aer and IonQ sit behind the same API.

To keep it responsive, frequently-used patterns are precomputed and cached while rare or highly-parameterized circuits trigger fresh hardware runs, balancing hardware cost against live interactivity.

The same circuit renders to music outside the browser, too. This is the gist of the script you can copy onto Qollab's Playground to turn a circuit into a MIDI file: each qubit is a track, each shot is a beat, and a separate track writes how entangled each pair of qubits is as a MIDI control signal.

# 'backend' is pre-created as a global on Qollab
from qiskit import QuantumCircuit
from qiskit.providers.jobstatus import JobStatus
import time, random

NUM_QUBITS = 4
BPM = 104
SHOTS = 104  # 104 shots ≈ one minute at 104 BPM

# qubit index → instrument (each qubit is a track)
SOUNDS = {0: "clap", 1: "clap", 2: "bell", 3: "tom"}

# Build the circuit. Each layer (column of gates) is a beat.
circuit = QuantumCircuit(NUM_QUBITS, NUM_QUBITS)
circuit.h(0)?Superposition. About a 50% chance this track fires on any given beat.circuit.h(2)
circuit.ry(0.976411, 3)?A rotation tunes how often this track hits: the "how often" knob.circuit.cx(0, 1)?Entanglement. Tracks 0 and 1 fire together, though each one alone still looks like a coin flip.circuit.measure(range(NUM_QUBITS), range(NUM_QUBITS))

def main(shots=SHOTS):
    job = backend.run(circuit, shots=shots)?Runs on a trapped-ion IonQ machine through Qollab. backend is provided for you.    while job.status() is not JobStatus.DONE:
        time.sleep(10)
    counts = job.get_counts()

    # Each shot is one beat. Rebuild an ordered shot list from the counts,
    # then shuffle so identical outcomes aren't clumped at the start.
    shots = []
    for bits, c in counts.items():
        shots.extend([bits.replace(" ", "")] * c)
    random.shuffle(shots)
    write_midi(shots)?Writes one MIDI track per qubit, plus an entanglement track where each pair's mutual information becomes a MIDI control signal.

Learning by ear

Beyond making music, the project is a way into quantum thinking. Concepts like superposition, measurement, and entanglement become tangible when they are mapped to something you can hear: experiment with a circuit, watch the probability distribution shift, and listen to the pattern change with it.

Francisco's hope is specific. Just as synthesizers once pulled artists into electronics and then software in search of new sounds, building real intuition along the way, he wants this to do the same for quantum.

Even if you don't understand a thing about quantum, you get a good sense of what a circuit does to the outputs, hopefully in a less intimidating way, so you feel comfortable diving into the rabbit hole.

The whole thing is open source, including the circuits, the front-end code, example projects, and documentation. Developers can extend it into new domains, artists can remix it, and educators can adapt it for workshops, lowering the barrier to quantum while showing a genuinely new way to interact with it.

Where it's headed

Francisco has a long list of where this goes: richer preset circuits built with quantum researchers, richer compositions and sound design with musicians, and a physical version you could play like a real instrument, something he is already eyeing for festivals. On the software side, he wants external signal inputs, a plugin for music software, and quantum-generated scales, chords, and instruments.

The nearest piece is the sound design itself, entanglement especially.

When I have entanglement it's not doing anything yet, and I want to play with that, how to mix the two sounds so they represent that connection. It'll be more of an ambient sound that shifts as you get closer to the state.

Underneath the feature list is the conviction that keeps pulling him back to quantum in the first place.

Now more than ever, people are tuned to how technologies can influence our lives quicker than we're ready for. Becoming familiar with them is an important tool in adapting.

Make it yours

If you want to hear what a quantum circuit sounds like, this is a good place to start. Superposition Sequencer is open for forking on both Qollab and GitHub, and there is a live demo you can play with right now.