I built Quantum4J because I couldn’t find a clean, dependency-free way to experiment with multi-qubit unitaries from Java. Most QC libraries target Python, so this is meant to bring quantum circuit construction and state-vector simulation to the JVM.

It includes: - state-vector simulator (~25 qubits) - standard gates (X, Y, Z, H, S, T, RX/RY/RZ, CX, CZ, SWAP, ISWAP, CCX) - measurement + classical registers - OpenQASM 2.0 exporter

Example: QuantumCircuit.create(2).h(0).cx(0,1).measureAll();

Would love feedback on the architecture, gate engine, or ideas for what to add next. Iam considering expanding Quantum4J into a more complete JVM quantum tooling ecosystem. Interested in feedback from practitioners or researchers using Java in QC or simulation.