A*STAR Put an 18-Variable Drug-Docking Problem on Six Qubits of IBM's ibm_kingston

Six qubits for an eighteen-variable docking problem

On August 20, 2026 six researchers at institutes of Singapore's Agency for Science, Technology and Research, the National University of Singapore and Nanyang Technological University posted a preprint describing a hybrid quantum-classical method for molecular docking, and executed its circuits on IBM's ibm_kingston processor. Molecular docking is the everyday question of early drug research: given a candidate molecule and a target protein, how does the molecule seat itself in the pocket, and how well. The team recast that question as a graph problem, where each plausible contact between ligand and protein is a weighted vertex and the winning binding pose is the heaviest set of contacts that can all coexist.

An encoding that carries three variables on one qubit

The contribution is an encoding the authors call full-basis encoding, which uses all three orthogonal directions of a qubit's Bloch sphere to carry information instead of one. That put an 18-variable problem on six qubits for the streptavidin-biotin complex 1STP, and a 14-variable problem on five qubits for trypsin with benzamidine, entry 9AW2. The paper also proves that a global minimizer of its objective can always be chosen to be a pure product state, so the optimum requires no entanglement between qubits and the circuits can stay shallow enough for current hardware. What changed for a reader tracking this field is the qubit cost of a docking problem, since the number of good qubits a problem consumes is the binding constraint on machines available today.

What the hardware runs did and did not settle

On both instances the runs on ibm_kingston recovered the same vertex selections as the classical simulation and matched the known clique structure under realistic gate noise and readout error. The authors state plainly that this is evidence of feasibility and that quantum advantage is not demonstrated, since both test problems were deliberately kept small enough for classical verification. Streptavidin with biotin and benzamidine in the trypsin pocket are textbook complexes, though their records differ in age: entry 1STP has been public since 1992, while entry 9AW2 is a 2025 redetermination of a complex first characterized in the mid-1970s. Either way the correct answer was known before the circuits ran, which is what made the check against ground truth possible and also what limits the claim. The open question the authors name themselves is whether the compression ratio survives realistic docking graphs with hundreds of vertices, alongside better ansatz design and hardware-aware circuit compilation.