{"ID":5937704,"CreatedAt":"2026-07-07T03:14:33.014478982Z","UpdatedAt":"2026-07-08T13:59:33.486573123Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2607.04320","arxiv_id":"2607.04320","title":"Fundamental limits on state preparation for an open qubit","abstract":"We analytically determine the ultimate limits of state preparation in two-level open quantum systems driven by coherent control. For a dissipative qubit governed by a GKSL master equation, we give an exact characterization of the reachable set in the Bloch ball. Dissipation excludes a region of states in the Bloch ball which cannot be approached even under arbitrarily strong coherent driving, and we prove that this region has a nontrivial geometry whose boundary is a surface of revolution around the $x$-axis which is analytic except for two conical singularities. We derive a closed-form control protocol for moving on this boundary, and construct an explicit protocol that steers the system arbitrarily close to any prescribed boundary state. These results provide a complete geometric constructive description of reachable qubit states in the standard dissipative environment, establishing fundamental bounds on controllability and state-preparation fidelity for open two-level quantum systems.","short_abstract":"We analytically determine the ultimate limits of state preparation in two-level open quantum systems driven by coherent control. For a dissipative qubit governed by a GKSL master equation, we give an exact characterization of the reachable set in the Bloch ball. Dissipation excludes a region of states in the Bloch ball...","url_abs":"https://arxiv.org/abs/2607.04320","url_pdf":"https://arxiv.org/pdf/2607.04320v1","authors":"[\"D. A. Abraamian\",\"L. V. Lokutsievskiy\",\"A. N. Pechen\"]","published":"2026-07-05T14:09:53Z","proceeding":"quant-ph","tasks":"[\"quant-ph\",\"math.OC\"]","methods":"[]","has_code":false}