2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/88810We consider quantum computing in the k-qubit model where the starting state of a quantum computer consists of k qubits in a pure state and n-k qubits in a maximally mixed state. We ask the following question: is there a general method for simulating an arbitrary m-qubit pure state quantum computation by a quantum computation in the k-qubit model? We show that, under certain constraints, this is impossible, unless m=O(k+ log n).8 pages, 3 figures, to appear in proceedings of STOC'00Quantum Physicstext