Quantum chaos border for quantum computing

We study a generic model of quantum computer, composed of many qubits coupl ed by short-range inter action. Above a critical interqubit coupling streng th, quantum chaos sets in, leading to quantum ergodicity of the computer ei genstates. In this regime the noninteracting qubit structure disappears, th e eigenstates become complex, and the operability of the computer is destro yed. Despite the fact that the spacing between multiqubit states drops expo nentially with the number of qubits n, we show that the quantum chaos borde r decreases only linearly with n. This opens a broad parameter region where the efficient operation of a quantum computer remains possible.