  A modern computer system, based on the von Neumann architecture, is a
complicated system with several interactive modular parts. Quantum computing,
as the most generic usage of quantum information, follows a hybrid architecture
so far, namely, quantum algorithms are stored and controlled classically, and
mainly the executions of them are quantum, leading to the so-called quantum
processing units. Such a quantum-classical hybrid is constrained by its
classical ingredients, and cannot reveal the computational power of a fully
quantum computer system as conceived from the beginning of the field. Recently,
the nature of quantum information has been further recognized, such as the
no-programming and no-control theorems, and the unifying understandings of
quantum algorithms and computing models. As a result, in this work we propose a
model of universal quantum computer system, the quantum version of the von
Neumann architecture. It uses ebits (i.e., Bell states) as elements of the
quantum memory unit, and qubits as elements of the quantum control unit and
processing unit. As a digital quantum system, its global configurations can be
viewed as tensor-network states. Its universality is proved by the capability
to execute quantum algorithms based on a program composition scheme via a
universal quantum gate teleportation. It is also protected by the uncertainty
principle, the fundamental law of quantum information, making it quantum-secure
distinct from the classical case. In particular, we introduce a few variants of
quantum circuits, including the tailed, nested, and topological ones, to
characterize the roles of quantum memory and control, which could also be of
independent interest in other contexts. In all, our primary study demonstrates
the manifold power of quantum information and paves the way for the creation of
quantum computer systems in the near future.
