A prototype of quantum von Neumann architecture

Abstract

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. 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.

Quantum circuit simulation of superchannels

“…This feature actually has already been employed, even before the emergence of superchannels, for quantum teleportation and entanglement-assisted quantum communication [60]. Recently, we also pointed out the potential of using superchannels to design quantum superalgorithms and applications in quantum von Neumann architecture [30,51]. Given the growing importance of superchannels for quantum information science, it is therefore crucial to develop closer physical and algorithmic study of them.…”

“…The circuit form in figure 1 takes the channels as input directly, plugged in the circuit 'board' [23] at suitable locations instead of starting from the initial time. This can also be equivalently realized by a circuit acting on their Choi states as input at the initial time [51], based on the channel-state duality, in particular, the map between the identity operator and the ebit state. It is apparent that superchannels are special channels, so they can be simulated by circuits for channels.…”

Universal resources for quantum computing

“…Besides, we leave the study of the evolution family to the future, which is relatively less well studied. It may relate to superchannels [63], dynamical resource theory [29], and quantum von Neumann architecture [64]. Also we believe there should be at least one codingbased family, which contains models based on errorcorrection codes [37].…”

“…Given the ebits |ω ⊗n AB as the initial state, a CZ e gate is applied between the nearest neighbor of party A for each edge e of the square lattice. Such a circuit is an example of tailed quantum circuits [64].…”

On quantum channel capacities: an additive refinement

“…for ρ t as the transpose of a state ρ ∈ D(X ). As has been shown [18,19], this is sufficient to simulate the channel Φ. With a binary positive operator-valued measure (POVM) { ρ t , 1 − ρ t } acting on A, any observation O on Φ(ρ) can be measured on site B.…”