Asynchronous Telegate and Teledata Protocols for Distributed Quantum Computing

TL;DR

Distributed quantum operations such as telegate and teledata incur high latency from entangled-photon and classical information distribution. The authors propose asynchronous variants that allow local operations to proceed while the remote operation finishes, by introducing nonunitary operators $F$ and $G$ and a pre-measurement block; a potential hardware interface is illustrated with a Quantum Network Card (QNC). The paper discusses the benefits and limitations of asynchronous protocols, including conditions under which latency hiding is effective and the need for $U^{-1} Z U$ sequences when a conditional $Z$ is required. A concrete system-level example (QNC) shows how entanglement routing, storage qubits, and local computation can be organized to support asynchronous distributed quantum operations. Overall, the work outlines a path toward reducing classical-communication bottlenecks in distributed quantum computing and highlights engineering challenges for realizing asynchronous protocols.

Abstract

The cost of distributed quantum operations such as the telegate and teledata protocols is high due to latencies from distributing entangled photons and classical information. This paper proposes an extension to the telegate and teledata protocols to allow for asynchronous classical communication which hides the cost of distributed quantum operations. We then discuss the benefits and limitations of these asynchronous protocols and propose a potential way to improve these asynchronous protocols using nonunitary operators. Finally, a quantum network card is described as an example of how asynchronous quantum operations might be used.

Figures (3)

• Figure 1: These are quantum circuits made with Qiskit showing teledata (top) and telegate (bottom) operations. The qubits Entangled represent an entangled state that is transmitted to two different quantum computers, with $Entangled_0$ going to computer A and $Entangled_1$ going to computer B. The classical bits cA start at computer A and classical bits cB start at computer B. After measurement, cA is transmitted to computer B, and cB is transmitted to computer A. Each circuit is divided into sections which are marked by the vertical lines.
• Figure 2: These are quantum circuits made with Qiskit showing async-teledata (top) and async-telegate (bottom) operations. The gates labelled "U" represent arbitrary unitary operations applied to the corresponding qubit.
• Figure 3: This is a diagram of a quantum network card. The circles represent qubits, and the lines are connection between them.