# Nonreciprocal Signal Routing in an Active Quantum Network

## TL;DR

This paper introduces a method for nonreciprocal quantum signal routing in superconducting circuits using active, driven lattice networks, enabling efficient and noise-optimized photon transfer between nodes.

## Contribution

It presents a general, implementable strategy for nonreciprocal photon routing in quantum networks using existing superconducting circuit components and dual oscillator lattices.

## Key findings

- Optimal routing solutions are found at the exceptional point of the network's dynamical matrix.
- Signal and noise transmission can be independently optimized.
- The approach is applicable to large-scale superconducting quantum circuits.

## Abstract

As superconductor quantum technologies are moving towards large-scale integrated circuits, a robust and flexible approach to routing photons at the quantum level becomes a critical problem. Active circuits, which contain parametrically driven elements selectively embedded in the circuit offer a viable solution. Here, we present a general strategy for routing nonreciprocally quantum signals between two sites of a given lattice of oscillators, implementable with existing superconducting circuit components. Our approach makes use of a dual lattice of overdamped oscillators linking the nodes of the main lattice. Solutions for spatially selective driving of the lattice elements can be found, which optimally balance coherent and dissipative hopping of microwave photons to nonreciprocally route signals between two given nodes. In certain lattices these optimal solutions are obtained at the exceptional point of the dynamical matrix of the network. We also demonstrate that signal and noise transmission characteristics can be separately optimized.