Nonreciprocity realized with quantum nonlinearity

TL;DR

This paper demonstrates a passive quantum nonreciprocal device using superconducting artificial atoms in a waveguide, exploiting quantum nonlinearities and correlations to achieve direction-dependent transmission without magnetic fields.

Contribution

It introduces a minimal passive nonreciprocal device based on quantum nonlinear behavior of artificial atoms, advancing quantum signal routing technology.

Findings

Achieved nonreciprocal transmission over a wide power range.

Nonreciprocity linked to population of entangled quasi-dark states.

Device operates without magnetic fields, enabling integration into quantum circuits.

Abstract

Nonreciprocal devices are a key element for signal routing and noise isolation. Rapid development of quantum technologies has boosted the demand for a new generation of miniaturized and low-loss nonreciprocal components. Here we use a pair of tunable superconducting artificial atoms in a 1D waveguide to experimentally realize a minimal passive nonreciprocal device. Taking advantage of the quantum nonlinear behavior of artificial atoms, we achieve nonreciprocal transmission through the waveguide in a wide range of powers. Our results are consistent with theoretical modeling showing that nonreciprocity is associated with the population of the two-qubit nonlocal entangled quasi-dark state, which responds asymmetrically to incident fields from opposing directions. Our experiment highlights the role of quantum correlations in enabling nonreciprocal behavior and opens a path to building passive quantum nonreciprocal devices without magnetic fields.