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Nonreciprocity Realized with Quantum Nonlinearity

Due to their microscopic nature, quantum devices are extremely sensitive to interactions with their environment. This is a desirable property when it comes to designing very responsive sensors, but in the case of quantum processing, where noise has a detrimental effect on performance, one typically aims to isolate quantum systems from unwanted interactions with the environment.

A key element to control such interactions is to establish a one-directional channel for light, such that quantum information can flow out of the system while at the same time avoiding back action from the photonic environment. Devices that exhibit a preferential direction for the transmission of light are called nonreciprocal.

Nonreciprocal devices form part of the standard setup of many quantum computation platforms, however, current technologies are bulky and inherently lossy. Therefore, an active field of research devotes to the design of nonreciprocal devices on chip, minimizing losses and allowing for integration with quantum computing technologies.

Our experiment addresses these issues by exploiting a familiar physical phenomenon, super- and sub-radiance, in the simplest possible scenario needed to achieve nonreciprocity: two artificial atoms in a waveguide. Making use of quantum nonlinearities, we achieve nonreciprocal transmission through the device in a wide range of frequencies and powers.

While not yet competitive for practical applications, our results open a path for the realization of more efficient devices with multiple artificial atoms and demonstrate a novel mechanism to achieve nonreciprocity.

See more in our paper