Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity

TL;DR

This paper reports the experimental characterization of an optically controlled Kerr non-linearity system capable of inducing deterministic phase shifts on single-photon level quantum states, crucial for quantum information processing.

Contribution

The authors demonstrate a complete experimental quantum process tomography of a system utilizing electromagnetically induced transparency and Kerr non-linearity for controlled phase shifts.

Findings

Achieved precise quantum process characterization of the phase shift device.

Demonstrated the ability to modify arbitrary quantum states with the system.

Validated the use of coherent state quantum process tomography for device assessment.

Abstract

Any optical quantum information processing machine would be comprised of fully-characterized constituent devices for both single state manipulations and tasks involving the interaction between multiple quantum optical states. Ideally for the latter, would be an apparatus capable of deterministic optical phase shifts that operate on input quantum states with the action mediated solely by auxiliary signal fields. Here we present the complete experimental characterization of a system designed for optically controlled phase shifts acting on single-photon level probe coherent states. Our setup is based on a warm vapor of rubidium atoms under the conditions of electromagnetically induced transparency with its dispersion properties modified through the use of an optically triggered N-type Kerr non-linearity. We fully characterize the performance of our device by sending in a set of input probe states and measuring the corresponding output via balanced homodyne tomography and subsequently performing the technique of coherent state quantum process tomography. This method provides us with the precise knowledge of how our optical phase shift will modify any arbitrary input quantum state engineered in the mode of the reconstruction.