Photonic two-qubit parity gate with tiny cross-Kerr nonlinearity

TL;DR

This paper proposes a highly resource-efficient two-qubit parity gate using tiny cross-Kerr nonlinearities, enabling practical photonic quantum computing with weak nonlinear effects.

Contribution

It introduces a novel scheme for a two-photon polarization-parity gate that operates effectively with significantly weaker nonlinearity than previous methods.

Findings

The scheme can function with nonlinearity strengths orders of magnitude weaker.

It uses a ring cavity and photon-number resolving detectors for effective measurement.

The approach enables practical implementation of two-qubit gates in photonic systems.

Abstract

The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years, much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in the experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits.