Universal quantum computation using atoms in cross-cavity systems

TL;DR

This paper proposes a theoretical method for implementing universal quantum gates, including CNOT and Fredkin gates, in a cross-cavity system with a three-level atom, enabling efficient quantum computation with high success probability.

Contribution

It introduces a single-step implementation of universal quantum gates in a cross-cavity setup, avoiding complex gate chaining and utilizing high-cooperativity regimes for effective quantum control.

Findings

High success probability of gate implementation with current parameters

Effective manipulation of light states via atom in the system

Feasibility in both weak- and strong-coupling regimes

Abstract

Quantum gates are the building blocks of quantum circuits, which in turn are the cornerstones of quantum information processing. In this work, we theoretically investigate a single-step implementation of both a universal two- (CNOT) and three-qubit (quantum Fredkin) gates in a cross-cavity setup coupled to a $\Lambda$-type three-level atom. Within a high-cooperativity regime, the system exhibits an atomic-state-dependent $\pi$-phase gate involving the two-mode single-photon bright and dark states of the input light pulses. This allows for the controlled manipulation of light states by the atom and vice versa. Our results indicate these quantum gates can be implemented with high probability of success using the state-of-the-art parameters, either for the weak- or strong-coupling regime, where the quantum interference is due to an electromagnetically-induced-transparency-like phenomenon and the Autler-Townes splitting, respectively. This work not only paves the way for implementing quantum gates in a single step using simple resources, thus avoiding the need to chain basic gates together in a circuit, but it also endorses the potential of cross-cavity systems for realizing universal quantum computation.