Wavelength-Multiplexed Quantum Networks with Ultrafast Frequency Combs

TL;DR

This paper demonstrates a scalable, single-step method to create a multimode quantum network using ultrafast frequency combs, leveraging wavelength-division multiplexing to enhance quantum channel capacity.

Contribution

It introduces a novel approach for fabricating large-scale quantum networks via parametric downconversion of femtosecond frequency combs, enabling multiple entangled channels simultaneously.

Findings

Entangled spectral regions in the comb confirmed for all bipartitions.

Identified eight independent quantum channels within the comb.

The quantum frequency comb is robust, addressable, and scalable.

Abstract

Highly entangled quantum networks cluster states lie at the heart of recent approaches to quantum computing \cite{Nielsen2006,Lloyd2012}. Yet, the current approach for constructing optical quantum networks does so one node at a time \cite{Furusawa2008,Furusawa2009,Peng2012}, which lacks scalability. Here we demonstrate the \emph{single-step} fabrication of a multimode quantum network from the parametric downconversion of femtosecond frequency combs. Ultrafast pulse shaping \cite{weiner2000} is employed to characterize the comb's spectral entanglement \cite{vanLoock2003}. Each of the 511 possible bipartitions among ten spectral regions is shown to be entangled; furthermore, an eigenmode decomposition reveals that eight independent quantum channels \cite{Braunstein2005} (qumodes) are subsumed within the comb. This multicolor entanglement imports the classical concept of wavelength-division multiplexing (WDM) to the quantum domain by playing upon frequency entanglement as a means to elevate quantum channel capacity. The quantum frequency comb is easily addressable, robust with respect to decoherence, and scalable, which renders it a unique tool for quantum information.