The creation of a scalable quantum-enabled machine, e.g. a quantum computer or a quantum communication system, requires the development of many components, such as sources, memories, processing elements, measurement devices and a network able to inter-connect the different resources \cite{Shapiro_2002, Kimble_2008}. Optical connections are indeed good candidates for the transmission of quantum information, in the form of flying qubits, as single photons or other nonclassical states, that can travel undisturbed over long distances. The major obstacle to such scheme is that often different elements work at different energies, and it may be difficult to link together at a fixed optical frequency.
Frequency translation \cite{Kumar_1990} provides a mean to shift and in general modify the carrier frequency of an optical quantum state while preserving the other quantum features (such as coherence \cite{Tanzilli_2005} and entanglement \cite{Ramelow_2012}), thus linking the different resources, e.g. IR flying qubits with efficient silicon detectors \cite{Albota_2004, Langrock_2005,Vandevender_2004,Ates_2012}. More recently, frequency translation has emerged as a mean to directly manipulate the optical waveform in the full temporal and spectral space: using concepts borrowed from parametric time-lens, both temporal compression \cite{Agha_2013} and magnification \cite{Lavoie_2013} of quantum states can be implemented. In addition, using time-dependent conversion, it is possible to select and convert different temporal modes, realizing an optical pulse gate \cite{Reddy_2014,christensen_temporal_2015} that encode and decode high-dimensional qubits. While sum- and difference-generation in \(\chi^{(2)}\) has been the base for many demonstrations, thanks to the high nonlinearity and ease of setup, optical frequency translation as been seen in other systems, including cross-phase modulation \cite{Bradford_2012, Matsuda_2014}, opto-mechanical hybrid systems \cite{Hill_2012, Preble_2012}, electro-optical modulation \cite{M_rolla_1999}, Alkali-vapor cells \cite{Donvalkar_2014}, microwave superconductor resonators \cite{Zakka_Bajjani_2011}, Diamond based atomic memories \cite{Fisher_2016}. Among parametric \(\chi^{(3)}\) processes, Bragg Scattering is known to frequency translate quantum states without the addition of parametric noise \cite{McKinstrie_2005}. Follow up realizations include photonic crystal fiber \cite{McKinstrie_2005, McGuinness_2010, Mejling_2012}, highly nonlinear fiber \cite{Gnauck_2006,Clark_2013,Krupa_2012} and SiN and S waveguides and resonators \cite{Agha_2013, Li_2016,Bell_2016}. This implementation supports translation across any span of energy, enabling conversion between frequencies in the same communication band and small tuning. In addition, \(\chi^{(3)}\) implementations are compatible with integrated photonics.
Both \(\chi^{(2)}\) and \(\chi^{(3)}\) implementations have to grapple with technical noise, usually generated by the strong pump driving the nonlinear process. In the case of the other implementations conversion efficiency close to 100% with limited residual noise has been obtained, for Bragg-Scattering, conversion at unitary efficiency was only obtained at the expenses of a signal polluted by large Raman noise \cite{Clark_2013}. In this work, thanks to an optimal choice of medium and operating wavelength, we show Four Wave Mixing Bragg Scattering (FWM-BS) setup that performs frequency translation at very low noise regime, with almost unity efficiency on weak coherent states and single photons alike.