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\section{Experimental Setup}  An optimal choice of nonlinear medium and operating regime enables BS frequency translation in the quantum regime. There are two major design decisions that affect the choice of medium. First, one must fulfill the phase matching phasematching  for a given set of pumps and signals. In fact, given the selectivity of the process, a very specific dispersion profile must be used for any given configuration. The second design decision is the balance between nonlinearity and dispersion properties: an optimal ratio between the amount of pump power required for full conversion and the acceptance bandwidth, as well as the minimum frequency separation $\Delta \omega$ for which cascaded BS becomes prominent. In order to maximize the former with respect to the latter, it is convenient to operate at large dispersion values . $|\beta^{(2)}(\omega_{1,2,s,i}|\simeq |\beta^{(3)}\Delta\Omega$.  As a reference, the demonstrations reported above showed translation over $\Delta \Omega > 10$ nm. As mentioned, one obstacle for most quantum implementation of BS is technical noise, in the form of spontaneous FWM spurious non-linear  and Raman noise processes  \cite{Lefrancois_2015}. Modulation instability (MI) (purple in figure \ref{fig:tech_noise}) is a competing FWM process, its gain profile given by $G_{MI} = 1 + (\gamma P / g_{MI})^2 \sinh^2(g_{MI} L)$ where $g_{MI} = \sqrt{(\gamma P)^2 - (k_{MI} + \gamma P)^2}$ and $\kappa_{MI} = \left[\beta(\omega_p + \delta\omega) + \beta(\omega_p - \delta\omega) - 2 \beta(\omega_p)\right]/2$ are respectively the MI wavevector and linear phasematching term for a frequency detuning $\delta \omega$ from the a strong pump set at $\omega_p$. Modulation instability affects BS in multiple ways, either by depleting the pump and generating spurious sidebands, or amplifying the vacuum fluctuations and generating pairs of energy correlated photons. It can be managed placing the pump on the normal dispersion, where parametric gain is forbidden and the bandwidth for pair generation is minimized, as well as detuning the signal far from the pump frequencies. Spontaneous and Stimulated Raman Scattering are processes that couple light with the thermal phonons bath  of the medium. Scattering strength depends on the density of occupied states as well as the Raman spectrum . $g_r(\delta\omega)$.  The probability of a spontaneous Stokes scattering (i.e. the photon losing energy) is given by $p_S = g(\delta\omega) g_r(\delta\omega)  \frac{1}{1-exp(-\delta\omega \hbar/ k_b T)}$ while for anti-Stokes it is $p_S = g(\delta\omega) g_r(\delta\omega)  \frac{exp(-\delta\omega \hbar/ k_b T)}{1-exp(-\delta\omega \hbar/ k_b T)}$ The spectrum depends on the material: amorphous materials have a broad spectrum (i.e. for glass it extends to about $40$ THz \cite{Stolen_1973}), while crystalline materials have strong, sharp features. Both processes become less probable for very large detuning, though the anti-Stoke probability depends exponentially on the temperature when $-\delta\omega \hbar \gg k_b T$ ($6$ THz for room temperature), so that cooling the fiber can further reduce the noise by several order of magnitude (red $300$ K and blue $90$ K on figure \ref{fig:tech_noise}) \cite{Li_2004, Takesue_2008}.   Thanks In both cases, noise is reduced the farther we place the signal from the pumps: because of  to the BS phasematching flexibility, there are no limitations on the amount of detuning $\Delta\Omega$ [Mechin2006a] \cite{M_chin_2006}  between pumps and signal, the only fundamental parameter being $\omega_{ZDW}$ (rather than $\beta^{(3)}$ ), easily tunable via dispersion engineering. We operate using a dispersion-shifted fiber (Vistacor, Corning): although the fiber is not optimized for nonlinear interactions ( $\gamma \simeq 3$ W/km), a sufficiently long spool makes up for the reduced nonlinear parameter. Measurement of the dispersion (shown in figure \ref{fig:dispersion}) measures , with $\lambda_{ZDW} = 1420 $ nm that corresponds to a $\omega_{ZDW} = 1330 $ THz, with the signal/idler and the pumps placed respectively in the O-Band (1260 nm - 1320 nm ) and the C-Band (1530 nm - 1565 nm) ΔΩ ~ 120 THz . This is an attractive configuration because it enables the large detuning needed for a low-noise operation, while still operating at wavelengths where off-the-shelf equipment is available. For $\delta\omega = 5 $ THz (~6.5 nm for pumps and ~4.3 nm for the signal/idler) the acceptance bandwidth is ( FWHM).