%!TEX root = qlight-poster2017.tex
\begin{center}
  \begin{center} {\bf \Large \textsf {Bell tests \& Randomness generation without detection loophole}}\\[.2cm]
collaborators:~Thomas Gerrits$^2$, Adriana~E.~Lita$^2$, Sae~Woo~Nam$^2$,
Thinh~Le~Phuc, Jean-Daniel~Bancal$^1$, Valerio~Scarani.
\end{center}
\end{center}

Quantum physics can provide sources of randomness
that can be certified as being uncorrelated to any outside process or
variable, i.e. sources of private randomness, based on a violation of a Bell
inequality [3].
With advancements in high efficiency infrared photon detectors [4] in combination with a high efficiency pair source,
a loophole free experimental violation of the Bell inequality becomes feasible, allowing for the realization of
a source of certified randomness.
%
% This violation can also be observed as long as the overall efficiency is
% larger than 2/3 and the state and measurement basis are chosen
% appropriately~[7].

\begin{figurehere}
\begin{minipage}{0.45\linewidth}
    \centering
    \includegraphics[width=\columnwidth]{bell_violation/Sagnac2017.pdf}
\end{minipage}
\begin{minipage}{0.55\linewidth}
    \centering
    \includegraphics[width=1\columnwidth]{bell_violation/vio_exp.pdf}
\end{minipage}\\[.5cm]
\figcaption{Left: Efficient polarization-entangled pair source and detection
  scheme  involving superconducting transition edge sensors (TES).
  Top right:
  Violation of CHSH inequality observed as a function of the time bin width.
  Bottom right:
  Rate of random bits that can be extracted as a function of the time bin width.
  }
\end{figurehere}

Our pair source can be stably locked to the non-maximally entangled states with
a high fidelity,
and,
in combination with TES detectors, we measured detection efficiencies reliably above 80\%.
This allowed us to test a version of CHSH inequality using a CW source of photon pairs and with events defined by dividing the measurement time in discrete time bins of fixed length. Numerical simulation and initial experimental results support the intuition that this approach can generate randomness with efficiency equal or larger than system based on pulsed sources.
