We experimentally observe four-photon state generation through four-wave
mixing in Rb vapor, providing narrowband photons near an atomic resonance.
This transfers an idea from parametric down conversion from a pulsed pumped
chi-2 medium to generate (wideband) multi-photon states into a regime
providing photons compatible with atomic transition bandwidths. This could be
an extremely useful resource for distributed quantum computing with atoms as
stationary qubits, possibly allowing entangled multi-photon states like graph
states compatible with stationary qubits. The relatively long coherence time
of the photons invites also exploration of states that can be experimentally
resolved.

Dear Editor,

our manuscript presents the experimental success of transferring the idea of
multi-photon generation from parametric conversion in a pulsed pumping regime
that lead to a huge number of works with multiphoton states in a range where
the photons are so narrow-band that they can effectively interact with atomic
systems.

We believe this could be an extremely useful resource for quantum networks
with atoms as stationary nodes, as it seems conceivable that the
time-correlated photon quadruple we observe with a reasonable rates can be
engineered in complex multi-photon states like cluster states.

Our observation should also invite theoretical physicists to closer
investigate the exact state, as the coherence time is orders of magnitude
larger than what has been observed with pulse-pumped SPDC in the past.

Therefore we feel PRL is a platform that could be of wider interest in the
physics community, especially for providing a new pathway for the large
resonance multi-photon experiments demonstrated so far found.

Looking forward for your reply!

With Best Regards on behalf of all authors,

Christian Kurtsiefer