  We propose a quantum repeater architecture that can operate without
cryogenics. Each node in our architecture builds on a cell of hot alkali atoms
and noble-gas spins which offer a storage time as long as a few hours. Such a
cell of hybrid gases is placed in a ring cavity, which allows us to suppress
the detrimental four-wave mixing (FWM) noise in the system. We investigate the
protocol based on a single-photon source made of an ensemble of the same hot
alkali atoms. A single photon emitted from the source is either stored in the
memory or transmitted to the central station to be detected. We quantify the
fidelity and success probability of generating entanglement between two remote
ensembles of noble-gas spins by taking into account finite memory efficiency,
channel loss, and dark counts in detectors. We describe how the entanglement
can be extended to long distances via entanglement swapping operations by
retrieving the stored signal. Moreover, we quantify the performance of this
proposed repeater architecture in terms of repeater rates and overall
entanglement fidelities and compare it to another recently proposed
non-cryogenic quantum repeater architecture based on nitrogen-vacancy (NV)
centers and optomechanical spin-photon interfaces. As the system requires a
relatively simple setup, it is much easier to perform multiplexing, which
enables achieving rates comparable to the rates of repeaters with NV centers
and optomechanics, while the overall entanglement fidelities of the present
scheme are higher than the fidelities of the previous scheme. Our work shows
that a scalable long-distance quantum network made of hot hybrid atomic gases
is within reach of current technological capabilities.
