Ultra-broadband photon storage in hot atomic barium vapor

Quantum memories are critical in quantum computing and quantum communication, where they enable synchronization and deterministic photon output. Here we experimentally demonstrate storage of THz-bandwidth optical pulses in a hot atomic barium vapor using the off-resonance Raman protocol, indicating its potential for an ultra-broadband quantum memory. The large energy splitting in barium between the ground and storage states of $\sim 340$ THz enables storage of $< 100$ fs photons, leading to a time-bandwidth product $> 1000$ and minimal thermal population in the storage state, resulting in low noise in single-photon operation. Our preliminary results show storage of $500$ fs photons with an efficiency of $0.4\%$ at barium densities of $5.1\times10^{19}\,\mathrm{m}^{-3}$ . As a next step we are amplifying the control field and anticipate substantial improvement in efficiency. To date, researchers have shown storage of GHz-bandwidth photons in atomic systems and THz-bandwidth photons in molecular and solid state systems, but not broadband storage in the telecom range. Barium has a transition between state $6s6p\,\,^1P_1$ and $6s5d\,\,^1D_2$ at telecom wavelengths, making it feasible for telecom photon storage if one prepares the ground state $6s^2\,\,^1S_0$ as the storage state.