Optical quantum memory describes the process of on-demand storage and retrieval of single photon-level quantum states, and is a critical enabling technology for many quantum applications. Memory bandwidth plays an important role in these applications, as it determines the pulse durations compatible with the memory and places an upper bound on the clock rate and processing speed of a quantum device. Here we present experimental results of an atomic barium quantum memory that enables storage and retrieval of ultra-broadband
(>800GHz) signal photons with high storage efficiency [95.6(3)%] and low noise [3.8(6)
×10−5noise photons]. Experimental Results.- The quantum memory operation is based on the ground
(6s2 1S0), excited
(6s6p 1P1), and metastable
(6s5d 1D2)orbital states of atomic barium in a
Λ-type configuration. The barium vapor is created in an 800–900 °C barium heat pipe oven with 0–1000 torr tunable argon buffer gas pressure. The ground-excited transition at 553.5 nm features large and tunable homogeneous collisional broadening due to the argon buffer gas and a peak optical depth of
d=50. The memory operates in the so-called absorb-then-transfer (ATT) regime, in which the signal field is linearly absorbed along the ground-excited transition, whose collisionally broadened lineshape enables efficient absorption of ultra-broadband photons; the resulting atomic polarization is transferred into a so-called spin wave by application of a strong
[O(10 uJ),100 fs]control pulse along the excited-metastable transition at 1500 nm. The storage state has a 0(0.1) second coherence lifetime in the bare atom [1], but this is reduced to the
O(ns)level due to motional dephasing [0.49(1) ns measured memory lifetime]. The memory experiment is repeated at a repetition rate of 1 kHz. The total end-to-end efficiency of the memory at 900°C is 31(1)%, which is limited by available control field power.
Tomorrow's quantum Internet will be powered by light and will work over today's telecommunication infrastructure, so we need low-noise, high-bandwidth, telecom-band quantum optical memory to enable scaling in the presence of loss and quantum operations. The authors have built such a device, using coherent two-photon absorption in warm rubidium vapor. This quantum memory stores gigahertz-bandwidth telecom-band light pulses with mean photon number less than one, and retrieves them with a signal-to-noise ratio exceeding 10
4. This makes possible ultrahigh-fidelity storage of single-photon qubits and is compatible with quantum-dot light sources, for hybridized quantum photonic networking.
The efficient storage and on-demand retrieval of quantum optical states that are compatible with the telecommunications C-band is a requirement for future terrestrial-based quantum optical networking. Spectrum in the C-band minimises optical fiber-propagation losses, and broad optical bandwidth facilitates high-speed networking protocols. Here we report on a telecommunication wavelength and bandwidth compatible quantum memory. Using the Off-Resonant Cascaded Absorption protocol in hot
87Rb vapour, we demonstrate a total memory efficiency of
20.90(1)% with a Doppler-limited storage time of
1.10(2)ns. We characterise the memory performance with weak coherent states, demonstrating signal-to-noise ratios greater than unity for mean photon number inputs above
4.5(6)×10−6 per pulse.