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arXiv:2102.13113 · Optics Letters

Gigahertz-bandwidth optical memory in Pr 3+ :Y 2 SiO 5

M. Nicolle, Jonas N. Becker, Christian Weinzetl, Ian A. Walmsley, Patrick M. Ledingham

Published Apr 14, 2021• 12 citations
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Abstract

We experimentally study a broadband implementation of the atomic frequency comb (AFC) rephasing protocol with a cryogenically cooled P r 3 + : Y 2 S i O 5 crystal. To allow for storage of broadband pulses, we explore a novel, to the best of our knowledge, regime where the input photonic bandwidth closely matches the inhomogeneous broadening of the material ( ∼ 5 G H z ) , thereby significantly exceeding the hyperfine ground and excited state splitting ( ∼ 10 M H z ) . Through an investigation of different AFC preparation parameters, we measure a maximum efficiency of 10% after a rephasing time of 12.5 ns. With a suboptimal AFC, we witness up to 12 rephased temporal modes.

DOI
10.1364/ol.423642

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We experimentally study a broadband implementation of the atomic frequency comb (AFC) rephasing protocol with a cryogenically cooled P r 3 + : Y 2 S i O 5 crystal. To allow for storage of broadband pulses, we explore a novel, to the best of our knowledge, regime where the input photonic bandwidth closely matches the inhomogeneous broadening of the material ( ∼ 5 G H z ) , thereby significantly exceeding the hyperfine ground and excited state splitting ( ∼ 10 M H z ) . Through an investigation of different AFC preparation parameters, we measure a maximum efficiency of 10% after a rephasing time of 12.5 ns. With a suboptimal AFC, we witness up to 12 rephased temporal modes.
We demonstrate coherent storage and retrieval of pulsed light using the atomic frequency comb protocol in a room temperature alkali vapor. We utilize velocity-selective optical pumping to prepare multiple velocity classes in the F = 4 hyperfine ground state of cesium. The frequency spacing of the classes is chosen to coincide with the F ′ = 4 − F ′ = 5 hyperfine splitting of the 6 2 P 3 / 2 excited state, resulting in a broadband periodic absorbing structure consisting of two usually Doppler-broadened optical transitions. Weak coherent states of duration 2 n s are mapped into this atomic frequency comb with pre-programmed recall times of 8 n s and 12 n s , with multi-temporal mode storage and recall demonstrated. Utilizing two transitions in the comb leads to an additional interference effect upon rephasing that enhances the recall efficiency.
We present a light-storage experiment in a praseodymium-doped crystal where the light is mapped onto an inhomogeneously broadened optical transition shaped into an atomic frequency comb. After absorption of the light, the optical excitation is converted into a spin-wave excitation by a control pulse. A second control pulse reads the memory (on-demand) by reconverting the spin-wave excitation to an optical one, where the comb structure causes a photon-echo-type rephasing of the dipole moments and directional retrieval of the light. This combination of photon-echo and spin-wave storage allows us to store submicrosecond (450 ns) pulses for up to 20 mus. The scheme has a high potential for storing multiple temporal modes in the single-photon regime, which is an important resource for future long-distance quantum communication based on quantum repeaters.
Abstract In this work we present an implementation of cavity-assisted atomic frequency comb (AFC) memory protocol in an isotopically pure 143 Nd 3+ :YLiF 4 crystal. We use a tunable confocal Fabry–Perot cavity that is placed inside the cryostat. For a 1 mm thick sample with optical depth of 0.2 we obtain total storage efficiency of 3%, which is a 15-fold enhancement compared to the no cavity case. The memory bandwidth is limited by the inhomogeneous broadening of the optical transition and allows us to store short 30 ns pulses.
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We describe a quantum memory spectral preparation strategy that optimizes memory efficiency and bandwidth in materials such as 167 Er 3+ :Y 2 SiO 5 in a high-field regime, where the hyperfine structure is resolved.We demonstrate the method in 167 Er 3+ :Y 2 SiO 5 by preparing spectrally isolated 18-dB-absorbing features on a <1 dB background.Using these features we create an atomic frequency comb and show a quantum storage of 200-ns pulses with 22% efficiency, limited by the background absorption which arises from laser instability.We describe the experimental improvements needed to reach the material limits: O(1)-s spin-state storage, O(100) MHz bandwidth, and >90% efficiency.
An efficient multimode quantum memory is a crucial resource for long-distance quantum communication based on quantum repeaters. We propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb (AFC). The spectral width of the AFC allows efficient storage of multiple temporal modes without the need to increase the absorption depth of the storage material, in contrast to previously known quantum memories. Efficient readout is possible thanks to rephasing of the atomic dipoles due to the AFC structure. Long-time storage and on-demand readout is achieved by use of spin states in a lambda-type configuration. We show that an AFC quantum memory realized in solids doped with rare-earth-metal ions could store hundreds of modes or more with close to unit efficiency, for material parameters achievable today.