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arXiv:2103.04581 · Physical Review Research

Initialization protocol for efficient quantum memories using resolved hyperfine structure

James S. Stuart, Morgan P. Hedges, Rose L. Ahlefeldt, Matthew J. Sellars

Published Aug 27, 2021• 36 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physrevresearch.3.l032054

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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.
We created high-resolution atomic frequency combs (AFCs) and optimized the pulse sequence used in AFC memory to realize highly efficient AFC quantum memory using the 167 Er 3+ :Y 2 SiO 5 hyperfine level system. As a result, the formation and relaxation times of AFCs were revealed, and AFCs with a resolution of 800 kHz were created by using an appropriate pump light intensity. An efficiency of 0.16% with a memory time of 0.5 µs was achieved even under a zero magnetic field and a 10 ppm Er concentration sample. This result paves the way for realizing highly efficient communication-wavelength AFC quantum memory.
Abstract Optical quantum memories are essential components for realizing the full potential of quantum networks. Among these, rare-earth-doped crystal memories stand out due to their large multimode storage capabilities. To maximize the multimode capacity in the time domain, it is key to simultaneously achieve large memory bandwidth and long optical storage time. Here, we demonstrate an atomic frequency comb optical memory in 171 Yb 3+ :Y 2 SiO 5 , with a memory bandwidth of 250 MHz and a storage time of up to 125 µ s. The efficiency reaches 20% at short storage times, and 5% at 125 µ s. These results were enabled by an optimized optical pumping scheme, guided by numerical modelling. Our approach is specifically designed for future spin-wave storage experiments, with the theoretical bandwidth limit set at 288 MHz by the hyperfine structure of 171 Yb 3+ :Y 2 SiO 5 . Additionally, we introduce an efficient method for synthesizing the optical pumping waveforms required for generating combs with tens of thousands of teeth, as well as a simple yet frequency-agile laser setup for optical pumping across a 10 GHz bandwidth.
We report on the experimental demonstration of an optical spin-wave memory, based on the atomic frequency comb (AFC) scheme, where the storage efficiency is strongly enhanced by an optical cavity. The cavity is of low finesse, but operated in an impedance matching regime to achieve high absorption in our intrinsically low-absorbing Eu 3+ :Y 2 SiO 5 crystal. For storage of optical pulses as an optical excitation (AFC echoes), we reach efficiencies of 53% and 28% for 2 μ s and 10 μ s delays, respectively. For a complete AFC spin-wave memory we reach an efficiency of 12%, including spin-wave dephasing, which is a 12-fold increase with respect to previous results in this material. This result is an important step towards the goal of making efficient and long-lived quantum memories based on spin waves, in the context of quantum repeaters and quantum networks.
Optical quantum memories are essential components for realizing the full potential of quantum networks. Among these, rare-earth-doped crystal memories stand out due to their large multimode storage capabilities. To maximize the multimode capacity in the time domain, it is key to simultaneously achieve large memory bandwidth and long optical storage time. Here, we demonstrate an atomic frequency comb optical memory in 171Yb3+:Y2SiO5 , with a memory bandwidth of 250 MHz and a storage time of up to 125 µs. The efficiency reaches 20% at short storage times, and 5% at 125 µs. These results were enabled by an optimized optical pumping scheme, guided by numerical modelling. Our approach is specifically designed for future spin-wave storage experiments, with the theoretical bandwidth limit set at 288 MHz by the hyperfine structure of 171Yb3+:Y2SiO5 . Additionally, we introduce an efficient method for synthesizing the optical pumping waveforms required for generating combs with tens of thousands of teeth, as well as a simple yet frequency-agile laser setup for optical pumping across a 10 GHz bandwidth.