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arXiv:2412.12379 · Physical Review Applied

Efficient pumping of atomic frequency combs in a Tm 3 + :YAG crystal for broadband quantum optical storage

Yisheng Lei, Zongfeng Li, Mahdi Hosseini

Published May 27, 2025• 5 citations
arXivHTMLPDF

Abstract

Quantum memory devices with high storage efficiency and bandwidth are essential elements for future quantum networks. Here, we report a storage efficiency greater than 28% in a $\mathrm{Tm}$${}^{3+}$:YAG crystal (where YAG is yttrium aluminum garnet) at elevated temperatures, achieving this milestone without relying on optical cavities and without compromising memory bandwidth. We introduce different pumping techniques for $\mathrm{Tm}$-based memories that enable multifrequency-window storage and high memory bandwidth reaching 630 MHz, significantly surpassing previous $\mathrm{Tm}$-based memory demonstrations, considering the operating temperature of 3.5 K. Furthermore, we propose a general method for large-bandwidth atomic frequency memory using non-Kramers rare-earth ions (REIs) in solids, paving the way for storage efficiencies and bandwidths approaching fundamental limits. The compatibility of $\mathrm{Tm}$ memories with neutral-atom quantum processors and their seamless integration with scalable photonic platforms, such as lithium niobate on insulator, underscore their potential for distributed quantum computing, hybrid quantum networks, and space-based quantum communication. Our study represents a significant advancement toward practical high-performance quantum memories based on REI-doped crystals, where we predict that gigahertz bandwidth and storage efficiencies exceeding 30% are achievable at lower temperatures.

DOI
10.1103/physrevapplied.23.054076

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Quantum memory devices with high storage efficiency and bandwidth are essential elements for future quantum networks. Here, we report a storage efficiency greater than 28% in a \mathrm{Tm}$${}^{3+}:YAG crystal (where YAG is yttrium aluminum garnet) at elevated temperatures, achieving this milestone without relying on optical cavities and without compromising memory bandwidth. We introduce different pumping techniques for Tm\mathrm{Tm}Tm-based memories that enable multifrequency-window storage and high memory bandwidth reaching 630 MHz, significantly surpassing previous Tm\mathrm{Tm}Tm-based memory demonstrations, considering the operating temperature of 3.5 K. Furthermore, we propose a general method for large-bandwidth atomic frequency memory using non-Kramers rare-earth ions (REIs) in solids, paving the way for storage efficiencies and bandwidths approaching fundamental limits. The compatibility of Tm\mathrm{Tm}Tm memories with neutral-atom quantum processors and their seamless integration with scalable photonic platforms, such as lithium niobate on insulator, underscore their potential for distributed quantum computing, hybrid quantum networks, and space-based quantum communication. Our study represents a significant advancement toward practical high-performance quantum memories based on REI-doped crystals, where we predict that gigahertz bandwidth and storage efficiencies exceeding 30% are achievable at lower temperatures.
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.
Long optical storage times are an essential requirement to establish high-rate entanglement distribution over large distances using memory-based quantum repeaters. Rare earth ion-doped crystals are arguably well-suited candidates for building such quantum memories. Toward this end, we investigate the 795.32 nm 3H6 ↔ 3H4 transition of 1% thulium-doped yttrium gallium garnet crystal (Tm3+:Y3Ga5O12 : Tm3+:YGG). Most essentially, we find that the optical coherence time can reach 1.1 ms, and, using laser pulses, we demonstrate optical storage based on the atomic frequency comb (AFC) protocol up to 100 µs. In addition, we demonstrate multiplexed storage, including feed-forward selection, shifting, and filtering of spectral modes, as well as quantum state storage using members of non-classical photon pairs. Our results show that Tm:YGG can be a potential candidate for creating multiplexed quantum memories with long optical storage times.
Quantum memories are a key building block for optical quantum computers and quantum networks. Rare-earth ion-doped crystals are a promising material to achieve quantum memory using an atomic frequency comb protocol. However, current atomic frequency comb memories typically use bulk materials or waveguides with large cross sections or rely on fabrication techniques not easily adaptable to wafer scale processing. Here, we demonstrate a compact chip-integrated atomic frequency comb in rare-earth-doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz and optical storage time as long as 250 ns. The enhanced optical confinement in this device leads to three orders of magnitude reduction in optical power required for a coherent control as compared to ion-diffused waveguides. These compact atomic frequency comb memories pave the way toward scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.
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.
Atomic frequency combs memories that coherently store optical signals are a key building block for optical quantum computers and quantum networks. Integrating such memories into compact and chip-scale devices is essential for scalable quantum technology, but to date most demonstrations have been in bulk materials or waveguides with large cross-sections, or using fabrication techniques not easily adaptable to wafer scale processing. We demonstrate compact chip-integrated atomic frequency comb storage in rare earth doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz, and optical storage time of over 250 ns. The enhanced optical confinement in this device structure enables three orders of magnitude reduction in optical power as compared to large ion-diffused waveguides for the same Rabi frequency. These compact atomic frequency comb memories pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.
Multiplexing is essential for improving entanglement distribution rates in quantum communication. Frequency multiplexing provides a promising and scalable path toward large-capacity quantum networks. Further progress requires increasing the number of frequency modes and developing broadband photon-pair sources and quantum memories that are spectrally compatible. Here, we report the integration of a cavity-enhanced spontaneous parametric down-conversion source in the telecom C-band with a frequency-multiplexed atomic frequency comb memory. The bow-tie cavity source was simultaneously resonant at 606 nm and 1550 nm, generating non-degenerate photon pairs exhibiting a clustered frequency-comb spectrum. The atomic frequency comb memory, implemented in Praseodymium-doped Yttrium Orthosilicate crystals, provided up to 83 frequency modes with 123 MHz spacing and enabled broadband storage of 606 nm signal photons. By filtering the main cluster, we obtained 32.7±4.832.7 \pm 4.832.7±4.8 effective modes, as confirmed from coincidence measurements. Importantly, we observed strong nonclassical correlations after storage, with cross-correlation values of gs,i(2)=8.1±0.7g_{s,i}^{(2)} = 8.1\pm0.7gs,i(2)​=8.1±0.7. Our experimental results demonstrate the feasibility of integrating cavity-enhanced photon-pair sources with rare-earth-ion-doped solid-state memories. The integration reveals a high frequency multiplicity that is essential for scalable quantum networks.