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Optics Continuum

Creation of a high-resolution atomic frequency comb and optimization of the pulse sequence for high-efficiency quantum memory in 167 Er:Y 2 SiO 5

S. Yasui, Masaya Hiraishi, Atsushi Ishizawa, Hiroo Omi, Tomohiro Inaba, Xuejun Xu, R. Kaji, S. Adachi, Takehiko Tawara

Published Aug 10, 2022• 9 citations
Publisher

Abstract

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.

DOI
10.1364/optcon.457429

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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.
We demonstrated a highly efficient optical memory operation using an atomic frequency comb (AFC) created from a spectrally flattened optical frequency comb with an isotopically pure 167 Er 3+ :Y 2 SiO 5 crystal under zero magnetic field. Compared with standard AFC creation methods such as pulse train method, our method, called comb transfer method, can create a broadband and high-efficiency AFC at lower power and with less effort. This technique can make a significant improvement in the quality of AFCs in crystals doped with low concentrations of rare-earth ions.
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.
Quantum memory will be a key component in future quantum networks, and atomic frequency combs (AFCs) in rare-earth-doped crystals are one promising platform for realizing this technology. We theoretically and experimentally investigate the formation of AFCs in Pr3+:Y2SiO5, with an overall bandwidth of 120 MHz and tooth spacing ranging from 0.1 MHz to 20 MHz, showing agreement between our calculations and measurements. We observe that the echo efficiency depends crucially on the AFC tooth spacing. Our results suggest approaches to developing a high-efficiency AFC quantum memory.
Quantum memories are used for storing the quantum mechanical states of photons and release identical photons at a later time. This has many applications within the field of quantum computing and is also essential in order to achieve long range quantum communication and cryptography. In this thesis Atomic frequency comb (AFC) quantum memories were investigated. In particular, three-level memory schemes were investigated in detail and a program for simulating these protocols was developed. These schemes make use of control pulses to transfer the population from the optically excited state to a ground state hyperfine level, as well as radio frequency fields to swap the population in the two ground state hyperfine levels. In this work control and RF pulses, tailored to give good transfer rates, are suggested and effects due to off resonant excitation was investigated. A memory protocol which could give efficiencies up to 60% for Praseodymium doped Yttrium Silicate based AFC memories is proposed. The main bottleneck for reaching higher efficiencies is that the AFC peak spacing needs to be small in order to give enough time to transfer the population to the spin state with the control pulses. With the control pulses suggested in this work and the current technology of tailoring AFC peaks in Pr-based memories, this gives a maximum finesse of 6 of the AFC structure.
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.