Long-Lived Solid-State Optical Memory for High-Rate Quantum Repeaters

Abstract

We argue that long optical storage times are required to establish entanglement at high rates over large distances using memory-based quantum repeaters. Triggered by this conclusion, we investigate the 795.325 nm 3 H 6 ↔ 3 H 4 transition of Tm∶Y 3 Ga 5 O 12 (Tm:YGG). Most importantly, 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 protocol during up to 100 μs as well as a memory decay time T m of 13.1 μs. Possibilities of how to narrow the gap between the measured value of T m and its maximum of 275 μs are discussed. In addition, we demonstrate multiplexed storage, including with feed-forward selection, shifting and filtering of spectral modes, as well as quantum state storage using members of nonclassical photon pairs. Our results show the potential of Tm:YGG for creating multiplexed quantum memories with long optical storage times, and open the path to repeater-based quantum networks with high entanglement distribution rates.

Performance Improvement of Single-Frequency CW Laser Using a Temperature Controller Based on Machine Learning

“…All-solid-state continuous wave (CW) single-frequency lasers have been applied in quantum optics and quantum information [ 1 , 2 ], precision measurement [ 3 ], optical holography [ 4 ], optical storage [ 5 ], cutting [ 6 ], welding [ 7 , 8 , 9 ], sensing [ 10 , 11 ] and so on, owing to their intrinsic advantages of compact structure, high stability, low intensity noise and high beam quality [ 12 , 13 ]; however, in order to attain a stable all-solid-state single-frequency CW laser with high output power, the temperatures of the pump source and gain crystal as well as nonlinear crystal must be precisely controlled in addition to the design of a unidirectional resonator to eliminate the spatial hole burning effect [ 14 ]. Especially for the gain crystal, in the process of laser emission, a lot of waste heat is generated due to quantum defect, energy transfer upconversion (ETU), excited state absorption (ESA) and cross relaxation (CR), and dissipates within the host lattice, which can change the operating temperature of the gain crystal and further induce the thermal lens effect, thermal astigmatism and so on [ 15 , 16 ].…”

A long-lived spectrally multiplexed solid-state optical quantum memory for high-rate quantum repeaters

“…We show that its optical coherence time T 2 can reach upto 1.1 ms, which is one of the longest times reported for any rare-earth-doped systems. 6,8 We show the storage of classical optical pulses up to 100 µs of optical storage time, 12 using the two-level atomic frequency comb (AFC) protocol 13 where the optical excitation is stored in Tm 3+ ions as a collective delocalized atomic excitation. We Find that the memory decay time T m is around 13 µs which is 20 times smaller than the T 2 -imposed maximum of 275 µs.…”

Remote distribution of non-classical correlations over 1250 modes between a telecom photon and a $^{171}$Yb$^{3+}$:Y$_2$SiO$_{5}$ crystal

“…Ensemblebased quantum memories are of great interest for quantum repeaters due to their multimode (or multiplexing) capacity, which is crucial for achieving practical rates [5,6]. The main systems currently under investigation are laser-cooled alkali gases [7][8][9][10][11] and rare-earth ion doped crystals [12][13][14][15][16].…”

“…a long optical coherence time, to maximize the number of comb lines. AFC experiments featuring long optical coherence times, in the range of 10 to 100 µs, have so far only been achieved in nuclear-spin based RE-crystals (non-Kramer ions), namely Eu 3+ :Y 2 SiO 5 [16,21,22], Pr 3+ :Y 2 SiO 5 [13,14] and Tm 3+ :Y 3 Ga 5 O 12 (YGG) [12]. However, experiments in Eu 3+ and Pr 3+ doped materials have shown AFC bandwidths of around 10 MHz or less, fundamentally limited by the nuclear hyperfine splittings of the same order, which reduces the temporal multimode capacity to the range of 10 to 100 modes [21].…”