Efficient Quantum Memory Using a Weakly Absorbing Sample

Abstract

A light-storage experiment with a total (storage and retrieval) efficiency η=56% is carried out by enclosing a sample, with a single-pass absorption of 10%, in an impedance-matched cavity. The experiment is carried out using the atomic frequency comb (AFC) technique in a praseodymium-doped crystal (0.05%Pr(3+):Y2SiO5) and the cavity is created by depositing reflection coatings directly onto the crystal surfaces. The AFC technique has previously by far demonstrated the highest multimode capacity of all quantum memory concepts tested experimentally. We claim that the present work shows that it is realistic to create efficient, on-demand, long storage time AFC memories.

Memory-assisted quantum key distribution resilient against multiple-excitation effects

“…Reference [42] utilizes a low-finesse cavity to show (up to 50%) efficient and on-demand storage of strong pulses. Efficient storage using a low-finesse cavity is achieved in [43], while on-demand storage of qubits and heralded single photons are shown in [44,45], respectively. As shown in figure 7, again we simulate the key rate of the quasi-EPR scheme and find that none of the rare-earth-ion-doped crystal implementations will surpass the nomemory performance.…”

“…Specifically, we suggest memory parameters that could be obtained with realistic experimental improvements to the memories of [34][35][36][37][38][39][40][41][42][43][44][45]. We attempt to be conservative with our suggested parameters, in particular with those of efficiency and coherence time, and acknowledge that there are fundamental limitations of some parameters, e.g.…”

“…We consider the five atomic frequency comb experiments described in [41][42][43][44][45]. Europium-doped Y 2 SiO 5 crystals are employed in the investigations of [41,42] while the well-studied Pr:Y 2 SiO 5 is featured in [44,45].…”

“…The latter may differ in coherence time, efficiency, bandwidth and access time, reading and writing procedures, and operating wavelength for example. In particular, we consider a selection of state-of-the-art memories based on warm vapors at room temperature [34][35][36][37], cold ensembles of rubidium atoms [38][39][40], and cryogenically-cooled rare-earth-ion-doped crystals [41][42][43][44][45]. In the latter case, we utilize the possibility of spectral multi-mode storage [46] in such memories.…”

“…Even with perfect efficiency, we find that neither of the quantum memories overcome the bound, mainly due to their limited bandwidth in comparison to the Raman quantum memories. To gain an advantage, we first assume the cavity enhanced setups of [42,43] in conjunction with memories Eu+DD and Pr+DD, respectively. We then consider the possibility of multi-mode storage, which we refer to as memories Eu+MM and Pr+MM for Euand Pr-doped Y 2 SiO 5 , respectively.…”