Multimode capacity of atomic-frequency comb quantum memories

Abstract

Ensemble-based quantum memories are key to developing multiplexed quantum repeaters, able to overcome the intrinsic rate limitation imposed by finite communication times over long distances. Rare-earth ion doped crystals are main candidates for highly multimode quantum memories, where time, frequency and spatial multiplexing can be exploited to store multiple modes. In this context the atomic frequency comb (AFC) quantum memory provides large temporal multimode capacity, which can readily be combined with multiplexing in frequency and space. In this article, we derive theoretical formulas for quantifying the temporal multimode capacity of AFC-based memories, for both optical memories with fixed storage time and spin-wave memories with longer storage times and on-demand read out. The temporal multimode capacity is expressed in key memory parameters, such as AFC bandwidth, fixed-delay storage time, memory efficiency, and control field Rabi frequency. Current experiments in europium- and praseodymium-doped Y$_2$SiO$_5$ are analyzed within this theoretical framework, which is also tested with newly acquired data as prospects for higher temporal capacity in these materials are considered. In addition we consider the possibility of spectral and spatial multiplexing to further increase the mode capacity, with examples given for both rare earth ions.

Storage of 1650 modes of single photons at telecom wavelength

“…Towards a future quantum network [1][2][3][4] compatible with existing telecom infrastructure, this requirement must also be applied 5,6 . One challenge in pursuing such a quantum network is to develop a multimode quantum memory [7][8][9][10][11] , which is able to simultaneously store and process multiple modes of single photons in various degrees of freedom, such as in temporal degree [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] , spectral degree [27][28][29] , spatial degree [30][31][32][33][34][35][36][37][38] , or any combination of these 39,40 . In addition to the usual figures-of-merit for quantum memories, i.e., efficiency and fidelity, the multimode performance of a quantum memory is also important, which is mainly determined by the number of storage channels, storage time, and storage bandwidth.…”

“…Towards a future quantum network [1][2][3][4] compatible with existing telecom infrastructure, this requirement must also be applied [5,6]. One challenge in pursuing such a quantum network is to develop a multimode quantum memory [7][8][9][10][11], which is able to simultaneously store and process multiple modes of single photons in various degrees of freedom, such as in temporal degree [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], spectral degree [27][28][29], spatial degree [30][31][32][33][34][35][36][37][38],…”

Long-distance multiplexed quantum teleportation from a telecom photon to a solid-state qubit

“…In order to further extend the distance between Alice and Bob we could increase the storage time of our matter qubits using the long lived spin state of the Pr 3+ ions with dynamical decoupling techniques [29,35,36], which would also allow on-demand read-out of the stored qubits [27]. Moreover, higher rates of teleportation attempts can be achieved by combining the already existing temporal multimodality with other degrees of freedom already demonstrated in this system [22][23][24].…”

“…They provide a compact platform composed of a large number of atoms naturally trapped in the crystalline structure. At cryogenic temperatures they feature excellent coherence properties and moreover they allow for multiplexing in several degrees of freedom [22][23][24], a significant advantage with respect to other systems [7,18]. The use of rare-earth doped crystals has lead to demonstrations of storage [25][26][27] and generation [28][29][30][31] of quantum states of light.…”

Non-classical correlations over 1250 modes between telecom photons and 979-nm photons stored in 171Yb3+:Y2SiO5

“…Solid-state ensemble quantum memories based on rare-earth (RE) ion doped crystals can be multiplexed in time 5 , 19 , frequency 8 , 20 and space 20 – 22 . Time-domain multimode storage can be achieved with the atomic frequency comb (AFC) quantum memory 19 , where the mode capacity is proportional to the number of comb lines in the AFC 19 , 23 . By consequence, a large capacity requires both a large AFC bandwidth and a narrow homogeneous linewidth, i.e., a long optical coherence time, to maximize the number of comb lines.…”