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Future quantum repeater architectures, capable of efficiently distributing information encoded in quantum states of light over large distances, rely on quantum memories for light [1]. Quantum repeaters can benefit from a modal multiplexing implementation of the memory, essentially scaling up the repeater's throughput [2].
In this work we demonstrate a temporally multiplexed quantum repeater node in a laser-cooled cloud of 87-Rb atoms (as proposed in [3]). We employ the DLCZ protocol where pairs of photons and single collective spin excitations (so called spin-waves) are created [4]. The latter can then be efficiently transferred into a second single photon. For selective readout, we need to control the dephasing and rephasing of the spin-waves created in different temporal modes. We achieve this by a magnetic field gradient, which induces an inhomogeneous broadening of the involved atomic hyperfine levels [5]. By employing this steering technique, combined with cavity-enhanced noise suppression and feed forward readout, we demonstrate distinguishable retrieval of up to 10 temporal modes. For each mode, we prove non-classical correlations between the first and second photon. Furthermore, an enhancement in rates of correlated photon-photon pairs is observed as we increase the number of temporal modes stored in the memory. The reported device is a crucial key element of a quantum repeater architecture implementing multiplexed quantum memories.
[1] H.-J. Briegel, W. Dür, J. Cirac and P. Zoller; Phys. Rev. Lett. 81 5932 (1998)
[2] C. Simon, H. de Riedmatten, M. Afzelius,N. Sangouard, H. Zbinden and N. Gisin; Phys. Rev. Lett. 98 190503 (2007)
[3] C. Simon, H. de Riedmatten and M. Afzelius; Phys. Rev. A 82 010304(R) (2010)
[4] L. Duan, M. Lukin, J. Cirac and P. Zoller, P; Nature 414 413 (2001)
[5] B.Albrecht, P. Farrera, G. Heinze, M. Cristiani and H. de Riedmatten; Phys. Rev. Lett. 115 160501 (2015)
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