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Timestamp: 2019-04-24 13:01:27+00:00

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A number of techniques exist to use an ensemble of atoms as a quantum memory for light. Many of these propose to use backward retrieval as a way to improve the storage and recall efficiency. We report on a demonstration of an off-resonant Raman memory that uses backward retrieval to achieve an efficiency of 65 ± 6% at a storage time of one pulse duration. The memory has a characteristic decay time of 60 μs, corresponding to a delay-bandwidth product of 160.
H.-J. Briegel, W. Dür, J. I. Cirac, and P. Zoller, “Quantum repeaters: The role of imperfect local operations in quantum communication,” Phys. Rev. Lett. 81, 5932–5935 (1998).
J. Nunn, N. K. Langford, W. S. Kolthammer, T. F. M. Champion, M. R. Sprague, P. S. Michelberger, X.-M. Jin, D. G. England, and I. A. Walmsley, “Enhancing multiphoton rates with quantum memories,” Phys. Rev. Lett. 110, 133601 (2013).
D. Felinto, C. W. Chou, J. Laurat, E. W. Schomburg, H. de Riedmatten, and H. J. Kimble, “Conditional control of the quantum states of remote atomic memories for quantum networking,” Nat. Phys. 2, 844–848 (2006).
M. Afzelius, C. Simon, H. De Riedmatten, and N. Gisin, “Multimode quantum memory based on atomic frequency combs,” Phys. Rev. A 79, 052329 (2009).
A. E. Kozhekin, K. Mølmer, and E. Polzik, “Quantum memory for light,” Phys. Rev. A 62, 033809 (2000).
S. A. Moiseev and S. Kröll, “Complete Reconstruction of the Quantum State of a Single-Photon Wave Packet Absorbed by a Doppler-Broadened Transition,” Phys. Rev. Lett. 87, 173601 (2001).
G. Hétet, J. J. Longdell, A. L. Alexander, P. K. Lam, and M. J. Sellars, “Electro-Optic Quantum Memory for Light Using Two-Level Atoms,” Phys. Rev. Lett 100, 023601 (2008).
J. J. Longdell, G. Hétet, P. K. Lam, and M. J. Sellars, “Analytic treatment of controlled reversible inhomogeneous broadening quantum memories for light using two-level atoms,” Phys. Rev. A 78, 032337 (2008).
A. V. Gorshkov, A. André, M. D. Lukin, and A. S. Sørensen, “Photon storage in Λ-type optically dense atomic media. ii. free-space model,” Phys. Rev. A 76, 033805 (2007).
J. Nunn, I. A. Walmsley, M. G. Raymer, K. Surmacz, F. C. Waldermann, Z. Wang, and D. Jaksch, “Mapping broadband single-photon wave packets into an atomic memory,” Phys. Rev. A 75, 011401 (2007).
J.-L. Le Gouët and P. R. Berman, “Raman scheme for adjustable-bandwidth quantum memory,” Phys. Rev. A 80, 012320 (2009).
S. A. Moiseev and W. Tittel, “Optical quantum memory with generalized time-reversible atom-light interaction,” New J. Phys. 13, 063035 (2011).
K. F. Reim, P. Michelberger, K. C. Lee, J. Nunn, N. K. Langford, and I. A. Walmsley, “Single-Photon-Level Quantum Memory at Room Temperature,” Phys. Rev. Lett. 107, 053603 (2011).
D. G. England, P. S. Michelberger, T. F. M. Champion, K. F. Reim, K. C. Lee, M. R. Sprague, X.-M. Jin, N. K. Langford, W. S. Kolthammer, J. Nunn, and I. A. Walmsley, “High-fidelity polarization storage in a gigahertz bandwidth quantum memory,” J. Phys. B 45, 124008 (2012).
J. Nunn, K. Reim, K. C. Lee, V. O. Lorenz, B. J. Sussman, I. A. Walmsley, and D. Jaksch, “Multimode memories in atomic ensembles,” Phys. Rev. Lett. 101, 260502 (2008).
M. R. Sprague, P. S. Michelberger, T. F. M. Champion, D. G. England, J. Nunn, X.-M. Jin, W. S. Kolthammer, A. Abdolvand, P. S. J. Russell, and I. A. Walmsley, “Broadband single-photon-level memory in a hollow-core photonic crystal fibre,” Nat. Photonics 8, 287–291 (2014).
P. J. Bustard, R. Lausten, D. G. England, and B. J. Sussman, “Toward quantum processing in molecules: A THz-bandwidth coherent memory for light,” Phys. Rev. Lett. 111, 083901 (2013).
K. C. Lee, B. J. Sussman, M. R. Sprague, P. Michelberger, K. F. Reim, J. Nunn, N. K. Langford, P. J. Bustard, D. Jaksch, and I. A. Walmsley, “Macroscopic non-classical states and terahertz quantum processing in room-temperature diamond,” Nat. Photonics 6, 41–44 (2012).
D.-S. Ding, W. Zhang, Z.-Y. Zhou, S. Shi, G.-Y. Xiang, X.-S. Wang, Y.-K. Jiang, B.-S. Shi, and G.-C. Guo, “Quantum storage of orbital angular momentum entanglement in an atomic ensemble,” Phys. Rev. Lett. 114, 050502 (2015).
F. Grosshans and P. Grangier, “Quantum cloning and teleportation criteria for continuous quantum variables,” Phys. Rev. A 64, 010301 (2001).
W. Ketterle, K. B. Davis, M. A. Joffe, A. Martin, and D. E. Pritchard, “High densities of cold atoms in a dark spontaneous-force optical trap,” Phys. Rev. Lett. 70, 2253–2256 (1993).
M. Hush, “M-loop: Machine-learning online optimization package,” (2016).
P. B. Wigley, P. J. Everitt, A. v. d. Hengel, J. W. Bastian, M. A. Sooriyabandara, G. D. McDonald, K. S. Hardman, C. D. Quinlivan, P. Manju, C. C. N. Kuhn, I. R. Petersen, A. N. Luiten, J. J. Hope, N. P. Robins, and M. R. Hush, “Fast machine-learning online optimization of ultra-cold-atom experiments,” Sci. Rep. 6, srep25890 (2016).
S. Mavadia, V. Frey, J. Sastrawan, S. Dona, and M. J. Biercuk, “Prediction and real-time compensation of qubit decoherence via machine learning,” Nat. Comm. 8, ncomms14106 (2017).
M. August and X. Ni, “Using recurrent neural networks to optimize dynamical decoupling for quantum memory,” Phys. Rev. A 95, 012335 (2017).
N. Sangouard, C. Simon, M. Afzelius, and N. Gisin, “Analysis of a quantum memory for photons based on controlled reversible inhomogeneous broadening,” Phys. Rev. A 75, 032327 (2007).
K. Surmacz, J. Nunn, K. Reim, K. C. Lee, V. O. Lorenz, B. Sussman, I. A. Walmsley, and D. Jaksch, “Efficient spatially resolved multimode quantum memory,” Phys. Rev. A 78, 033806 (2008).
P. S. Michelberger, T. F. M. Champion, M. R. Sprague, K. T. Kaczmarek, M. Barbieri, X. M. Jin, D. G. England, W. S. Kolthammer, D. J. Saunders, J. Nunn, and I. A. Walmsley, “Interfacing GHz-bandwidth heralded single photons with a warm vapour Raman memory,” New J. Phys. 17, 043006 (2015).
D. J. Saunders, J. H. D. Munns, T. F. M. Champion, C. Qiu, K. T. Kaczmarek, E. Poem, P. M. Ledingham, I. A. Walmsley, and J. Nunn, “Cavity-enhanced room-temperature broadband raman memory,” Phys. Rev. Lett. 116, 090501 (2016).
K. F. Reim, J. Nunn, X.-M. Jin, P. S. Michelberger, T. F. M. Champion, D. G. England, K. C. Lee, W. S. Kolthammer, N. K. Langford, and I. A. Walmsley, “Multipulse Addressing of a Raman Quantum Memory: Configurable Beam Splitting and Efficient Readout,” Phys. Rev. Lett. 108, 263602 (2012).
K. F. Reim, J. Nunn, V. O. Lorenz, B. J. Sussman, K. C. Lee, N. K. Langford, D. Jaksch, and I. A. Walmsley, “Towards high-speed optical quantum memories,” Nat. Photonics 4, 218–221 (2010).
S. D. Jenkins, T. Zhang, and T. A. B. Kennedy, “Motional dephasing of atomic clock spin waves in an optical lattice,” J. Phys. B 45, 124005 (2012).
G. Campbell, M. Hosseini, B. M. Sparkes, P. K. Lam, and B. C. Buchler, “Time- and frequency-domain polariton interference,” New J. Phys. 14, 033022 (2012).
O. Pinel, J. L. Everett, M. Hosseini, G. T. Campbell, B. C. Buchler, and P. K. Lam, “A mirrorless spinwave resonator,” Sic. Rep. 5, srep17633 (2015).
A. Datta, L. Zhang, J. Nunn, N. K. Langford, A. Feito, M. B. Plenio, and I. A. Walmsley, “Compact Continuous-Variable Entanglement Distillation,” Phys. Rev. Lett. 108, 060502 (2012).
D. A. Braje, V. Balić, S. Goda, G. Y. Yin, and S. E. Harris, “Frequency mixing using electromagnetically induced transparency in cold atoms,” Phys. Rev. Lett. 93, 183601 (2004).
K. Tikhonov, T. Golubeva, and Y. Golubev, “Atomic thermal motion effect on efficiency of a high-speed quantum memory,” Eur. Phys. J. D 69, 252 (2015).
B. Chen, K. Zhang, C. Bian, C. Qiu, C.-H. Yuan, L. Q. Chen, Z. Y. Ou, and W. Zhang, “Efficient raman frequency conversion by coherent feedback at low light intensity,” Opt. Express 21, 10490–10495 (2013).
J. Guo, L. Q. Chen, P. Yang, Z. Li, Y. Wu, X. Feng, C.-H. Yuan, Z. Y. Ou, and W. Zhang, “88% conversion efficiency with an atomic spin wave mediated mode selection,” Opt. Lett. 42, 1752–1755 (2017).
Fig. 1 The atomic level configuration. Trapping is performed with light that is red-detuned from the |5S1/2, F = 2〉 → |5S3/2, F′ = 3〉 transition and a repump is applied on the |5S1/2, F = 1〉 → |5S3/2, F′ = 2〉 transition. After trapping and compression of the ensemble, a σ+-polarized optical pumping beam is applied to the |5S1/2, F = 1〉 → |5S3/2, F′ = 3〉 transition in conjunction with the repump to populate the |5S1/2, F = 2, mf = +2〉 state. Inset: Left: A signal ℰ + traverses an elongated atomic cloud where a two-photon resonant control beam Ω+ converts it to a collective atomic excitation. Right: A backward-propagating control beam Ω− subsequently retrieves the signal in the backward direction, as ℰ −.
Fig. 2 The atomic preparation sequence. The compression and polarisation-gradient cooling sequences are divided into 20 and 5 time bins, respectively, and are passed onto a machine-learning algorithm. This algorithm determines the optimal values of repump and cooling beam frequencies, and current through the transverse coils for magnetic trapping. A typical optimised set of parameters is presented here.
Fig. 3 The signal ℰ + traverses the atomic cloud where a two-photon resonant control beam Ω+ converts it to a collective atomic excitation. A reference without atoms or the fraction which is not absorbed is monitored on the right-hand detector. A backward-propagating control Ω− subsequently retrieves the signal in the backward direction, as ℰ + which is sent to the left-hand detector.
Fig. 4 a) Decay of the memory efficiency with storage time. The error bars correspond to the standard deviation. The efficiency is fitted to a motional dephasing model with an initial efficiency η0 = (69 ± 6)% and diffusion and transit times τD = 110 μs and τT = 170 μs, respectively. b) Storage and recall of a 360 ns 1/e2-width pulse. Photodiode signal for reference (scaled down) and recalls at storage times t1 = 1.5 μs and t2 = 41 μs are shown. The characteristic decay time corresponds to a delay-bandwidth product of 160.
Fig. 5 Schematic of an equivalent beam-splitter array. The input light is partially converted to a spin-wave and the rest leaks through the atomic ensemble and is detected on the photodiode. It is estimated about 35% of the light that is absorbed is not mode-matched to be efficiently recalled, in this short-pulse configuration. At the given control beam intensity, each retrieval pulse extracts only about 60 ± 4% of the stored spin-wave, the remainder is left for a subsequent retrieval step. The memory decay between retrievals is ignored at this time scale.

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