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Quantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation [1] and long-distance quantum communication [2]. A long standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived [3,4] or long-lived but inefficient quantum memories [5][6][7] have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a longwavelength spin wave, and arranging the setup in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1) ms. This realization provides an essential tool towards scalable linearoptical quantum information processing.A high-performance quantum memory is of crucial importance for large-scale linear-optical quantum computation[1], distributed quantum computing, and long-distance quantum communication [2]. The lifetime and the retrieval efficiency of a quantum memory are two important quantities that determine the scalability of realistic quantum information protocols. For a certain quantum information task, e.g. creating a large-scale cluster state [8] or distributing entanglement through the quantum repeater protocol [9-12], the time overhead T r is inversely proportional to a power law of the retrieval efficiency R, T r ∝ R −n , where n is determined by the scale of the quantum computation or the communication distance. In order to implement one of those tasks, the lifetime of the quantum memory must be larger than this time overhead. To satisfy this condition, one has to improve the lifetime of the quantum memory and reduce the time overhead by improving the retrieval efficiency. Besides, different protocols also set thresholds on the retrieval efficiency and lifetime. For example, in loss-tolerant linear-optical quantum computation the minimum retrieval efficiency required is 50% [13] and in long-distance quantum communication distributing en-tanglement over 1000 km requires a communication time of at least 3.3 ms.Quantum memories for light have been demonstrated with atomic ensembles [14][15][16], solid state systems [17,18], and single atoms [19]. With these quantum memories, the principle of some quantum information protocols have been demonstrated, e.g., functional quantum repeater nodes were realized with atomic ensembles [20,21]. However, due to the low retrieval efficiency and short lifetime, the implementation of further steps is extremely difficult. Therefore, in recent years, many efforts have been devoted towards improving the retrieval efficiency and the lifetime of the quantum memories and significant progress has been achieved. However, an efficient and long-lived quantum memory remai...

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The sub-nanoscale size of typical diatomic molecules hinders direct optical access to their constituents. Rydberg macrodimers -bound states of two highly-excited Rydberg atoms -feature interatomic distances easily exceeding optical wavelengths. Here we report the direct microscopic observation and detailed characterization of such molecules in a gas of ultracold atoms in an optical lattice. The bond length of about 0.7 µm, comparable to the size of small bacteria, matches the diagonal distance of the lattice. By exciting pairs in the initial two-dimensional atom array, we resolve more than 50 vibrational resonances. Using our spatially resolved detection, we observe the macrodimers by correlated atom loss and demonstrate control of the molecular alignment by the choice of the vibrational state. Our results allow for rigorous testing of Rydberg interaction potentials and highlight the potential of quantum gas microscopy for molecular physics. arXiv:1812.07533v3 [physics.atom-ph]