Abstract
Quantum memories with long storage times are key elements in long-distance quantum networks. The atomic frequency comb (AFC) memory in particular has shown great promise to fulfill this role, having demonstrated multimode capacity and spin–photon quantum correlations. However, the memory storage times have so-far been limited to about 1 ms, realized in a Eu3+ doped Y2SiO5 crystal at zero applied magnetic field. Motivated by studies showing increased spin coherence times under applied magnetic field, we developed an AFC spin-wave memory utilizing a weak 15 mT magnetic field in a specific direction that allows efficient optical and spin manipulation for AFC memory operations. With this field configuration the AFC spin-wave storage time increased to 40 ms using a simple spin-echo sequence. Furthermore, by applying dynamical decoupling techniques the spin-wave coherence time reaches 530 ms, a 300-fold increase with respect to previous AFC spin-wave storage experiments. This result paves the way towards long duration storage of quantum information in solid-state ensemble memories.
Highlights
A future quantum internet relies on the capability of remotely sharing quantum information, and the last few years have seen rapid progress in increasing the distances over which it can be distributed
Storage experiments with fixed number of pulses We start by characterizing the atomic frequency comb (AFC) spin-wave memory performance using a single sequence consisting of two identical π-pulses, which is the minimum number of required pulses in an optical storage experiment in order to compensate the inhomogeneous broadening of the spin transition
Taking into account the AFC and the control efficiencies ηAFC = 10.2 ± 0.7% and ηctrl = 61 ± 2%, equation (2) suggests that the spin wave efficiency ηspin is close to unity, within the error
Summary
A future quantum internet relies on the capability of remotely sharing quantum information, and the last few years have seen rapid progress in increasing the distances over which it can be distributed. Recent experiments have demonstrated fiber-based quantum communication of over 400 km [1, 2], but reaching continental distances using fiber networks will require quantum repeaters [3]. These will require multiplexed quantum memories, i.e. devices that allow storage of quantum states of light in different modes in time, space or frequency [4]. The storage time of spin-wave AFC memories in RE ion doped crystals, has been limited to a few milliseconds, realized in Eu3+ doped Y2SiO5 crystals [16, 20, 24]. In these experiments the spin storage is realized on a zero-field nuclear quadrupole resonance where, at zero applied magnetic field, each quadrupole state is composed of two degenerate nuclear Zeeman states
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