Spatial Spin-Wave Modulator in Multimode Cold Rubidium Quantum Memory
Adam Leszczyński, Michał Lipka, Mateusz Mazelanik +3 more
While several methods of information processing have been realized in quantum memories, thorough utilization of the spatial degree of freedom in highly-multimode memories demands a flexible method analogous to spatial light modulators (SLM) widely exploited in the broad field of optics to modulate the amplitude or phase of light. We want to present a spatial spin-wave modulator (SSM), allowing engineering of a spatial phase of spin-waves stored in a cold atomic memory. Using the SLM and polarizers we are able to shape a laser beam into an arbitrary shape. Such a prepared beam illuminates a cold rubidium cloud and due to ac-Stark effect the spatial phase of stored spin-waves is modified. The relative standard deviation of phase given by our SSM amounts to about 10%. We have also shown that losses scale quadratically with given phase. On one hand, that strongly limits the efficiency of SSM for strong phase modulation, but on the other hand enables efficient modulation in small range of several radians. During our research we have demonstrated a compensation of the quadratic phase introduced by a cylindrical lens placed in a readout path of our quantum memory. Moreover, introducing more complicated shapes of the ac-Stark beam, like saw or sine shape, we can shift and split spin-waves in Fourier domain [1]. Therefore we were able to interfere spin-waves stored in different spatial and temporal modes. This makes our SSM very robust tool which in conjugation with gradient echo memory can potentially allow to implement some new quantum protocols [2]. Finally, going to the single photon level we successfully observed a Hong-Ou-Mandel interference of two spin-waves stored in different spatial modes of our memory [3].
Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2019•0 citations