德布罗意波的自发四波混频：超越光学
Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics
摘要：
我们研究了两个亚稳态氦原子的玻色-爱因斯坦凝聚体（BEC）的碰撞过程中光子简并四波混频的原子光学模拟，并利用时空分辨探测器测量了散射原子的动量分布。对于光子的情况，相位匹配条件完全定义了系统的最终状态，并且在两个碰撞BEC的情况下，简单的类比意味着散射原子的球形动量分布。然而，我们发现散射原子的最终动量反而位于一个半径小于初始碰撞动量的椭圆体上。数值和解析计算与测量结果吻合良好，并揭示了多体效应、平均场相互作用和源凝聚各向异性之间的相互作用。
英文摘要：
We investigate the atom-optical analog of degenerate four-wave mixing of photons by colliding two Bose-Einstein condensates (BECs) of metastable helium and measuring the resulting momentum distribution of the scattered atoms with a time and space resolved detector. For the case of photons, phase matching conditions completely define the final state of the system, and in the case of two colliding BECs, simple analogy implies a spherical momentum distribution of scattered atoms. We find, however, that the final momenta of the scattered atoms instead lie on an ellipsoid whose radii are smaller than the initial collision momentum. Numerical and analytical calculations agree well with the measurements, and reveal the interplay between many-body effects, mean-field interaction, and the anisotropy of the source condensate.
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