Free motion of a quantum particle with the wave function entirely comprised of plane waves with non-negative momenta may be accompanied by negative probability current, an effect called quantum backflow. The effect is weak and fragile and has not yet been observed experimentally. Here we show that quantum backflow becomes significantly more pronounced and more amenable to experimental observation if, instead of letting the particle move along a straight line, one forces it to move in a circular ring.

中文翻译：

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环形中的量子回流

具有完全由非负动量的平面波组成的波函数的量子粒子的自由运动可能伴随着负概率电流，这种效应称为量子回流。该作用微弱且易碎，尚未通过实验观察到。在这里，我们表明，如果不是让粒子沿直线移动，而是迫使粒子沿圆环移动，则量子逆流将变得更加明显，并且更易于进行实验观察。