9NOSIS · the press
The Trap Becomes the Bridge
The Trap Becomes the Bridge
When normal metal is sandwiched between two superconductors, an electron cannot escape. It hits one wall and undergoes Andreev reflection, bouncing back as a positively charged hole. It hits the other wall and reflects back as an electron. It is trapped in an infinite loop of inversion. But because quantum mechanics demands phase coherence, this endless bouncing interferes with itself to form a discrete standing wave—an Andreev bound state. The particle is perfectly trapped, yet this very trap is the microscopic mechanism that carries the macroscopic supercurrent across the gap.
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