We describe a superconducting three-terminal device that uses a simple geometric effect known as current crowding to sense the flow of current and actuate a readout signal. The device consists of a Y-shaped current combiner, with two currents (sense and bias) entering through the top arms of the Y, intersecting, and then exiting through the bottom leg of the Y. This geometry--mixing two inputs at a sharp intersection point--takes its inspiration from Y-shaped combiners in fluid flow systems, where variations in the input pressures can produce at turbulence and mixing at the intersection. When current is added to or removed from one of the arms (the sense arm), the superconducting critical current in the other arm (the bias arm) is modulated. The current in the sense arm can thus be determined by measuring the critical current of the bias arm. The dependence of the bias critical current on the sense current is possible because current crowding causes the sense current to interact locally with the bias arm. Measurement of the critical current in the bias arm does not break the superconducting state of the sense arm or of the bottom leg, and thus the signal to be sensed is fully restored after the measurement process. This device thus has potential for broad applicability across superconducting technologies and materials.
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