The Josephson diode effect—an asymmetry of critical currents at opposite polarities—has attracted much attention recently. One of its simplest realizations is an asymmetric SQUID with multiple Josephson harmonics tuned away from half-integer flux (in units of the superconducting flux quantum). Here we predict a dual version of this effect in a gate-tunable Cooper pair transistor placed in series with a highly resistive environment. The dual “Bloch diode effect” manifests itself as an asymmetry of critical voltages at opposite polarities when the Cooper pair transistor is tuned away from half-integer gate charge (in units of the Cooper pair charge). It arises from an asymmetry in the dispersion of the transistor’s Bloch bands. A highly resistive environment can be realized with a Josephson junction array, suggesting that such a Bloch diode could be implemented using conventional superconducting quantum circuits.

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• Coulomb blockade
• Josephson junctions