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A quantum dot is like a tiny island where one or a few electrons can settle. In this new work, such an island was connected to two 'seas' of electrons: one flat like a pancake, the other bulky like an ocean. Electrons can hop from the island to the seas and back, and this hop depends on the shape of the electron's wave on the island.

It turns out that some electron states on the island are 'dark': electrons get stuck in them for a long time because their wave barely overlaps with the waves in the seas. Such a dark state is like a trion, three electrons with entangled spins, that can't easily fall apart. As a result, the current through the dot drops sharply, and on the current-voltage plot (the so-called Coulomb diamond), one side bulges asymmetrically.

This discovery helps explain how the shape of electron waves controls current in nanodevices. In the future, such dark states could be used as memory cells or qubits that are protected from accidental readout.

Original abstract

as written by the authors arXiv:2603.18726

We fabricated a quantum dot coupled laterally to a two-dimensional electron gas and vertically to a three-dimensional electron gas in order to investigate the eigenstate dependence of tunneling rate to these gases. We observed a bias-dependent ``geometric" current blockade. By tunneling via the asymmetric couplings, population inversion is induced and a dark metastable triplet state is revealed. The metastable state stops the current transport process, suppresses the current and asymmetrically widens the Coulomb diamond. By analyzing the current as a function of source-drain and gate voltage and the magnetic field, we concluded that this effect is due to the geometric shape of the electronic states in the dot and the current is limited by the tunneling rate due to the eigenstates, that is, artificial $$\sigma$$-coupling and $$\pi$$-coupling.