We experimentally investigate the charge (isospin) frustration induced by a geometrical symmetry in a triangular triple quantum dot. We observe the ground-state charge configurations of six-fold degeneracy, the manifestation of the frustration. The f
rustration results in omnidirectional charge transport, and it is accompanied by nearby nontrivial triple degenerate states in the charge stability diagram. The findings agree with a capacitive interaction model. We also observe unusual transport by the frustration, which might be related to elastic cotunneling and the interference of trajectories through the dot. This work demonstrates a unique way of studying geometrical frustration in a controllable way.
Complementarity, the incomplete nature of a quantum measurement - a core concept in quantum mechanics - stems from the choice of the measurement apparatus. The notion of complementarity is closely related to Heisenbergs uncertainty principle, but the
exact relation between the two remains a source of debate. For example, knowledge of a particles position in a double slit interference experiment will quench its wave-like nature and, vice versa, observing the wave property via interference implies lack of knowledge of the particles path. A canonical system for exploring complementarity is the quantum eraser (QE), predominantly studied thus far in photonic systems. A QE is an interference experiment consisting of two stages. First, one of the interfering paths is coupled to a which path (WP) detector - demonstrating loss of interference due to acquisition of WP information. Second, the WP information is being erased by projecting the detectors wavefunction on a particular basis; this renders the WP information inaccessible, thus allowing reconstruction of the interference pattern. In this work, we present a first implementation of a QE in an electronic system. Our system consists of two identical electronic Mach-Zehnder interferometers (MZIs) entangled via Coulomb interactions. Such novel setup has already attracted a considerable theoretical attention. With one MZI serving as a path detector and the other as the system interferometer, the visibility of the Aharonov-Bohm oscillation in the System can be controlled by the Detector. We demonstrate how a continuous change of the measurement basis, followed by post selection (via cross correlation of current fluctuations), allows a smooth transition between keeping and erasing the WP information.
Controlled dephasing of electrons, via which path detection, involves, in general, coupling a coherent system to a current driven noise source. However, here, we present a case in which a nearly isolated electron puddle at thermal equilibrium strongl
y affects the coherence of a nearby electronic interferometer. Moreover, for certain average electron occupations of the puddle, the interferometer exhibits complete dephasing. This robust phenomenon stems from the Friedel Sum Rule, which relates a systems occupation with its scattering phases. The interferometer opens a peeping window into physics of the isolated electron puddle, which cannot be accessed otherwise.
