Josephson junctions with three or more superconducting leads have been predicted to exhibit topological effects in the presence of few conducting modes within the interstitial normal material. Such topological behavior manifests itself as signatures in the transport properties between different terminals, with topological phase transitions occurring as a function of phase and voltage bias. Here we study the superconducting properties of a top-gated three-terminal Josephson device, based on an InAs heterostructure two-dimensional electron gas (2DEG) proximitized with epitaxial aluminum. The top gate is used to control the 2DEG carrier density, and differential resistances are analyzed under various bias currents and magnetic fields. We find that the character of the features in a 2D resistance map of the device substantially change under different gate and magnetic field conditions. A computational model of a network of three resistively and capacitively shunted junctions (RCSJ) suggests that depletion of the interstitial 2DEG drives the system further toward this non-interacting network regime. A perpendicular magnetic field has the opposite effect of increasing interactions between supercurrents in each branch.

The phenomenon of non-reciprocal critical current in a Josephson device, termed the Josephson diode effect, has garnered much recent interest. Realization of the diode effect requires inversion symmetry breaking, typically obtained by spin-orbit interactions. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon an InAs quantum well two-dimensional electron gas proximitized by an epitaxial aluminum superconducting layer. We demonstrate that the diode efficiency in our devices can be tuned by a small out-of-plane magnetic field or by electrostatic gating. We show that the Josephson diode effect in these devices is a consequence of the artificial realization of a current-phase relation that contains higher harmonics. We also show nonlinear DC intermodulation and simultaneous two-signal rectification, enabled by the multi-terminal nature of the devices. Furthermore, we show that the diode effect is an inherent property of multi-terminal Josephson devices, establishing an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, agnostic to the underlying material platform. These Josephson devices may also serve as gate-tunable building blocks in designing topologically protected qubits.

The Andreev bound state spectra of multi-terminal Josephson junctions form an artificial band structure, which is predicted to host tunable topological phases under certain conditions. However, the number of conductance modes between the terminals of a multi-terminal Josephson junction must be few in order for this spectrum to be experimentally accessible. In this work, we employ a quantum point contact geometry in three-terminal Josephson devices to demonstrate independent control of conductance modes between each pair of terminals and access to the single-mode regime coexistent with the presence of superconducting coupling. These results establish a full platform on which to realize tunable Andreev bound state spectra in multi-terminal Josephson junctions.

The phenomenon of non-reciprocal critical current in a Josephson device, termed Josephson diode effect, has garnered much recent interest. It is typically attributed to spin-orbit interaction and time reversal symmetry breaking in these systems. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon InAs quantum well two-dimensional electron gas proximitized by epitaxial aluminum. We demonstrate that the diode efficiency can be tuned by a small out-of-plane magnetic field and electrostatic gating. We show that the diode effect in this device is a consequence of artificial realization of a current-phase relation that is non-2π-periodic.These Josephson devices may serve as gate tunable building blocks in designing topologically protected qubits. Furthermore, we show that the diode effect is an inherent property of multiterminal Josephson devices. This establishes an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, which is agnostic to the underlying material platform.

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