43 research outputs found
Selective Control of Conductance Modes in Multi-terminal Josephson Junctions
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 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. We
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.Comment: 15 pages, 4 figure
Gate-tunable Superconducting Diode Effect in a Three-terminal Josephson Device
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
Parity transitions in the superconducting ground state of hybrid InSb-Al Coulomb islands
The number of electrons in small metallic or semiconducting islands is
quantized. When tunnelling is enabled via opaque barriers this number can
change by an integer. In superconductors the addition is in units of two
electron charges (2e), reflecting that the Cooper pair condensate must have an
even parity. This ground state (GS) is foundational for all superconducting
qubit devices. Here, we study a hybrid superconducting-semiconducting island
and find three typical GS evolutions in a parallel magnetic field: a robust
2e-periodic even-parity GS, a transition to a 2e-periodic odd-parity GS,and a
transition from a 2e- to a 1e-periodic GS. The 2e-periodic odd-parity GS
persistent in gate-voltage occurs when a spin-resolved subgap state crosses
zero energy. For our 1e-periodic GSs we explicitly show the origin being a
single zero-energy state gapped from the continuum, i.e. compatible with an
Andreev bound states stabilized at zero energy or the presence of Majorana zero
modes