4 research outputs found
Conduction channels of an InAs-Al nanowire Josephson weak link
We present a quantitative characterization of an electrically tunable
Josephson junction defined in an InAs nanowire proximitized by an
epitax-ially-grown superconducting Al shell. The gate-dependence of the number
of conduction channels and of the set of transmission coefficients are
extracted from the highly nonlinear current-voltage characteristics. Although
the transmissions evolve non-monotonically, the number of independent channels
can be tuned, and configurations with a single quasi-ballistic channel
achieved.Comment: Added reference in New Journal of Physics, corrected a few typos, and
updated reference
Topological Phases in InAs1−xSbx:From Novel Topological Semimetal to Majorana Wire
Superconductor proximitized one-dimensional semiconductor nanowires with
strong spin-orbit interaction (SOI) are at this time the most promising
candidates for the realization of topological quantum information processing.
In current experiments the SOI originates predominantly from extrinsic fields,
induced by finite size effects and applied gate voltages. The dependence of the
topological transition in these devices on microscopic details makes scaling to
a large number of devices difficult unless a material with dominant intrinsic
bulk SOI is used. Here we show that wires made of certain ordered alloys
InAsSb have spin-splittings up to 20 times larger than those
reached in pristine InSb wires. In particular, we show this for a stable
ordered CuPt-structure at , which has an inverted band ordering and
realizes a novel type of a topological semimetal with triple degeneracy points
in the bulk spectrum that produce topological surface Fermi arcs.
Experimentally achievable strains can drive this compound either into a
topological insulator phase, or restore the normal band ordering making the
CuPt-ordered InAsSb a semiconductor with a large intrinsic
linear in bulk spin splitting.Comment: 6 pages, 5 figure
Gatemon benchmarking and two-qubit operations
Recent experiments have demonstrated superconducting transmon qubits with
semiconductor nanowire Josephson junctions. These hybrid gatemon qubits utilize
field effect tunability characteristic for semiconductors to allow complete
qubit control using gate voltages, potentially a technological advantage over
conventional flux-controlled transmons. Here, we present experiments with a
two-qubit gatemon circuit. We characterize qubit coherence and stability and
use randomized benchmarking to demonstrate single-qubit gate errors below 0.7%
for all gates, including voltage-controlled rotations. We show coherent
capacitive coupling between two gatemons and coherent swap operations. Finally,
we perform a two-qubit controlled-phase gate with an estimated fidelity of 91%,
demonstrating the potential of gatemon qubits for building scalable quantum
processors
InAs-Al Hybrid Devices Passing the Topological Gap Protocol
We present measurements and simulations of semiconductor-superconductor
heterostructure devices that are consistent with the observation of topological
superconductivity and Majorana zero modes. The devices are fabricated from
high-mobility two-dimensional electron gases in which quasi-one-dimensional
wires are defined by electrostatic gates. These devices enable measurements of
local and non-local transport properties and have been optimized via extensive
simulations for robustness against non-uniformity and disorder. Our main result
is that several devices, fabricated according to the design's engineering
specifications, have passed the topological gap protocol defined in Pikulin
{\it et al.}\ [arXiv:2103.12217]. This protocol is a stringent test composed of
a sequence of three-terminal local and non-local transport measurements
performed while varying the magnetic field, semiconductor electron density, and
junction transparencies. Passing the protocol indicates a high probability of
detection of a topological phase hosting Majorana zero modes. Our experimental
results are consistent with a quantum phase transition into a topological
superconducting phase that extends over several hundred millitesla in magnetic
field and several millivolts in gate voltage, corresponding to approximately
one hundred micro-electron-volts in Zeeman energy and chemical potential in the
semiconducting wire. These regions feature a closing and re-opening of the bulk
gap, with simultaneous zero-bias conductance peaks at {\it both} ends of the
devices that withstand changes in the junction transparencies. The measured
maximum topological gaps in our devices are 20-eV. This demonstration
is a prerequisite for experiments involving fusion and braiding of Majorana
zero modes.Comment: Fixed typos. Fig. 3 is now readable by Adobe Reade