5 research outputs found
Interferometric Single-Shot Parity Measurement in an InAs-Al Hybrid Device
The fusion of non-Abelian anyons or topological defects is a fundamental
operation in measurement-only topological quantum computation. In topological
superconductors, this operation amounts to a determination of the shared
fermion parity of Majorana zero modes. As a step towards this, we implement a
single-shot interferometric measurement of fermion parity in indium
arsenide-aluminum heterostructures with a gate-defined nanowire. The
interferometer is formed by tunnel-coupling the proximitized nanowire to
quantum dots. The nanowire causes a state-dependent shift of these quantum
dots' quantum capacitance of up to 1 fF. Our quantum capacitance measurements
show flux h/2e-periodic bimodality with a signal-to-noise ratio of 1 in 3.7
s at optimal flux values. From the time traces of the quantum capacitance
measurements, we extract a dwell time in the two associated states that is
longer than 1 ms at in-plane magnetic fields of approximately 2 T. These
results are consistent with a measurement of the fermion parity encoded in a
pair of Majorana zero modes that are separated by approximately 3 m and
subjected to a low rate of poisoning by non-equilibrium quasiparticles. The
large capacitance shift and long poisoning time enable a parity measurement
error probability of 1%.Comment: Added data on a second measurement of device A and a measurement of
device B, expanded discussion of a trivial scenario. Refs added, author list
update
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