14 research outputs found
Observation of the 4-periodic Josephson effect in indium arsenide nanowires
Quantum computation by non-Abelian Majorana zero modes (MZMs) offers an
approach to achieve fault tolerance by encoding quantum information in the
non-local charge parity states of semiconductor nanowire networks in the
topological superconductor regime. Thus far, experimental studies of MZMs
chiefly relied on single electron tunneling measurements which leads to
decoherence of the quantum information stored in the MZM. As a next step
towards topological quantum computation, charge parity conserving experiments
based on the Josephson effect are required, which can also help exclude
suggested non-topological origins of the zero bias conductance anomaly. Here we
report the direct measurement of the Josephson radiation frequency in InAs
nanowires with epitaxial aluminium shells. For the first time, we observe the
-periodic Josephson effect above a magnetic field of mT,
consistent with the estimated and measured topological phase transition of
similar devices.Comment: Published version. Supplementary Information is available as
ancillary file, raw data and calculations can be downloaded from
http://dx.doi.org/10.4121/uuid:1f936840-5bc2-40ca-8c32-1797c12cacb
Observation of 2e-periodic Supercurrents in Nanowire Single-Cooper-Pair Transistors
Parity control of superconducting islands hosting Majorana zero modes (MZMs)
is required to operate topological qubits made from proximitized semiconductor
nanowires. We, therefore, study parity effects in hybrid InAs-Al
single-Cooper-pair transistors (SCPTs) as a first step. In particular, we
investigate the gate-charge supercurrent modulation and observe a consistent
2-periodic pattern indicating a general lack of low-energy subgap states in
these nanowires at zero magnetic field. In a parallel magnetic field, an
even-odd pattern develops with a gate-charge spacing that oscillates as a
function of field demonstrating that the modulation pattern is sensitive to the
presence of a single subgap state. In addition, we find that the parity
lifetime of the SCPT decreases exponentially with magnetic field as the subgap
state approaches zero energy. Our work highlights the important role that
intentional quasiparticle traps and superconducting gap engineering would play
in topological qubits that require quenching of the island charge dispersion.Comment: 8 pages, 4 figures, supplemental material included as ancillary fil
Microwave susceptibility observation of interacting many-body Andreev states
Electrostatic charging affects the many-body spectrum of Andreev states, yet
its influence on their microwave properties has not been elucidated. We
developed a circuit quantum electrodynamics probe that, in addition to
transition spectroscopy, measures the microwave susceptibility of different
states of a semiconductor nanowire weak link with a single dominant
(spin-degenerate) Andreev level. We found that the microwave susceptibility
does not exhibit a particle-hole symmetry, which we qualitatively explain as an
influence of Coulomb interaction. Moreover, our state-selective measurement
reveals a large, -phase shifted contribution to the response common to all
many-body states which can be interpreted as arising from a phase-dependent
continuum in the superconducting density of states
Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces
We investigate the transport properties of a ferromagnet-superconductor
interface within the framework of a modified three-dimensional
Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge
inhomogeneity forms via two unique transport mechanisms, namely, evanescent
Andreev reflection and evanescent quasiparticle transmission. Furthermore, we
take into account the influence of charge inhomogeneity on the interfacial
barrier potential and calculate the conductance as a function of bias voltage.
Point-contact Andreev reflection (PCAR) spectra often show dip structures,
large zero-bias conductance enhancement, and additional zero-bias conductance
peak. Our results indicate that transport-induced charge inhomogeneity could be
a source of all these anomalous characteristics of the PCAR spectra.Comment: 9 pages, 6 figure
Formation and electronic properties of InSb nanocrosses
Signatures of Majorana fermions have recently been reported from measurements on hybrid superconductor–semiconductor nanowire devices. Majorana fermions are predicted to obey special quantum statistics, known as non-Abelian statistics. To probe this requires an exchange operation, in which two Majorana fermions are moved around one another, which requires at least a simple network of nanowires. Here, we report on the synthesis and electrical characterization of crosses of InSb nanowires. The InSb wires grow horizontally on flexible vertical stems, allowing nearby wires to meet and merge. In this way, near-planar single-crystalline nanocrosses are created, which can be measured by four electrical contacts. Our transport measurements show that the favourable properties of the InSb nanowire devices—high carrier mobility and the ability to induce superconductivity—are preserved in the cross devices. Our nanocrosses thus represent a promising system for the exchange of Majorana fermions
Formation and electronic properties of InSb nanocrosses
Signatures of Majorana fermions have recently been reported from measurements on hybrid superconductor–semiconductor nanowire devices. Majorana fermions are predicted to obey special quantum statistics, known as non-Abelian statistics. To probe this requires an exchange operation, in which two Majorana fermions are moved around one another, which requires at least a simple network of nanowires. Here, we report on the synthesis and electrical characterization of crosses of InSb nanowires. The InSb wires grow horizontally on flexible vertical stems, allowing nearby wires to meet and merge. In this way, near-planar single-crystalline nanocrosses are created, which can be measured by four electrical contacts. Our transport measurements show that the favourable properties of the InSb nanowire devices—high carrier mobility and the ability to induce superconductivity—are preserved in the cross devices. Our nanocrosses thus represent a promising system for the exchange of Majorana fermions
Formation and electronic properties of InSb nanocrosses
Signatures of Majorana fermions have recently been reported from measurements on hybrid superconductor–semiconductor nanowire devices. Majorana fermions are predicted to obey special quantum statistics, known as non-Abelian statistics. To probe this requires an exchange operation, in which two Majorana fermions are moved around one another, which requires at least a simple network of nanowires. Here, we report on the synthesis and electrical characterization of crosses of InSb nanowires. The InSb wires grow horizontally on flexible vertical stems, allowing nearby wires to meet and merge. In this way, near-planar single-crystalline nanocrosses are created, which can be measured by four electrical contacts. Our transport measurements show that the favourable properties of the InSb nanowire devices—high carrier mobility and the ability to induce superconductivity—are preserved in the cross devices. Our nanocrosses thus represent a promising system for the exchange of Majorana fermions
Microwave spectroscopy of spinful Andreev bound states in ballistic semiconductor Josephson junctions
The superconducting proximity effect in semiconductor nanowires has recently enabled the study of new superconducting architectures, such as gate-tunable superconducting qubits and multiterminal Josephson junctions. As opposed to their metallic counterparts, the electron density in semiconductor nanosystems is tunable by external electrostatic gates, providing a highly scalable and in situ variation of the device properties. In addition, semiconductors with large g-factor and spin-orbit coupling have been shown to give rise to exotic phenomena in superconductivity, such as †0 Josephson junctions and the emergence of Majorana bound states. Here, we report microwave spectroscopy measurements that directly reveal the presence of Andreev bound states (ABS) in ballistic semiconductor channels. We show that the measured ABS spectra are the result of transport channels with gate-tunable, high transmission probabilities up to 0.9, which is required for gate-tunable Andreev qubits and beneficial for braiding schemes of Majorana states. For the first time, we detect excitations of a spin-split pair of ABS and observe symmetry-broken ABS, a direct consequence of the spin-orbit coupling in the semiconductor.QRD/Kouwenhoven LabQuTechQRD/Geresdi La