20 research outputs found
Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs)
generates a nonlinear inductance that is used extensively in quantum
information processors based on superconducting circuits, from setting qubit
transition frequencies and interqubit coupling strengths, to the gain of
parametric amplifiers for quantum-limited readout. The inductance is either set
by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by
parallelizing multiple JJs in superconducting quantum interference devices
(SQUIDs) with local current-biased flux lines. JJs based on
superconductor-semiconductor hybrids represent a tantalizing all-electric
alternative. The gatemon is a recently developed transmon variant which employs
locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control.
Here, we go beyond proof-of-concept and demonstrate that semiconducting
channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a
suitable platform for building a scalable gatemon-based quantum computer. We
show 2DEG gatemons meet the requirements by performing voltage-controlled
single qubit rotations and two-qubit swap operations. We measure qubit
coherence times up to ~2 us, limited by dielectric loss in the 2DEG host
substrate
Evidence of topological superconductivity in planar Josephson junctions
Majorana zero modes are quasiparticle states localized at the boundaries of
topological superconductors that are expected to be ideal building blocks for
fault-tolerant quantum computing. Several observations of zero-bias conductance
peaks measured in tunneling spectroscopy above a critical magnetic field have
been reported as experimental indications of Majorana zero modes in
superconductor/semiconductor nanowires. On the other hand, two dimensional
systems offer the alternative approach to confine Ma jorana channels within
planar Josephson junctions, in which the phase difference {\phi} between the
superconducting leads represents an additional tuning knob predicted to drive
the system into the topological phase at lower magnetic fields. Here, we report
the observation of phase-dependent zero-bias conductance peaks measured by
tunneling spectroscopy at the end of Josephson junctions realized on a InAs/Al
heterostructure. Biasing the junction to {\phi} ~ {\pi} significantly reduces
the critical field at which the zero-bias peak appears, with respect to {\phi}
= 0. The phase and magnetic field dependence of the zero-energy states is
consistent with a model of Majorana zero modes in finite-size Josephson
junctions. Besides providing experimental evidence of phase-tuned topological
superconductivity, our devices are compatible with superconducting quantum
electrodynamics architectures and scalable to complex geometries needed for
topological quantum computing.Comment: main text and extended dat
Link between supercurrent diode and anomalous Josephson effect revealed by gate-controlled interferometry
In Josephson diodes the asymmetry between positive and negative current
branch of the current-phase relation leads to a polarity-dependent critical
current and Josephson inductance. The supercurrent nonreciprocity can be
described as a consequence of the anomalous Josephson effect -- a
-shift of the current-phase relation -- in multichannel ballistic
junctions with strong spin-orbit interaction. In this work, we simultaneously
investigate -shift and supercurrent diode efficiency on the same
Josephson junction by means of a superconducting quantum interferometer. By
electrostatic gating, we reveal a direct link between -shift and
diode effect. Our findings show that the supercurrent diode effect mainly
results from magnetochiral anisotropy induced by spin-orbit interaction in
combination with a Zeeman field.Comment: 15 pages, 8 figure
Sign reversal of the AC and DC supercurrent diode effect and 0--like transitions in ballistic Josephson junctions
The recent discovery of intrinsic supercurrent diode effect, and its prompt
observation in a rich variety of systems, has shown that nonreciprocal
supercurrents naturally emerge when both space- and time-inversion symmetries
are broken. In Josephson junctions, nonreciprocal supercurrent can be
conveniently described in terms of spin-split Andreev states. Here, we
demonstrate a sign reversal of the supercurrent diode effect, in both its AC
and DC manifestations. In particular, the AC diode effect -- i.e., the
asymmetry of the Josephson inductance as a function of the supercurrent --
allows us to probe the current-phase relation near equilibrium. Using a minimal
theoretical model, we can then link the sign reversal of the AC diode effect to
the so-called 0--like transition, a predicted, but still elusive feature
of multi-channel junctions. Our results demonstrate the potential of inductance
measurements as sensitive probes of the fundamental properties of
unconventional Josephson junctions.Comment: 13 pages, 6 figure
Effect of Rashba and Dresselhaus spin-orbit coupling on supercurrent rectification and magnetochiral anisotropy of ballistic Josephson junctions
Simultaneous breaking of inversion- and time-reversal symmetry in Josephson junction leads to a possible violation of the I(ϕ) = −I(−ϕ) equality for the current-phase relation. This is known as anomalous Josephson effect and it produces a phase shift ϕ0 in sinusoidal current-phase relations. In ballistic Josephson junctions with non-sinusoidal current phase relation the observed phenomenology is much richer, including the supercurrent diode effect and the magnetochiral anisotropy of Josephson inductance. In this work, we present measurements of both effects on arrays of Josephson junctions defined on epitaxial Al/InAs heterostructures. We show that the orientation of the current with respect to the lattice affects the magnetochiral anisotropy, possibly as the result of a finite Dresselhaus component. In addition, we show that the two-fold symmetry of the Josephson inductance reflects in the activation energy for phase slips
Josephson Inductance as a Probe for Highly Ballistic Semiconductor Superconductor Weak Links
We present simultaneous measurements of Josephson inductance and dc transport characteristics of ballistic Josephson junctions based upon an epitaxial Al-InAs heterostructure. The Josephson inductance at finite current bias directly reveals the current-phase relation. The proximity-induced gap, the critical current and the average value of the transparency τ are extracted without need for phase bias, demonstrating, e.g., a near-unity value of τ=0.94. Our method allows us to probe the devices deeply in the nondissipative regime, where ordinary transport measurements are featureless. In perpendicular magnetic field the junctions show a nearly perfect Fraunhofer pattern of the critical current, which is insensitive to the value of ¯τ. In contrast, the signature of supercurrent interference in the inductance turns out to be extremely sensitive to τ
Data for "Phase engineering of anomalous Josephson effect derived from Andreev molecules"
<p>An Igor file stores source data for the figures in the main manuscript and the supplementary figures. The raw data contain the I-V traces to evaluate the switching currents. The waves in the Igor file are obtained from the raw data with the same names as the waves.</p>
Data archive for the article: "Josephson inductance as a probe for highly ballistic semiconductor-superconductor weak links"
Data for the article "Josephson inductance as a probe for highly ballistic semiconductor-superconductor weak links", loaded on arXiv (arXiv:2007.08371) and submitted for publication
Data archive of "Anisotropic vortex squeezing in synthetic Rashba superconductors: a manifestation of Lifshitz invariants"
Data archive of the article "Anisotropic vortex squeezing in synthetic Rashba superconductors: a manifestation of Lifshitz invariants" - preprint available at https://arxiv.org/abs/2201.0251
Engineering of anomalous Josephson effect in coherently coupled Josephson junctions
A Josephson junction (JJ) is a key device in the development of
superconducting circuits, wherein a supercurrent in the JJ is controlled by the
phase difference between the two superconducting electrodes. Recently, it has
been shown that the JJ current is nonlocally controlled by the phase difference
of another nearby JJ via coherent coupling. Here, we use the nonlocal control
to engineer the anomalous Josephson effect. We observe that a supercurrent is
produced by the nonlocal phase control even without any local phase difference,
using a quantum interference device. The nonlocal phase control simultaneously
generates an offset of a local phase difference giving the JJ ground state.
These results provide novel concepts for engineering superconducting devices
such as phase batteries and dissipationless rectifiers.Comment: 15 pages and 4 figures for the main manuscript, 8 pages and 6 figures
for the supplementary informatio