374 research outputs found
Photon Assisted Tunneling of Zero Modes in a Majorana Wire
Hybrid nanowires with proximity-induced superconductivity in the topological
regime host Majorana zero modes (MZMs) at their ends, and networks of such
structures can produce topologically protected qubits. In a double-island
geometry where each segment hosts a pair of MZMs, inter-pair coupling mixes the
charge parity of the islands and opens an energy gap between the even and odd
charge states at the inter-island charge degeneracy. Here, we report on the
spectroscopic measurement of such an energy gap in an InAs/Al double-island
device by tracking the position of the microwave-induced quasiparticle (qp)
transitions using a radio-frequency (rf) charge sensor. In zero magnetic field,
photon assisted tunneling (PAT) of Cooper pairs gives rise to resonant lines in
the 2e-2e periodic charge stability diagram. In the presence of a magnetic
field aligned along the nanowire, resonance lines are observed parallel to the
inter-island charge degeneracy of the 1e-1e periodic charge stability diagram,
where the 1e periodicity results from a zero-energy sub-gap state that emerges
in magnetic field. Resonant lines in the charge stability diagram indicate
coherent photon assisted tunneling of single-electron states, changing the
parity of the two islands. The dependence of resonant frequency on detuning
indicates a sizable (GHz-scale) hybridization of zero modes across the junction
separating islands
Spin-degeneracy breaking and parity transitions in three-terminal Josephson junctions
Harnessing spin and parity degrees of freedom is of fundamental importance
for the realization of emergent quantum devices. Nanostructures embedded in
superconductor--semiconductor hybrid materials offer novel and yet unexplored
routes for addressing and manipulating fermionic modes. Here we
spectroscopically probe the two-dimensional band structure of Andreev bound
states in a phase-controlled hybrid three-terminal Josephson junction. Andreev
bands reveal spin-degeneracy breaking, with level splitting in excess of 9 GHz,
and zero-energy crossings associated to ground state fermion parity
transitions, in agreement with theoretical predictions. Both effects occur
without the need of external magnetic fields or sizable charging energies and
are tuned locally by controlling superconducting phase differences. Our results
highlight the potential of multiterminal hybrid devices for engineering quantum
states
Zeeman and Orbital Driven Phase Transitions in Planar Josephson Junctions
We perform supercurrent and tunneling spectroscopy measurements on
gate-tunable InAs/Al Josephson junctions (JJs) in an in-plane magnetic field,
and report on phase shifts in the current-phase relation measured with respect
to an absolute phase reference. The impact of orbital effects is investigated
by studying multiple devices with different superconducting lead sizes. At low
fields, we observe gate-dependent phase shifts of up to
which are consistent with a Zeeman field coupling to highly-transmissive
Andreev bound states via Rashba spin-orbit interaction. A distinct phase shift
emerges at larger fields, concomitant with a switching current minimum and the
closing and reopening of the superconducting gap. These signatures of an
induced phase transition, which might resemble a topological transition, scale
with the superconducting lead size, demonstrating the crucial role of orbital
effects. Our results elucidate the interplay of Zeeman, spin-orbit and orbital
effects in InAs/Al JJs, giving new understanding to phase transitions in hybrid
JJs and their applications in quantum computing and superconducting
electronics
Suppressed Charge Dispersion via Resonant Tunneling in a Single-Channel Transmon
We demonstrate strong suppression of charge dispersion in a
semiconductor-based transmon qubit across Josephson resonances associated with
a quantum dot in the junction. On resonance, dispersion is drastically reduced
compared to conventional transmons with corresponding Josephson and charging
energies. We develop a model of qubit dispersion for a single-channel
resonance, which is in quantitative agreement with experimental data
Flip-chip-based fast inductive parity readout of a planar superconducting island
Properties of superconducting devices depend sensitively on the parity (even
or odd) of the quasiparticles they contain. Encoding quantum information in the
parity degree of freedom is central in several emerging solid-state qubit
architectures. Yet, accurate, non-destructive, and time-resolved parity
measurement is a challenging and long-standing issue. Here we report on control
and real-time parity measurement in a superconducting island embedded in a
superconducting loop and realized in a hybrid two-dimensional heterostructure
using a microwave resonator. Device and readout resonator are located on
separate chips, connected via flip-chip bonding, and couple inductively through
vacuum. The superconducting resonator detects the parity-dependent circuit
inductance, allowing for fast and non-destructive parity readout. We resolved
even and odd parity states with signal-to-noise ratio SNR with an
integration time of s and detection fidelity exceeding 98%. Real-time
parity measurement showed state lifetime extending into millisecond range. Our
approach will lead to better understanding of coherence-limiting mechanisms in
superconducting quantum hardware and provide novel readout schemes for hybrid
qubits
Microwave-induced conductance replicas in hybrid Josephson junctions without Floquet-Andreev states
Light-matter interaction enables engineering of non-equilibrium quantum
systems. In condensed matter, spatially and temporally cyclic Hamiltonians are
expected to generate energy-periodic Floquet states, with properties
inaccessible at thermal equilibrium. A recent work explored the tunnelling
conductance of a planar Josephson junction under microwave irradiation, and
interpreted replicas of conductance features as evidence of steady
Floquet-Andreev states. Here we realise a similar device in a hybrid
superconducting-semiconducting heterostructure, which utilises a tunnelling
probe with gate-tunable transparency and allows simultaneous measurements of
Andreev spectrum and current-phase relation of the planar Josephson junction.
We show that, in our devices, spectral replicas in sub-gap conductance emerging
under microwave irradiation are caused by photon assisted tunnelling of
electrons into Andreev states. The current-phase relation under microwave
irradiation is also explained by the interaction of Andreev states with
microwave photons, without the need to invoke Floquet states. The techniques
outlined in this study establish a baseline to distinguish photon assisted
tunnelling from Floquet-Andreev states in mesoscopic devices, a crucial
development towards understanding light-matter coupling in hybrid
nanostructures
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Precise measurement of the W-boson mass with the CDF II detector
We have measured the W-boson mass MW using data corresponding to 2.2/fb of
integrated luminosity collected in proton-antiproton collisions at 1.96 TeV
with the CDF II detector at the Fermilab Tevatron collider. Samples consisting
of 470126 W->enu candidates and 624708 W->munu candidates yield the measurement
MW = 80387 +- 12 (stat) +- 15 (syst) = 80387 +- 19 MeV. This is the most
precise measurement of the W-boson mass to date and significantly exceeds the
precision of all previous measurements combined
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