8 research outputs found
Fast switching current detection at low critical currents
A pulse-and-hold technique is used to measure the switching of small critical
current Josephson junctions. This technique allows one to achieve a good binary
detection and therefore measure switching probabilities. The technique
overcomes limitations on simple square pulses and allows for the measurement of
junctions with critical currents of the order of 10nA with bias pulses of the
order of 100ns. A correlation analysis of the switching events is performed to
show how the switching probability depends on the wait time between repeated
bias pulses.Comment: Changed abstract Added reference 1
Phase-Charge Duality of a Josephson junction in a fluctuating electromagnetic environment
We have measured the current-voltage characteristics of a single Josephson
junction placed in a high impedance environment. The transfer of Cooper pairs
through the junction is governed by overdamped quasicharge dynamics, leading to
Coulomb blockade and Bloch oscillations. Exact duality exists to the standard
overdamped phase dynamics of a Josephson junction, resulting in a dual shape of
the current-voltage characteristic, with current and voltage changing roles. We
demonstrate this duality with experiments which allow for a quantitative
comparison with a theory that includes the effect of fluctuations due to finite
temperature of the electromagnetic environment
Superconducting Nanocircuits for Topologically Protected Qubits
For successful realization of a quantum computer, its building blocks
(qubits) should be simultaneously scalable and sufficiently protected from
environmental noise. Recently, a novel approach to the protection of
superconducting qubits has been proposed. The idea is to prevent errors at the
"hardware" level, by building a fault-free (topologically protected) logical
qubit from "faulty" physical qubits with properly engineered interactions
between them. It has been predicted that the decoupling of a protected logical
qubit from local noises would grow exponentially with the number of physical
qubits. Here we report on the proof-of-concept experiments with a prototype
device which consists of twelve physical qubits made of nanoscale Josephson
junctions. We observed that due to properly tuned quantum fluctuations, this
qubit is protected against magnetic flux variations well beyond linear order,
in agreement with theoretical predictions. These results demonstrate the
feasibility of topologically protected superconducting qubits.Comment: 25 pages, 5 figure
Coulomb blockade of Cooper pair tunneling and parity effects in the Cooper pair transistor
Measurement of the effect of quantum phase-slips in a Josephson Junction chain
5 pages, 5 figuresInternational audienceWe investigate experimentally the physics of quantum phase slips in one-dimensional Josephson Junction chains. These quantum phase-slips are induced by quantum phase fluctuations occurring on single junctions of the chain. In our experiment we can tune the strength of these fluctuations as each chain junction is realized in form of a SQUID leading to tunable Josephson coupling. We determine the ground state of the chain via switching current measurements of the chain shunted by a large Josephson junction. Our results can be well fitted with a tight binding Hamiltonian taking into account quantum phase-slips