82 research outputs found
Comparison of coherence times in three dc SQUID phase qubits
We report measurements of spectroscopic linewidth and Rabi oscillations in
three thin-film dc SQUID phase qubits. One device had a single-turn Al loop,
the second had a 6-turn Nb loop, and the third was a first order gradiometer
formed from 6-turn wound and counter-wound Nb coils to provide isolation from
spatially uniform flux noise. In the 6 - 7.2 GHz range, the spectroscopic
coherence times for the gradiometer varied from 4 ns to 8 ns, about the same as
for the other devices (4 to 10 ns). The time constant for decay of Rabi
oscillations was significantly longer in the single-turn Al device (20 to 30
ns) than either of the Nb devices (10 to 15 ns). These results imply that
spatially uniform flux noise is not the main source of decoherence or
inhomogenous broadening in these devices.Comment: 4 pages, 5 figures, accepted for publication in IEEE Trans. Appl.
Supercon
Magnetic sensors-a review and recent technologies
Magnetic field sensors are an integral part of many industrial and biomedical applications, and their utilization continues to grow at a high rate. The development is driven both by new use cases and demand like internet of things as well as by new technologies and capabilities like flexible and stretchable devices. Magnetic field sensors exploit different physical principles for their operation, resulting in different specifications with respect to sensitivity, linearity, field range, power consumption, costs etc. In this review, we will focus on solid state magnetic field sensors that enable miniaturization and are suitable for integrated approaches to satisfy the needs of growing application areas like biosensors, ubiquitous sensor networks, wearables, smart things etc. Such applications require a high sensitivity, low power consumption, flexible substrates and miniaturization. Hence, the sensor types covered in this review are Hall Effect, Giant Magnetoresistance, Tunnel Magnetoresistance, Anisotropic Magnetoresistance and Giant Magnetoimpedance
Entanglement in a quantum annealing processor
Entanglement lies at the core of quantum algorithms designed to solve
problems that are intractable by classical approaches. One such algorithm,
quantum annealing (QA), provides a promising path to a practical quantum
processor. We have built a series of scalable QA processors consisting of
networks of manufactured interacting spins (qubits). Here, we use qubit
tunneling spectroscopy to measure the energy eigenspectrum of two- and
eight-qubit systems within one such processor, demonstrating quantum coherence
in these systems. We present experimental evidence that, during a critical
portion of QA, the qubits become entangled and that entanglement persists even
as these systems reach equilibrium with a thermal environment. Our results
provide an encouraging sign that QA is a viable technology for large-scale
quantum computing.Comment: 13 pages, 8 figures, contact corresponding author for Supplementary
Informatio
Multi-level Spectroscopy of Two-Level Systems Coupled to a dc SQUID Phase Qubit
We report spectroscopic measurements of discrete two-level systems (TLSs)
coupled to a dc SQUID phase qubit with a 16 \mu\m2 area Al/AlOx/Al junction.
Applying microwaves in the 10 GHz to 11 GHz range, we found eight avoided level
crossings with splitting sizes from 10 MHz to 200 MHz and spectroscopic
lifetimes from 4 ns to 160 ns. Assuming the transitions are from the ground
state of the composite system to an excited state of the qubit or an excited
state of one of the TLS states, we fit the location and spectral width to get
the energy levels, splitting sizes and spectroscopic coherence times of the
phase qubit and TLSs. The distribution of splittings is consistent with
non-interacting individual charged ions tunneling between random locations in
the tunnel barrier and the distribution of lifetimes is consistent with the
AlOx in the junction barrier having a frequency-independent loss tangent. To
check that the charge of each TLS couples independently to the voltage across
the junction, we also measured the spectrum in the 20-22 GHz range and found
tilted avoided level crossings due to the second excited state of the junction
and states in which both the junction and a TLS were excited
Graphene on quartz modified with rhenium oxide as a semitransparent electrode for organic electronic
Our research shows that commercially available graphene on quartz modified
with rhenium oxide meets the requirements for its use as a conductive and
transparent anode in optoelectronic devices. The cluster growth of rhenium
oxide enables an increase in the work function of graphene by 1.3 eV up to 5.2
eV, which guarantees an appropriate adjustment to the energy levels of the
organic semiconductors used in OLED devices.Comment: 8 pages, 3 figure
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