5,022 research outputs found
Cooling of a Micro-mechanical Resonator by the Back-action of Lorentz Force
Using a semi-classical approach, we describe an on-chip cooling protocol for
a micro-mechanical resonator by employing a superconducting flux qubit. A
Lorentz force, generated by the passive back-action of the resonator's
displacement, can cool down the thermal motion of the mechanical resonator by
applying an appropriate microwave drive to the qubit. We show that this onchip
cooling protocol, with well-controlled cooling power and a tunable response
time of passive back-action, can be highly efficient. With feasible
experimental parameters, the effective mode temperature of a resonator could be
cooled down by several orders of magnitude.Comment: 10 pages, 4 figure
Coherent Operation of a Gap-tunable Flux Qubit
We replace the Josephson junction defining a three-junction flux qubit's
properties with a tunable direct current superconducting quantum interference
devices (DC-SQUID) in order to tune the qubit gap during the experiment. We
observe different gaps as a function of the external magnetic pre-biasing field
and the local magnetic field through the DC-SQUID controlled by high-bandwidth
on chip control lines. The persistent current and gap behavior correspond to
numerical simulation results. We set the sensitivity of the gap on the control
lines during the sample design stage. With a tuning range of several GHz on a
qubit dynamics timescale, we observe coherent system dynamics at the degeneracy
point.Comment: 3 pages, 4 figure
Long-range and selective coupler for superconducting flux qubits
We propose a qubit-qubit coupling scheme for superconducting flux quantum
bits (qubits), where a quantized Josephson junction resonator and microwave
irradiation are utilized. The junction is used as a tunable inductance
controlled by changing the bias current flowing through the junction, and thus
the circuit works as a tunable resonator. This enables us to make any qubits
interact with the resonator. Entanglement between two of many qubits whose
level splittings satisfy some conditions, is formed by microwave irradiation
causing a two-photon Rabi oscillation. Since the size of the resonator can be
as large as sub-millimeters and qubits interact with it via mutual inductance,
our scheme makes it possible to construct a quantum gate involving remote
qubitsComment: 8 pages, 4 figure
Quantum Zeno effect with a superconducting qubit
Detailed schemes are investigated for experimental verification of Quantum
Zeno effect with a superconducting qubit. A superconducting qubit is affected
by a dephasing noise whose spectrum is 1/f, and so the decay process of a
superconducting qubit shows a naturally non-exponential behavior due to an
infinite correlation time of 1/f noise. Since projective measurements can
easily influence the decay dynamics having such non-exponential feature, a
superconducting qubit is a promising system to observe Quantum Zeno effect. We
have studied how a sequence of projective measurements can change the dephasing
process and also we have suggested experimental ways to observe Quantum Zeno
effect with a superconducting qubit. It would be possible to demonstrate our
prediction in the current technology
Influence of deflocculant on the isoelectric point of refractory powders: Considerations on the action of deflocculant
Isoelectric point changes in suspensions of refractory materials vis-a-vis the role of deflocculants used in monolithic refractories were investigated by considering the mineral compositions and adsorbed ions in four kinds of clay. Three types of curves represented the relation between the isoelectric point and the deflocculant. The surface charge of clay particles in the suspensions became negative as a result of the deflocculant, since the isoelectric point of suspensions decreased as the deflocculant was added. The isoelectric point changes of calcined alumina were also compared with those of the clays, and a similar phenomenon was observed, except that the deflocculant dispersed the calcined alumina better than it did the clays. A simple model was used to analyze the results
A superconducting qubit as a quantum transformer routing entanglement between a microscopic quantum memory and a macroscopic resonator
We demonstrate experimentally the creation and measurement of an entangled
state between a microscopic two level system and a macroscopic superconducting
resonator where their indirect interaction is mediated by an artificial atom, a
superconducting persistent current qubit (PCQB). We show that the microscopic
two level system, formed by a defect in an oxide layer, exhibits an order of
magnitude longer dephasing time than the PCQB, while the dephasing time of the
entangled states between the microscopic two level system and macroscopic
superconducting resonator is significantly longer than the dephasing time in
the persistent current qubits. This demonstrates the possibility that a qubit
of moderate coherence properties can be used in practice to address low
decoherence quantum memories by connecting them to macroscopic circuit QED
quantum buses, leading future important implications for quantum information
processing tasks.Comment: 4 figure
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