Superconducting qubits are employed for the practical
implementation of scalable quantum information processors. Fault-tolerant
quantum computation schemes using superconducting qubits is under intensive
study. Among the various kinds of superconducting qubits, flux qubits have a
significant advantage in that they can be made insensitive to randomly
fluctuating charges in the substrate. Here, the characterization results of a
double-loop four-Josephson-junction flux qubit is reported. By varying the
magnetic flux in one of the two loops, the energy gap at the classical
degeneracy point can be controlled in situ. The basic operation of the system
is illustrated by the appearance of a qubit step on a two-dimensional flux map.
The energy gap can be indirectly estimated from the shape of the qubit step.
The dependence of the shape of the qubit step on the control flux, which is
analyzed in terms of the step height and maximum slope, is in good agreement
with the simulation results, thereby implicitly indicating that the energy gap
is varied from almost zero, less than the thermal energy, to a value higher
than 50 GHz. Spectroscopic measurements directly demonstrated the
controllability of the energy gap. In addition, doublet splitting due to
intercell tunneling was observed for the first time.
Author(s)
Details
Y.
Shimazu
Department of Physics, Yokohama National University, Yokohama
240-8501, Japan, Semiconductor and Quantum Integrated Electronics Research
Center, Institute of Advanced Research, Yokohama National University, Yokohama
240-8501, Japan and Quantum Information Research Center, Institute of Advanced
Sciences, Yokohama National University, Yokohama 240-8501, Japan.
Y.
Saito
Department of Physics, Yokohama National University, Yokohama
240-8501, Japan.
Z. Wada
Department of Physics, Yokohama National University, Yokohama
240-8501, Japan.
Please see the book here:- https://doi.org/10.9734/bpi/crpps/v3/1313
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