24 research outputs found
Noise properties of a Josephson parametric oscillator
We perform the noise spectroscopy of a Josephson parametric oscillator (JPO)
by implementing a microwave homodyne interferometric measurement scheme. We
observe the fluctuations in the self-oscillating output field of the JPO for a
long 10 s time interval in a single shot measurement and characterize the phase
and amplitude noise. Furthermore, we investigate the effects of the pump
strength on the output noise power spectra of the JPO. We found strong
fluctuations in the phase with a characteristics in the phase noise
power spectrum, which is suppressed by increasing the pump strength
Ultrastrong tunable coupler between superconducting LC resonators
We investigate the ultrastrong tunable coupler for coupling of
superconducting resonators. Obtained coupling constant exceeds 1 GHz, and the
wide range tunability is achieved both antiferromagnetics and ferromagnetics
from MHz to 604 MHz. The ultrastrong coupler is composed of rf-SQUID
and dc-SQUID as tunable junctions, which connected to resonators via shared
aluminum thin film meander lines enabling such a huge coupling constant. The
spectrum of the coupler obviously shows the breaking of the rotating wave
approximation, and our circuit model treating the Josephson junction as a
tunable inductance reproduces the experimental results well. The ultrastrong
coupler is expected to be utilized in quantum annealing circuits and/or NISQ
devices with dense connections between qubits.Comment: 12pages, 7 figure
One photon simultaneously excites two atoms in a ultrastrongly coupled light-matter system
We experimentally investigate a superconducting circuit composed of two flux
qubits ultrastrongly coupled to a common resonator. Owing to the large
anharmonicity of the flux qubits, the system can be correctly described by a
generalized Dicke Hamiltonian containing spin-spin interaction terms. In the
experimentally measured spectrum, an avoided level crossing provides evidence
of the exotic interaction that allows the \textit{simultaneous} excitation of
\textit{two} artificial atoms by absorbing \textit{one} photon from the
resonator. This multi-atom ultrastrongly coupled system opens the door to
studying nonlinear optics where the number of excitations is not conserved.
This enables novel processes for quantum-information processing tasks on a
chip.Comment: 11pages,5gigure
Active Initialization Experiment of Superconducting Qubit Using Quantum-circuit Refrigerator
The initialization of superconducting qubits is one of the essential
techniques for the realization of quantum computation. In previous research,
initialization above 99\% fidelity has been achieved at 280 ns. Here, we
demonstrate the rapid initialization of a superconducting qubit with a
quantum-circuit refrigerator (QCR). Photon-assisted tunneling of quasiparticles
in the QCR can temporally increase the relaxation time of photons inside the
resonator and helps release energy from the qubit to the environment.
Experiments using this protocol have shown that 99\% of initialization time is
reduced to 180 ns. This initialization time depends strongly on the relaxation
rate of the resonator, and faster initialization is possible by reducing the
resistance of the QCR, which limits the ON/OFF ratio, and by strengthening the
coupling between the QCR and the resonator