27 research outputs found
Single microwave-photon detector using an artificial -type three-level system
Single photon detection is a requisite technique in quantum-optics
experiments in both the optical and the microwave domains. However, the energy
of microwave quanta are four to five orders of magnitude less than their
optical counterpart, making the efficient detection of single microwave photons
extremely challenging. Here, we demonstrate the detection of a single microwave
photon propagating through a waveguide. The detector is implemented with an
"impedance-matched" artificial system comprising the dressed states
of a driven superconducting qubit coupled to a microwave resonator. We attain a
single-photon detection efficiency of with a reset time of
~ns. This detector can be exploited for various applications in
quantum sensing, quantum communication and quantum information processing.Comment: 5 pages (4 figures) + 4 pages (5 figures
Power-dependent internal loss in Josephson bifurcation amplifiers
We have studied nonlinear superconducting resonators: lambda/2
coplanar-waveguide (CPW) resonators with Josephson junctions (JJs) placed in
the middle and lambda/4 CPW resonators terminated by JJs, which can be used for
the qubit readout as "bifurcation amplifiers." The nonlinearity of the
resonators arises from the Josephson junctions, and because of the
nonlinearity, the resonators with appropriate parameters are expected to show a
hysteretic response to the frequency sweep, or "bifurcation," when they are
driven with a sufficiently large power. We designed and fabricated resonators
whose resonant frequencies were around 10 GHz. We characterized the resonators
at low temperatures, T<0.05 K, and confirmed that they indeed exhibited
hysteresis. The sizes of the hysteresis, however, are sometimes considerably
smaller than the predictions based on the loaded quality factor in the weak
drive regime. When the discrepancy appears, it is mostly explained by taking
into account the internal loss, which often increases in our resonators with
increasing drive power in the relevant power range. As a possible origin of the
power-dependent loss, the quasiparticle channel of conductance of the JJs is
discussed.Comment: 8 pages, 9 figure
Microwave characterization of tantalum superconducting resonators on silicon substrate with niobium buffer layer
Tantalum thin films sputtered on unheated silicon substrates are
characterized with microwaves at around 10 GHz in a 10 mK environment. We show
that the phase of tantalum with a body-centered cubic lattice (-Ta) can
be grown selectively by depositing a niobium buffer layer prior to a tantalum
film. The physical properties of the films, such as superconducting transition
temperature and crystallinity, change markedly with the addition of the buffer
layer. Coplanar waveguide resonators based on the composite film exhibit
significantly enhanced internal quality factors compared with a film without
the buffer layer. The internal quality factor approaches at a
large-photon-number limit. While the quality factor decreases at the
single-photon level owing to two-level system (TLS) loss, we have identified
the primary cause of TLS loss to be the amorphous silicon layer at the
film-substrate interface, which originates from the substrate cleaning before
the film deposition rather than the film itself. The temperature dependence of
the internal quality factors shows a marked rise below 200 mK, suggesting the
presence of TLS-TLS interactions. The present low-loss tantalum films can be
deposited without substrate heating and thus have various potential
applications in superconducting quantum electronics.Comment: 6 pages, 4 figures + Supplementary Material (7 pages, 5 figures
Single-photon-driven high-order sideband transitions in an ultrastrongly coupled circuit quantum electrodynamics system
We report the experimental observation of high-order sideband transitions at
the single-photon level in a quantum circuit system of a flux qubit
ultrastrongly coupled to a coplanar waveguide resonator. With the coupling
strength reaching 10% of the resonator's fundamental frequency, we obtain clear
signatures of higher-order red and first-order blue-sideband transitions, which
are mainly due to the ultrastrong Rabi coupling. Our observation advances the
understanding of ultrastrongly-coupled systems and paves the way to study
high-order processes in the quantum Rabi model at the single-photon level.Comment: Accepted in Physical Review A. 12 pages, 6 figure