70 research outputs found
On-demand microwave generator of shaped single photons
We demonstrate the full functionality of a circuit that generates single
microwave photons on demand, with a wave packet that can be modulated with a
near-arbitrary shape. We achieve such a high tunability by coupling a
superconducting qubit near the end of a semi-infinite transmission line. A dc
superconducting quantum interference device shunts the line to ground and is
employed to modify the spatial dependence of the electromagnetic mode structure
in the transmission line. This control allows us to couple and decouple the
qubit from the line, shaping its emission rate on fast time scales. Our
decoupling scheme is applicable to all types of superconducting qubits and
other solid-state systems and can be generalized to multiple qubits as well as
to resonators.Comment: 10 pages, 7 figures. Published versio
Josephson squelch filter for quantum nanocircuits
We fabricated and tested a squelch circuit consisting of a copper powder
filter with an embedded Josephson junction connected to ground. For small
signals (squelch-ON), the small junction inductance attenuates strongly from DC
to at least 1 GHz, while for higher frequencies dissipation in the copper
powder increases the attenuation exponentially with frequency. For large
signals (squelch-OFF) the circuit behaves as a regular metal powder filter. The
measured ON/OFF ratio is larger than 50dB up to 50 MHz. This squelch can be
applied in low temperature measurement and control circuitry for quantum
nanostructures such as superconducting qubits and quantum dots.Comment: Corrected and completed references 6,7,8. Updated some minor details
in figure
Observation of the Bloch-Siegert Shift in a Qubit-Oscillator System in the Ultrastrong Coupling Regime
We measure the dispersive energy-level shift of an resonator
magnetically coupled to a superconducting qubit, which clearly shows that our
system operates in the ultrastrong coupling regime. The large mutual kinetic
inductance provides a coupling energy of ~GHz, requiring the
addition of counter-rotating-wave terms in the description of the
Jaynes-Cummings model. We find a 50~MHz Bloch-Siegert shift when the qubit is
in its symmetry point, fully consistent with our analytical model.Comment: Published version (4 pages, 4 figures), including supplementary
material (2 pages, 4 figures
Generating Multimode Entangled Microwaves with a Superconducting Parametric Cavity
In this Letter, we demonstrate the generation of multimode entangled states
of propagating microwaves. The entangled states are generated by parametrically
pumping a multimode superconducting cavity. By combining different pump
frequencies, applied simultaneously to the device, we can produce different
entanglement structures in a programable fashion. The Gaussian output states
are fully characterized by measuring the full covariance matrices of the modes.
The covariance matrices are absolutely calibrated using an in situ microwave
calibration source, a shot noise tunnel junction. Applying a variety of
entanglement measures, we demonstrate both full inseparability and genuine
tripartite entanglement of the states. Our method is easily extensible to more
modes.Comment: 5 pages, 1 figures, 1 tabl
Superconducting nitridized-aluminum thin films
We report the direct observation of superconductivity in nitridized-aluminum thin films. The
films are produced by sputtering deposition of aluminum in a controlled mixture of nitrogen
diluted in argon. The concentration of applied nitrogen directly determines the properties of the
superconducting thin films. We observe samples displaying critical temperatures up to
3.38 ± 0.01 K and resilience to in-plane magnetic fields well above 1 T, with good
reproducibility of the results. This work represents an unambiguous demonstration of tunable
superconductivity in aluminum-based nitridized thin films. Our results put forward nitridized
aluminum as a promising material to be employed in superconducting quantum circuits for
quantum technology applications
Driven dynamics and rotary echo of a qubit tunably coupled to a harmonic oscillator
We have investigated the driven dynamics of a superconducting flux qubit that
is tunably coupled to a microwave resonator. We find that the qubit experiences
an oscillating field mediated by off-resonant driving of the resonator, leading
to strong modifications of the qubit Rabi frequency. This opens an additional
noise channel, and we find that low-frequency noise in the coupling parameter
causes a reduction of the coherence time during driven evolution. The noise can
be mitigated with the rotary-echo pulse sequence, which, for driven systems, is
analogous to the Hahn-echo sequence
Deep strong light-matter coupling in plasmonic nanoparticle crystals
In the regime of deep strong light–matter coupling, the coupling strength exceeds the transition energies of the material, fundamentally changing its properties; for example, the ground state of the system contains virtual photons and the internal electromagnetic field gets redistributed by photon self-interaction. So far, no electronic excitation of a material has shown such strong coupling to free-space photons. Here we show that three-dimensional crystals of plasmonic nanoparticles can realize deep strong coupling under ambient conditions, if the particles are ten times larger than the interparticle gaps. The experimental Rabi frequencies (1.9 to 3.3 electronvolts) of face-centred cubic crystals of gold nanoparticles with diameters between 25 and 60 nanometres exceed their plasmon energy by up to 180 per cent. We show that the continuum of photons and plasmons hybridizes into polaritons that violate the rotating-wave approximation. The coupling leads to a breakdown of the Purcell effect—the increase of radiative damping through light–matter coupling—and increases the radiative polariton lifetime. The results indicate that metallic and semiconducting nanoparticles can be used as building blocks for an entire class of materials with extreme light–matter interaction, which will find application in nonlinear optics, the search for cooperative effects and ground states, polariton chemistry and quantum technology
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