Traveling wave parametric amplifiers based on kinetic or Josephson nonlinear inductance are known to be microwave quantum limited amplifiers. Usually, a perfectly impedance-matchedmodel is used to describe their characteristics in terms of standard coupled mode theory. In practice, the amplifiers are unmatched nonlinear devices with finite length, exhibiting ripples in the transmission. Since commonly used models fail to describe the ripples of real parametric amplifiers, here we are introducing a theoretical approach with non-negligible reflections, which provides their gain and bandwidth properly for both 3-wave and 4-wave mixing. Predictions of the model are experimentally demonstrated on two types of TWPA, based on coplanar waveguides with a central wire consisting of i) high kinetic inductance superconductor, and ii) array of 2000 Josephson junctions.
We demonstrate amplification (and attenuation) of a probe signal by a driven two-level quantum system in the Landau-Zener regime. In the experiment, a superconducting qubit was stronglycoupled to a microwave cavity, the conventional arrangement of circuit quantum electrodynamics. Two different types of flux qubits show a similar result, lasing at the points where amplification takes place. The experimental data are explained by the interaction of the probe signal with Rabi-like oscillations. The latter are created by constructive interference of Landau-Zener-St\“{u}ckelberg-Majorana (LZSM) transitions during the driving period of the qubit. A detailed description of the occurrence of these oscillations and a comparison of obtained data with both analytic and numerical calculations are given.
We present a design for the experimental integration of ion trapping and superconducting qubit systems as a step towards the realization of a quantum hybrid system. The scheme addressestwo key difficulties in realizing such a system; a combined microfabricated ion trap and superconducting qubit architecture, and the experimental infrastructure to facilitate both technologies. Developing upon work by Kielpinski et al. [1] we describe the design, simulation and fabrication process for a microfabricated ion trap capable of coupling an ion to a superconducting microwave LC circuit with a coupling strength in the tens of kHz. We also describe existing difficulties in combining the experimental infrastructure of an ion trapping setup into a dilution fridge with superconducting qubits and present solutions that can be immediately implemented using current technology.
We study the response of a magnetic-field-driven superconducting qubit strongly coupled to a superconducting coplanar waveguide resonator. We observed a strong amplification/dampingof a probing signal at different resonance points corresponding to a one and two-photon emission/absorption. The sign of the detuning between the qubit frequency and the probe determines whether amplification or damping is observed. The larger blue detuned driving leads to two-photon lasing while the larger red detuning cools the resonator. Our experimental results are in good agreement with the theoretical model of qubit lasing and cooling at the Rabi frequency.
We report the parametric amplification of a microwave signal in a Kerr medium formed from superconducting qubits. Two mutually coupled flux qubits, embedded in the current antinodeof a superconducting coplanar waveguide resonator, are used as a nonlinear element. Shared Josephson junctions provide the qubit-resonator coupling, resulting in a device with a measured gain of about 20 dB. We argue, that this arrangement represents a unit cell which can be straightforwardly extended to a quasi one-dimensional quantum metamaterial with a large tunable Kerr nonlinearity.
We demonstrate amplification of a microwave signal by a strongly driven
two-level system in a coplanar waveguide resonator. The effect known from
optics as dressed-state lasing is observedwith a single quantum system formed
by a persistent current (flux) qubit. The transmission through the resonator is
enhanced when the Rabi frequency of the driven qubit is tuned into resonance
with one of the resonator modes. Amplification as well as linewidth narrowing
of a weak probe signal has been observed. The laser emission at the resonator’s
fundamental mode has been studied by measuring the emission spectrum. We
analyzed our system and found an excellent agreement between the experimental
results and the theoretical predictions obtained in the dressed-state model.