72 research outputs found
Tunable coupling to a mechanical oscillator circuit using a coherent feedback network
We demonstrate a fully cryogenic microwave feedback network composed of
modular superconducting devices connected by transmission lines and designed to
control a mechanical oscillator coupled to one of the devices. The network
features an electromechanical device and a tunable controller that coherently
receives, processes and feeds back continuous microwave signals that modify the
dynamics and readout of the mechanical state. While previous electromechanical
systems represent some compromise between efficient control and efficient
readout of the mechanical state, as set by the electromagnetic decay rate, the
tunable controller produces a closed-loop network that can be dynamically and
continuously tuned between both extremes much faster than the mechanical
response time. We demonstrate that the microwave decay rate may be modulated by
at least a factor of 10 at a rate greater than times the mechanical
response rate. The system is easy to build and suggests that some useful
functions may arise most naturally at the network-level of modular, quantum
electromagnetic devices.Comment: 11 pages, 6 figures, final published versio
Remote Sensing and Control of Phase Qubits
We demonstrate a remote sensing design of phase qubits by separating the
control and readout circuits from the qubit loop. This design improves
measurement reliability because the control readout chip can be fabricated
using more robust materials and can be reused to test different qubit chips.
Typical qubit measurements such as Rabi oscillations, spectroscopy, and
excited-state energy relaxation are presented.Comment: 3 pages, 4 figure
Entangled State Synthesis for Superconducting Resonators
We present a theoretical analysis of methods to synthesize entangled states
of two superconducting resonators. These methods use experimentally
demonstrated interactions of resonators with artificial atoms, and offer
efficient routes to generate nonclassical states. We analyze physical
implementations, energy level structure, and the effects of decoherence through
detailed dynamical simulations.Comment: 14 pages, 10 figure
Quantum interference between two single photons of different microwave frequencies
We have measured quantum interference between two single microwave photons
trapped in a superconducting resonator, whose frequencies are initially about 6
GHz apart. We accomplish this by use of a parametric frequency conversion
process that mixes the mode currents of two cavity harmonics through a
superconducting quantum interference device, and demonstrate that a two-photon
entanglement operation can be performed with high fidelity.Comment: 6 pages and 3 figure
Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits
Low-loss microwave components are used in many superconducting resonant
circuits from multiplexed readouts of low-temperature detector arrays to
quantum bits. Two-level system defects in amorphous dielectric materials cause
excess energy loss. In an effort to improve capacitor components, we have used
optical lithography and micromachining techniques to develop superconducting
parallel-plate capacitors in which lossy dielectrics are replaced by vacuum
gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate
these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as
4x10^{-5}, significantly lower than with capacitors using amorphous
dielectrics. VGCs are structurally robust, small, and easily scaled to
capacitance values above 100 pF.Comment: 5 pages, 6 figures, .docx forma
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