Fabrication of sub-micron Josephson junctions is demonstrated using standard processing techniques for high-coherence, superconducting qubits. These junctions are made in two separatelithography steps with normal-angle evaporation. Most significantly, this work demonstrates that it is possible to achieve high coherence with junctions formed on aluminum surfaces cleaned in situ with Ar milling before the junction oxidation. This method eliminates the angle-dependent shadow masks typically used for small junctions. Therefore, this is conducive to the implementation of typical methods for improving margins and yield using conventional CMOS processing. The current method uses electron-beam lithography and an additive process to define the top and bottom electrodes. Extension of this work to optical lithography and subtractive processes is discussed.
It has been known since the early days of quantum mechanics that hyperbolic secant pulses possess the unique property that they can perform cyclic evolution on two-level quantum systemsindependently of the pulse detuning. More recently, it was realized that they induce detuning- controlled phases without changing state populations. Here, we experimentally demonstrate the properties of hyperbolic secant pulses on superconducting transmon qubits and contrast them with the more commonly used Gaussian and square waves. We further show that these properties can be exploited to implement phase gates, nominally without exiting the computational subspace. This enables us to demonstrate the first microwave-driven Z-gates with a single control parameter, the detuning.
We demonstrate a fully cryogenic microwave feedback network composed of
modular superconducting devices interconnected by transmission lines and
designed to control a mechanical oscillatorcoupled to one of the devices. The
network is partitioned into an electromechanical device and a dynamically
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, this flexible controller
yields 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 $10^4$ times the mechanical response rate.