This report results from a contract tasking University of Erlangen-Nuremberg as follows: The Grantee will investigate physical properties and improve the performance of two groups of Josephson devices: Josephson junction array oscillators and Josephson Qubits. They will continue study of series-parallel Josephson junction array oscillators from earlier research. The goal is to significantly increase the detected radiated power from 80 GHz to 120 GHz by improving the resonance frequency match between the devices and the receiver. They will also test the compact arrays of similar oscillator devices which incorporate antenna wires. Second, they will design and fabricate Josephson qubit devices for characterization from 4.2 K down to 20 mK. The energy profile will be characterized in the classical regime and projected into the quantum range and the coupling of the qubits to the environment will be examined according to the approach detailed in the technical proposal.
This report results from a contract tasking University of Erlangen-Nuremberg as follows: The Grantee will investigate physical properties and improve the performance of two groups of Josephson devices: Josephson junction array oscillators and Josephson Qubits. They will continue study of series-parallel Josephson junction array oscillators from earlier research. The goal is to significantly increase the detected radiated power from 80 GHz to 120 GHz by improving the resonance frequency match between the devices and the receiver. They will also test the compact arrays of similar oscillator devices which incorporate antenna wires. Second, they will design and fabricate Josephson qubit devices for characterization from 4.2 K down to 20 mK. The energy profile will be characterized in the classical regime and projected into the quantum range and the coupling of the qubits to the environment will be examined according to the approach detailed in the technical proposal.
This report results from a contract tasking University of Erlangen-Nuremberg as follows: The contractor will investigate coupled Josephson devices of two different kinds. First, the contractor will test a new concept of active antennas to couple radiation out from Josephson arrays. Using a mixed series-parallel array-biasing scheme, the contractor will design and perform waveguide-coupled emission experiments with single- and double-row arrays at 80-120 GHz. If successful, this scheme will be further implemented and tested using dipole antennas for the 400-500 GHz range. The contractor will also investigate the loop antenna array scheme as detailed in the technical proposal. The experiments will be done with Nb/Al- AOx/Nb Josephson junction arrays. The second Josephson device to be investigated (including design, fabrication, and testing) are novel q-bit devices. These q-bits are hoped to be more flexible and therefore more suitable hardware for quantum computing than single- loop SQUIDs currently pursued by other researcher groups. Full details are provided in the accompaning technical proposal.
This report results from a contract tasking University of Erlangen-Nuremberg as follows: contractor will investigate novel designs of triangular Josephson Junction arrays attempting to improve the high-frequency performance of the arrays in two ways; first, increase the operation frequencies and second, increase the output power of the millimeter-band radiation to level enabling practical application of the arrays. Three approaches will be investigated. First, trimming of currents at the array edges is expected to stabilize coherent oscillations and increase the operation margins (output power). Second, it appears promising to set up a traveling wave in a transmission line that contains an array comparable with the wavelength. Third, testing dipole-like active antennas to couple radiation out from arrays is a high priority task for emission in free space at high frequencies. The contractor will experimentally verify the above concepts by designing new circuits and performing experiments with Nb/AOx/Nb Josephson Junction arrays. For these experiments, the contractor will use a millimeter-wave band receiver as well an on-chip detection circuits up to 300 GHz. Spatially-resolved measurements using low temperature scanning laser microscopy will be performed in order to monitor array dynamics at the junction level. Furthermore, the contractor intends to design a dipole antenna and test it with an integrated receiver in 400-500 GHz frequency range. For this purpose, improvements for a flux-flow oscillator as a local oscillator may be needed. Finally, the contractor will perform experiments with shunted junction arrays in order to simulate intrinsically overdamped high-Tc junctions and explore a possibility of using high Tc layered junctions for oscillator application
The goal of this program was to demonstrate a Quasioptical Josephson Oscillator with Integrated Tuning Elements using standard Conductus niobium technology. This device is based on a novel approach that incorporates integrated tuning and impedance-matching structures at every Josephson junction/ antenna pair. The device has been designed, fabricated and successfully tested. A new, unit cell has been devised, incorporating a sub-array of 1 to 16 Josephson junctions. Microstrip transformers are used locally between each sub- array and its antenna. The oscillator with 110 Josephson junctions and bow-tie antennas was found to radiate close to its maximum available power at 115 GHz. The on-chip SIS radiation detector has detected 2.64 nW of power. The oscillator was tuned across 19 GHz, or 16% of fractional bandwidth, in reasonable agreement with the predicted value of 19%. This is the first demonstration of a distributed array Josephson oscillator, where each junction feeds its own antenna and phase-locks to the radiation of other junctions. It is also the first demonstration of using integrated microstrip tuning and impedance matching elements at every Josephson junction of an oscillator. Finally, this is the first distributed Josephson oscillator reported to date that appears to radiate close to its maximum available power. Submillimeter, Oscillators, Antenna arrays, Superconducting electronics, Quasioptical.
This is a new contract for a projected multi-year investigation of Superconducting Quantum Interference Device (SQUID) arrays and their application to microwave technology. The focus of this contract is the investigation and demonstration of a SQUID voltage-controlled oscillator (VCO). The array is then projected to increase the available power and operating impedance. The approach adopted will utilize monolithic superconducting integrated circuits which will be designed, fabricated, and tested at TRW. The project has three tasks: (1) Analysis of dc SQUID Arrays; (2) Design of dc SQUID Generator; and (3) SQUID VCO Fabrication and Measurement which are being carried out.
Work with large two-dimensional arrays of Josephson junctions for submillimeter power generation is discussed. The basic design of the quasioptical Josephson oscillator (QJO) is presented. The reasons for each design decision are discussed. Superconducting devices have not yet been fabricated, but scale models and computer simulations have been done. A novel method for characterizing array RF coupling structures is described, and initial results with this model are presented. Microwave scale models of the radiation structure were built, and a series of measurements was made with a network analyzer. These measurements were summed in a computer to find properties of the structure when all elements in it are operating in phase. The goal of these measurements was to develop structures for oscillators which are tunable over a very broad band. Computer programs simulating a Josephson junction in any frequency-dependent coupling structure have been developed. An iterative harmonic balance technique finds the time-domain current and voltage waveforms across the junction for an arbitrary frequency-dependent RF load impedance. DC bias, and therefore oscillator frequency, can be held fixed in this technique, in contrast to time-domain techniques where the oscillation frequency is found after the waveform is found. With these programs design goals for maximum oscillator power and design limits to achieve tolerable harmonic distortion were found.
As the need for scaling up quantum computers increases there is also an increased need for more compact adjacent circuitry surrounding the quantum processor. In the amplification of a qubit's readout-signal there is a need for quantum-limited amplifiers achieving a high signal-to-noise ratio. Today, it is common to use traveling-wave parametric amplifiers (TWPAs), which are currently powered by an external microwave pump. To further reduce the circuitry an option is to use an on-chip pump only requiring DC-wires to operate. This is possible due to the AC Josephson effect which can convert a DC voltage to an AC current. By connecting multiple Josephson junctions in series it is possible to increase the output power by utilizing their coherent oscillations. The purpose of this project was to simulate and characterize Josephson voltage controlled oscillators in terms of power and frequency-output, with the goal of providing the pump to a TWPA. This also included bandpass filters utilizing the Josephson inductance, to remove higher order harmonics of the oscillations. These bandpass filters were also characterized both in simulations and in measurements. To evaluate these components, a cryogenic testbed was implemented, and benchmarked, with a capacity of 12 parallel experiments. Simulations showed that it was possible to use Josephson junctions to produce stable oscillations which were filtered to give a pure 5 GHz signal with a -86.78 dBm power. When the corresponding device was measured it was not possible to observe the harmonic spectrum, likely due to noise in the DC-biasing system. The measured bandpass filters exhibited either high insertion loss or limited bandwidth as compared to design-specifications. A power-threshold was identified at approximately -90 dBm at which the bandpass filters showed severe non-linear effects, both in simulations and in measurements.