arXiv subjects

Edward Romans

Publications and source records attributed to Edward Romans.

2 recordsLinked to original sources

arXiv2026

Parametric amplification in a Kerr Oscillator based on Ne FIB Nanobridges

Superconducting circuits play a crucial role in the advancement of quantum computing and quantum sensing. Typically such circuits require the presence of a non-linear element, where the engineered anharmonicity (Kerr factor) and resonant linewidth determine the potential applications of the circuit. In this work we have fabricated Nb-based CPW resonators embedded with a DC SQUID incorporating Nb nanobridges as the weak links. We use two-tone spectroscopy to study the non-linear behaviour of the device at 15 mK up to a field of 2.48 mT. Under the application of a blue-detuned pump, the device shows a decrease in the resonant frequency which is used to estimate the Kerr factor. We further apply a red-detuned pump to go beyond the bifurcation threshold and observe the appearance of an additional idler mode with net gain. The gain of the device was maximized by further decreasing the pump frequency, showing a maximum amplification of 15 dB. Finally, we show agreement between the Kerr non-linear oscillator model and the measured transmission spectrum, and highlight further design modifications to improve the gain and bandwidth of such devices.

quant-ph↗

arXiv2017

Ballistic Josephson junctions based on CVD graphene

Josephson junctions with graphene as the weak link between superconductors have been intensely studied in recent years, with respect to both fundamental physics and potential applications. However, most of the previous work was based on mechanically exfoliated graphene, which is not compatible with mass production. Here we present our research using graphene grown by chemical vapour deposition (CVD) as the weak link of Josephson junctions. We demonstrate that CVD-graphene-based Josephson junctions with Nb electrodes can work effectively without any thermal hysteresis from 1.5 K down to a base temperature of 320 mK, and they show an ideal Fraunhofer-like interference pattern in a perpendicular magnetic field. We also show that the critical current of the junction can be tuned by a gate voltage. Furthermore, for our shortest junctions (50 nm in length), we find that the normal state resistance oscillates with the gate voltage, indicating that the junctions are in the ballistic regime, a feature not previously observed in CVD-graphene-based Josephson junctions.

cond-mat.supr-con↗