Direct Measurement of the Josephson Plasma Resonance Frequency From I-V Characteristics

Abstract

The speed of Josephson circuits such as those required for Rapid Single Flux Quantum logic is limited by the Josephson plasma frequency, p , which (with few exceptions) increases monotonically with increasing critical current density, J c . Here we describe a new technique for directly measuring p , using the current-voltage characteristics of a simple structure based on externally-shunted, series-connected tunnel junctions. We present both experimental and theoretical demonstrations of the technique and describe its application to the determination of the junction capacitance, a property poorly characterized for high-J c junctions.

Superconducting on-chip spectrometer for mesoscopic quantum systems

“…Despite these early efforts coupling Josephson junctions to bulk samples, there have been few applications of the technique for spectroscopy of mesoscopic systems, artificial quantum coherent structures. Using specialized circuits in each case, researchers have measured Josephson plasma modes [5], resonances in microresonators [6,7], the energy levels of Cooper pair transistors [8][9][10], spin-wave resonances [11], and Andreev bound states [12,13]. Although Josephson junction based absorption spectroscopy has the potential to access a frequency range spanning GHz to THz with unprecedented sensitivity, progress has been impeded by several technical challenges.…”

All-NbN DC-SQUID Magnetometer Based on NbN/AlN/NbN Josephson Junctions

“…Table II lists the key parameters of our all-NbN SQUID magnetometer. The junction capacitance is estimated by observing the conductance dip of current-voltage characteristics of a structure based on externally-shunted, series-connected tunnel junction [16]. The specific capacitance C s of the junction is about 27 fF/μm 2 , and Stewart-McCumber parameter β c of the NbN SQUID is estimated to be less than 1.…”

Properties of Unshunted and Resistively Shunted Nb/AlOx-Al/Nb Josephson Junctions With Critical Current Densities From 0.1 to 1 mA/μm2

“…One of the methods of measuring ω p and the junction capacitance is to excite the Josephson plasma resonance in a large-area junction, J2 using a small junction J1 as a source of electromagnetic oscillations. A circuit where J2 is coupled via resistor R sh was described in [42] and shown in Fig. 15.…”

“…This requires the critical current of J1, I c1 be much smaller that the critical current of J2, I c2 . The circuit was used in [15], [42], [43] for extracting ω p and the junction specific capacitance C s . Below, we will give a more detailed analysis of the circuit in order to extract ω p and C s in high-J c junctions.…”

“…16c. In [42], this peak was associated with the Josephson plasma resonance in J2, and its position was used to extract C s in [15], [42], [43].…”