Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance

Abstract

We study the microwave impedance of extremely high aspect ratio (length/width ≈ 5,000) superconducting niobium nitride nanowires. The nanowires are fabricated in a compact meander geometry that is in series with the center conductor of a 50  coplanar waveguide transmission line. The transmission coefficient of the sample is measured up to 20 GHz. At high frequency, a peak in the transmission coefficient is seen. Numerical simulations show that this is a half-wave resonance along the length of the nanowire, where the nanowire acts as a high impedance, slow wave transmission line. This resonance sets the upper frequency limit for these nanowires as inductive elements. Fitting simulations to the measured resonance enables a precise determination of the nanowire's complex sheet impedance at the resonance frequency. The real part is a measure of dissipation, while the imaginary part is dominated by kinetic inductance. We characterize the dependence of the sheet resistance and sheet inductance on both temperature and current and compare the results to recent theoretical predictions for disordered superconductors. These results can aid in the understanding of high frequency devices based on superconducting nanowires. They may also lead to the development of novel superconducting devices such as ultra-compact resonators and slowwave structures.2

Single-photon imager based on a superconducting nanowire delay line

“…Despite its wide popularity, a lumped-element model cannot completely describe the electrical behavior of nanowire detectors because nanowires in these detectors are typically longer than the wavelength of the electrical signals they carry. In such situations, a distributed-element model must be used 21,22 .Here, we describe an experiment in which we used a superconducting nanowire as the center conductor in a microwave plasmonic coplanar transmission line to determine the position of the hot-spot along the nanowire while preserving information about the time of arrival of the photon. This approach uses the photon-sensitive nanowire to realize a scalable single-photon imager, which we refer to as a superconducting nanowire single-photon imager (SNSPI) to 4 distinguish it from an SNSPD.…”

Transmission lines and resonators based on quantum Hall plasmonics: Electromagnetic field, attenuation, and coupling to qubits

“…The characteristic impedance of these devices was estimated to be proportional to the resisitance quantum, and so orders of magnitude higher than the typical value ∼ 50Ω of microwave circuits [16]. There has been a growing interest in high impedance transmission lines in the quantum information community [17][18][19][20][21] and different implementations have been proposed [22][23][24][25][26][27][28][29][30]. In fact, the excitations in devices with a large characteristic impedance have a high electric field: this property can enhance the electrostatic coupling between the photon and the qubit.…”

Geometrical Jitter and Bolometric Regime in Photon Detection by Straight Superconducting Nanowire

“…According to Ref. [14], [15], [18] the propagation speed ν p of the voltage pulse in a nanowire is ν p ≈ (0.03 ± 0.01)c. Thus, the geometrical jitter should linearly depend on the length l of the nanowire. For uniformly distributed probability of photon absorption and in the absence of noise, PDF of the geometrical jitter is also uniform with the FWHM ∆t ≈ l/ν p and STD σ = ∆t/2 √ 3 .…”

“…Since the main focus has been on the local jitter inherent in the detection process, experimental studies have been performed on short nanowires in order to eliminate the contribution of the nanowire length to the measured system jitter. Due to large kinetic inductance, long nanowire in a typical SNSPD behaves as a high-impedance transmission line with a phase velocity of only 0.03c (c the speed of light in vacuum) [14], [15]. Therefore, in practical SNSPD devices, contributions due to detector geometry (nanowire length) and due to electrical noise often exceed together the local jitter.…”