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arXiv:1410.5314

Al/AlO$_{\rm {x}}$/Al-Josephson-junction-based microwave generators for weak-signal applications below 100 mK

Behdad Jalali‐Jafari, S. V. Lotkhov, Alexander B Zorin

Published Oct 20, 2014• 0 citations
arXivHTMLPDF

Abstract

An application-specific Josephson generator is being developed as an on-chip calibration source for single-microwave-photon detectors operating below $T \sim $100 mK in the frequency range from 110 to 170 GHz. The targeted calibration power corresponds to the photon detection rate of 0.01 to 10 counts per second. We analyze the Josephson oscillations within the framework of the tunnel junction microscopic (TJM) model and find the corrections to be made to a standard RSJ model of the junction, operating as a quasi-monochromatic source of microwaves. Experimentally, we implemented a number of aluminium-based two-junction interferometers connected to the leads via microstripline resistors made of partly oxidized titanium films. The $I$-$V$ curves exhibit a behaviour ensuring generation of the microwave signal in the frequency range required. By setting the biasing point $\bar{V}$ and applying the magnetic field, one can tune the generator's frequency and power, respectively. A small oscillation linewidth, down to a few GHz, and a low level of black-body radiation emitted by hot parts of the circuit are predicted, using the experimental parameters.

DOI
10.48550/arxiv.1410.5314

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Al/AlOx_{\rm {x}}x​/Al-Josephson-junction-based microwave generators for weak-signal applications below 100 mK
An application-specific Josephson generator is being developed as an on-chip calibration source for single-microwave-photon detectors operating below T∼T \sim T∼100 mK in the frequency range from 110 to 170 GHz. The targeted calibration power corresponds to the photon detection rate of 0.01 to 10 counts per second. We analyze the Josephson oscillations within the framework of the tunnel junction microscopic (TJM) model and find the corrections to be made to a standard RSJ model of the junction, operating as a quasi-monochromatic source of microwaves. Experimentally, we implemented a number of aluminium-based two-junction interferometers connected to the leads via microstripline resistors made of partly oxidized titanium films. The III-VVV curves exhibit a behaviour ensuring generation of the microwave signal in the frequency range required. By setting the biasing point Vˉ\bar{V}Vˉ and applying the magnetic field, one can tune the generator's frequency and power, respectively. A small oscillation linewidth, down to a few GHz, and a low level of black-body radiation emitted by hot parts of the circuit are predicted, using the experimental parameters.
The present work addresses quantum interaction phenomena of microwave radiation with a single-electron tunneling system. For this study, an integrated circuit is implemented, combining on the same chip a Josephson junction (Al/AlO x /Al) oscillator and a single-electron transistor (SET) with the superconducting island (Al) and normal-conducting leads (AuPd). The transistor is demonstrated to operate as a very sensitive photon detector, sensing down to a few tens of photons per second in the microwave frequency range around f ∼ 100 GHz. On the other hand, the Josephson oscillator, realized as a two-junction SQUID and coupled to the detector via a coplanar transmission line (Al), is shown to provide a tunable source of microwave radiation: controllable variations in power or in frequency were accompanied by significant changes in the detector output, when applying magnetic flux or adjusting the voltage across the SQUID, respectively. It was also shown that the effect of substrate-mediated phonons, generated by our microwave source, on the detector output was negligibly small.
In this Letter, we experimentally demonstrated that Josephson threshold detectors (JTDs) could be developed to implement the sensitive detection of broadband microwave photons. Beginning with the numerical simulations of the damped dynamics for the macroscopic phase particle generated by a Josephson junction (JJ), we showed that the time-domain threshold voltage state switched measurements of the JJ driven by a low-frequency triangular wave current, which could be utilized to implement the sensitive microwave photons detection. The detectable signal power can be determined by using the Kumar–Caroll index to quantify the distinguishability between two statistical distributions on the measured threshold switched durations of the JJ with and without the signal input. Experimentally, we fabricated the Al/AlOx/Al JJ and measured its threshold responses, at 50 mK temperature, to the input microwave photons at the frequency of ∼5 GHz. The experimental results indicated that the weak microwave signals, which are phenomenologically threatened by the additional thermal noise that modifies the damped phase dynamics of the JJ, can be detected by the fabricated JTD. The detectable power of the microwave signals demonstrated here was calibrated as about −92 dBm (corresponding to the photons rate of ∼2×108 photons/ms). Based on the numerical simulations for optimizing the relevant performance indicators of the detectors, we further argue that the JTDs could be utilized to achieve the sensitive detection of broadband microwave photons at the single-photon level.
Abstract Josephson junctions, in appropriate configurations, can be excellent candidates for detection of single photons in the microwave frequency band. Such possibility has been recently addressed in the framework of galactic axion detection. Here are reported recent developments in the modelling and simulation of dynamic behaviour of a Josephson junction single microwave photon detector. For a Josephson junction to be enough sensitive, small critical currents and operating temperatures of the order of ten of mK are necessary. Thermal and quantum tunnelling out of the zero-voltage state can also mask the detection process. Axion detection would require dark count rates in the order of 0.001 Hz. It is, therefore, is of paramount importance to identify proper device fabrication parameters and junction operation point.
Extensive measurements of radiation emitted from long Josephson junctions d.c.-current biased on zero-field and Fiske-steps are reported. The measurements were made in the band 8-10 GHz on long Nb-Nb oxide-Pb overlap tunnel junctions with the lengths 0.5 mm and 1.0 mm having fundamental frequencies of 10 GHz and 5 GHz, respectively. Depending on the fundamental frequency of the junction 1st or 2nd harmonic detection was employed. In the fundamental scheme the frequency f n vs. the d.c.-voltage V n along the steps follows a modified Josephson voltage/frequency relation f n / V n = 2 e/nh , where n is the step-number n = 1, 2, 3,... for Fiske-steps and n = 2, 4, 6,... for zero-field steps. On a given step the frequency could be tuned (200-500 MHz) by varying the bias point. The linewidth was measured to be less than 5 kHz. All the observed phenomena are consistent with a novel unified dynamic bunched fluxon model applicable to both zero-field and Fiske-steps and are in good agreement with recent numerical solutions of the perturbed sine-Gordon equation with proper boundary conditions. Taking advantage of operation on higher order steps and strong harmonic generation the present upper frequency limit for the Josephson fluxon oscillator is above 200 GHz. The maximum power observed so far is only 5 pW, but the estimated available power is of the order 1 μW, which is quite sufficient to pump other Josephson devices.
Abstract Providing radio frequency (RF) signals to cryogenic circuits requires bulky and expensive cabling interfacing specialized RF electronics at room temperature. Superconducting-normal metal-superconducting Josephson junction arrays (JJAs) can change this paradigm by placing the RF source and detector on-chip. In this work, we demonstrate that DC-biased JJAs can emit signals in the C-band frequency spectrum and beyond, with a minimal linewidth of 106.5 ± 0.1 MHz and maximum power of 11.9 fW. We fabricate JJAs comprised of amorphous MoGe or NbTiN superconducting islands and metallic Au weak links. Temperature, magnetic field, applied current, and device design are explored to control the RF sources, while we identify important features that affect the ideal source behavior. Combined with the ability of these JJAs to detect microwave radiation, these sources allow us to propose a fully DC-operated cryogenic on-chip measurement platform that is an alternative to the high-frequency circuitry currently required for quantum applications.
We predict that the threshold detectors based on Al Josephson junctions, with critical currents below 100 nA, exhibiting a phase diffusion regime, can be exploited for the microwave photon detection both at 17 mK and 700 mK. We demonstrate a detection of two- and one-photon energies at 5 GHz with 90% and 15% efficiency and dark count time of about 0.1 s and 0.01 s, respectively. The observed weak temperature dependence of the detector's performance in the sub-kelvin range fully confirms its phase-diffusion mode of operation. On the other hand, these results show that inevitable thermal fluctuations are not the main source of the detector noise. Consequently, there is still a room to optimize the detector's performance. These results are important for axion search experiments in the range of 5-25 GHz (20-100 μμμeV).