High Kinetic Inductance in Platinum‐Coated Aluminum Nanobridge Interferometers

Yakovlev D.S., Frolov A.V., Nazhestkin I.A., Temiryazev A.G., Orlov A.P., Shvartzberg J., Dizhur S.E., Gurtovoi V.L., Hovhannisyan R., Stolyarov V.S.

AbstractTopological insulator nanostructures became an essential platform for studying novel fundamental effects emerging at the nanoscale. However, conventional nanopatterning techniques, based on electron beam lithography and reactive ion etching of films, have inherent limitations of edge precision, resolution, and modification of surface properties, all of which are critical factors for topological insulator materials. In this study, an alternative approach for the fabrication of ultrathin Bi2Se3 nanoribbons is introduced by utilizing a diamond tip of an atomic force microscope (AFM) to cut atomically thin exfoliated films. This study includes an investigation of the magnetotransport properties of ultrathin Bi2Se3 topological insulator nanoribbons with controlled cross‐sections at ultra‐low 14 mK) temperatures. Current‐dependent magnetoresistance oscillations are observed with the weak antilocalization effect, confirming the coherent propagation of 2D electrons around the nanoribbon surface's perimeter and the robustness of topologically protected surface states. In contrast to conventional lithography methods, this approach does not require a highly controlled clean room environment and can be executed under ambient conditions. Importantly, this method facilitates the precise patterning and can be applied to a wide range of 2D materials.

Bafia D., Murthy A., Grassellino A., Romanenko A.

Zakharov R.V., Tikhonova O.V., Klenov N.V., Soloviev I.I., Antonov V.N., Yakovlev D.S.

AbstractA basic element of a quantum network based on two single‐mode waveguides is proposed with different frequencies connected by a solid‐state qubit. Using a simple example of a possible superconducting implementation, the usefulness of the simplifications used in the general theoretical consideration has been justified. The non‐classical field in a single‐mode with a frequency of is fed to the input of a qubit controller and transformed into a non‐classical field in an output single‐mode with a frequency of . The interface can establish a quantum connection between solid‐state and photonic flying qubits with adjustable pulse shapes and carrier frequencies. This allows quantum information to be transferred to other superconducting or atomic‐based quantum registers or chips. The peculiarities of the wave‐qubit interactions are described, showing how they help to control the quantum state of the non‐classical field. On this basis, the operating principles of solid‐state and flying qubits for the future quantum information platforms are considered.

Kozlov S., Lesueur J., Roditchev D., Feuillet-Palma C.

AbstractThe electron transport in current-biased superconducting nano-bridges is determined by the motion of the quantum vortex confined in the internal disorder landscape. Here we consider theoretically a simple case of a single or two neighbouring linear defects crossing a nano-bridge. The strong anharmonicity of the vortex motion along the defect leads, upon radio frequency (RF) excitation, to fractional Shapiro steps. In the case of two defects, the vortex motion becomes correlated, characterised by metastable states that can be locked to the RF-drive. The lock-unlock process causes sudden voltage jumps and drops in the voltage-current characteristics that can be observed in experiments. We analyse the parameters that promote these metastable dynamic states and discuss their possible experimental realisations.

Hovhannisyan R.A., Golod T., Krasnov V.M.

The utilization of Josephson vortices as information carriers in superconducting digital electronics is hindered by the lack of reliable displacement and localization mechanisms. In this Letter, we experimentally investigate planar Nb junctions with an intrinsic phase shift and nonreciprocity induced by trapped Abrikosov vortices. We demonstrate that the entrance of a single Josephson vortex into such junctions triggers the switching between metastable ±π semifluxon states. We showcase controllable manipulation between these states using short current pulses and achieve a nondestructive readout by a nearby junction. Our observations pave the way toward ultrafast and energy-efficient digital Josephson electronics. Published by the American Physical Society 2024

Bal M., Murthy A.A., Zhu S., Crisa F., You X., Huang Z., Roy T., Lee J., Zanten D.V., Pilipenko R., Nekrashevich I., Lunin A., Bafia D., Krasnikova Y., Kopas C.J., et. al.

AbstractWe present a transmon qubit fabrication technique that yields systematic improvements in T1 relaxation times. We encapsulate the surface of niobium and prevent the formation of its lossy surface oxide. By maintaining the same superconducting metal and only varying the surface, this comparative investigation examining different capping materials, such as tantalum, aluminum, titanium nitride, and gold, as well as substrates across different qubit foundries demonstrates the detrimental impact that niobium oxides have on coherence times of superconducting qubits, compared to native oxides of tantalum, aluminum or titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T1 relaxation times 2–5 times longer than baseline qubit devices with native niobium oxides. When capping niobium with tantalum, we obtain median qubit lifetimes above 300 μs, with maximum values up to 600 μs. Our comparative structural and chemical analysis provides insight into why amorphous niobium oxides may induce higher losses compared to other amorphous oxides.

Smirnov N.S., Krivko E.A., Solovyova A.A., Ivanov A.I., Rodionov I.A.

AbstractQuantum processors using superconducting qubits suffer from dielectric loss leading to noise and dissipation. Qubits are usually designed as large capacitor pads connected to a non-linear Josephson junction (or SQUID) by a superconducting thin metal wiring. Here, we report on finite-element simulation and experimental results confirming that more than 50% of surface loss in transmon qubits can originate from Josephson junctions wiring and can limit qubit relaxation time. We experimentally extracted dielectric loss tangents of qubit elements and showed that dominant surface loss of wiring can occur for real qubits designs. Finally, we experimentally demonstrate up to 20% improvement in qubit quality factor by wiring design optimization.

Zotova J., Semenov A., Wang R., Zhou Y., Astafiev O., Tsai J.

We develop a compact four-port superconducting switch with tunable operating frequency in the range from 4.8 to 7.3 GHz. Isolation between channels exceeds 20 dB over a bandwidth of several hundred megahertz, exceeding 40 dB at some frequencies. The footprint of the device is $80\ifmmode\times\else\texttimes\fi{}420\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}$. The tunability requires only a global flux bias without either permanent magnets or microelectromechanical structures. As the switch is superconducting, the heat dissipation during operation is negligible. The device can operate at up to $\ensuremath{-}80\phantom{\rule{0.2em}{0ex}}\mathrm{dBm}$, which corresponds to $2.5\ifmmode\times\else\texttimes\fi{}{10}^{6}$ photons per microsecond at a frequency of 6 GHz. The device shows the possibility to be operated as a beam splitter with tunable splitting ratio.

Splitthoff L.J., Wesdorp J.J., Pita-Vidal M., Bargerbos A., Liu Y., Andersen C.K.

Reading out the state of a quantum system at low temperature is generally challenging, as weak quantum signals must be amplified while adding as little noise as possible. Also, some qubit types rely on external magnetic fields and require magnetic-field-compatible superconducting parametric amplifiers. Here an innovative amp design leverages the nonlinear response of the gate-tunable kinetic inductance of proximitized semiconducting nanowires. The tunability allows integration with superconducting quantum systems, thanks to minimal crosstalk, and this amp can work with semiconductor-based spin qubits and other hybrid systems in magnetic fields of 500 mT.

Bogatskaya A.V., Klenov N.V., Popov A.M., Schegolev A.E., Titovets P.A., Tereshonok M.V., Yakovlev D.S.

It is known that the dielectric layer (resonator) located behind the conducting plate of the bolometer system can significantly increase its sensitivity near the resonance frequencies. In this paper, the possibility of receiving broadband electromagnetic signals in a multilayer bolometric meta-material made of alternating conducting (e.g., silicon semiconductor) and dielectric layers is demonstrated both experimentally and numerically. It is shown that such a multilayer structure acts as a lattice of resonators and can significantly increase the width of the frequency band of efficient electromagnetic energy absorption. The parameters of the dielectric and semiconductor layers determine the frequency bands. Numerical modeling of the effect has been carried out under the conditions of our experiment. The numerical results show acceptable qualitative agreement with the experimental data. This study develops the previously proposed technique of resonant absorption of electromagnetic signals in bolometric structures.

Vodolazov D.Y.

The concept of nonlinear kinetic inductance sensor (NKIS) of electromagnetic radiation is proposed. The idea is based on divergency of kinetic inductance $${{L}_{k}} \sim dq{\text{/}}dI$$ ( $$\hbar q$$ is a momentum of superconducting electrons, I is a supercurrent) of hybrid superconductor/normal metal (SN) bridge at current $$I{\text{*}} < {{I}_{{{\text{dep}}}}}$$ ( $${{I}_{{{\text{dep}}}}}$$ is a depairing current of the hybrid) and temperature T* much smaller than critical temperature $${{T}_{c}}$$ . It makes possible to have large change of phase difference $$\delta \phi $$ along SN bridge in current biased regime at $$I \simeq I{\text{*}}$$ even for small electron temperature increase. Appearance of $$\delta \phi $$ is accompanied by the change of the current and magnetic flux through the coupled superconducting ring which could be measured with help of superconducting quantum interference device (SQUID). In some respect proposed sensor may be considered as a superconducting counterpart of transition edge sensor (TES) those work is based on large derivative $$dR{\text{/}}dT$$ ( $$R$$ is a resistance) near $${{T}_{c}}$$ . Because at $$I \simeq I{\text{*}}$$ SN bridge is in gapless regime there is no low boundary for frequency of detected electromagnetic radiation. Our calculations show that such a sensor can operate in single photon regime and detect single photons with frequency $$\nu \gtrsim $$ 10 GHz. We argue that the nontrivial dependence $$I(q)$$ of SN bridge could be also used in detectors of continuous electromagnetic radiation, current and magnetic field sensors.

Avraham S., Bachar S., Glezer Moshe A., Farber E., Deutscher G.

Granular aluminum (grAl) is an applied quantum material. We present nano-superconducting quantum interference devices (nanoSQUIDs) based on grAl thin films. These devices exhibit non-hysteretic behavior, allowing conventional SQUID readout down to temperatures well below the critical temperature as well as detection properties comparable to those of Dayem bridge-based devices of greater complexity. Despite being much longer than the coherence length, the current–phase relation of these grAl constrictions appears to be single valued at least down to half their critical temperature. This suggests that grAl thin films should be described as a network of inter-grain Josephson junctions.

Amari P., Kozlov S., Recoba-Pawlowski E., Velluire-Pellat Z., Jouan A., Couëdo F., Ulysse C., Briatico J., Roditchev D., Bergeal N., Lesueur J., Feuillet-Palma C.

The realization of superconducting single-photon detectors operating above the liquid-helium temperature is currently the focus of intense research efforts. Here, we present the fabrication of ultraclean encapsulated nanowires from commercially available thin films of $\mathrm{YBa}$${}_{2}$$\mathrm{Cu}$${}_{3}$$\mathrm{O}$${}_{7\ensuremath{-}\ensuremath{\delta}}$ by high-energy oxygen-ion irradiation. The structured nanowires, ranging from 0.1 to $5\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$ in width, exhibit sharp resistive transitions to the superconducting state above 85 K. The $I$-$V$ characteristics reveal that the evolution from the superconducting to the normal state shows a large voltage jump in the volt range. This demonstrates that the entire nanowire transits---a prerequisite for the development of a hot spot upon absorption of a single photon. Our results pave the way for the fabrication of $\mathrm{YBa}$${}_{2}$$\mathrm{Cu}$${}_{3}$$\mathrm{O}$${}_{7\ensuremath{-}\ensuremath{\delta}}$-based scalable superconducting single-photon-detection devices.

Velluire Pellat Z., Maréchal E., Moulonguet N., Saïz G., Ménard G.C., Kozlov S., Couëdo F., Amari P., Medous C., Paris J., Hostein R., Lesueur J., Feuillet-Palma C., Bergeal N.

AbstractSuperconducting microwave resonators are crucial elements of microwave circuits, offering a wide range of potential applications in modern science and technology. While conventional low-T$$_c$$ c superconductors are mainly employed, high-T$$_c$$ c cuprates could offer enhanced temperature and magnetic field operating ranges. Here, we report the realization of $$\textrm{YBa}_2\textrm{Cu}_3\textrm{O}_{7-\delta }$$ YBa 2 Cu 3 O 7 - δ superconducting coplanar waveguide resonators, and demonstrate a continuous evolution from a lossy undercoupled regime, to a lossless overcoupled regime by adjusting the device geometry, in good agreement with circuit model theory. A high-quality factor resonator was then used to perform electron spin resonance measurements on a molecular spin ensemble across a temperature range spanning two decades. We observe spin-cavity hybridization indicating coherent coupling between the microwave field and the spins in a highly cooperative regime. The temperature dependence of the Rabi splitting and the spin relaxation time point toward an antiferromagnetic coupling of the spins below 2 K. Our findings indicate that high-Tc superconducting resonators hold great promise for the development of functional circuits. Additionally, they suggest novel approaches for achieving hybrid quantum systems based on high-T$$_c$$ c superconductors and for conducting electron spin resonance measurements over a wide range of magnetic fields and temperatures.

Flokstra M., Stewart R., Yim C., Trainer C., Wahl P., Miller D., Satchell N., Burnell G., Luetkens H., Prokscha T., Suter A., Morenzoni E., Bobkova I.V., Bobkov A.M., Lee S.

AbstractManipulating the spin state of thin layers of superconducting material is a promising route to generate dissipationless spin currents in spintronic devices. Approaches typically focus on using thin ferromagnetic elements to perturb the spin state of the superconducting condensate to create spin-triplet correlations. We have investigated simple structures that generate spin-triplet correlations without using ferromagnetic elements. Scanning tunneling spectroscopy and muon-spin rotation are used to probe the local electronic and magnetic properties of our hybrid structures, demonstrating a paramagnetic contribution to the magnetization that partially cancels the Meissner screening. This spin-orbit generated magnetization is shown to derive from the spin of the equal-spin pairs rather than from their orbital motion and is an important development in the field of superconducting spintronics.