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The transport properties of two types of quasi-one-dimensional superconducting microstructures were investigated at ultra-low temperatures: the narrow channels close-packed in the shape of meander, and the chains of tunneling contacts "superconductor-insulator-superconductor." Both types of the microstructures demonstrated high value of high-frequency impedance and-or the dynamic resistance. The study opens up potential for using of such structures as current stabilizing elements with zero dissipation.

A chain of superconductor–insulator–superconductor junctions based on Al–AlOx–Al nanostructures and fabricated using conventional lift-off lithography techniques was measured at ultra-low temperatures. At zero magnetic field, the low current bias dynamic resistance can reach values of ≈1011 Ω. It was demonstrated that the system can provide a decent quality current biasing circuit, enabling the observation of Coulomb blockade and Bloch oscillations in ultra-narrow Ti nanowires associated with the quantum phase-slip effect.

The Coulomb Blockade Thermometer (CBT) is a primary thermometer for cryogenic temperatures, with demonstrated operation from below 1 mK up to 60 K. Its performance as a primary thermometer has been verified at temperatures from 20 mK to 200 mK at uncertainty level below 1 % (k = 2). In a new project, our aim is to extend the metrologically verified temperature range of the primary CBT up to 25 K. We also demonstrate close-to-ideal operation of a CBT with only two tunnel junctions when the device is embedded in a low-impedance environment., 2 pages, 3 figures, 2020 Conference on Precision Electromagnetic Measurements (CPEM), Denver (Aurora), CO, USA, 2020

We report on ambipolar gate-defined quantum dots in silicon on insulator (SOI) nanowires fabricated using a customised complementary metal-oxide-semiconductor (CMOS) process. The ambipolarity was achieved by extending a gate over an intrinsic silicon channel to both highly doped n-type and p-type terminals. We utilise the ability to supply ambipolar carrier reservoirs to the silicon channel to demonstrate an ability to reconfigurably define, with the same electrodes, double quantum dots with either holes or electrons. We use gate-based reflectometry to sense the inter-dot charge transition(IDT) of both electron and hole double quantum dots, achieving a minimum integration time of 160(100) $\mu$s for electrons (holes). Our results present the opportunity to combine, in a single device, the long coherence times of electron spins with the electrically controllable holes spins in silicon., Comment: 5 pages, 4 figures

Controlling electron and phonon flows through a solid junction enables novel on-chip cooling and sensing functionalities., Electrothermal elements are used in various energy harvesters, coolers, and radiation detectors. The optimal operation of these elements relies on mastering two competing boundary conditions: the maximization of the electrothermal response and the blockade of lattice (phonon) thermal conduction. In this work, we propose and demonstrate that efficient electrothermal operation and phonon blocking can be achieved in solid-state thermionic junctions, paving the way for new phonon-engineered high-efficiency refrigerators and sensors. Our experimental demonstration uses semiconductor-superconductor (Sm-S) junctions where the electrothermal response arises from the superconducting energy gap and the phonon blocking results from the acoustic transmission bottleneck at the junction. We demonstrate a cooling platform where a silicon chip, suspended only from the Sm-S junctions, is cooled by ~40% from the bath temperature. We also show how the observed effect can be used in radiation detectors and multistage electronic refrigerators suitable for cooling of quantum technology devices.

—Volt-ampere characteristics of narrow superconducting titanum wires have been studied experimentally. The narrowest specimens measured by means of high-resistance contacts have revealed a behavior nontrivial for superconductors: the Coulomb blockade. The Coulomb gap size correlates with the frequency of quantum phase slips. The observation confirms the identity of quantum dynamics of charge in the Josephson junctions and in the quasi-one-dimensional superconducting channels in the regime of quantum fluctuations of the order parameter.

The current–voltage characteristics of superconductor–insulator–semiconductor (S1–I–S2) tunnel junctions, where superconducting electrode S2 is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij–Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the regime of quantum fluctuations of the order parameter. The model gives results that are in a reasonable qualitative agreement with the experimental data.

Quasi-one-dimensional superconducting channels host sound-like plasma modes propagating along the sample which are associated with fluctuations of the phase of the superconducting order parameter. Interaction between these electromagnetic excitations and charge carriers affects the electron density of states (DOS). I-V characteristics of tunnel S1-I-S2 junctions, where superconducting S2 electrode is a thin nanowire in the regime of quantum fluctuations have been studied. The observed broadening of the I-V dependencies at the gap edge is interpreted as the renormalization of DOS. The results are in reasonable agreement with the model, taking into consideration plasma modes in quasi-one-dimensional superconductors.

An accurate standard of electric current is a long-standing challenge of modern metrology. It has been predicted that a superconducting nanowire in the regime of quantum fluctuations can be considered as the dynamic equivalent of a chain of conventional Josephson junctions. In full analogy with the quantum standard of electric voltage based on the Josephson effect, the quantum phase slip phenomenon in ultrathin superconducting nanowires could be used for building the quantum standard of electric current. This work presents advances toward this ultimate goal.

We present experimental results on a Josephson parametric amplifier tailored for readout of ultra-sensitive thermal microwave detectors. In particular, we discuss the impact of fabrication details on the performance. We show that the small volume of deposited dielectric materials enabled by the side-wall passivated spacer niobium junction technology leads to robust operation across a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier has gain in excess of 20 dB in three-wave mixing and its center frequency is tunable between 540 MHz and 640 MHz. At 600 MHz, the amplifier adds 105 mK $\pm$ 9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device.

We suspend a heavily doped conducting silicon chip by tunnel junctions and aluminum leads, which permits the measurement and control of electrical and phonon heat fluxes. Experiments and analysis on heat conduction and electrical cooling utilize techniques developed for electron pumps and primary thermometry, and the techniques developed for the cooler may also be useful for the development quantum phase slip based devices.

Several silicide compounds are promising materials for studies and applications of quantum phase slips (QPS) in superconducting nanowires (SNWs). This paper describes two nanofabrication processes, which were applied to manufacture silicide SNWs. Experiments on MoSi nanowires indicate size dependent crossover from conventional superconductivity to transport influenced by thermal and quantum fluctuations. Results of the first experiments on other silicide SNWs will be presented in the conference.

We have fabricated disordered superconducting nanowires of molybdenium silicide. A molybdenium nanowire is first deposited on top of silicon, and the alloy is formed by rapid thermal annealing. The method allows tuning of the crystal growth to optimise, e.g., the resistivity of the alloy for potential applications in quantum phase slip devices and superconducting nanowire single-photon detectors. The wires have effective diameters from 42 to 79 nm, enabling the observation of crossover from conventional superconductivity to regimes affected by thermal and quantum fluctuations. In the smallest diameter wire and at temperatures well below the superconducting critical temperature, we observe residual resistance and negative magnetoresistance, which can be considered as fingerprints of quantum phase slips.

We present a structure and a fabrication method for superconducting tunnel junctions down to the dimensions of 200 nm using i-line UV lithography. The key element is a side-wall-passivating spacer structure (SWAPS) which is shaped for smooth crossline contacting and low parasitic capacitance. The SWAPS structure enables formation of junctions with dimensions at or below the lithography-limited linewidth. An additional benefit is avoiding the excessive use of amorphous dielectric materials which is favorable in sub-Kelvin microwave applications often plagued by nonlinear and lossy dielectrics. We apply the structure to niobium trilayer junctions, and provide characterization results yielding evidence on wafer-scale scalability, and critical current density tuning in the range of 0.1 -- 3.0 kA/cm$^2$. We discuss the applicability of the junction process in the context of different applications, such as, SQUID magnetometers and Josephson parametric amplifiers., 8 pages, 4 figures

Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. Fundamental attributes of superconductivity such as zero resistivity, persistent currents in closed loops, energy gap in excitation spectra can be drastically violated by fluctuations. Here we report the experimental study of I-V characteristics of thin superconducting titanium nanowires governed by quantum phase slips. The thinnest samples imbedded in high-ohmic environment demonstrated counterintuitive behavior for a superconductor: Coulomb blockade. The magnitude of the Coulomb gap correlates with the rate of quantum phase slips. The observation confirms the similarity of quantum charge dynamics in a Josephson junction and in a quasi-one-dimensional superconducting channel governed by quantum fluctuations of the order parameter.

Minimizing microwave background of cryogenic environment is crucial for quantum devices where single microwave photon energy is sufficient to disturb the measured system. Microwave photons with sufficient energy originate from the warmer parts of the cryostat, for example from parts at liquid helium temperature (4.2 K), which can be about three orders of magnitude higher than the sample temperature. Reduction of the microwave background is possible with careful design of both shielding and filtering of the sample holder. Additionally, on-chip filtering of the actual quantum device can improve the device performance significantly.

A normal metal - superconductor hybrid single-electron trap with tunable barrier is utilized as a tool for spectrum analysis at the extremely low signal levels, using only well filtered cryogenic microwave background as a photon source in the frequency range from about 50 to 210 GHz. We probe millimeter wave propagation in two superconducting systems: a Josephson junction array around its plasma frequency, and a superconducting titanium film in the limit when the photon energies are larger than the superconducting energy gap. This regime is relevant for improving the performance of cryogenic quantum devices but is hard to access with conventional techniques. We show that relatively simple models can be used to describe the essential properties of the studied components.

Quantum phase slip (QPS) is the topological singularity of the complex order parameter of a quasi-one-dimensional superconductor: momentary zeroing of the modulus and simultaneous 'slip' of the phase by 2\pi. The QPS event(s) are the dynamic equivalent of tunneling through a conventional Josephson junction containing static in space and time weak link(s). Here we demonstrate the operation of a superconducting single electron transistor (Cooper pair transistor) without any tunnel junctions. Instead a pair of thin superconducting titanium wires in QPS regime were used. The current-voltage characteristics demonstrate the clear Coulomb blockade with magnitude of the Coulomb gap modulated by the gate potential. The Coulomb blockade disappears above the critical temperature, and at low temperatures can be suppressed by strong magnetic field., Comment: 6 pages, 3 figures

Quantum phase slip (QPS) is the particular manifestation of quantum fluctuations of the order parameter of a current-biased quasi-1D superconductor. The QPS event(s) can be considered a dynamic equivalent of tunneling through conventional Josephson junction containing static in space and time weak link(s). At low temperatures T<, Comment: 3 pages, 3 figures

We measure the current noise of several cryogenic cables in a pulse tube based dilution refrigerator at frequencies between about 1~mHz and 50~kHz. We show that vibration-induced noise can be efficiently suppressed by using vacuum-insulated cables between room temperature and the 2nd pulse tube stage. A noise peak below 4 fA at the 1.4~Hz operation frequency of the pulse tube, and a white noise density of 0.44 fA/\sqrt{Hz} in the millihertz range are obtained.

Real-time detection and generation of single microwave photons would be important in many quantum technology applications. For single-microwave-photon sources, much of the groundwork has been done already within the framework of circuit quantum electrodynamics (cQED) in the frequency range 4 GHz - 8 GHz. However, currently there are no detectors that can reliably resolve single microwave photon events, unlike at optical frequencies. In June 2013, we started a joint research project to develop both microwave detectors and sources working at the single-photon level as a final goal. All devices operate at cryogenic temperatures, most of them below 100 mK. We also aim at improving the performance of other cryoelectronic quantum devices by understanding and eliminating the detrimental effects caused by microwave radiation. The work is done in project MICROPHOTON of the European Metrology Research Programme (EMRP). The goals and status of the project will be described in the presentation.

In a number of recent experiments it has been demonstrated that in ultra-narrow superconducting channels quantum fluctuations of the order parameter, alternatively called quantum phase slips, are responsible for the finite resistance well below the critical temperature. The acceptable agreement between those experiments and the models describing quantum fluctuations in quasi-one-dimensional superconductors has been established. However the very concept of the phase slip is justified when these fluctuations are the relatively rare events, meaning that the effective resistance of the system should be much smaller than the normal state equivalent. In this paper we study the limit of the strong quantum fluctuations where the existing models are not applicable. In particular case of ultra-thin titanium nanowires it is demonstrated that below the expected critical temperature the resistance does not demonstrate any trend towards the conventional for a superconductor zero-resistivity state even at negligibly small measuring currents. Application of a small magnetic field leads to an unusual negative magnetoresistance, which becomes more pronounced at lower temperatures. The origin of the negative magnetoresistance effect is not clear.

Quantum fluctuations in quasi-one-dimensional superconducting channels leading to spontaneous changes of the phase of the order parameter by $2\pi$, alternatively called quantum phase slips (QPS), manifest themselves as the finite resistance well below the critical temperature of thin superconducting nanowires and the suppression of persistent currents in tiny superconducting nanorings. Here we report the experimental evidence that in a current-biased superconducting nanowire the same QPS process is responsible for the insulating state -- the Coulomb blockade. When exposed to RF radiation, the internal Bloch oscillations can be synchronized with the external RF drive leading to formation of quantized current steps on the I-V characteristic. The effects originate from the fundamental quantum duality of a Josephson junction and a superconducting nanowire governed by QPS -- the QPS junction (QPSJ)., Comment: 5 pages, 4 figures

Electron transport properties of titanium nanowires were experimentally studied. Below the effective diameter $\lesssim$ 50 nm all samples demonstrated a pronounced broadening of the $R(T)$ dependencies, which cannot be accounted for thermal flcutuations. An extensive microscopic and elemental analysis indicates the absence of structural or/and geometrical imperfection capable to broaden the the $R(T)$ transition to such an extent. We associate the effect with quantum flucutuations of the order parameter., Comment: 6 pages, 6 figures

The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T-->0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for suppression of another basic attribute of superconductivity - persistent currents - dramatically affecting their magnitude, the period and the shape of the current-phase relation. The effect is of fundamental importance demonstrating the impact of quantum fluctuations on the ground state of a macroscopically coherent system, and should be taken into consideration in various nanoelectronic applications., 20 pages, 4 figures

Refrigeration is an important enabler for quantum technology. The very low energy of the fundamental excitations typically utilized in quantum technology devices and systems requires temperature well below 1 K. Expensive cryostats are utilized in reaching sub-1 K regime and solid-state cooling solutions would revolutionize the field. New electronic micro-coolers based on phonon-blocked semiconductor-superconductor junctions could provide a viable route to such miniaturization. Here, we investigate the performance limits of these junction refrigerators., 5 pages, 3 figures, published in 2020 International Electron Devices Meeting (IEDM)