Electron transport properties of titanium nanowires were experimentally studied. Below the effective diameter 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.PACS numbers: 74.25.F-, 74.78.-w Since the early years of experimental studies in superconductivity it has been noticed that the supercondcunting transition R(T ) has always a finite width. Very often the broadening can be accounted for sample inhomogeneity. However, soon it became clear that, at least in low dimensional samples, the transition width remains finite even with the refined material purity and improved fabrication. The effect has been attributed to fluctuations typically more pronounced in objects with reduced dimensionality. The finite resistance R(T ) ∼ exp (−F 0 /k B T ) at a temperature T below the critical temperature T c of a quasi-one-dimensional superconducting channel with cross section σ has been explained by the thermal fluctuations of the order paprameter: the so called thermal activation of phase slips (TAPS), 1 , 2 . Here the condensation energy F 0 ∼ B 2 c ξσ of the smallest statistically independent volume ξσ, where ξ is the supercondcuting coherence length and B c is the critical magnetic field, competes with the thermal energy k B T . The effect manifests itself only sufficiently close to the critical temperature, and in extreemly homogeneous samples with micrometer-size diameter (e.g. pure whiskers) leads to the experimentally observable width of the R(T ) transition of about few mK 3 , 4 , 5 . In less homogeneous objects (e.g. lithographically fabricated nanowires) separation of the impact of the thermal fluctuations from the trivial inhomogeneity-determined R(T ) broadening is rather problematic 6 . Nevertheless with development of nanotechnology 7 it became clear that in extreemly narrow superconducting wires, with diameters ∼10 nm, the shape of the R(T ) transition by no means can be explained by sample inhomogeneity or/and thermal fluctuations 8 . The effect has been attributed to quantum fluctuations, also called -quantum phase slips (QPS) -and has been observed in a rather limited number of experiments studying the transport properties of ultra-narrow nanowires made of various superconducting materials: amorphous M oGe 9 , 10

Quantum fluctuations in quasi-one-dimensional superconducting channels leading to spontaneous changes of the phase of the order parameter by 2π, 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.

Since the introduction of bolometers more than a century ago, they have been applied in a broad spectrum of contexts ranging from security and the construction industry to particle physics and astronomy. However, emerging technologies and missions call for faster bolometers with lower noise. Here, we demonstrate a nanobolometer that exhibits roughly an order of magnitude lower noise equivalent power, 20 zW/ √ Hz, than previously reported for any bolometer. Importantly, it is more than an order of magnitude faster than other low-noise bolometers, with a time constant of 30 µs at 60 zW/ √ Hz. These results suggest a calorimetric energy resolution of 0.3 zJ = h × 0.4 THz with a time constant of 30 µs. Thus the introduced nanobolometer is a promising candidate for future applications requiring extreme precision and speed such as those in astronomy and terahertz photon counting.

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.

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.