Josephson oscillation linewidth of ion-irradiated YBa2_2Cu3_3O7_7 junctions

We report on the noise properties of ion-irradiated YBa$_2$Cu$_3$O$_7$ Josephson junctions. This work aims at investigating the linewidth of the Josephson oscillation with a detector response experiment at $\simeq$132 GHz. Experimental results are compared with a simple analytical model based on the Likharev-Semenov equation and the de Gennes dirty limit approximation. We show that the main source of low-frequency fluctuations in these junctions is the broadband Johnson noise and that the excess ($\frac{1}{f}$) noise contribution does not prevail in the temperature range of interest, as reported in some other types of high-T$_c$ superconducting Josephson junctions. Finally, we discuss the interest of ion-irradiated junctions to implement frequency-tunable oscillators consisting of synchronized arrays of Josephson junctions

Kerr Enhanced Backaction Cooling in Magnetomechanics

Precise control over massive mechanical objects is highly desirable for testing fundamental physics and for sensing applications. A very promising approach is cavity optomechanics, where a mechanical oscillator is coupled to a cavity. Usually, such mechanical oscillators are in highly excited thermal states and require cooling to the mechanical ground state for quantum applications, which is often accomplished by utilising optomechanical backaction. However, this is not possible for increasingly massive oscillators, as due to their low frequencies conventional cooling methods are less effective. Here, we demonstrate a novel cooling scheme by using an intrinsically nonlinear cavity together with a low frequency mechanical oscillator. We demonstrate outperforming an identical, but linear, system by more than one order of magnitude. While currently limited by flux noise, theory predicts that with this approach the fundamental cooling limit of a linear system can not only be reached, but also outperformed. These results open a new avenue for efficient optomechanical cooling by exploiting a nonlinear cavity

New absorbing materials for applications in decimeter and millimeter wavelengths ranges

The results of tests of the several absorbing materials in the millimeter band are presented. It is shown that at frequencies 140 GHz the absorbing-diffusing materials decrease the reflection from the metallic plate by a value of 34 dB for wide angles range. For the equipment of anechoic chambers there were developed the versions of materials with the lowered combustibility and improved operating characteristics, including the material, closed with a case, laminated by polyethylene fiberglass fabric. There were investigated the composite materials on the basis of magnetoamorphous and nano-crystalline alloys of Fe-Si-B type for 300-1500 MHz frequency region. The two-layered material provided to reduction in the reflection by a value of 10...22 dB in 400-800 MHz frequency band

HTS Josephson junctions arrays for high-frequency mixing

International audienceWe designed, fabricated and measured short one-dimensional arrays of masked ion-irradiated YBa 2 Cu 3 O 7 Josephson junctions embedded into log-periodic spiral antennas. They consist of 4 or 8 junctions separated either by 960 nm or 80 nm long areas of pristine material. Large spacing arrays show " Giant " Shapiro steps in the hundreds-GHz band at 66 K and are tested as Josephson mixers with improved impedance matching. On the contrary, small spacing arrays behave as one junction with a lower superconducting transition temperature, hence forming a single weak link on distances up to 880 nm. Such design opens a new way to increase the I c R n product of the devices, and therefore the efficiency of the Josephson mixers. Hints on the origin of the observed long range proximity effect are proposed

High-temperature superconducting nano-meanders made by ion irradiation

International audienceIn this article, we report on the fabrication of very long YBa2Cu3O7 nanowires in a meander shape patterned in a CeO2-capped thin film by high-energy oxygen ion irradiation. DC and RF characterizations outline the good superconducting properties of the nanowires whose geometryapproaches the one used in single photon detectors. Their inductance, which mainly sets the maximum speed of these devices, has been measured on a wide range of temperature by mean of a resonant method. The extracted values are in agreement with the ones calculated from the geometry of the meanders and from the known London penetration depth in YBa2Cu3O7 thin films