Ch. Häussler

N o n − Φ 0 − p e r i o d i c macroscopic quantum interference in one-dimensional parallel Josephson junction arrays with unconventional grating structure

A theoretical study is presented on a number N of resistively shunted Josephson junctions connected in parallel as a disordered 1D array by superconducting wiring in such a manner that there are N-1 individual SQUID loops with arbitrary shape formed.

Nonperiodic flux to voltage conversion of series arrays of dc superconducting quantum interference devices

A theoretical study on the voltage response functionof a series array of dc SQUIDs is presented in which the elementary dc SQUID loops vary in size and, possibly, in orientation. Such series arrays of two-junction SQUIDs possess voltage response functions vs. external magnetic field B that differ substantially from those of corresponding regular series arrays with identical loop-areas, while maintaining a large voltage swing as well as a low noise level. Applications include the design of current amplifiers and quantum interference filters.We present a theoretical study on the voltage response function 〈V〉 of series arrays of dc superconducting quantum interference devices (SQUIDs) for which the elementary dc SQUID loops vary in size and, possibly, in orientation. If the distribution of the array loop sizes is chosen according to an arithmetic relation, 〈V〉 is not a Φ0-periodic function of the strength of external magnetic field B. For arithmetic arrays the periodicity of 〈V〉 is controlled by the geometry of the array alone and does not depend on spreads in the array junction parameters. If small fluctuations are added to the loop size distribution, 〈V〉 becomes a unique function around a global minimum at B=0 without possessing significant additional minima for finite B. This filter property does not apply for conventional SQUIDs and series arrays of identical or nearly identical SQUID loops. Applications of arithmetic series arrays include the design of current amplifiers and novel quantum interference filters, which possess large voltage ...

High-performance magnetic field sensor based on superconducting quantum interference filters

We have developed an absolute magnetic field sensor using a superconducting quantum interference filter (SQIF) made of high-Tc grain-boundary Josephson junctions. The device shows the typical magnetic-field-dependent voltage response V(B), which is a sharp deltalike dip in the vicinity of zero-magnetic field. When the SQIF is cooled with magnetic shield, and then the shield is removed, the presence of the ambient magnetic field induces a shift of the dip position from B0≈0 to a value B≈B1, which is about the average value of the Earth’s magnetic field, at our latitude. When the SQIF is cooled in the ambient field without shielding, the dip is first found at B≈B1, and the further shielding of the SQIF results in a shift of the dip towards B0≈0. The low hysteresis observed in the sequence of experiments (less than 5% of B1) makes SQIFs suitable for high precision measurements of the absolute magnetic field. The experimental results are discussed in view of potential applications of high-Tc SQIFs in magnetom...

Highly sensitive magnetometers for absolute magnetic field measurements based on quantum interference filters

We present an experimental study on absolute field magnetometers based on superconducting quantum interference filters (SQIFs). Two different prototype SQIF circuits have been designed and fabricated. The first type comprises a one dimensional Josephson junction array possessing unconventional grating structure. The second type is a series array of loops with different areas each loop having two Josephson junctions. The flux to voltage transfer function of both SQIFs has a unique voltage signal around zero applied flux. Our results show that SQIFs can be applied as highly sensitive magnetometers for absolute magnetic field measurements.

Two dimensional superconducting quantum interference filters

We have successfully developed a novel superconducting quantum interferometer based on Josephson junction networks with unconventional loop size distribution. For distinct theoretically determined distributions, the magnetic field B dependent dc voltage V(B) of the interferometer possesses a unique delta-peak like characteristics around B=0. Such devices are called Superconducting Quantum Interference Filters (SQIFs). The unique voltage response of SQIFs allows novel applications, e.g., absolute magnetic field sensors, high speed logical switches and non hysteretic low noise amplifiers which can be directly connected to standard room temperature electronics. In this paper we present new experimental and theoretical results on high performance two dimensional Superconducting Quantum Interference Filters (2D SQIFs). Such 2D SQIFs can be used as absolute magnetic field sensors. Our results indicate that due to the scaling behavior of the flux to voltage transfer function and the scaling of the white output noise, a highly sensitive absolute field sensor based on 2D SQIFs can be very small in size.

Effects of magnetic field on two-dimensional superconducting quantum interference filters

We present an experimental study of two-dimensional (2D) superconducting quantum interference filters (SQIFs) in the presence of a magnetic field B. Although the nonlinear dynamics of the 2D SQIF are much more complex than those of previously studied one-dimensional SQIFs, we found for the 2D SQIF a similar dependence of the voltage V on the magnetic field applied, which is characterized by a unique delta-like dip at B=0. The voltage span of the dip depends on the distribution of areas of the individual loops, and on the bias current, and it scales proportionally to the number of rows simultaneously operating at the same working point. In addition, the voltage response of individual rows of the 2D SQIF is sensitive to the field gradient generated by a control line superimposed on the homogeneous field of a coil. This feature suggests the use of these devices as highly sensitive absolute detectors of spatial gradients of the magnetic field.

Quadratic mixing of radio frequency signals using superconducting quantum interference filters

The authors demonstrate quadratic mixing of weak time harmonic electromagnetic fields applied to superconducting quantum interference filters (SQIFs), manufactured from high-Tc grain boundary Josephson junctions and operated in active microcooler. The authors use the parabolic shape of the dip in the dc voltage output around B=0 to mix quadratically two external rf signals, at frequencies f1 and f2 well below the Josephson frequency fJ, and detect the corresponding mixing signal at ∣f1−f2∣. Quadratic mixing also takes place when the SQIF is operated without magnetic shield. The experimental results are well described by a simple analytical model based on the adiabatic approximation.

Dynamic electromagnetic response of three-dimensional Josephson junction arrays

We present a theoretical study on the dynamical properties of three-dimensional arrays of Josephson junctions. Our results indicate that such superconducting networks represent highly sensitive three-dimensional superconducting quantum interference devices (3D SQUIDs) having some major advantages in comparison with conventional planar SQUIDs. The voltage response function of 3D SQUIDs is directly related to the vector character of external electromagnetic fields. The theory developed here allows the three-dimensional reconstruction of a detected external field including phase information about the field variables. Applications include the design of magnetometers, gradiometers, and particle detectors.

Two-Tone Response of Radiofrequency Signals Using the Voltage Output of a Superconducting Quantum Interference Filter

In the presence of weak time-harmonic electromagnetic fields, superconducting quantum interference filters (SQIFs) show the typical behavior of nonlinear mixers. The SQIFs are manufactured from high-Tc grain boundary Josephson junctions and operated in active microcooler. The dependence of dc voltage output Vdc versus static external magnetic field B is nonperiodic and consists of a well pronounced unique dip at zero field, with marginal side modulations at higher fields. We have successfully exploited the parabolic shape of the voltage dip around B = 0 to mix quadratically two external time-harmonic rf-signals, at frequencies f1 and f2 below the Josephson frequency fJ, and detect the corresponding mixing signal at |f1− f2|. When the mixing takes place on the SQIF current–voltage characteristics, the component at 2f2−f1 is present. The experiments suggest potential applications of a SQIF as a nonlinear mixing device, capable to operate at frequencies from dc to few gigahertz with a large dynamic range.

Two-Tone Response in Superconducting Quantum Interference Filters

We successfully exploit the parabolic shape of the dc voltage output dip around B = 0 of a superconducting quantum interference filter (SQIF) to mix weak external r f signals. The two-tone response of weak time harmonic electromagnetic fields has been detected on the spectral voltage output of the SQIF at frequency f₀ = f₁ - f₂, for various frequencies f₁ and f₂ ranging from few MHz up to 20 GHz. The two-tone response is a characteristic function of static magnetic field B and of bias current I_b, related to the second derivative of the dc voltage output.