Visa Vesterinen

Kinetic inductance magnetometer

Sensing ultra-low magnetic fields has various applications in the fields of science, medicine and industry. There is a growing need for a sensor that can be operated in ambient environments where magnetic shielding is limited or magnetic field manipulation is involved. To this end, here we demonstrate a new magnetometer with high sensitivity and wide dynamic range. The device is based on the current nonlinearity of superconducting material stemming from kinetic inductance. A further benefit of our approach is of extreme simplicity: the device is fabricated from a single layer of niobium nitride. Moreover, radio frequency multiplexing techniques can be applied, enabling the simultaneous readout of multiple sensors, for example, in biomagnetic measurements requiring data from large sensor arrays.

Submillimeter-wave kinetic inductance bolometers on free-standing nanomembranes

We introduce a microwave submillimeter-wave detector based on an integrated micromesh absorber and superconducting kinetic inductance thermometer on a through-wafer released sub-micron thick membrane. Equilibrium operation achieved by thermal isolation through the membrane geometry enables operation at elevated thermal bath temperatures of 5–10 K. The bolometer operates in a phonon-noise limited regime with a measured noise equivalent temperature difference of below 10 mK at 1 s integration time, which is sufficient for radiometric imaging in terrestrial systems. We also measured and analyzed the bolometer frequency response in the band 0.1–1.4 THz. Performance improvements through further dimensional scale-down and temperature dependency are discussed.

Josephson junction microwave amplifier in self-organized noise compression mode

The fundamental noise limit of a phase-preserving amplifier at frequency is the standard quantum limit . In the microwave range, the best candidates have been amplifiers based on superconducting quantum interference devices (reaching the noise temperature at 700 MHz), and non-degenerate parametric amplifiers (reaching noise levels close to the quantum limit at 8 GHz). We introduce a new type of an amplifier based on the negative resistance of a selectively damped Josephson junction. Noise performance of our amplifier is limited by mixing of quantum noise from Josephson oscillation regime down to the signal frequency. Measurements yield nearly quantum-limited operation, at 2.8 GHz, owing to self-organization of the working point. Simulations describe the characteristics of our device well and indicate potential for wide bandwidth operation.

Advanced Concepts in Josephson Junction Reflection Amplifiers

Low-noise amplification at microwave frequencies has become increasingly important for the research related to superconducting qubits and nanoelectromechanical systems. The fundamental limit of added noise by a phase-preserving amplifier is the standard quantum limit, often expressed as noise temperature

Bolometric kinetic inductance detector technology for sub-millimeter radiometric imaging

T_q=\hbar \omega /2k_B

Tunable Impedance Matching for Josephson Junction Reflection Amplifier

Tq=ħω/2kB. Towards the goal of the quantum limit, we have developed an amplifier based on intrinsic negative resistance of a selectively damped Josephson junction. Here we present measurement results on previously proposed wide-band microwave amplification and discuss the challenges for improvements on the existing designs. We have also studied flux-pumped metamaterial-based parametric amplifiers, whose operating frequency can be widely tuned by external DC-flux, and demonstrate operation at

Side-wall spacer passivated sub-μm Josephson junction fabrication process

2\omega