Noise properties of the Bloch oscillating transistor

We have measured the current noise spectral density of the Bloch oscillating transistor as a function of current gain. We find, as expected from theory and simulations, that the equivalent input noise that shows up in the output is less than the shot noise of the normal-insulating-superconductor tunnel junction (base junction). At the optimal operating point we find a reduced input current noise of 1.0fA/√Hz and a corresponding noise temperature of 0.4 K. The differential current gain at the same point is as large as 30 and the power gain amounts to 35.Peer reviewe

Design of cryogenic 700 MHz HEMT amplifier

We present a way to design a high-frequency low-temperature pHEMT-based balanced amplifier. The design is based on measured cryogenic S-parameters combined with a small-signal noise model. Using the design process we constructed an amplifier that was measured to have a gain of 16 dB and a noise temperature of ∼3 K when cooled to 4.2 K.Non Peer reviewe

Electron-beam welded Cu-to-Ag joints for thermal contact at low temperatures

Electrical resistance measurements at 4.2 K on an electron‐beam welded Cu‐Ag joint and a simple screw‐fastened Cu‐Ag joint are reported. It was found that the welded joint, when annealed, gives a contact resistance that is about three times smaller than the resistances for the best screw‐fastened joints.Peer reviewe

Nuclear spin relaxation at ultralow temperatures

Nuclear spin relaxation induced by hyperfine coupling is studied theoretically at positive and negative submicrokelvin temperatures. By avoiding the assumption of the high-temperature limit, adopted in conventional theories, we derive a formula in which the relaxation rate is expressed in terms of thermal averages of nuclear spin energies. The exchange interaction induces an asymmetry in the energy spectrum, which leads to relaxation rates that depend on whether the nuclear spin temperature is positive or negative. High-temperature expansion methods and Monte Carlo simulations are applied to explain the anomalous results by Hakonen et al. in rhodium qualitatively.Peer reviewe

Differential Bloch Oscillating Transistor Pair

We examine a Bloch Oscillating Transistor pair as a differential stage for cryogenic low-noise measurements. Using two oppositely biased, nearly symmetric Bloch Oscillating Transistors, we measured the sum and difference signals in the current gain and transconductance modes while changing the common mode signal, either voltage or current. From the common mode rejection ratio we find values $\sim 20$ dB even under non-optimal conditions. We also characterize the noise properties and obtain excellent noise performance for measurements having source impedances in the M$\Omega$ range.Comment: 8 pages, 3 figure

The Inductive Single-Electron Transistor (L-SET)

We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity $1.4 \times 10^{-4}e/\sqrt{Hz}$, limited by preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than two orders of magnitude lower dissipation than the existing method of radio-frequency electrometry. With an optimized sample, we expect uncoupled energy sensitivity below $\hbar$ in the same experimental scheme.Comment: 10 page

Vortex-free state of 3He-B in a rotating cylinder

Vortex-free states have been observed in 3B at rotation speeds up to 0.9 rad/s in a cylinder of 5-mm diameter. The measured cw NMR spectra, reflecting the order-parameter structure, respond very differently to rotation in opposite directions. The sign of this asymmetry is not linked to the direction of the applied magnetic field, as expected for a gyromagnetic effect, but varies randomly from one cooldown to another.Peer reviewe