P.W. Josephs-Franks

Miniature dc SQUID devices for the detection of single atomic spin-flips

Abstract We report progress towards a superconducting quantum interference device (SQUID) based system capable of detecting single atomic spin-flips. The scaling of the flux sensitivity with SQUID loop dimension of miniature Nb dc SQUIDs is examined and shown experimentally to vary as predicted. Our smallest device, with loop size 3×3 μm 2 , is capable of detecting a few spins in a 1 Hz bandwidth. We address the task of depositing a sample, of nanoscale dimension, within the SQUID loop.

Inductive superconducting transition-edge detector for single-photon and macro-molecule detection

We present a new type of transition-edge sensor for single-photon and macro-molecule detection. In our detector the absorber element is an isolated, passive absorber of extremely low thermal mass, maintained close to, but below, its superconducting–normal transition, and strongly inductively coupled to a SQUID sensor. Incoming particles or photons are sensed in terms of a transient change in the inductive coupling, rather than a change in resistance. The detectors energy sensitivity and response time can be defined by the thermal mass of the absorber and its thermal contact with a substrate, independently of any electrical connections. We have modelled the energy sensitivity of our inductive superconducting transition-edge sensor using a sub-micron SQUID as an inductive read-out device. An ultimate energy resolution of order 10−25 J Hz−1 is theoretically estimated based on the properties of the read-out SQUID and the dimensions of the absorber. We also report our initial work on fabrication of the Nb nanoscale SQUID where we have used the same material deposited on top of the SQUID as a thin-film absorber.

Development of miniature DC SQUID devices for the detection of single atomic spin-flips

We report progress toward a superconducting quantum interference device (SQUID)-based system capable of detecting a few atomic spin-flips. The scaling of the flux sensitivity with SQUID loop dimension of miniature niobium dc SQUID devices is examined and shown experimentally to vary as predicted. Our smallest device, with loop size 3 /spl mu/m/spl times/3 /spl mu/m, is capable of detecting 40 spins in a 1-Hz bandwidth. We address the task of depositing a sample, of nanoscale dimension, within the SQUID loop.

Self-organization of Mn12 single-molecule magnets into ring structures induced by breath-figures as templates

Cooling evaporation of a CH2Cl2 solution of Mn12 clusters on highly oriented pyrolitic graphite (HOPG) initiates the formation of water droplets that act as templates for the formation of self-assembled molecular magnetic rings.

Outgassing of water vapour, and its significance in experiments to determine the Boltzmann constant

The rate of outgassing of water vapour from metal tubing and spheres is estimated and formulae given for the expected amount fraction of water added to otherwise pure gases. The relevance of these estimates to current efforts to redetermine the Boltzmann constant with relative uncertainty of measurement uR(kB) ≈ 1 × 10−6 is supported with experimental results using trace moisture sensors and combined acoustic and microwave resonators. The outgassing does not represent an insuperable obstacle to accurate determinations of the Boltzmann constant in any of the current experiments. However, all workers in this field need to evaluate the extent of outgassing and devise a strategy for estimating and minimizing its effect.

Small area, low-inductance niobium SQUID for the detection of single atomic spin-flips

Abstract We report progress towards a superconducting quantum interference device (SQUID) based system capable of detecting single atomic spin-flips. To date we have designed and had manufactured a niobium SQUID with a loop area of 3×10 −6 m by 3×10 −6 m. We present calculations which show that it is capable of detecting a few spins in a 1 Hz bandwidth, and experimental results are given which show that it operates close to the quantum-limit regime with the expected sensitivity. The SQUID is designed so that it will fit into a sample holder that will be loaded into a low-temperature ultra-high vacuum scanning tunnelling microscope (LT UHV STM). The STM will be used to image and manipulate trapped ad-atoms within the SQUID loop.

Progress towards a precision measurement of the helion magnetic moment in Bohr magnetons

We describe progress on a measurement of the magnetic moment of the helion in units of the Bohr magneton. An apparatus has been constructed which allows the exchange of helium-3 for atomic hydrogen in situ. Both helium-3 NMR and hydrogen atom ESR have been observed at a flux density of 0.6 T.

Optically pumped /sup 3/He NMR and atomic hydrogen ESR at 0.6 T

We report the successful observation of high-fields optically pumped nuclear magnetic resonance (NMR) of helium-3 and electron spin resonance (ESR) of atomic hydrogen, both at 0.6 T. Also described are our findings on the relative optical pumping efficiencies of the various components of the 1083 nm line in helium-3. These are a precursor to a measurement of the magnetic moment of the helion in Bohr magnetons. For this measurement the two signal frequencies must be measured sucessively in the same apparatus. This work is aimed at overcoming the limitations for high-accuracy magnetometry of using water as an NMR substance.

Nano-Scale Squids Application for Single Particle Detection and Spectroscopy

The advantages gained by a reduction in feature size towards the sub-micrometre or nanometre scale have opened the way to new applications for SQUlDs. We describe our work to employ sub-micron or nanoscale SQUIDs for single particle detection and spectroscopy using a novel inductive superconducting transition edge technique

The magnetic moment of the helion in Bohr magnetons

We have previously described an experiment to measure the magnetic moment of the helion in Bohr magnetons. We now have preliminary results using the first of two proposed methods, an irreversible seal-breaking method. Improvements obtainable with the second method are discussed.