National Physical Laboratory

NanoSQUIDs NanoSQUIDs

NanoSQUIDs - nanoscale superconducting quantum interference devices - represent a new manifestation of an old but exciting superconducting technology.


The requirements of quantum metrology and nanoscience are driving the need for single particle detection and measurement capability across a wide range of physics, including quantum information processes (QIP), single photon detection, nanoelectro-mechanical resonator system (NEMS), nanomagnetism and spintronics. NanoSQUIDs - nanoscale superconducting quantum interference devices - represent a new manifestation of an old but exciting superconducting technology which addresses some of these requirements [1,2].

At NPL we have developed a particularly straightforward method for nanoSQUIDs using focussed ion beam (FIB) fabrication. Starting with a simple bilayer film of Nb/W in a single lithography step, this milling process allows the loop diameter to be reduced down to 100 nm, with the incorporation of nanobridge junctions of the order of 60 nm width [3]. Our nanoSQUIDs have shown non- hysteretic I-V characteristics over a temperature range from 6K to 8.5K, also demonstrating exceptionally low magnetic flux noise performance (<200 nφ0/Hz1/2 at 6.8K where f0 =2x10-15 Wb is the quantum of magnetic flux) [4].

It is well known that limitations on SQUID sensitivity set by thermal noise can be reduced by lowering the inductance and capacitance of the SQUID device. What has not been attempted until recently is to achieve this by minimising both the size of the SQUID superconducting loop and the capacitance of the Josephson junctions, by using microbridge technology rather than tunnel-effect junctions. At NPL we were able to demonstrate that our nanoSQUIDs have the best magnetic flux resolution achieved with a SQUID at normal liquid helium operating temperatures. These high performance devices and the fabrication technologies on which they are based are expected to find uses in a number of projects.

Detecting Nanomagnetic Particle

Detection of ever-smaller magnetic-particles is of crucial technological and scientific importance, driven both by the needs of the information technology and telecom communities but also by medical and biological requirements, in addition to improved understanding of the physics of small numbers of coupled spins. SQUIDs, not only the most sensitive detectors for a wide range of physical parameters, are also exquisitely suitable for the measurements on magnetic nanoparticles. We have predicted that the sensitivity of a sufficiently small SQUID should be adequate to detect the reversal of a single Bohr magneton moment [5].

At NPL we have used an ultralow noise nanoSQUID to measure the hysteretic magnetization behaviour of a single FePt nanobead at a temperature of around 7 K in a magnetic field of only10 mT. We also shown that, using nanomanipulation, the nanobead can be accurately positioned with respect to the SQUID loop and then removed without affecting SQUID performance. This system is capable of further development with wide ranging applications in nanomagnetism.

NanoSQUID for NEMS

View the NEMS page

ISTED Nano-bolometers and microdosimetry 

Nano-bolometer:

 Another use of the nanoSQUID technology has led to an energy resolving (0.1 eV) non-dissipative bolometer. The NPL-invented superconductor-based ISTED (Inductive Superconductive Transition Edge Detector) [6] is a non-dissipative nano-bolometer combining extremely small heat capacity (~ 10-15 JK-1) with an energy resolution approaching ~1 yoctojoule (10-24 J) in unit bandwidth. This already allows for a single particle measurement of photons with 0.1 eV spectral resolution while operating at relatively high temperatures (~8 K) and in future may be used for detection of single macromolecules and even phonons.

Microdosimetry of ionisation radiation for cancer treatments:

The SQUID bolometer work is also an important step in response to the requirement, expressed by the BIPM, for a new physical quantity more closely related to the biological response of ionising radiation than absorbed dose, in particular for proton and light-ion beam radiotherapy.

Our aim is to investigate the same ISTED SQUID bolometry methods to measure directly the energy deposited by single ionising radiation events [7]. This work involves collaboration between the Quantum Detection Group and Radiation Dosimetry Group at NPL, together with Surrey University and the Royal Surrey County Hospital.

The main activity at this early stage involves modelling and design of ISTED bolometers and identification of a material to act as a suitable tissue 'phantom'. A small portable cryostat is under construction which will allow the ISTED device to be mounted on the microbeam facility at Surrey University. This superconducting technology also forms the basis for an experiment-based Ph.D. project, jointly supervised with Surrey University, with the funding from NHS.

Quantum limited measurement by Nano-scale SQUIDs

NanoSQUIDs will continue to contribute to the development and accuracy of quantum metrology. Further improvements arising from novel SQUID readout techniques should enable faster quantum-limited detectors. A better understanding of back-action of the detectors onto the quantum state of a system under measurement, along with reduction in other external and internal sources of decoherence, will enable widespread use of SQUID measurement schemes for quantum non-demolition readout.

References

  1. J.C. Gallop, 'SQUIDs: some limits to measurement', Supercond. Sci. Technol. Vol. 16 pp 1575-82 (2003)
  2. L. Hao, 'Quantum Detection Applications of NanoSQUIDs fabricated by Focussed Ion Beam, Journal of Physics: Conference Series 286, 012013 (2011)
  3. L. Hao, D. C. Cox and J C Gallop,  'Characteristics of focussed ion beam (FIB) nano Josephson devices',  Supercond. Sci. Technol. 22 , 064011 (2009)
  4. L. Hao, J. C. Macfarlane, J. C. Gallop, D. Cox, J. Beyer, D. Drung, and T. Schurig, 'Measurement and noise performance of nano-superconducting quantum interference devices fabricated by focused-ion-beam', Appl. Phys. Lett. Vol. 92, 192507 (2008)
  5. L. Hao, C. Aßmann,  J. C. Gallop, D. Cox, F. Ruede, O. Kazakova, P. Josephs-Franks, D. Drung, and Th. Schurig, 'Detection of single magnetic nanobead with a nano-superconducting quantum interference device', Appl. Phys. Lett. Vol. 98, 092504 (2011)
  6. L. Hao, J.C. Macfarlane, S.K.H. Lam, C.P Foley, P. Josephs-Franks and J.C. Gallop 'Inductive Sensor Based on Nano-scale SQUIDs', IEEE Trans. Appl. Supercond.,  Vol. 15 No. 2 pp.514-517 (2005)
  7. S. Galer, L. Hao, J. Gallop, H. Palmans, K. Kirkby and A. Nisbet, 'Design concept of a novel SQUID-based microdosemeter',  Radiation Protection Dosimetry  Vol.143, issue2-4, pp427-431 (2011).

People working on project

External Collaborators

Recent Publications

Measurement and noise performance of nano-superconducting quantum interference devices fabricated by focused-ion-beam
L. Hao, J. C. Macfarlane, J. C. Gallop, D. Cox, J. Beyer, D. Drung, and T. Schurig
Appl. Phys. Lett. Vol. 92, 192507 (2008)

Characteristics of focussed ion beam (FIB) nano Josephson devices
L. Hao, D. C. Cox and J C Gallop
Supercond. Sci. Technol. 22, 064011 (2009).

Focussed Ion Beam NanoSQUIDs as Novel NEMS Resonator Readouts
L. Hao, J. C. Gallop, D. Cox, E. J. Romans, J. C. Macfarlane and J. Chen
IEEE Trans. Appl. Supercond., Vol.19, no.3, p693-696, 2009.

Quantum Detection Applications of NanoSQUIDs fabricated by Focussed Ion Beam
L. Hao
Journal of Physics: Conference Series 286, 012013 (2011)

Detection of single magnetic nanobead with a nano-superconducting quantum interference device
L. Hao, C. Aßmann, J. C. Gallop, D. Cox, F. Ruede, O. Kazakova, P. Josephs-Franks, D. Drung, and Th. Schurig
Appl. Phys. Lett. Vol. 98, 092504 (2011)

Design concept of a novel SQUID-based microdosemeter
S. Galer, L. Hao, J. Gallop, H. Palmans, K. Kirkby and A. Nisbet
Radiation Protection Dosimetry vol.143, issue2-4, pp427-431 (2011)

Noise Performance of Niobium Nano-SQUIDs in Applied Magnetic Fields NanoSQUID
Ed J. Romans, S. Rozhko, L. Young, A. Blois, L. Hao, D. Cox, and J. C. Gallop
Accepted for IEEE Trans. Appl. Supercond., (2011)

Posters, Papers and other media

  • L. Hao et al  -  Fabrication, measurement and Noise Performance of nanoSQUIDs made by Focussed Ion beam (paper)

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