NPL is developing nano-scale devices for moving electrons one at a time around an electrical circuit.

In these electron pumps, a periodic clock signal at a frequency f causes a precise number n (usually one) of electrons to pass through during each clock period. The current is then given by I = nef, where e is the charge on each electron. This behaviour is in contrast to everyday electronics - even the most miniaturised transistors in modern computers move thousands of electrons per clock cycle.

The motivation for developing single electron pumps is to enable the metrological triangle experiment to be carried out. This experiment will verify the consistency of the existing electrical standards - the quantum Hall effect resistance standard and the Josephson effect voltage standard.

Our electron pumps use a dynamical quantum dot formed using metal gates to create a confining potential with a two dimensional electron gas. At low temperature and high magnetic field, these devices can trap and release 100,000,000 electrons per second with an error rate smaller than 1 in 100,000.

An alternative method of forming a quantum current standard is to use the phenomenon of quantum phase slip in extremely narrow superconducting wires, narrower than the superconducting coherence length. In such wires the amplitude of the order parameter can fluctuate to zero, allowing the phase of the wavefunction to slip by 2π.

Theoretical predictions have shown that such a nanowire, when embedded in a circuit containing the correct combination of inductance and resistance, will form a phase-slip junction whose properties are dual to those of the Josephson junction.

The Josephson Voltage standard is based on the AC Josephson effect, in which a microwave drive causes coherent transport of fluxons across an array of Josephson junctions, leading to very flat plateaux of voltage when the device is current biased. The dual effect in a phase-slip junction is expected to cause coherent transport of Cooper pairs (pairs of electrons) along the superconducting nanowire, leading to very flat plateaux of current when the device is voltage biased.

Phase-slip junctions have the potential to transport larger currents than electron pumps and with higher accuracy.

People working on project

• Masaya Kataoka
• Jon Fletcher
• Stephen Giblin
• Carol Webster
• Jon Fenton
• JT Janssen

Recent publications

• Tunable Nonadiabatic Excitation in a Single-Electron Quantum Dot
  M. Kataoka, J. D. Fletcher, P. See, S. P. Giblin, T. J. B. M. Janssen, J. P. Griffiths, G. A. C. Jones, I. Farrer, and D. A. Ritchie
  Phys. Rev. Lett. 106, 126801 (2011)
• An accurate high-speed single-electron quantum dot pump
  S P Giblin, S J Wright, J D Fletcher, M Kataoka, M Pepper, T J B M Janssen, D A Ritchie, C A Nicoll, D Anderson and G A C Jones
  S P Giblin et al
  New J. Phys. 12, 073013, (2010)
• Materials for superconducting nanowires for quantum phase-slip devices
  J C Fenton, C H Webster and P A Warburton
  J. Phys.: Conf. Series 286 012024 (2011)