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Single electron pumps: Current standards, tomography of single electron wavepackets and electron quantum optics

24 October 2018
Dr Jonathan Fletcher, Quantum Detection Group, National Physical Laboratory

The ability to control the flow of electrical current at the single electron level enables a conceptually simple signal source - the single-electron pump.

Work is ongoing among national measurement laboratories and other research institutes to establish such devices as primary current standards within the redefined system of SI units expected next year. I will give a brief introduction to the SI redefinition and highlight some of this work by NPL and others on quantum current standards.

Also using single-electron technology, the goal of electron quantum optics is to use single-electron excitations to facilitate the transmission of quantum information between components, or provide quantum-enhanced sensing capability. One requirement that we have recently addressed is the need to resolve the structure of injected excitations in the energy-time plane.

Using the selective transmission of a time-dependent barrier as a projection ‘mask’, we can recover the energy-time distribution of electrons emitted from an on-demand GaAs-based single-electron source. This scheme is compatible with recovery of the Wigner quasi-probability function.

At this point we have found that the purity of our injected states is generally low (~7%), but we did find a way of shaping the energy distribution in situ. This kind of read-out and control tools may be essential for establishing single-electron interference effects, for instance in the Hong-Ou-Mandel geometry.

Figure 1: Idealised view of a single-electron pump.

Figure 2: Tomography of single electron excitations.

Figure 3: Interference between single electron wavepackets from two different sources.