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New measurements and manipulation of single electrons for the “second quantum revolution”

At the dawn of the 20th century a new way of looking at the world resulted in what is now known as the first “quantum revolution”. This resulted in the replacement of vacuum tubes with transistors, that allowed not only the development of such things as transistor radios but led to spaceflight, photovoltaics, and silicon chips. This period also saw the advent of lasers, atomic clocks, and MRI scanners.

We are now at the start of the second quantum revolution where technology allows us to organise and control individual particles and quasi-particles that are governed by quantum physics. However, these new ways of looking at the world and new developments, like quantum computing and quantum sensing, require new measurements.

The EMPIR project Single-electron quantum optics for quantum-enhanced measurements (17FUN04, SEQUOIA) set out to utilise the extreme sensitivity of charged particles to their environment to design quantum sensors of the electromagnetic field and to develop quantum metrology for single electrons.

In this the project was highly successful publishing new research in a series of articles in the prestigious Nature journals:

• Quantum tomography of electrical currents (2019) Nature Communications  
• Continuous-Variable Tomography of Solitary Electrons (2019) Nature Communications  
• Excitonic nature of magnons in a quantum Hall ferromagnet (2021) Nature Physics

The project also  published two papers:

• Time-resolved Coulomb collision of single electrons (2023) Nature Nanotechnology.
• Two electrons interacting at a mesoscopic beam splitter (2023) Nature Nanotechnology

Along  with a third paper from one of the stakeholders of the project: Coulomb-mediated antibunching of an electron pair surfing on sound (2023) Nature Nanotechnology.

These important experimental results have been supported – and understood – using a common framework based around a theory developed in the project and published in the journal Physical Review B: Collision of two interacting electrons on a mesoscopic beam splitter: Exact solution in the classical limit. An overview of this topic can also be found in Interacting electrons collide at a beam splitter (2023) Nature Nanotechnology, news & views.

To further understanding of this ‘exotic’ field the consortium also published a white paper entitled Single-electron wave packets for quantum metrology: concepts, implementations, and applications.

In practical terms these results will help in the development of new technology such as quantum computation, simulation and the practical realisation of integrated quantum circuitry. They also form a natural platform for the realisation of in-situ quantum sensors for technology applications.

The project’s research on the optimisation of high-energy single-electron pumps has contributed to a roadmap on quantum nanotechnologies and will also be used in further improvements of single-electron quantised current pumps for the realisation of the quantum ampere in the new SI.

As well as demonstrating new quantum phenomena – such as the first observation of the excitonic nature of magnons in a quantum Hall ferromagnet - in the long term this body of work will form the basis of technological innovation. This includes the miniaturisation of devices down to nanometer length scales, and the development of sensors with vastly improved performance over what can be achieved within a classical physics framework.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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