MPhys projects

MPhys projects are available only to current Lancaster undergraduates, and advertised to third years by the department’s project coordinator.

These are recent projects offered in the group.

An atomic clock in your pocket using endohedral fullerenes

Electromagnetic resonator for measuring the clock transition of N@C60 spins.

Atomic clocks are some of the most precise scientific instruments ever made, and are key to advanced navigation, communication, and radar technologies. In the most advanced existing clocks, the atom trap and associated optics take up an entire room. This project will pursue an alternative approach that promises to miniaturise this entire setup into a cell phone.

The technology is based on a unique class of material – endohedral fullerenes. The molecular structure of these materials places single atoms in the hollow space inside a C60 cage. In other words, they are nature’s nanoscale atom traps. The cage protects the quantum state of the atom, leading to a long spin lifetime and therefore a well-defined resonance frequency, which is exactly what is needed for a clock.

This project will focus on overcoming the physics challenges to make this clock a reality. One project place, focusing on theory, will use simulations of the spin energy levels to identify the operating conditions that lead to the most stable clock frequency. The other project place, focusing on experiments, will make spin resonance measurements to characterise the absorption frequencies of the endohedral fullerenes.

We recently described the vision for this technology in our article “Keeping perfect time with caged atoms”, published in IEEE Spectrum (see Publications)

Phonon lasing in a quantum electronic device

The phonon laser

Below: Carbon nanotube electro-mechanical device. When individual electrons (red) tunnel through a suspended nanotube, they excite mechanical motion (blue). Above: Signature of laser behaviour. The signal voltage is proportional to the instantaneous displacement. Below the lasing threshold, the most likely displacement is zero: above threshold, the device oscillates with fixed amplitude.

The laser was invented first for microwaves and then for visible light, but its fundamental physical principles apply to any boson field. This poses an exciting question: can one make a laser for sound?

We have recently created an electronic device whose vibrations show several key signatures of phonon lasing. In place of the photon cavity it uses a vibrating carbon nanotube; in place of the atomic medium it uses a single-electron transistor. However, for reasons not yet understood, the emission fluctuates much more than that of an ideal coherent source. This project aims to understand why.

You will simulate the distribution of emission power predicted for this device and compare with the observed output statistics. In this way you will discover whether the existing theory of electromechanical feedback can explain this novel device.

The phonon laser is described in our paper “A coherent nanomechanical oscillator driven by single-electron tunnelling” (see Publications).

This is a joint project with the group of Alessandro Romito.