The programme is divided into four projects, each of which is designed to answer one of four main research challenges necessary to achieve the overall aim of producing a single atom quantum information device in silicon.
Project 1. Atomic Scale Device Fabrication
The outcome of the programme will be the development of devices based on multiple species of impurities placed with atomic precision. Challenge 1: to develop atomic-scale patterning techniques for new impurity species and combinations. We shall commence with sequential doping of single species using implantation at the Surrey Ion Beam Centre. We will fabricate atomically precise single and few atom buried dopant devices in silicon for subsequent transport measurements and electrically detected magnetic resonance measurements (EDMR).
More about building a single atom silicon device
Project 2. Atomic state readout
To study certain quantum effects such as entanglement, we will need to readout the state of single spins. This readout must occur more quickly than the T1 time so that the spin state does not decay. Single spin readout has not yet been demonstrated in silicon, Challenge 2: To readout the quantum state of a single spin in silicon in a time faster than the relaxation time, T1. An important experimental route toward this demanding goal will be scanning tunnelling microscopy, which functions as a test-bed for relevant nanodevice concepts (most likely to be variants on single electron transistors) to be implemented in WP1 and tested with microwaves in this workpackage and subsequently at FELIX in WP4.
More about magnetic sensing a single electron spin in silicon
Project 3. Theory and Modelling of Molecular Defects and Interactions
The theoretical understanding of the time-dependent magnetic exchange interaction6, has so far only exploited theory appropriately scaled from the wave- functions of a hydrogen atom in free space. The major theoretical differences between impurities and atoms in traps are that de-excitation can be via lattice vibrations, and that the wave-functions have cubic symmetry imposed by the crystal. Challenge 3: to extend the theory to impurities in crystals with realistic molecular wavefunctions and appropriate inputs for the relaxation and dephasing times. We will generate and solve the effective Hamiltonians describing the interaction of infrared and microwave photons with the spin and orbital degrees of freedom in silicon.
More about modelling the interactions between atoms, electrons and spins
Project 4. Two-colour THz/microwave coherent control
Quantum coherence and the associated physics in atoms in traps has predominantly been observed and controlled using pulsed visible lasers. The primary reason that this physics has not been exploited in impurities is that the corresponding transitions are in the far-infrared, where sources flexible enough are rare. Challenge 4: to develop new electromagnetic techniques for the far-infrared coherent spectroscopy, equivalent to the visible wavelength techniques used for atoms in traps. We shall combine FELIX with microwave pulsed EPR, to simultaneously control the spin and orbital wavefunctions of defects in silicon, exploiting the electrical detection methods developed in WP1 and WP2 to move towards single-impurity sensitivity. Our new techniques will also enable the FEL to become a source for performing molecule- specific vibrational excitations while monitoring conformation with pulsed EPR. In keeping with what occurred for NMR and X-ray crystallography, we anticipate a long-term impact on biomedicine.
Measuring the effect of FELIX requires different techniques for different scales of device. Working down from the large scale to the nanoscale requires measuring low numbers of donors in ways which minimally disturb the surrounding crystal. Part of the work involves using Donor Bound Excitons to sensitively measure the spin of electrons which FELIX manipulates, which allows us to investigate the dynamics of the spin.
More about controlling the quantum superpositions of orbital and spin motion in silicon