Quantum spin dynamics group

Our research
The magnetic moments of nuclei, atoms and molecules in condensed matter can exhibit strongly quantum behaviour, with discrete energy levels and weak coupling to other degrees of freedom. We study the dynamics of these systems, principally using magnetic resonance, to establish...

how best to exploit spins in condensed matter for quantum information applications;
the environment of the spin, which can tell us about materials properties, molecular structures, conformation changes, and relaxation mechanisms;
the interaction of spins with other excitations, to allow detection of magnetic resonance through optical or transport phenomena;
and more!

Reflecting the interdisciplinary nature of our research, our group spans the interface between the Departments of Materials and of Physics at Oxford.

News stories

Recent results

Storing the triplet electron spin coherence in 29Si nuclear spins in silicon.

Triplet states have been used in a number of studies to hyperpolarize nuclear spins and mediate entanglement in mutually coupled nuclear spin systems on timescales dictated by the electron spin processing times. In this collaborative work with the Itoh group in Keio University, we apply pulsed magnetic resonance techniques on the triplet state of the oxygen vacancy center in silicon to demonstrate almost 100% electron polarization. Despite the equal population of the triplet sublevels the high polarization arizes from their different decay rates to the ground state. Furthermore we investigate the coherent storage and retrieval of the highly polarized triplet electron spin coherence in the 29Si nuclear spin using electron nuclear double resonance. Interestingly, the presence of the triplet state doesn't affect the 29Si nuclear spin coherence time which is measured to be similar to the bulk value given by NMR.

Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon
Waseem Akhtar, Vasileia Filidou, Takeharu Sekiguchi, Erika Kawakami, Tatsumasa Itahashi, Leonid Vlasenko, John J. L. Morton, and Kohei M. Itoh y
Physical Review Letters in press (2012)
Recombination centres in Czochralski silicon containing oxide precipitates

Electrically detected magnetic resonance (EDMR) is a very sensitive technique, which can be used for the spectroscopic characterisation of photovoltaic materials on the nanoscale. We have studied the most important recombination centres in Czochralski silicon (Cz-Si) containing strained oxide precipitates (OPs) with a wide range of densities. Cz-Si is used for the vast majority of silicon integrated circuits and ~40% of solar cells, and is known to suffer from various impurities. Strained OPs reveal a square platelet-like shape and are used to confine detrimental impurities to inactive regions of the wafer in a process called internal gettering. The recombination centres associated with intentionally grown OPs as well as with iron-related impurities, such as interstitial iron and the iron-boron pair, are identified via EDMR and discussed. Our results demonstrate that OPs are associated with Pb0 and Pb1 dangling bonds forming at the corners of those platelets.

Spin-dependent recombination in Czochralski silicon containing oxide precipitates
V. Lang, J. D. Murphy, R. J. Falster, and J. J. L. Morton
J Appl Phys 111 013710 (2012) Link
Ideal Leggett-Garg test applied to nuclear spins

The idea that objects can be in two places at the same time is difficult to reconcile with our intuition, and even our logic; this is especially true when one considers proposals to place larger objects into quantum superpositions. Establishing quantum coherence in the macroscopic world remains a considerable technical challenge, but if it could be demonstrated it would represent a significant conceptual advance in our understanding. It could confirm that in principle there are no reasons why macroscopic objects (such as cats, or the moon) cannot exist in paradoxical quantum states. Two ingredients are necessary for this ambitious goal. Firstly, one requires sufficient control over a quantum system to isolate it from the environment and set up the delicate quantum state. Secondly, a rigorous experimental method is needed - one which can exclude alternative theories that describe the system as being either here or there (rather than both here and there, which is what quantum theory tells us). By using an electron spin to 'measure' the nuclear spin in a non-invasive way, it was possible to show inescapable evidence that the nuclear spin state was indeed in a superposition of both up and down at the same time. This was possible thanks to a protocol invented by Leggett and Garg, which was extended to apply to imperfect measurement procedures. Most would consider this system microscopic, and therefore not be terribly surprised by the results - but the experiment will inspire future work probing larger and more complex objects.

Violation of a Leggett-Garg inequality with ideal non-invasive measurements
GC Knee, S Simmons, EM Gauger, JJL Morton, H Riemann, NV Abrosimov, P Becker, H-J Pohl, KM Itoh, MLW Thewalt, GAD Briggs, SC Benjamin
Nature Communications 3 606 (2012) Link