Electron Spin Dynamics on the Surface of Superfluid Helium

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Nontechnical AbstractElectrons are a fundamental constituent of all atoms, and it is the tremendous variety of forms their interactions can take which is largely responsible for the wide range of material properties we see in the world around us. In addition to having a negative electric charge, every electron also acts like an extremely weak bar magnet. For an individual electron, the direction that its weak magnet points is described by quantum mechanics, which allows the electron spin ('spin' is another term for describing the weak magnetic field of an electron) to be used as a quantum bit, or 'qubit', for quantum information processing. When a group of electrons are started with all their spins pointing in some direction, and a large external magnetic field pointing in a different direction is turned on, the magnetic field of the electrons rotates around the direction of the external field. The spin coherence is a measure of how accurately the electrons' spins do not change their rotation rate. Long spin coherence is desirable for quantum simulation and quantum computing and has been predicted for electrons on the surface of liquid helium. This experimental project is aimed at making the first measurements of the spin coherence of these electrons, and understanding the physical processes which limit their coherence. Measuring and understanding these processes are a key step towards constructing a quantum computer that uses the magnetic moments of individual electrons as its bits. Quantum computing is an important research area for future high technology industries and national security. This project will support the continuing education of a Postdoctoral Fellow, and partially support a Ph.D. student, together with the participation of undergraduate researchers, working at the boundary between fundamental physics and its applications to new technological opportunities. The Fellow and students will learn how to use the most advanced tools of modern nanoscience research, which has proven to be excellent training for careers in both academia and high technology industries.Technical AbstractThis project will use Electron Spin Resonance (ESR) to measure the spin relaxation and coherence of electrons on the surface of superfluid helium. Calculations and indirect experimental evidence suggest that the spin coherence of these electrons is long, even when they are mobile, but the relaxation and coherence times have never been directly measured. Earlier ESR experiments were stymied by an inability to thermalize the spins, but devices have been designed which are expected to enable rapid spin thermalization. Mobile electrons with long coherence will be particularly valuable quantum bits, or qubits, since the ability to move qubits can reduce the overhead for quantum error correction by two or more orders of magnitude in some architectures. This research will be performed by a Postdoctoral Fellow with partial support of a Ph.D. student and part-time undergraduate students. The Fellow and students will learn nanofabrication, low-temperature techniques, high-sensitivity microwave measurements and quantum information. These skills, requiring resourcefulness and attention to detail have proven themselves to be excellent training for scientific careers in academia, national labs, and high technology industries.