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Ando lab

The Ando Laboratory, nicknamed Topological Matter Laboratory Cologne, focuses on experimental studies of topological matter and their applications in quantum information technology. Topological matter is a peculiar class of materials in which a nontrivial topology of the quantum-mechanical wavefunctions leads to unusual, and often useful, physical properties. We use nanofabrication and ultra-low-temperature techniques to explore the novel physics of topological matter, in particular topological superconductors hosting Majorana fermions. One of our main goals is to use Majorana fermions for realizing a topological qubit, which would be a game changer for quantum computing.

Postdoc position in topological-insulator circuit Quantum Electrodynamics
We are researching topological quantum computing based on superconductor/topological-insulator hybrid devices. Our group has successfully demonstrated Josephson junctions based on state-of-the-art topological insulator materials that are synthesized in-house, including exfoliated BiSbTeSe2 flakes, MBE-grown (Bi,Sb)2Te3 thin films, and VLS-grown (Bi,Sb)2Te3 nanowires. We are currently focusing on integrating those junctions in devices aimed at realizing Majorana zero modes.
The postdoc will join our circuit quantum electro-dynamics (cQED) team within Ando lab. Responsibilities would be design, simulation, fabrication, and measurement of cQED devices at gigahertz frequencies.

Research areas

Fundamentals of Topological matter

Topological matter is a most fertile ground for new discoveries. Many new types of topological matter are waiting for discoveries, and they are expected to present fundamentally new phenomena. We grow bulk single crystals, epitaxial thin films, and nano-structures of topological matter to explore their novel properties. We also search for new materials and design new topological matter in artificial heterostructures. 

Topological devices

Many novel phenomena expected for topological matter are fundamentally quantum mechanical and are best probed in the “mesoscopic” world. We therefore employ advanced nanofabrication techniques to make suitable devices to address such topological quantum phenomena. Measurements of these devices are usually done at ultra-low temperature down to 10 mK using state-of-the-art instrumentations.

Topological quantum computing

A major theme in our lab is the realization of topological quantum computing, which is expected to be fault-tolerant. It relies on non-local encoding of quantum information in a pair of Majorana zero-modes obeying non-Abelian statistics. In this research area, we are trying to elucidate the existence and properties of Majorana zero-modes in candidate platforms synthesized in our lab, and build qubits to perform the proof-of-principle for topological quantum computing. 

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What is Topological Insulator?

In the topologically-protected surface states of topological insulators, the orientation of electron spin is perpendicularly locked to the momentum.

Topological insulators are a new class of materials where an insulating bulk state supports an intrinsically metallic surface state that is “topologically protected” by time reversal symmetry. Intriguingly, the resulting metallic surface state is helically spin-polarized (i.e., right- and left-moving electrons carry up and down spins, respectively) and consist of massless Dirac fermions (i.e., the energy of quasiparticles is linearly dependent on the momentum). Those peculiar properties of the surface state open exciting new opportunities for novel spintronics devices with ultra-low energy consumptions. Professor Ando is one of the pioneers of the research field of topological insulators, and his pedagogical review article (http://journals.jps.jp/doi/pdf/10.7566/JPSJ.82.102001) provides a good introduction to this new field.

What is Topological Superconductor?

The first data which probed the existence of Majorana fermions on the surface of a topological superconductor. This is a plot of differential conductivity vs bias voltage, measured in Ando Laboratory by point-contact spectroscopy on CuxBi2Se3, which is a superconductor derived from the topological insulator Bi2Se3. [Sasaki et al., Phys. Rev. Lett. 107, 217001 (2011).

Even more exotic state of matter is realized in topological superconductors, which are predicted to host exotic quasiparticles called “Majorana fermions” on the surface. Some superconductors derived from topological insulators are intrinsic bulk topological superconductors. Also, by putting a conventional superconductor on top of a topological insulator, one can induce 2D topological superconductivity on the surface.

Majorana fermions are peculiar in that particles are their own antiparticles, and they were originally conceived as a model for mysterious neutrinos. Currently their realization in condensed matter is of significant interest, because when they are localized, they become topologically-protected zero modes, which are predicted to obey non-Abelian statistics. This unusual statistics, which is distinct from neither Fermi nor Bose statistics, is fundamentally new in physics and allows for performing topologically-protected quantum computation. Also, Majorana fermions can store quantum information in a non-local manner and endow Majorana-based qubits with special robustness against decoherence. These remarkable characteristics of Majorana fermions make them a particularly promising building block of future quantum information technologies.

Who should join?

We offer excellent research environment and interesting projects to talented young physicists (or physicists to be) at all levels: Bachelor students, Master students, PhD students, Postdocs, and even summer-research students. If you are interested in doing research in the Topological Matter Laboratory Cologne, please contact Professor Ando.