Quantum System Theory Research Team

Principal Investigator

PI Name Daniel Loss
Degree Ph.D.
Title Team Leader
Brief Resume
1985 Ph.D. in Theoretical Physics, University of Zurich, Switzerland
1985 Postdoctoral Research Associate, University of Zurich, Switzerland
1989 Postdoctoral Research Fellow, University of Illinois at Urbana-Champaign, USA
1991 Research Scientist, IBM T. J. Watson Research Center, USA
1993 Assistant/Associate Professor, Simon Fraser University, Canada
1996 Professor, Department of Physics, University of Basel, Switzerland (-present)
2012 Team Leader, Emergent Quantum System Research Team, RIKEN
2013 Team Leader, Quantum System Theory Research Team, Quantum Information Electronics Division, RIKEN Center for Emergent Matter Science (-present)
2021 Team Leader, Semiconductor Quantum Information Device Theory Research Team, RIKEN Center for Quantum Computing (-present)


Our team works on the quantum theory of condensed matter with a focus on spin and topological phenomena in semiconducting and magnetic nanostructures. In particular, we investigate novel mechanisms and seek new platforms hosting topological or spin phases in solid-state systems, including helical spin texture, topological insulators and topological superconductors, which have potential hosting topological quantum states, such as Majorana fermions and parafermions. Moreover, we also investigate (quasi-)one-dimensional Tomonaga-Luttinger liquid, nuclear spins in semiconductors, many-body effects in low-dimensional systems, (fractional) quantum Hall effect, strongly correlated electron systems, spin-orbit interaction, and quantum transport phenomena.

Research Fields

Theoretical Physics, Quantum Theory of Condensed Matter


Strongly correlated electron system
Spin-orbit interaction
Topological quantum matter
Majorana fermions and parafermions


Helical Liquids in Semiconductors

One-dimensional helical liquids can appear at boundaries of certain condensed matter systems. Two prime examples are the edge of a quantum spin Hall insulator, also known as a two-dimensional topological insulator, and the hinge of a three-dimensional second-order topological insulator. The presence of such states serves as a signature of their nontrivial bulk topology.

We investigate various aspects of helical liquids, such as their realization, topological protection and stability, or possible experimental characterization. We focus especially on proximity-induced topological superconductivity, allowing for exciting applications towards topological quantum computation with the resulting Majorana bound states.

Helicity. (Left) In particle physics, the helicity of a particle is defined through the relative orientation between its spin and momentum. (Right) In a condensed matter system hosting spin-1/2 fermions with quadratic dispersion, we can label the degenerate states near the Fermi level either by their spins or by their helicities. Unlike the spin, the states with opposite helicities can be split in a time-reversal-invariant system.
Chen-Hsuan Hsu, Peter Stano, Jelena Klinovaja, and Daniel Loss, “Helical Liquids in Semiconductors”, Semicond. Sci. Technol. 36, 123003 (2021).© IOP Publishing


Majorana Kramers pairs in higher-order topological insulators

Higher order topological insulators are systems which realize the most recent flavor of topological matter. While being insulating in the bulk and on the surface, they host propagating states at the edges (hinges), where two facets meet. We designed a tune-free scheme to realize Kramers pairs of Majorana bound states in higher-order topological insulators with proximity-induced superconductivity.

Our scheme is an experimentally accessible setup, which proposes to use a bismuth wire half-covered by a superconductor. Namely, we find that when two hinges with the same helicity of the wire are in contact to an s-wave superconductor, moderate electron-electron interactions favor the inter-hinge pairing over the intra-hinge pairing, leading to formation of Majorana Kramers pairs. As a result, the proposed scheme does not require a magnetic field or local voltage gates, which is a highly desired property in the quest for topological states.


Left panel: Higher order topological insulator realized using a superconductor (yellow) and a wire (green). Right panel: The phase diagram of the model shown in the Left panel.
Chen-Hsuan Hsu, Peter Stano, Jelena Klinovaja, and Daniel Loss, “Majorana Kramers Pairs in Higher-Order Topological Insulators,” Phys. Rev. Lett. 121, 196801 (2018) © APS



Topological Floquet Phases in Driven Coupled Rashba Nanowires

Even though the most of the recent studies of topological matter were focused on static structures, it has been recently proposed to extend the investigations to non-equilibrium systems. We circumvent the difficulty of analysis of a two-dimensional system with electron-electron interactions by considering a strongly anisotropic 2D system formed by weakly coupled Rashba wires (see the figure), where each of them can be treated as a one-dimensional Luttinger liquid by bosonization. This allowed us to introduce the Floquet version not only of topological insulators but also of Weyl semimetals in driven 2D systems. Importantly, in this way we can also address fractional regimes and are able to obtain the Floquet version of fractional TIs and Weyl semimetals.

Upper panel: An array of quantum wires under a time dependent driving realizing the Floquet topological insulator.

Lower panel: The phase diagram of the model shown in the upper panel as a function of the Floquet coupling tF and the tunneling amplitude t2.

J. Klinovaja, P. Stano, D. Loss, “Topological Floquet Phases in Driven Coupled Rashba Nanowires”, Phys. Rev. Lett. 116, 176401 (2016) © APS




Daniel Loss

Team Leader loss.daniel[at]riken.jp

Peter Stano

Senior Research Scientist peter.stano[at]riken.jp


  1. O. Malkoc, P. Stano, and D. Loss

    Charge-Noise-Induced Dephasing in Silicon Hole-Spin Qubits

    Phys. Rev. Lett. 129, 247701 (2022)
  2. C.-H. Hsu, P. Stano, J. Klinovaja, and D. Loss

    Helical liquids in semiconductors

    Semicond. Sci. Technol. 36, 123003 (2021)
  3. C.-H. Hsu, F. Ronetti, P. Stano, J. Klinovaja, and D. Loss

    Universal conductance dips and fractional excitations in a two-subband quantum wire

    Phys. Rev. Research 2, 043208 (2020)
  4. P. P. Aseev, P. Marra, P. Stano, J. Klinovaja, and D. Loss

    Degeneracy lifting of Majorana bound states due to electron-phonon interactions

    Phys. Rev. B 99, 205435 (2019)
  5. C.-H. Hsu, P. Stano, J. Klinovaja, and D. Loss

    Majorana Kramers Pairs in Higher-Order Topological Insulators

    Phys. Rev. Lett. 121, 196801 (2018)



2-1 Hirosawa, Wako, Saitama 351-0198 Japan