Spin-based Floquet quantum information processor

• Applicant: Professorin Mónica Benito González, Ph.D.
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496173695

Important challenges concerning scalability of spin qubits defined on quantum dots (QDs) can be overcome by turning the qubits electrically tunable and addressable. One drawback then is that they are affected by charge noise, the main limitation of coherence times also for other solid-state quantum computing implementations. Another issue of this implementation is related to connectivity, since the natural spin-spin interactions are short-ranged. Although long-distance interactions mediated by superconducting resonators have been demonstrated, to take full advantage of this architecture the qubits should be conveniently, precisely, and quickly connected and disconnected from the common interaction channel.In time-periodically driven systems, the time dimension provides a higher-dimensional configuration space that effectively permits physical phenomena that are out of reach for static systems. Researchers often refer to this field as Floquet engineering, because of the method commonly employed to treat time-periodic problems. I present here a research plan to systematically incorporate time-periodic modulations into the basic functioning of a coherent and efficient spin quantum register. With this theoretical project I will contribute to the development of a scalable spin-based quantum information processor that overcomes present limitations.To tackle the issue of decoherence in state-of-the-art QD spin qubits, I will employ monochromatic and modulated driving fields. If those are properly adapted to the qubit features, they situate the qubits in points of the parameter space which are insensitive to charge noise, increasing the coherence time while keeping some degree of tunability. Moreover, I will exploit time-periodic driving for noise spectroscopy, providing tools to detect spatio-temporal correlations in the noise of a few spin qubits. In a Floquet time crystal the discrete time-translational symmetry is broken and this comes together with excellent stability, which led some researchers to suggest that these crystals could have an impact in quantum computing. I will explore Floquet time-crystal phases in arrays of QD spin qubits and will propose experimentally feasible protocols to realize a universal set of quantum gates while keeping the time crystallinity.A very timely research topic in the area of spin qubits is the efficient on/off switching of the spin-orbit interaction that would eliminate cross-talk problems in all-to-all connectivity setups. I will integrate a monochromatic electric driving field that effectively modifies the properties of the semiconductor nanostructure, providing a switching alternative that is more efficient than the recently used static electric fields. To offer a possibly more scalable alternative for long-distance couplings within a spin qubit register, I will explore Floquet engineered pulses to simulate complex Hamiltonians, which will allow to solve the first useful problems with this architecture.

• DFG Programme: Independent Junior Research Groups