Rudolf Gross

Technical Physics

Technical University Munich, Walther Meißner Institute

Walther-Meißner-Institute for Low Temperature Research

Walther-Meißner Strasse 8

85748 Garching

Tel. +49 89 289 14201


Group Webpage


Research focus: quantum information, quantum many-body physics, mathematical fundations

The research group is focused on solid state quantum information systems. Major achievements have been:

  • The realization of ultra-strong coupling in superconducting circuit-QED;
  • The demonstration of controlled symmetry breaking in a qubit-resonator system;
  • The realization of a novel dual-path state reconstruction scheme for propagating quantum microwaves; and
  • The demonstration of path entanglement of continuous-variable quantum microwaves.


Echo Trains in Pulsed Electron Spin Resonance of a Strongly Coupled Spin Ensemble

S. Weichselbaumer, M. Zens, C. W. Zollitsch, M. S. Brandt, S. Rotter, R. Gross, and H. Huebl.

Physical Review Letters 125, 137701 (2020).

Show Abstract

We report on a novel dynamical phenomenon in electron spin resonance experiments of phosphorus donors. When strongly coupling the paramagnetic ensemble to a superconducting lumped element resonator, the coherent exchange between these two subsystems leads to a train of periodic, self-stimulated echoes after a conventional Hahn echo pulse sequence. The presence of these multiecho signatures is explained using a simple model based on spins rotating on the Bloch sphere, backed up by numerical calculations using the inhomogeneous Tavis-Cummings Hamiltonian.


Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains

J. Vijayan, P. Sompet, G. Salomon, J. Koepsell, S. Hirthe, A. Bohrdt, F. Grusdt, I. Bloch, and C. Gross

Science 10, 186-189 (2020).

Show Abstract

Elementary particles carry several quantum numbers, such as charge and spin. However, in an ensemble of strongly interacting particles, the emerging degrees of freedom can fundamentally differ from those of the individual constituents. For example, one-dimensional systems are described by independent quasiparticles carrying either spin (spinon) or charge (holon). Here, we report on the dynamical deconfinement of spin and charge excitations in real space after the removal of a particle in Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we tracked the evolution of the excitations through their signatures in spin and charge correlations. By evaluating multipoint correlators, we quantified the spatial separation of the excitations in the context of fractionalization into single spinons and holons at finite temperatures.


Secure quantum remote state preparation of squeezed microwave states

S. Pogorzalek, K. G. Fedorov, M. Xu, A. Parra-Rodriguez, M. Sanz, M. Fischer, E. Xie, K. Inomata, Y. Nakamura, E. Solano, A. Marx, F. Deppe, R. Gross.

Nature Communications 10, 2604 (2019).

Show Abstract

Quantum communication protocols based on nonclassical correlations can be more efficient than known classical methods and offer intrinsic security over direct state transfer. In particular, remote state preparation aims at the creation of a desired and known quantum state at a remote location using classical communication and quantum entanglement. We present an experimental realization of deterministic continuous-variable remote state preparation in the microwave regime over a distance of 35 cm. By employing propagating two-mode squeezed microwave states and feedforward, we achieve the remote preparation of squeezed states with up to 1.6 dB of squeezing below the vacuum level. Finally, security of remote state preparation is investigated by using the concept of the one-time pad and measuring the von Neumann entropies. We find nearly identical values for the entropy of the remotely prepared state and the respective conditional entropy given the classically communicated information and, thus, demonstrate close-to-perfect security.


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