Non-unitary Quantum Materials

Novel functions from the edge of the quantum world

April 08, 2021

Novel categories of quantum materials and electronic devices can be obtained by pipelining the evolution of electron quantum states as described by Schrödinger’s equation with inelastic processes that interrupt the coherent propagation of electrons, as now presented in Nano Express 2 014008 (2021) (open access).

These materials and devices reside in the fascinating transition regime between quantum mechanics and classical physics. The materials are designed such that a nonreciprocal unitary state evolution, achieved by a broken inversion symmetry, is interrupted by individual inelastic scattering events caused by defects. Two-terminal non-unitary quantum devices, for example, feature nonreciprocal conductance in linear response. Thus, they are exemptions to Onsager’s reciprocal relation, and they challenge the second law of thermodynamics. Materials and metamaterials featuring such functionalities may be realized by embedding such nanostructures into their unit cells.

Fig. 1: Sketch illustrating the principle of the novel quantum materials. These materials contain noncentrosymmetric unit cells with embedded inelastic scattering centers, drawn as gold dots. These centers break the phase coherence of the electron wave packets. From original publication.
Fig. 2: Illustration of the evolution of quantum states according to the calculational processes given by the axioms of quantum physics. If isolated from the environment, a quantum state evolves unitarily as described by Schrödinger’s equation. If coupled to the environment, the state evolution is accurately described mathematically by Born’s rule and von Neumann’s projection. From original publication.

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