Kavli Affiliate: Birgitta Whaley
| First 5 Authors: , , , ,
| Summary:
Non-Hermitian systems have been at the center of intense research for over a
decade, partly due to their nontrivial energy topology formed by intersecting
Riemann manifolds with branch points known as exceptional points (EPs). This
spectral property can be exploited, e.g., to achieve topologically controlled
state permutations that are necessary for implementing a wide class of
classical and quantum information protocols. However, the complex-valued
spectra of typical non-Hermitian systems lead to instabilities, losses, and
breakdown of adiabaticity, which impedes the practical use of EP-induced energy
topologies in quantum information protocols based on state permutation
symmetries. Indeed, in a given non-Hermitian multiqubit system, the dynamical
winding around EPs always results in a predetermined set of attenuated final
eigenstates, due to the interplay of decoherence and non-adiabatic transitions,
irrespective of the initial conditions. In this work, we address this
long-standing problem by introducing a model of interacting qubits governed by
an effective non-Hermitian Hamiltonian that hosts novel types of EPs while
maintaining a completely real energy spectrum, ensuring the absence of losses
in the system’s dynamics. We demonstrate that such non-Hermitian Hamiltonians
enable the realization of genuine, in general, non-Abelian permutation groups
in the multiqubit system’s eigenspace while dynamically encircling these EPs.
Our findings indicate that, contrary to previous beliefs, non-Hermiticity can
be utilized to achieve controlled topological state permutations in
time-modulated multiqubit systems, thus paving the way for the advancement and
development of novel quantum information protocols in real-world non-Hermitian
quantum systems.
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