Faster than Hermitian Time Evolution

TL;DR

This paper demonstrates that non-Hermitian PT-symmetric Hamiltonians can evolve quantum states faster than Hermitian ones under the same energy constraints, potentially impacting quantum computing speed limits.

Contribution

It introduces a method to achieve arbitrarily fast quantum state transformations using PT-symmetric Hamiltonians, surpassing Hermitian bounds.

Findings

PT-symmetric Hamiltonians can reduce evolution time to near zero.

The shortest path between states can be made arbitrarily small in PT-symmetric quantum theory.

Potential applications in increasing quantum computing speeds.

Abstract

For any pair of quantum states, an initial state |I> and a final quantum state |F>, in a Hilbert space, there are many Hamiltonians H under which |I> evolves into |F>. Let us impose the constraint that the difference between the largest and smallest eigenvalues of H, E_max and E_min, is held fixed. We can then determine the Hamiltonian H that satisfies this constraint and achieves the transformation from the initial state to the final state in the least possible time \tau. For Hermitian Hamiltonians, \tau has a nonzero lower bound. However, among non-Hermitian PT-symmetric Hamiltonians satisfying the same energy constraint, \tau can be made arbitrarily small without violating the time-energy uncertainty principle. The minimum value of \tau can be made arbitrarily small because for PT-symmetric Hamiltonians the path from the vector |I> to the vector |F>, as measured using the Hilbert-space metric appropriate for this theory, can be made arbitrarily short. The mechanism described here is similar to that in general relativity in which the distance between two space-time points can be made small if they are connected by a wormhole. This result may have applications in quantum computing.