Quantum Dynamics via a Hidden Liouville Space

Abstract

Quantum dynamics for arbitrary system are traditionally realized by time evolutions of wave functions in Hilbert space and/or density operators in Liouville space. However, the traditional simulations may occasionally turn out to be challenging for the quantum dynamics, particularly those governed by the nonlinear Hamiltonians. In this letter, we introduce a nonstandard iterative technique where time interval is divided into a large number of discrete subintervals with an ultrashort duration; and the Liouville space is briefly expanded with an additional (virtual) space only within these subintervals. We choose two-state spin raising and lowering operators for virtual space operators because of their simple algebra. This tremendously reduces the cost of time-consuming calculations. We implement our technique for an example of a charged particle in both harmonic and anharmonic potentials. The temporal evolutions of the probability for the particle being in the ground state are obtained numerically and compared to the analytical solutions. We further discuss the physics insight of this technique based on a thought-experiment. Successive processes intrinsically 'hitchhiking' via virtual space in discrete ultrashort time duration, are the hallmark of our simple iterative technique. We believe that this novel technique has potential for solving numerous problems which often pose a challenge when using the traditional approach based on time-ordered exponentials.