NMR investigations of Dynamical Tunneling in Spin Systems

TL;DR

This paper reports an experimental study of dynamical tunneling in spin systems using NMR, demonstrating size-dependent tunneling behavior and the critical role of quantum coherence in the process.

Contribution

The study provides the first experimental realization of dynamical tunneling in spin systems via NMR, exploring its dependence on system size and noise effects.

Findings

Size-dependent tunneling behavior observed.

Quantum coherence is essential for dynamical tunneling.

Dephasing noise suppresses tunneling oscillations.

Abstract

In the usual quantum tunneling, a low-energy quantum particle penetrates across a physical barrier of higher potential energy, by traversing a classically forbidden region, and finally escapes into another region. In an analogous scenario, a classical particle inside a closed regular region in the phase space is dynamically bound from escaping to other regions of the phase space. Here, the physical potential barrier is replaced by dynamical barriers which separate different regions of the phase space. However, in the quantum regime, the system can overcome such dynamical barriers and escape through them, giving rise to dynamical tunneling. In chaotic Hamiltonian systems, dynamical tunneling refers to quantum tunneling between states whose classical limit correspond to symmetry-related regular regions separated by a chaotic zone between which any classical transport is prohibited. Here, an experimental realization of dynamical tunneling in spin systems is reported using nuclear magnetic resonance (NMR) architecture. In particular, dynamical tunneling in quantum kicked tops of spin-1 and spin-3/2 systems using two- and three-qubit NMR registers is investigated. By extracting time-dependent expectation values of the angular momentum operator components, size-dependent tunneling behaviour for various initial states is systematically investigated. Further, by monitoring the adverse effects of dephasing noise on the tunneling oscillations, we assert the importance of quantum coherence in enabling dynamical tunneling.