Topological Quantum Switching via Light-Driven Raman Coherence

Depiction of Raman coherence
a) Intense THz pulses drive coherent Raman phonon oscillations that controls band topology and gaps. b) Spectrum of the coherent phonon emission (red) reveals Raman phonon modes in the THz driven states. This is obtained from the time-domain coherent oscillation traces after THz pumping with various field strengths in c). 

Wide-scale adoption of quantum computing requires building devices in which fragile quantum states are protected from their noisy environments. One approach is based on “symmetry-protected” topological quasiparticles that are theoretically immune to noise.

Such topological control principles are demonstrated using a few-cycle THz pulse to driven coherent Raman phonons and, in turn, induce a topological phase transition in a Dirac semimetal ZrTe5. This is achieved by periodically driving using vibrational coherence of the lattice due to excitation of its lowest Raman-active mode.  Above a critical THz pump field threshold, there emerges a long-lived (~100 ps) metastable phase ~100 ps with unique Raman phonon-assisted topological switching dynamics, which is absent for optical pumping.

This quantum control principle is achieved by a mode-selective Raman phonon coherent oscillations, i.e. light-induced atomic motions of Raman symmetry about the equilibrium position. Experimental results combined with first-principles modeling shows that the system transitions from strong to weak topological insulators with a Dirac semimetal phase in-between. The critical atomic displacements are controlled by the phonon coherent pumping. This work opens a new arena of light-wave speed topological electronics and phase transitions controlled by quantum coherence. 

C. Vaswani, L.-L. Wang, D.H. Mudiyanselage, Q. Li, P. M. Lozano, G. Gu, D. Cheng, B. Song,  L. Luo, R. H. J. Kim, C. Huang, Z. Liu, M. Mootz, I.E. Perakis, Y. Yao, K. M. Ho, and J. Wang “Light-Driven Raman Coherence as a Non-Thermal Route to Ultrafast Topology Switching in a Dirac Semimetal”,  Physical Review X, 021013 (2020):