Quantum Quench in a Model Ising Magnet

The Kibble-Zurek (KZ) mechanism predicts the defect density as a function of time after a quench into an ordered state. Extending this formalism from classical to quantum phase transitions (QPTs) entails a quantum tuning parameter that can be varied rapidly compared to the system’s equilibration times. To this end, we study the model transverse Ising magnet LiHoF₄, which undergoes a ferromagnet-paramagnet QPT as a function of transverse magnetic field. Pumping with S-band microwaves can saturate the nuclear spin levels, suppressing an effective rescaling of the electronic spin at temperatures below 0.4 K. This should move the phase boundary through a fixed transverse field at frequencies comparable to the 100 kHz single-spin attempt frequency. Using a compact high-Q resonator, we report on initial measurements of the ordering behavior following a quantum quench in the linear and nonlinear response regimes.