Selective Transient Cooling by Impulse Perturbations in a Simple Toy Model

Abstract

We show in a simple exactly solvable toy model that a properly designed impulse perturbation can transiently cool down low-energy degrees of freedom at the expense of high-energy ones that heat up. The model consists of two infinite-range quantum Ising models: one, the high-energy sector, with a transverse field much bigger than the other, the low-energy sector. The finite-duration perturbation is a spin exchange that couples the two Ising models with an oscillating coupling strength. We find a cooling of the low-energy sector that is optimized by the oscillation frequency in resonance with the spin exchange excitation. After the perturbation is turned off, the Ising model with a low transverse field can even develop a spontaneous symmetry breaking despite being initially above the critical temperature.

Light-induced evaporative cooling of holes in the Hubbard model

“…The specific protocol involves coupling a hole-doped Mott insulator by dipolar excitations to the initially filled narrow band. Since the entropy increase per hole is large in a full narrow band, a transfer of holes at constant total entropy results in strong cooling; a feature shared with other isentropic cooling schemes 11,22,23 . In the rotating frame, optical driving between the bands induces a tunneling from the Hubbard band to the flat band, whose energy is shifted by the driving frequency .…”

Dissipative cooling induced by pulse perturbations

“…Based on the last observation, Ref. [21] devised a strategy to exploit the high energy sector as an entropy sink able to cool down the low energy one, which we briefly sketch in this section. We assume that the system is prepared in the equilibrium state corresponding to a temperature T c T 2h 2 .…”

“…It follows that the population of particle-hole excitations gets reduced, as if its internal temperature were lower, for a transient time after the pulse that is longer the smaller the non-radiative decay rate of the high energy mode. This idea was later tested [21] with success in a fully-connected toy model subject to a time dependent perturbation of finite duration, mimicking a 'laser pulse'. This model is trivially solvable since infinite connectivity implies that mean-field theory is exact in the thermodynamic limit.…”

Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

“…Quantum dynamics out of equilibrium can be used to disentangle interesting mechanisms of materials' properties, such as origin of ordered states and their subsequent control. Recent experimental progress in pump-probe-spectroscopical approaches to excitonic insulator [1], charge-density wave [2], and superconducting phases [3,4] has prompted extensive research interest in both simulating [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] and measuring [4,[24][25][26][27][28][29] ultrafast quantum correlation effects far from equilibrium.…”