{'fraction_non_alphanumeric': 0.016789087093389297, 'fraction_numerical': 0.0, 'mean_word_length': 5.053968253968254, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Cooling the mechanical resonator by Gaussian pulses

The optomechanical system has been widely used torealize the quantum ground state cooling of mechanical resonator, which is the way to create macroscopic quantum state. How to get the better cooling effect is evidently the central point. However, it has been demonstrated that there is a cooling limit if using only one single continuous-wave pump to drive the mechanical resonator, i.e., the cooling rate cannot be decreased by increasing the drive intensity or the mechanical frequency, so that the new dynamics should be developed. Here we present an approach to cool the mechanical resonator by the Gaussian pulses. For the pulsed optomechanical system, the common steady-state expansion approach is not available, since no steady state can be found in most cases. We use the new linearized approach to get the effective Hamiltonian and the dynamical evolution of the optomechanical system, with which the thermal phonon number of the mechanical resonator can be achieved directly. After investigating how the pulse profile, drive intensity and pulse duration affect the evolution of thermal phonon number in details, we show that the mechanical resonator can be well cooled down to the ground state by a single pulse, and can be well preserved by the multiple pulses, with the appreciated drive intensity, duration. Moreover, the character of drive intensity increasing and decreasing of the pulse profile, enables one to delay the squeezing effect which results in the heating of the mechanical resonator. As a result, the cooling limit of single continuous-wave driven optomechanical system can be broken by the pulsed optomechanical system. Even the half of the cooling limit of the continuous optomechanical system can be achieved by the short and strong Gaussian pulses, which is the main advantage of the ground state cooling by pulse drives.