External-level assisted cooling by measurement

A quantum resonator in a thermal-equilibrium state with a high temperature has a large average population and is featured with significant occupation over Fock states with a high excitation number. The resonator could be cooled down via continuous measurements on the ground state of a coupled two-level system (qubit). We find, however, that the measurement-induced cooling might become inefficient in the high-temperature regime. Beyond the conventional strategy, we introduce strong driving between the excited state of the qubit and an external level. It can remarkably broaden the cooling range in regard to the nonvanishing populated Fock states of the resonator. Without any precooling procedure, our strategy allows a significant reduction of the populations over Fock states with a high excitation number, giving rise to nondeterministic ground-state cooling after a sequence of measurements. The driving-induced fast transition constrains the resonator and the ancillary qubit at their ground state upon measurement and then simulates the quantum Zeno effect. Our protocol is applied to cool down a high-temperature magnetic resonator. Additionally, it is generalized to a hybrid cooling protocol by interpolating the methods with and without strong driving, which can accelerate the cooling process and increase the overlap between the final state of the resonator and its ground state.

Automated summary

In a high-temperature thermal-equilibrium state, a quantum resonator with a large average population and significant occupation of Fock states with high excitation numbers can be efficiently cooled down using a strategy involving strong driving between the excited state of a qubit and an external level. This strategy broadens the cooling range for nonvanishing populated Fock states of the resonator and enables nondeterministic ground-state cooling. Additionally, the protocol can simulate the quantum Zeno effect by inducing fast transitions and constraining the system at its ground state.