Generating Fock-state superposition from coherent state by quantum measurement
69 浏览https://arxiv.org/html/2408.07403v1
High-level Fock states and their superpositions are essentially exotic testbeds for nonclassical physics and valuable resources for quantum technologies. We provide a simple protocol on quantum measurement to generate an arbitrary Fock state and selected superposed Fock states from a coherent state of a target resonator, without any carefully tailored external driving. This conditional protocol can be efficiently constructed by a sequence of joint free-evolution of the resonator and an ancillary qubit, that are coupled via a Jaynes-Cummings interaction, and projective measurements on the qubit. By properly choosing the duration of each evolution-measurement cycle and the initial state of the resonator, we can generate a desired Fock state |n⟩ and a superposed Fock state (|0⟩ + |n⟩)/√2, n ∼ 10, with a fidelity over 99% in less than 30 measurements. Moreover, our protocol can be straightforwardly extended to the generation of a multi-excitation Bell state (|00⟩ + |nn⟩)/√2 in a double-resonator system.
In summary, we design a protocol based on a sequence of projective measurements on the ancillary atomic sys- tem to generate desired Fock states and superposed Fock states from a coherent state of a resonator. The mea- surements are separated by dozens of joint free evolutions of the resonator and the ancillary system that are cou- pled with a simple JC interaction. Through the analysisover the population reduction factors induced by the ef- fective time-evolution operator for the target resonator, we can find optimal strategies with varying duration of the evolution-and-measurement cycles. Our protocol can therefore utilize less than 30 measurements to create a Fock state |n⟩ or a superposed Fock state (|0⟩ + |n⟩)/√2 of n ∼ 10 with a close-to-unit fidelity. The success prob- ability of our conditional protocol is exclusively deter- mined by the overlap between the initial state and the target state of the resonator. Moreover, the protocol can be generalized to prepare a multi-excitation Bell state in a double-resonator system assisted by a qutrit. Our work thus proves quantum measurement to be a powerful tool to manipulate composite systems and presents a path to the generation of high-level Fock states and entangled states.
