Generation of macroscopic Schrödinger-cat states in qubit-oscillator systems

Abstract

We propose a scheme to generate macroscopic Schrödinger-cat states in a quantum harmonic oscillator (electromagnetic field or mechanical resonator) coupled to a quantum bit (two-level system) via a conditional displacement mechanism. By driving the qubit monochromatically, the oscillation of the qubit state modifies the effective frequency of the driving force acting on the oscillator, and a resonant or near-resonant driving on the oscillator can be achieved. The displacement of the oscillator is then significantly enhanced due to the small detuning of the driving force and can exceed that of the zero-point fluctuation. This effect can be used to prepare quantum superpositions of macroscopically distinct coherent states in the oscillator. We present detailed studies on this state-generation scheme in both the closed-and open-system cases. This approach can be implemented in various experimental platforms, such as cavity-or circuit-QED systems, electromechanical systems, and spin-cantilever systems.

Generation of macroscopic entangled cat states in a longitudinally coupled cavity-QED model

“…To evaluate the validity of the RWA made in the approximate Hamiltonian (20), we calculate the fidelity F(t) = | Ψ(t)|ψ(t) | 2 between the approximate state |ψ(t) and the exact state |Ψ(t) , which are defined in Eqs. (31) and (43), re- spectively. The expression of this fidelity can be obtained as…”

“…Note that smaller values of the modulation frequency ω 0 can be chosen by choosing larger values of the Floquet-sideband indexes n a and n b . It has been analyzed that the realization of the cavity-frequency modulations is accessible with current or near-future experimental conditions [31]. However, the realization of the resonance frequency modulation for the molecular vibration remains a challenge.…”

“…The diverse interactions among these degrees of freedom in molecular cavity-QED systems have wide applications in the frontiers of quantum physics [21,22] and quantum chemistry [14,23,24]. As an example, one possible application associated with the conditional displacement interactions in molecular cavity-QED systems is to create superposed coherent states [25][26][27][28][29][30][31] and entangled coherent states [32,33], which can be widely used in modern quantum technologies * jfhuang@hunnu.edu.cn † jqliao@hunnu.edu.cn such as quantum metrology [34,35] and quantum teleportation based on coherent-state bases [36][37][38]. In these systems, the molecular vibration and the electromagnetic fields can provide natural candidates for local information memory and information transfer carrier in continuous-variable quantum information processing, respectively [39].…”

Simulating Anisotropic quantum Rabi model via frequency modulation

“…Superposition of coherent states plays an important role in quantum theory 79,80,[93][94][95] . In this subsection, we consider how to generate superposition of coherent states for a single-qubit case.…”

Generation of macroscopic Schrödinger cat state in diamond mechanical resonator

“…Experimentally, the macroscopic SCS has been observed in various physical systems including superconducting qubit system34, ion trap35, cavity QED36, and linear optical system37. However, generating coherent states with macroscopically distinct amplitudes in the phase space is a difficult task in nanomechanical systems383940, it remains a challenge to realize SCS in such systems.…”