Phase-preserving control of Floquet-engineered cavity quantum electrodynamics

Abstract

We propose a Floquet-engineered framework for the coherent control of the light-matter interaction in a two-level system (TLS) located in a time-modulated cavity. Strictly phase-preserving operation of the TLS-cavity interaction is demonstrated, allowing the interrupt and retrieval of coherent Rabi oscillations without the loss of quantum information. By introducing a phonon reservoir, it is proved that the frequency instability induced from non-Markovian processes does not produce significant phase decoherence during Floquet modulation. Our results provide new insights into the fundamental physics of a driven quantum system and establish Floquet engineering as a powerful tool for coherent quantum information processing.

Figures (11)

• Figure 1: Schematic of the proposed model with a two-level system (TLS) coupled to a cavity with periodically modulated resonance frequency. A phonon reservoir is included to account for dephasing processes. When the coherent destruction of tunneling (CDT) condition is satisfied, the effective coupling between the TLS and the cavity mode is strongly suppressed.
• Figure 2: The dependence of two quasi-energies of the Floquet Hamiltonian on the modulation depth $A$. The modulation effectively renormalizes the cavity–TLS coupling strength according to the zero-order Bessel function $J_0(\frac{A}{\Omega})$. When $J_0(\frac{A}{\Omega})=0$, the Floquet eigenstates become degenerate, corresponding to the condition for CDT, where the TLS is effectively decoupled from the cavity mode.
• Figure 3: Bloch sphere representation of quantum states in the single-excitation subspace spanned by $\{|0,e\rangle,|1,g\rangle\}$. The Bloch vector $\mathbf r$ can be specified either by Cartesian coordinates $(u,v,w)$ or by spherical angles $(\theta,\varphi)$.
• Figure 4: The Floquet control scheme. Left: Population $\langle a^\dagger a \rangle$ and coherence $C(t)=e^{i\Phi(t)}\langle a^\dagger \sigma \rangle$ (real and imaginary parts), whose argument determines the relative phase of wavefunction $|\psi(t)\rangle$ between $|0,e\rangle$ and $e^{i\Phi(t)}|1,g\rangle$. Right: Corresponding Bloch sphere trajectory. The calculations are performed with parameters $A_0\approx 2.4\Omega$, $\Omega/(2\pi)=50\,\mathrm{GHz}$, $g/(2\pi)=8\,\mathrm{GHz}$, $\sigma_t=0.02 \mathrm{ns}$, where $A_0$ is chosen to minimize the effective coupling. Unless otherwise specified, these parameters are used throughout the following calculations.
• Figure 5: The static detuning control scheme. Left: Population $\langle a^\dagger a \rangle$ and coherence $C(t)=\langle a^\dagger \sigma \rangle$ (real and imaginary parts), whose argument determines the relative phase between $|0,e\rangle$ and $|1,g\rangle$. Right: Corresponding Bloch sphere trajectory. The phase of the oscillations is not preserved when the interaction switched off at time $t_0$ and reactivated at time $t_1$ in the static cavity detuning scheme. The maximum modulation depth $A_0$ takes same maximum modulation depth with Fig. \ref{['fig:floquet-bloch']}.