Light Squeezing Transfers Quantum Links Between Systems

Quantum entanglement, a phenomenon where particles become interconnected such that the state of one instantly influences the other, is crucial for advancing technologies like secure communication and ultra-precise sensors. In hybrid systems combining light and mechanical components, maintaining and transferring this entanglement is key to practical quantum devices. A recent study by Smail Bougouffa and Mohannad Al-Hmoud explores how squeezed light—a special form of light with reduced fluctuations—can drive the transfer of entanglement in coupled optomechanical cavities, offering insights into robust quantum information processing.

The researchers found that stationary bipartite entanglement can be generated and transferred between subsystems in a hybrid optomechanical system when driven by squeezed light. This transfer depends strongly on the strength of the hopping process coupling the cavities and the matching of input modes. The entanglement remains stable against thermal fluctuations, with the system achieving a fidelity for coherent states that aligns with conditions for entanglement generation.

The methodology involved modeling a system of two optomechanical cavities coupled via a photon hopping process and driven by squeezed and coherent light sources. The authors derived a Hamiltonian to describe the system's dynamics and used quantum Langevin equations to account for noise and dissipation. By linearizing these equations around steady-state solutions, they analyzed fluctuations in operators representing cavity and mechanical modes. The covariance matrix was employed to quantify entanglement, using negativity as a measure, with stability conditions checked via the Routh-Hurwitz criterion to ensure the system reaches a steady state.

Results from the analysis show that entanglement between a cavity and its mechanical mirror decreases as the hopping strength increases, due to the transmission of correlated photons through the waveguide. For instance, with a hopping strength normalized to the mechanical frequency, negativity—a measure of entanglement—drops from around 0.25 at low hopping to near zero at higher values, as seen in Figure 3(c). When squeezed light is introduced, entanglement between optical modes increases, with negativity reaching up to 0.3 at large detuning values, while intracavity entanglement correspondingly decreases. The data indicate that entanglement persists up to thermal phonon numbers around 836, equivalent to temperatures of about 4 K, demonstrating robustness. Fidelity for coherent state teleportation exceeds 0.9 under optimal conditions, as shown in Figure 7, highlighting the system's potential for reliable quantum communication.

The context of this work lies in the authors' motivation to preserve and transfer correlations in quantum systems for applications such as quantum memory and displacement measurements. They explain that hybrid optomechanical systems, which combine optical and mechanical elements, are effective for continuous variable information processing. The findings build on previous investigations into multi-cavity setups, emphasizing how squeezed light can redistribute entanglement among subsystems, facilitating tasks like teleportation without adding external significance beyond the paper's scope.

Limitations acknowledged by the authors include the dependence of entanglement transfer on specific parameter regimes, such as the need for high driving power and precise detuning. The system's stability is constrained by conditions like effective damping rates and detuning values, where violations can lead to bistability or self-sustained oscillations. Uncertainties arise from thermal noise effects, though the entanglement shows resilience within experimental parameter ranges.

References: S. Bougouffa and M. Al-Hmoud, Int. J. Theor. Phys. manuscript No. (will be inserted by editor) (2020); arXiv:1904.12205v3 [quant-ph].