Utilizing the logarithmic negativity (E N ) entanglement measure, we present an analysis of (optomechanical) ponderomotive entanglement generation. Results predict a max E N of about 0.2 and are highly dependent on temperature, loss, and measurement precision.
Quantum entanglement is the key to many applications like quantum key distribution, quantum teleportation, and quantum sensing. However, reliably generating quantum entanglement in macroscopic systems has proven to be a challenge. Here, we present a detailed analysis of ponderomotive entanglement generation in a movable-end-mirror-type optomechanical cavity. These cavities utilize optomechanical interactions between the intracavity field and the end mirror to create quantum correlations. We numerically calculate an entanglement measure, the logarithmic negativity, for the quantitative assessment of the entanglement. Experimental limitations, including thermal noise and optical loss, from measurements of an existing experiment were included in the calculation, which is intractable to solve analytically. This analysis shows that lowering optical losses and measurement uncertainties is more important than temperature for observation of the entanglement in movable-end-mirror-type optomechanical cavity experiments. This work will play an important role in the development of ponderomotive entanglement devices.
Abstract Nano-optomechanical systems, capable of supporting enhanced light-matter interactions, have wide applications in studying quantum entanglement and quantum information processors. Yet, preparing optical telecom-band entanglement within a single optomechanical nanobeam remains blank. We propose and design a triply resonant optomechanical nanobeam to generate steady-state entangled propagating optical modes and present its quantum-enhanced performance for teleportation-based quantum state transfer under realistic conditions. Remarkably, the entanglement quantified by logarithmic negativity can obtain E N = 1. Furthermore, with structural imperfections induced by realistic fabrication processes considered, the device still shows great robustness. Together with quantum interfaces between mechanical motion and solid-state qubit processors, the proposed device potentially paves the way for versatile nodes in long-distance quantum networks.
Abstract Entanglement generation at a macroscopic scale offers an exciting avenue to develop new quantum technologies and study fundamental physics on a tabletop. Cavity quantum optomechanics provides an ideal platform to generate and exploit such phenomena owing to the precision of quantum optics combined with recent experimental advances in optomechanical devices. In this work, we propose schemes operating outside the resolved-sideband regime, to prepare and verify both optical–mechanical and mechanical–mechanical entanglement. Our schemes employ pulsed interactions with a duration much less than the mechanical period and, together with homodyne measurements, can both generate and characterize these types of entanglement. To improve the performance of our schemes, a precooling stage comprising prior pulses can be utilized to increase the amount of entanglement prepared, and local optical squeezers may be used to provide resilience against open-system dynamics. The entanglement generated by our schemes is quantified using the logarithmic negativity and is analysed with respect to the strength of the pulsed optomechanical interactions for realistic experimental scenarios including mechanical decoherence and optical loss. Two separate schemes for mechanical entanglement generation are introduced and compared: one scheme based on an optical interferometric design, and the other comprising sequential optomechanical interactions. The pulsed nature of our protocols provides more direct access to these quantum correlations in the time domain, with applications including quantum metrology and tests of quantum decoherence. By considering a parameter set based on recent experiments, the feasibility to generate significant entanglement with our schemes, even with large optical losses, is demonstrated.
Optomechanical systems are currently of great interest as they lie at the boundary between quantum and classical mechanics, promising fundamental insights as well as new technologies. The practical operation of an optomechanical system requires that it satisfy the criteria of mechanical stability. Further, for quantum applications, it is important to characterize the degree of nonclassical correlation present between the mechanical and optical subsystems. In this study, we analyze the stability and entanglement in an optomechanical system where couplings linear as well as quadratic in the mechanical displacement are present simultaneously. Such systems can be realized experimentally. Our analysis of the optomechanical system is accomplished by inspecting the equations of motion that characterize the system. By analyzing the steady state of the system, we find a stability diagram which differs dramatically from the case of pure linear coupling which has been studied earlier. Specifically, we find generally a major loss of stability and a disconnection of the stability diagram when a quadratic coupling is introduced. We derive and state analytically in this thesis the stability criteria for our more generalized system. Further, by linearizing the equations of motion, we characterize the entanglement present in the system, using the logarithmic negativity as a measure. We thereby characterize the changes in the system entanglement that result from the addition of a quadratic coupling to a linearly coupled system.
Measures of entanglement can be employed for the analysis of numerous quantum information protocols. Due to computational convenience, logarithmic negativity is often the choice in the case of continuous-variable systems. In this work, we analyze a continuous-variable measurement-based entanglement distillation experiment using a collection of entanglement measures. This includes logarithmic negativity, entanglement of formation, distillable entanglement, relative entropy of entanglement, and squashed entanglement. By considering the distilled entanglement as a function of the success probability of the distillation protocol, we show that the logarithmic negativity surpasses the bound on deterministic entanglement distribution at a relatively large probability of success. This is in contrast to the other measures which would only be able to do so at much lower probabilities, hence demonstrating that logarithmic negativity alone is inadequate for assessing the performance of the distillation protocol. In addition to this result, we also observed an increase in the distillable entanglement by making use of upper and lower bounds to estimate this quantity. We thus demonstrate the utility of these theoretical tools in an experimental setting.
As classical technology approaches its limits, exploration of quantum technologies is critical. Quantum optics will be the basis of various cutting-edge research and applications in quantum technology. In particular, quantum optics quite efficacious when applied to quantum networks and the quantum internet. Quantum Optomechanics, a subfield of quantum optics, contains some novel methods for entanglement generation. These entanglement production methods exploit the noise re-encoding process, which is most often associated with creating unwanted phase noise in optical circuits. Using the adapted two-photon formalism and experimental results, we simulate (in an experimentally viable parameter space) optomechanical entanglement generation experiments. These simulations consider dual coherent field input, displaced single-mode squeezed input, and displaced two-mode squeezed inputs. Unsqueezed inputs should yield an EN of about 0.1 at room temperature, although very high measurement certainty is needed to observe this in the laboratory. Squeezing the displaced input fields increases the expected output entanglement significantly (maximum of EN of about 1). Furthermore, when considering dual two-mode squeezed input (4 fields) in the simulation, the optomechanical cavity demonstrates squeezing angle-dependent entanglement distribution.