arXiv subjects

S. G. Nana Engo

Publications and source records attributed to S. G. Nana Engo.

16 recordsLinked to original sources

arXiv2025

Multipartite quantum entanglement in $\mathcal{PT}$-symmetric molecular optomechanics: Nonreciprocal enhancement and thermal resilience to \SI{500}{\kelvin}

We present a theoretical framework for a $\mathcal{PT}$-symmetric double-cavity molecular optomechanical system demonstrating nonreciprocal enhancement of multipartite quantum entanglement at elevated temperatures. All bipartite entanglement channels ($E_{ac}$, $E_{aB_1}$, $E_{cB_2}$, $E_{B_1B_2}$) simultaneously maximize at optimal nonreciprocal asymmetry $J_1/J_2 \approx 5$, with entanglement persisting to $T \sim \SIrange{400}{500}{\kelvin}$ (material-limited ceiling) two orders of magnitude beyond conventional optomechanical systems. This thermal resilience and balanced enhancement across all channels arise from synergistic combination of ultra-high-frequency molecular vibrations ($ω_m/2π= \SI{30}{\tera\hertz}$), collective $\sqrt{N}$ coupling enhancement with $N=\num{e6}$ molecules, and directional nonreciprocal coupling shielding entanglement-generating interactions from backaction noise. Unlike optical parametric amplifier schemes where vibration-vibration enhancement suppresses optical-vibration correlations, our $\mathcal{PT}$-symmetric architecture circumvents this fundamental trade-off, validated through rigorous stability analysis via Routh-Hurwitz criterion.

quant-ph↗

arXiv2025

Quantum correlations in molecular cavity optomechanics

Quantum correlations are interesting resources for modern quantum technologies such as quantum information processing, quantum communication, quantum teleportation, and quantum computation tasks. However, engineering these quantum states turns to be not an easy task. Here, we unveil a theoretical framework for generating and controlling quantum correlations within a double-cavity molecular optomechanical (McOM) system. Our approach leverages strong interactions between confined optical fields and collective molecular vibrations, creating a versatile environment for exploring robust quantum correlations. Our findings reveal that by judiciously optimizing the coupling strength between the cavity field and the molecular collective mode leads to significant enhancement of entanglement, quantum steering, and quantum discord. We demonstrate that cavity-cavity quantum correlations can be effectively mediated by the molecular collective mode, enabling a unique pathway for inter-cavity quantum connectivity. Moreover, the quantum entanglement generated in our McOM system exhibits robustness against thermal noise, persisting up to temperatures approaching $1000 K$. This strong resilience, qualifies molecular optomechanics as a compelling architecture for scalable, room-temperature quantum information processing and the practical realization of quantum networks. Additionally, the phase-dependent behaviour of quantum discord provides a fundamental basis for developing ultra-sensitive gas sensors, with potential applications in environmental monitoring, medical diagnostics, and industrial safety.

quant-ph↗

arXiv2025

Enhancing mechanical entanglement in molecular optomechanics

We propose a scheme for enhancing bipartite quantum entanglement in a double-cavity molecular optomechanical (McOM) system incorporating an intracavity optical parametric amplifier (OPA). Utilizing a set of linearized quantum Langevin equations and numerical simulations, we investigate the impact of the OPA on both optical-vibration and vibration-vibration entanglement. Our key findings reveal a counterintuitive trade-off: while the OPA significantly enhances vibration-vibration entanglement, a critical resource for quantum memories and transducers, it simultaneously suppresses optical-vibration entanglement. We demonstrate that maximal vibration-vibration entanglement is achieved when the molecular collective vibrational modes are symmetrically populated, providing a clear experimental guideline for optimizing entanglement sources. In particular, the vibration-vibration entanglement generated in our OPA-enhanced McOM system exhibits remarkable robustness to thermal noise, persisting at temperatures approaching \SI{e3}{\kelvin}, significantly exceeding conventional optomechanical systems, and highlighting the potential for room temperature quantum information processing. These results establish a promising theoretical foundation for OPA-enhanced McOM systems as a robust and scalable platform for quantum technologies, paving the way for future experimental implementations and advanced quantum information processing applications.

quant-ph↗

arXiv2025

Saturable nonlinearity induced quantum correlations in optomechanics

We propose a scheme that induces quantum correlations in optomtomechanical systems. Our benchmark system consists of two optically coupled optical cavities which interact with a common mechanical resonator. The optical cavities host saturable nonlinearity which triggers either gain or losses in each cavity. Without these nonlinearities, there are no quantum correlations, i.e., entanglement and steering, generated in the system. By turning on the nonlinearities, gain and losses are switched on, enabling flexible generation of both quantum entanglement and quantum steering in our proposal. These generated quantum correlations seem to be insensitive to the induced gain, while the induced losses through saturation effect efficiently enhance quantum correlations. Moreover, the robustness of the generated quantum correlations against thermal fluctuations is further improved under nonlinear saturation scenario. This work suggests a way of using nonlinear saturation effects to engineer quantum correlations even at room temperature, which are useful for quantum information processing, quantum computational tasks, and quantum technologies.

quant-ph↗

arXiv2025

Nonreciprocal entanglement in a molecular optomechanical system

We propose a theoretical scheme to generate nonreciprocal bipartite entanglement between a cavity mode and vibrational modes in a molecular cavity optomechanical system. Our system consists of $\mathcal{N}$ molecules placed inside a spinning whispering-gallery-mode (WGM) resonator. The vibrational modes of these molecules are coupled to the WGM resonator mode (which is analogous to a plasmonic cavity) and the resonator is also coupled to an auxiliary optical cavity. We demonstrate that nonreciprocal photon-vibration entanglement and nonreciprocal vibration-vibration entanglement can be generated in this system, even at high temperatures. These nonreciprocal entanglements arise due to the Sagnac-Fizeau effect induced by the spinning WGM resonator. We find that spinning the WGM resonator in the counter-clockwise (CCW) direction enhances both types of nonreciprocal entanglement, especially under blue-detuned driving of the optical cavity mode. Furthermore, we show that vibration-vibration entanglement can be significantly enhanced by increasing the number of molecules. Our findings have potential applications in quantum information transmission and in the development of nonreciprocal quantum devices.

quant-ph↗

arXiv2024

Quantum entanglement assisted via Duffing nonlinearity

We propose a scheme to enhance quantum entanglement in an optomechanical system by exploiting the so-called Duffing nonlinearity. Our model system consists of two mechanically coupled mechanical resonators, both driven by an optical field. One resonator supports Duffing nonlinearity, while the other does not.The resonators are coupled to each other via the so-called phonon hopping mechanism. The hopping rate is $θ$-phase-dependent that induces Exceptional Points (EPs) singularities in the system. Interestingly, while the resonator with Duffing nonlinearity exhibits vanishing entanglement with light, we observe an increase in entanglement between light and the other mechanical resonator. This enhanced entanglement persists longer against thermal fluctuations compared to the one without the nonlinearity. Additionally, this entanglement features a sudden death and revival phenomenon, where the peaks happen at the multiple of $θ=\fracπ{2}$. This work opens a new avenue for exploiting nonlinear resources to generate strong quantum entanglement, paving the way for advancements in quantum information processing, quantum sensing, and quantum computing within complex systems.

quant-ph↗

arXiv2024

Optomechanical entanglement induced by backward stimulated Brillouin scattering

We propose a scheme to generate robust optomechanical entanglement. This scheme is based on a Backward Stimulated Brillouin Scattering (BSBS) process, which is hosted within an optomechanical structure. Our benchmark system consists of an acoustic (mechanical) mode coupled to two optical modes through the BSBS (radiation pressure) process. For a moderate values of the effective mechanical coupling, the BSBS induces a relatively weak entanglement. This entanglement is greatly enhanced, for at least up to one order of magnitude, when the mechanical coupling strength is strong enough. The generated entanglement is robust enough against thermal fluctuation. Our work provides a new scheme for entanglement generation based on BSBS effect, and can be extended to microwaves and hybrid optomechanical structures. Such a generated entangled states can be used for quantum information processing, quantum sensing, and quantum computing.

quant-ph↗

arXiv2023

$\mathcal{PT}-$symmetry and chaos control via dissipative optomechanical coupling

We study a dissipative, mechanically coupled optomechanical system that accommodates gain and loss. The gain (loss) is engineered by driven a purely dispersive optomechanical cavity with a blue-detuned (red-detuned) electromagnetic field. By taking into account the dissipative coupling, the Exceptional Point (EP), which is the $\mathcal{PT}-$symmetry phase transition, occurs at low threshold driving strength compared to the purely dispersive system. In the linear regime, the $\mathcal{PT}-$symmetry is unbroken and the dissipative coupling induces strong coupling between the mechanical resonators, leading to an increase in energy exchange. For sufficiently strong driving, the system enters into a nonlinear regime where the $\mathcal{PT}-$symmetry is broken. In this regime, the mechanical resonators exhibit chaotic beats like-behaviour in the purely dispersive system. By switching on the dissipative coupling, the complex dynamics is switched off, restoring regular dynamics to the system. This work suggests ways to probe quantum phenomena in dissipative $\mathcal{PT}-$symmetric systems at low-threshold driving strength. It also provides a new way to control complex dynamics in optomechanics and related fields.

quant-ph↗

arXiv2023

Sensor sensitivity based on synthetic magnetism exceptional point

An efficient mass sensor based on exceptional points (EPs), engineered under synthetic magnetism requirement, is proposed. The benchmark system consists of an electromechanical (optomechanical) system where an electric (optical) field is driving two mechanical resonators which are mechanically coupled through a phase-dependent phonon-hopping. This phase induces series of EPs once it matches the condition of $\fracπ{2}(2n +1)$. For any perturbation of the system, the phase-matched condition is no longer satisfied and this lifts the EP-degeneracies leading to a frequency splitting that scales as the square root of the perturbation strength, resulting in a giant sensitivity-factor enhancement. Owing to the set of EPs, our proposal allows multiple sensing scheme and performs better than its anti-PT-symmetric sensor counterpart. This work sheds light on new platforms that can be used for mass sensing purposes, opening up new opportunities in nanoparticles or pollutants detection, and to water treatment.

cond-mat.mes-hall↗

arXiv2023

Synthetic magnetism for solitons in optomechanical array

We propose a synthetic magnetism to generate and to control solitonic waves in $\rm{1D}-$optomechanical array. Each optomechanical cavity in the array couples to its neighbors through photon and phonon coupling. We create the synthetic magnetism by modulating the phonon hopping rate through a modulation frequency, and a modulation phase between resonators at different sites. When the synthetic magnetism effect is not taken into account, the mechanical coupling play a scrucial role of controlling and switching the waves from bright to dark solitons, and it even induces rogue wave-like a shape in the array. For enough mechanical coupling strength, the system enters into a strong coupling regime through splitting/crossing of solitonic waves leading to multiple waves propagation in the array. Under the synthetic magnetism effect, the phase of the modulation enables a good control of the wave propagation, and it also switches soliton shape from bright to dark, and even induces rogue waves as well. Similarly to the mechanical coupling, the synthetic magnetism offers another flexible way to generate plethora of solitonic waves for specific purposes. This work opens new avenues for optomechanical platforms and sheets light on their potentiality of controlling and switching solitonic waves based on synthetic magnetism.

cond-mat.mes-hall↗

arXiv2017

Distant entanglement enhanced in $\mathcal{PT}$-symmetric optomechanics

We study steady-state continuous variable entanglement in a three-mode optomechanical system consisting of an active optical cavity (gain) coupled to a passive optical cavity (loss) supporting a mechanical mode. For a driving laser which is blue-detuned, we show that coupling between optical and mechanical modes is enhanced in the unbroken-$\mathcal{PT}$-symmetry regime. We analyze the stability and this shows that steady-state solutions are more stable in the gain and loss systems. We use these stable solutions to generate distant entanglement between the mechanical mode and the optical field inside the gain cavity. It results in a giant enhancement of entanglement compared to what is generated in the single lossy cavity. This work offers the prospect of exploring quantum state engineering and quantum information in such systems. Furthermore, such entanglement opens up an interesting possibility to study spatially separated quantum objects.

quant-ph↗

arXiv2015

Concise Quantum Associative Memories with Nonlinear Search Algorithm

The model of quantum associative memories (QAM) we propose here consists in simplifying and generalizing that of Rigui Zhou \etal \cite{zhou2012} who uses the quantum matrix with binary decision diagram and nonlinear search algorithm in his model. It is worth noting that David Rosenbaum put forth the quantum matrix with binary decision diagram \cite{Rosenbaum2010} and Abrams and Llyod did the nonlinear algorithm. \cite{Abrams1998} Our model gives the possibility to retrieve one of the sought states in multi-values retrieving scheme when a measure on the first register is done. It is better than Grover's algorithm and its modified form which need $\mathcal{O}(\sqrt{\frac{2^n} {m}})$ steps when they are used as the retrieval algorithm. $n$ is the number of qubit of the first register and $m$ the number of values $x$ for which $f(x)=1$. As the nonlinearity makes the system highly susceptible to noise, an analysis of the influence of the single qubit noise channels on the Nonlinear Search Algorithm of our model of QAM, shows a fidelity of about $0.7$ whatever the number of qubits present in the first register.

quant-ph↗

arXiv2014

Robustness of continuous-variable entanglement via geometrical nonlinearity

We propose a scheme to generate robust stationary continuous-variable entanglement in optomechanical systems, based on geometrical nonlinearity that occurs for large mechanical displacements. Such nonlinearity is often used to correct the dynamics of the systems in the strong coupling regime. It appears that geometrical nonlinearity enhances the entanglement and shifts its maximum towards high detuning values. Using the experimental parameters, we find that such a scheme generates a very robust entanglement against thermal decoherence even at room temperature. Our results show that geometrical nonlinearity affects entanglement as the optomechanical quantum interface.

quant-ph↗

arXiv2013

Quantum associative memory for the diagnosis of some tropical diseases

In this paper we present a model of Quantum Associative Memory which can be a helpful tool for physicians without experience or laboratory facilities, for the diagnosis of four tropical diseases (malaria, typhoid fever, yellow fever and dengue) which have similar symptoms. The memory can distinguish single infection from multi-infection. The algorithm used for Quantum Associative Memory is an improve model of original algorithm made by Ventura for Quantum Associative Memory. From the simulation results given, it appears that the efficiency of recognition is good when a particular symptom of a disease with a similar symptoms are inserted.

physics.med-ph↗

arXiv2013

Limiting effects of geometrical and optical nonlinearities on the squeezing in optomechanics

In recent experiments, the re-thermalization time of the mechanical resonator is stated as the limiting factor for quantum applications of optomechanical systems. To explain the origin of this limitation, an analytical nonlinear investigation supported by the recent successful experimental laser cooling parameters is carried out in this work. To this end, the effects of geometrical and the optical nonlinearities on the squeezing are studied and are in a good agreement with the experimental results. It appears that highly squeezed state are generated where these nonlinearities are minimized and that high nonlinearities are limiting factors to reach the quantum ground state.

quant-ph↗

arXiv2012

Quantum associative memory with improved distributed queries

The paper proposes an improved quantum associative algorithm with distributed query based on model proposed by Ezhov et al. We introduce two modifications of the query that optimized data retrieval of correct multi-patterns simultaneously for any rate of the number of the recognition pattern on the total patterns. Simulation results are given.

quant-ph↗