Research

Open AccessCommunication

Method for the Quantum Metric Tensor Measurement in a Continuous Variable System

by

Ling-Shan Lin

,

Hao-Long Zhang

and

Zhen-Biao Yang

Photonics 2023, 10(3), 256; https://doi.org/10.3390/photonics10030256 - 28 Feb 2023

Viewed by 646

Abstract

As a fundamental concept, geometry is widely used in understanding physical phenomena. In quantum mechanics, geometry is related to the system’s quantum state and can be characterized by the quantum geometric tensor (QGT), whose real part is referred to as the quantum metric [...] Read more.

As a fundamental concept, geometry is widely used in understanding physical phenomena. In quantum mechanics, geometry is related to the system’s quantum state and can be characterized by the quantum geometric tensor (QGT), whose real part is referred to as the quantum metric tensor (QMT), which defines the distance between two neighboring quantum states in the projected Hilbert space. Several pieces of research based on discrete variables have been proposed to extract the QMT, but research with the use of continuous variables is lacking. Here, we propose a method to extract the QMT of a continuous variable system, specified here as a cat-qubit. The method is developed by constructing the Kerr nonlinear parametric oscillator (KNPO) and by modulating it with external drives to induce adiabatic dynamics process within the state subspace spanned by the even and odd

S c h \ddot{o} d i n g e r

cat states. The method paves the way for exploring the geometry for continuous variable systems. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Phase-Controlled Entanglement in a Four-Mode Optomechanical System

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Photonics 2022, 9(11), 818; https://doi.org/10.3390/photonics9110818 - 29 Oct 2022

Viewed by 601

Abstract

We present a scheme for realizing phase-controlled entanglement in a microwave optomechanical system comprising two microwave cavities and two mechanical oscillators. Under specific driving conditions, we show that this optomechanical interface can be exploited to generate simultaneously the stationary cavity–cavity entanglement, mechanical–mechanical entanglement, [...] Read more.

We present a scheme for realizing phase-controlled entanglement in a microwave optomechanical system comprising two microwave cavities and two mechanical oscillators. Under specific driving conditions, we show that this optomechanical interface can be exploited to generate simultaneously the stationary cavity–cavity entanglement, mechanical–mechanical entanglement, and cavity–mechanical entanglement. Due to the closed loop interaction, we find that the entanglement can be controlled flexibly by tuning the phase difference between the optomechanical coupling strengths. The dependence of the entanglement on the amplitudes of the optomechanical coupling strengths is also explored in detail. Moreover, the bipartite entanglements are robust against temperature, and it is shown that the mechanical oscillators are cooled to the ground state in the parameter regimes for observing entanglement. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Integer and Fractional Floquet Resonances in a Driven Three-Well System

by

Liping Li

,

Bo Wang

and

Weibin Li

Photonics 2022, 9(10), 738; https://doi.org/10.3390/photonics9100738 - 08 Oct 2022

Viewed by 723

Abstract

We investigate Floquet dynamics of a particle held in a three-well system driven by a two-frequency field and identify integer and fractional photon resonances due to the dual-frequency driving. It is found that pairs of photon-assisted tunneling near the resonance originate from avoided [...] Read more.

We investigate Floquet dynamics of a particle held in a three-well system driven by a two-frequency field and identify integer and fractional photon resonances due to the dual-frequency driving. It is found that pairs of photon-assisted tunneling near the resonance originate from avoided level crossings in the Floquet spectra which, in essence, are quantum features of the hybridization between different quantum states. In particular, we establish a close connection between fractional-order resonances and Floquet mode properties under two-frequency driving conditions and illustrate their dependence on driving parameters. These results provide us a possibility to realize coherent control of quantum states with the assistance of classical external driving fields. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Optical Nonreciprocity in Double Optomechanical Systems with Quadratic Coupling

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Photonics 2022, 9(10), 728; https://doi.org/10.3390/photonics9100728 - 05 Oct 2022

Viewed by 681

Abstract

In this paper, the optical nonreciprocal phenomena in double optomechanical systems with quadratic coupling are studied. Our model belongs to an optomechanical system in which three coupling modes coexist, that is, the two cavity fields are coupled with the mechanical oscillator at the [...] Read more.

In this paper, the optical nonreciprocal phenomena in double optomechanical systems with quadratic coupling are studied. Our model belongs to an optomechanical system in which three coupling modes coexist, that is, the two cavity fields are coupled with the mechanical oscillator at the same time and the couplings are in the form of quadratic interactions. In addition, there is a linear coupling mode between the two cavity fields. In the entire system, each cavity field is effectively coupled by a control field and a probe field simultaneously. The expression of the transmission coefficient of the probe field is obtained by solving the dynamic evolution equation satisfied by the system. Using numerical analysis, we analyze the change in transmission coefficient of the probe field under the conditions of different physical parameters. The results show that we can realize optical nonreciprocal transmission in this system. Appropriate choices about physical parameters can achieve perfect nonreciprocity. Our theoretical scheme to realize optical nonreciprocal transmission in a double optomechanical system provides a theoretical basis for optical circulators, cyclic amplifiers and directional amplifiers. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessCommunication

Dynamics of Nano-Particles Inside an Optical Cavity in the Quantum Regime

by

Camilo M. Prada

and

Luis J. Martínez

Photonics 2022, 9(9), 641; https://doi.org/10.3390/photonics9090641 - 07 Sep 2022

Viewed by 831

Abstract

We investigate the optomechanical effect on a single nano-particle inside an optical cavity, by deriving the optical forces acting on the nano-particle by the cavity from quantum theory. We obtain the steady state of the system and found that the force contains three [...] Read more.

We investigate the optomechanical effect on a single nano-particle inside an optical cavity, by deriving the optical forces acting on the nano-particle by the cavity from quantum theory. We obtain the steady state of the system and found that the force contains three terms associated with the gradient force, the back-action force resulting from the intra-cavity photon energy change, as well as the reactive force associated with the coupling between the external field and the cavity. Moreover, we solve the dynamical system for a dielectric particle in a small mode volume cavity, which is characterized by a quasi-periodic pattern. These results are important for understanding the control of various types of levitated nano-particles through optomechanical coupling. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Controlling Resonance Fluorescence Spectra and Photon Statistics in a Driven V-Type Quantum Emitter—Metal Nanoparticle Coupled Structure

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Photonics 2022, 9(9), 629; https://doi.org/10.3390/photonics9090629 - 02 Sep 2022

Viewed by 715

Abstract

We study the resonant fluorescence emission spectrum and the intensity-intensity correlations of the emitted fluorescent field by a V-type quantum emitter (QE) which is located near a metal nanosphere. For the description of the studied phenomena, we use the density matrix equations methodology [...] Read more.

We study the resonant fluorescence emission spectrum and the intensity-intensity correlations of the emitted fluorescent field by a V-type quantum emitter (QE) which is located near a metal nanosphere. For the description of the studied phenomena, we use the density matrix equations methodology combined with electromagnetic calculations and obtain results for the profile of the resonant fluorescence spectrum and the second-order correlation functions associated with the fluorescent photons. The decay rates and the coupling term exhibit a strong dependence on the distance that separates the QE from the metal nanoparticle. This distance also influences the resonance fluorescence of the V-type QE. We find that, in the general case, the resonant fluorescence spectrum is composed of five Lorentzian-type peaks, for high interparticle distances, while, when the QE is located very close to the surface of the nanosphere, the central resonance becomes dominant, and a single-peaked spectral profile appears. The two-time correlation functions of the fluorescent photons evolve in an oscillatory manner around unity, for non-zero time delay, with a period that decreases with the increase of the field intensity. In the strong driving field regime, the antibunching to bunching crossing time does not depend on the interparticle distance, contrary to the results found in the weak driving field regime. We also find that, for a weak laser field and under specific conditions, the second-order correlation functions constantly remain in the antibunching region. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessCommunication

Gain Saturation Modified Quantum Noise Effect on Preparing a Continuous-Variable Entanglement

by

Saeid Vashahri-Ghamsari

and

Bing He

Photonics 2022, 9(9), 620; https://doi.org/10.3390/photonics9090620 - 30 Aug 2022

Viewed by 746

Abstract

We examine the gain saturation effect in non-Hermitian systems of coupled gain–loss waveguides and whispering-gallery-mode microresonators, through which a continuous-variable (CV) entanglement of light fields is generated. Here, we consider squeezed vacuum inputs for coupled waveguide setup and coherent drive for coupled microresonators, [...] Read more.

We examine the gain saturation effect in non-Hermitian systems of coupled gain–loss waveguides and whispering-gallery-mode microresonators, through which a continuous-variable (CV) entanglement of light fields is generated. Here, we consider squeezed vacuum inputs for coupled waveguide setup and coherent drive for coupled microresonators, and study the influence from the saturation of the used optical gain. Unlike the ideal situation without gain saturation, it is possible to generate stabilized entanglement measured by logarithmic negativity under gain saturation. Both types of setups realize steady CV entanglement, provided that the gain saturation is sufficiently quick. Particularly, with the coupled microresonators which are pumped by coherent drive, the created CV entanglement is actually out of the gain noise with a squeezing characteristic, under the condition of fast saturation of the initial optical gain. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Nonreciprocity Steered with a Spinning Resonator

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Photonics 2022, 9(8), 585; https://doi.org/10.3390/photonics9080585 - 18 Aug 2022

Viewed by 778

Abstract

An approach is presented to study the controllable nonreciprocal transmission in a spinning resonator. It has been demonstrated in optomechanics that an optical signal field can only be affected when it propagates in the same direction as the driving field. We show that [...] Read more.

An approach is presented to study the controllable nonreciprocal transmission in a spinning resonator. It has been demonstrated in optomechanics that an optical signal field can only be affected when it propagates in the same direction as the driving field. We show that such an optomechanically induced nonreciprocity can be controlled by rotating the resonator, which introduces a frequency shift with different signs for clockwise and counterclockwise optical fields in the resonator. In our scheme, the transmission probabilities of the clockwise and counterclockwise input signal fields can be reversed by tuning the rotation velocity of the resonator. By studying the transmission spectra of the signal field, we also reveal that the nonreciprocity response can be realized in the spinning resonators in the absence of optomechanical coupling, which extends its utility. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessCommunication

Manipulating Orbital Angular Momentum Entanglement in Three-Dimensional Spiral Nonlinear Photonic Crystals

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Photonics 2022, 9(7), 504; https://doi.org/10.3390/photonics9070504 - 21 Jul 2022

Cited by 3 | Viewed by 841

Abstract

We propose and theoretically investigate two-photon orbital angular momentum (OAM) correlation through spontaneous parameter down-conversion (SPDC) processes in three-dimensional (3D) spiral nonlinear photonic crystals (NPCs). By properly designing the NPC structure, one can feasibly modulate the OAM-correlated photon pair, which provides a potential [...] Read more.

We propose and theoretically investigate two-photon orbital angular momentum (OAM) correlation through spontaneous parameter down-conversion (SPDC) processes in three-dimensional (3D) spiral nonlinear photonic crystals (NPCs). By properly designing the NPC structure, one can feasibly modulate the OAM-correlated photon pair, which provides a potential platform to realize high-dimensional entanglement for quantum information processing and quantum communications. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessArticle

Cooling Effect and Cooling Speed for a Membrane-in-Middle Optomechanical System

by

Zhixin Chen

,

Qing Lin

and

Bing He

Photonics 2022, 9(6), 400; https://doi.org/10.3390/photonics9060400 - 06 Jun 2022

Cited by 1 | Viewed by 1085

Abstract

Optomechanical systems are suitable for realizing the ground-state cooling of macroscopic objects. Based on a dynamical approach that goes beyond the validity of the standard linearization approach, we simulate the detailed cooling processes for a membrane-in-middle optomechanical system. In addition to the cooling [...] Read more.

Optomechanical systems are suitable for realizing the ground-state cooling of macroscopic objects. Based on a dynamical approach that goes beyond the validity of the standard linearization approach, we simulate the detailed cooling processes for a membrane-in-middle optomechanical system. In addition to the cooling results, we especially study the cooling speed, which is indicated by how soon the first minimum thermal phonon number is reached. Their relevance to the system parameters provides essential knowledge about how to achieve the best and/or fastest cooling under various combinations of different driving fields. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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Open AccessCommunication

Deterministic Entanglement Swapping with Hybrid Discrete- and Continuous-Variable Systems

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Photonics 2022, 9(6), 368; https://doi.org/10.3390/photonics9060368 - 25 May 2022

Cited by 1 | Viewed by 1299

Abstract

The study of entanglement between discrete and continuous variables is an important theoretical and experimental topic in quantum information processing, for which entanglement swapping is one of the interesting elements. Entanglement swapping allows two particles without interacting with each other in any way, [...] Read more.

The study of entanglement between discrete and continuous variables is an important theoretical and experimental topic in quantum information processing, for which entanglement swapping is one of the interesting elements. Entanglement swapping allows two particles without interacting with each other in any way, to form an entangled state by the action of another pair of entangled particles. In this paper, we propose an experimentally feasible scheme to realize deterministic entanglement swapping in the hybrid system with discrete and continuous variables. The process is achieved by preparing two pairs of entangled states, each is formed by a qubit and two quasi-orthogonal coherent state elements of a cavity, performing a Bell-state analysis through nonlocal operations on the continuous variable states of the two cavities, and projecting the two qubits into a maximally entangled state. The present scheme may be applied to other physical systems sustaining such hybrid discrete and continuous forms, providing a typical paradigm for entanglement manipulation through deterministic swapping operations. Full article

(This article belongs to the Special Issue Nonlinear and Quantum Optics in Coupled Structures: Fundamentals and Applications)

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