Squeezed Vacuum Field Research Articles

Steering, bipartite and genuine tripartite entanglement in five-mode hybrid cavity electro-optomechanical systems

We propose a scheme to generate one-way steering, bipartite and genuine tripartite entanglement in a five-mode hybrid cavity electro-optomechanical system consisted of an optical cavity, a mechanical resonator, and three microwave cavity modes with the help of a squeezed vacuum field. The optical cavity is pumped by a squeezed vacuum field. The mechanical resonator is formed by a freely vibrating silicon nitride membrane which is a part of a capacitor in a inductor-capacitor circuit forming three microwave resonators. We find that there is robust entanglement and one-way steering between the optical cavity mode and microwave cavity modes in the presence of the squeezed vacuum field. Particularly, there is steady-state genuine tripartite entanglement between three microwave cavity modes which is robust against thermal fluctuations. Our scheme could be useful for various quantum tasks based on hybrid electro-optomechanical systems fabricated on chips.

Generation of squeezed vacuum state in the millihertz frequency band

The detection of gravitational waves has ushered in a new era of observing the universe. Quantum resource advantages offer significant enhancements to the sensitivity of gravitational wave observatories. While squeezed states for ground-based gravitational wave detection have received marked attention, the generation of squeezed states suitable for mid-to-low-frequency detection has remained unexplored. To address the gap in squeezed state optical fields at ultra-low frequencies, we report on the first direct observation of a squeezed vacuum field until Fourier frequency of 4 millihertz with the quantum noise reduction of up to 8.0 dB, by the employment of a multiple noise suppression scheme. Our work provides quantum resources for future gravitational wave observatories, facilitating the development of quantum precision measurement.

Enhanced Gaussian interferometric power, entanglement and Gaussian quantum steering in magnonics system with squeezed light

In this study, we propose a scheme to improve quantum correlations (QCs) between two magnons in a tripartite magnonical system. We use Gaussian interferometric power (GIP) to quantify QCs beyond entanglement. Additionally, Gaussian quantum steering is discussed. We investigate the enhancement of QCs via a squeezing parameter and an optical parametric amplifier (OPA). The Mancini criterion is considered to confirm the presence of shared entanglement between the two magnons. We observed a squeezing of about 7 dB for the first magnon. Additionally, the squeezed vacuum field and the OPA improve the generation of genuine tripartite entanglement. We hope that current experimental technology will allow the proposed scheme to be implemented.

Generating stationary entanglement and one-way steering in a hybrid cavity electro-optomechanical system via a squeezed vacuum field

Generating stationary entanglement and one-way steering in a hybrid cavity electro-optomechanical system via a squeezed vacuum field

Effects of squeezed vacuum field on force sensing for a dissipative optomechanical system

We investigate the force sensing of a mechanical membrane in a dissipative cavity optomechanical system (OMS) driven by a squeezed vacuum field accompanying a strong pump laser. Specifically, the red-detuned laser exhibits a more significant improvement for force sensing compared to the blue-detuned laser. The optimal phase angle contributes to achieving much better force sensing. When injecting a squeezed vacuum field with appropriate squeezing parameter and squeezing phase, the standard quantum limit of force measurement can be easily beaten. Furthermore, the adverse effects of the increase in environment temperature and mechanical damping can be suppressed, simultaneously. This scheme provides a theoretical basics for force sensing of mechanical membranes in dissipative OMS and has potential applications in force feedback control, precision measurement, and force sensor design.

Generation of entanglement and quantum steering via Josephson parametric amplifier in a dual cavity-magnon system

In the two microwave (MW) cross-shaped cavity magnon system, we describe a method to produce multipartite entanglement and quantum steering. To achieve squeezed states of the magnons, a Josephson parametric amplifier (JPA) creates a squeezed vacuum field that drives the two cavities. We theoretically demonstrate that the cavity-cavity entanglement can be generated at the resonance point, however, increasing the cavity and magnon decay rates generate the cavity-magnon entanglement. By changing the squeezing parameter and increasing the decay rates, we can transfer the cavity-cavity entanglement to cavity-magnon entanglement. Furthermore, the cavity-cavity entanglement (survive up to 2.8 K) was not only found to be much stronger but also more robust as compared to cavity-magnon entanglement (survive up to 0.4 K). More importantly, the genuine photon-magnon-photon tripartite entanglement could be achieved, which is robust against thermal fluctuations and depends strongly on the squeezing parameter. Furthermore, for the current dual cavity-magnon system, two-way quantum steering is found when the optomagnonical couplings are equal. The current study offers a straightforward and practical method for achieving multipartite quantum correlations.

Entanglement and steering in a cross-shaped double-cavity with a magnetic sphere and driven by a squeezed vacuum field

Entanglement and steering in a cross-shaped double-cavity with a magnetic sphere and driven by a squeezed vacuum field

Preparation of Distant Quantum Entanglement and One‐way Quantum Steering in Hybrid Cavity‐Magnonics‐and‐Cavity‐Optomechanical Systems

AbstractA hybrid system that combines cavity magnonics and cavity optomechanics is proposed to facilitate the generation of long‐distance entanglement and enable one‐way steering between magnons and phonons. This configuration involves two directly coupled cavities, with one interacting with magnons and the other coupling with a mechanical oscillator (i.e., phonons). By driving the microwave cavity with a weak squeezed vacuum field generated by a flux‐driven Josephson parametric amplifier, entanglement and one‐way steering can be further enhanced. Moreover, the results demonstrate that magnon–phonon entanglement and one‐way quantum steering exhibit robustness against temperature variations, which has significant implications for quantum information processing and storage.

Controlling Remote Entanglement and One‐Way Steering Via a Squeezed Vacuum Field and an Optical Parametric Amplifier

AbstractA scheme is proposed for generating remote entanglement and one‐way Einstein‐Podolsky‐Rosen (EPR) steering between two mechanical resonators in a cavity optomechanical system. Both mechanical resonators are coupled to a common cavity, which contains an optical parametric amplifier (OPA) and is driven by a squeezed vacuum field. The entanglement and EPR steering can be generated by the squeezed vacuum field and significantly enhanced by the gain of OPA. By manipulating the ratio of two effective optomechanical coupling strengths, the asymmetric EPR steering with excellent controllability on the direction, even the one‐way EPR steering can be achieved. Moreover, both the squeezed vacuum field and the OPA can effectively enhance the robustness of EPR steering against the environment temperature, and the temperature‐dependent one‐way EPR steering is explored. This work paves the way toward generating macroscopic mechanical entanglement and EPR steering with potential applications in quantum information processing.

Enhancing the quantum entanglement and EPR steering of a coupled optomechanical system with a squeezed vacuum field

Quantum entanglement and Einstein–Podolsky–Rosen (EPR) steering are valuable resources in quantum information processing. How to enhance the quantum entanglement and EPR steering of coupled optomechanical systems with a weak squeezed vacuum field is studied when the displacement of detuning induced by the mechanical mode is considered. Compared with the condition that the system interacts with a vacuum environment, the quantum entanglement and EPR steering are stronger when the squeezed vacuum field is applied. A squeezed vacuum field with a large degree is not beneficial to enhance the quantum entanglement and EPR steering. Rather than the squeezing parameter of the squeezed vacuum field, the reference phase plays a vital role in this model.

Entanglement generation and steering implementation in a double-cavity-magnon hybrid system.

We demonstrate a scheme for the generation of bipartite and tripartite entanglement, as well as he implementation of stable and controllable long-distance one-way and asymmetric two-way steering in a cavity-magnon hybrid system. This system consists of a magnon mode and two coupled microwave cavities. The first cavity is driven by a flux-driven Josephson parametric amplifier, which generates squeezed vacuum fields, and is coupled to the other cavity through optical tunneling interaction. The second cavity and magnon mode are coupled through magnetic dipole interaction. We find that under weak coupling between the two cavities, and strong coupling between the second cavity and magnon mode, remote controllable one-way steering and tripartite entanglement can be achieved. Our scheme may have potential applications in quantum information.

Quantum State Engineering for Dissipative Quantum Computation Via a Two-Qubit System Plunged in a Global Squeezed Vacuum Field Reservoir

Quantum State Engineering for Dissipative Quantum Computation Via a Two-Qubit System Plunged in a Global Squeezed Vacuum Field Reservoir

Squeezing-induced nonreciprocal photon blockade in an optomechanical microresonator.

We propose a scheme to generate nonreciprocal photon blockade in a stationary whispering gallery microresonator system based on two physical mechanisms. One of the two mechanisms is inspired by recent work [Phys. Rev. Lett.128, 083604 (2022)10.1103/PhysRevLett.128.083604], where the quantum squeezing caused by parametric interaction not only shifts the optical frequency of propagating mode but also enhances its optomechanical coupling, resulting in a nonreciprocal conventional photon blockade phenomenon. On the other hand, we also give another mechanism to generate stronger nonreciprocity of photon correlation according to the destructive quantum interference. Comparing these two strategies, the required nonlinear strength of parametric interaction in the second one is smaller, and the broadband squeezed vacuum field used to eliminate thermalization noise is no longer needed. All analyses and optimal parameter relations are further verified by numerically simulating the quantum master equation. Our proposed scheme opens a new avenue for achieving the nonreciprocal single photon source without stringent requirements, which may have critical applications in quantum communication, quantum information processing, and topological photonics.

Quantum fluctuations spatial mode profiler

The spatial mode is an essential component of an electromagnetic field description, yet it is challenging to characterize it for optical fields with the low average photon number, such as in a squeezed vacuum. We present a method for the reconstruction of the spatial modes of such fields based on the homodyne measurements of their quadrature noise variance performed with a set of structured masks. We show theoretically that under certain conditions, we can recover individual spatial mode distributions by using the weighted sum of the basis masks, where weights are determined using measured variance values and phases. We apply this approach to analyze the spatial structure of a squeezed vacuum field with various amount of excess thermal noise generated in Rb vapor.

Steady state coherence and entanglement in a dissipative two-qubit system and its application for decision making

Quantum decision theory was recently established based on the mathematics of Hilbert spaces to formalize the key concepts of quantum mechanics such as uncertainty and superposition that particularly manifest in cognitive processes. We aim to address how a two-qubit system interacting with a global squeezed vacuum field reservoir can be exploited as a black box model for quantum decision-making. To do so, we encode the input of the black box into the density matrix of the two-qubit system. The global reservoir drives the system towards its steady state via the decoherence process. The outcome of the black box can be obtained by performing measurement on the stationary state of the two-qubit system. We reveal that the squeezed reservoir can be used to control the coherence and entanglement of the black box’s output. Interestingly, it is shown that the steady state entanglement and coherence between two qubits, which have the same value, can be obtained by measuring the output state of the black box. Besides, we examine the potential application of the considered model for entanglement decision-making.

Quantum properties of a triple-coupled optical cavity with injection of a squeezed vacuum field

Subject of study. A scheme of quantum manipulation in a coupled optical cavity system composed of a triple-coupled optical cavity with injection of a squeezed vacuum field is proposed. Method. The scheme of quantum manipulation in a coupled optical cavity system is based on analysis of the absorption and dispersion characteristics of the reflection in the classical field and the quantum field. Main results. It was established that the absorption and dispersion of the reflection field with different coupled intensities under the classical field show different characteristics. An electromagnetic induction transparency like effect is observed as the coupled intensities increase and becomes more and more obvious as the coupled intensities increase until the absorption curve becomes completely independent due to the strong coupled intensities. The quantum noise fluctuation corresponding to the amplitude and phase of the reflection field in the quantum field also presented different characteristics. With the increase of coupled intensities, the quantum noise fluctuation curve begins to split. At the same time, the splitting of the quantum noise fluctuation curve changes from one to three, and it completely splits into three Lorentz curves finally. Practical significance. The theoretical results of the scheme demonstrated that multiple (three times) quantum manipulation can be implemented simultaneously in a device, which provides a method for quantum dense coding.

Stationary states of a dissipative two-qubit quantum channel and their applications for quantum machine learning

Entangled-state preparation and preservation are the cornerstones of any quantum information platform. However, the strongest adversaries in quantum information science are unwanted environmental effects such as decoherence and dissipation. Here, we address how to control and harness these unwanted effects that arise from the coupling of a system with its environment, to provide stationary entangled states for quantum machine learning (QML). To do so, we design a dissipative quantum channel, i.e., a two-qubit system interacting with a squeezed vacuum field reservoir, and study the output state of the channel by solving the corresponding master equation, especially, in the small squeezing regime. We show that the time-dependent output state of the channel is the so-called two-qubit X-states that generalize many families of entangled two-qubit states. Also, by considering a general Bell diagonal state as the initial state of the system, we reveal that this dissipative channel generates two well-known classes of entangled mixed state and Werner-like states in the steady-state regime. Moreover, this channel provides an efficient way to determine whether a given initial state results in a stationary entangled state or not. Finally, we examine the potential application of the designed two-qubit channel for QML. In this line, we propose a general theoretical scheme for quantum neural networks (QNNs) implemented with the variational quantum circuits, which encode data in continuous variables (CVs) of the two-qubit states. The linear (also referred to as affine) and nonlinear (activation function) transformations are enacted in the QNN using the stationary states of the two-qubit channel and measurement process, respectively. Finally, we proceed to test our proposed model by solving some supervised binary classification tasks. Integrating the non-unitary transformation and parallel-processed neural computing on such a two-qubit channel establishes the requirements for a meaningful QNN. Such a CV-QNN model with sufficient layers may execute any algorithm implementable on a universal CV quantum computer.

Quantum coherence versus quantum correlations in a double cavity magnomechanical system

In this paper, we investigate a system composed of two spatially separated cavities, each with a magnon mode of a yttrium iron garnet (YIG) sphere coupled to a microwave (MW) cavity and phonon modes, respectively, via linear beam splitter and magnetostrictive interactions. In addition, two-mode squeezed vacuum fields drive the two cavities. We investigate and compare the behavior of three nonclassicality indicators in two subsystems (i.e., magnon–magnon and phonon–phonon) under the influences of the temperature, the cavity–magnon damping rate, and the magnomechanical coupling rate. We use the entanglement of formation (EoF) to measure the degree of entanglement, the Gaussian quantum discord (GQD) to characterize the quantum correlations beyond entanglement and Gaussian quantum coherence (GQC) to quantify coherence. Considering that the quantifiers share the same entropic definition, we compare the three quantifiers and test the validity of the hypothesis that quantum states with nonzero discord are inherently entangled. We find, on the one hand, that both GQC and GQD exhibit freezing behavior and that they are more robust to the decoherence effect than the EoF. On the other hand, the EoF and the GQD are always upper bounded by GQC, and there is no simple dominance relationship between EoF and GQD; hence these two quantifiers should not be compared. The effect of other parameters is also discussed in detail.

Electromagnetically induced transparency with quantized fields in a dissipative optomechanical system

We study electromagnetically induced transparency (EIT) using quantized fields in a dissipative optomechanical system with two mechanical oscillators coupled to each other via the Coulomb interaction. The weak probe field is a finite bandwidth squeezed vacuum field. In the absence of the Coulomb coupling, we show that an EIT dip is observable in the homodyne spectrum of the output field even for the squeezed vacuum field at the single-photon level. We find that the thermal environment has a negative impact on the EIT behavior. In the presence of the Coulomb coupling, we show that double EIT dips appear in the homodyne spectrum of the output field. The separation between the two EIT dips can be used to measure the Coulomb coupling strength. Compared to the case of the purely dissipative coupling, the combined dispersive and dissipative coupling can make the EIT dip broader and the minimum value of the EIT dip smaller.

Electro-Optical Sampling of Single-Cycle THz Fields with Single-Photon Detectors

Electro-optical sampling of Terahertz fields with ultrashort pulsed probes is a well-established approach for directly measuring the electric field of THz radiation. This technique usually relies on balanced detection to record the optical phase shift brought by THz-induced birefringence. The sensitivity of electro-optical sampling is, therefore, limited by the shot noise of the probe pulse, and improvements could be achieved using quantum metrology approaches using, e.g., NOON states for Heisenberg-limited phase estimation. We report on our experiments on THz electro-optical sampling using single-photon detectors and a weak squeezed vacuum field as the optical probe. Our approach achieves field sensitivity limited by the probe state statistical properties using phase-locked single-photon detectors and paves the way for further studies targeting quantum-enhanced THz sensing.