Optimizing mechanical entanglement using squeezing and parametric amplification

The aim of this paper is to quantify the quantum correlations between mechanical and optical modes in an optomechanical system with two spatially separated Fabry–Pérot cavities. We use logarithmic negativity [Formula: see text] and entanglement of formation (EoF), respectively, to quantify entanglement between optical and mechanical modes, while Gaussian geometric discord (GGD) is used to capture all nonclassical correlations, including entanglement. These quantifiers are evaluated as functions of the physical parameters characterizing the environment and the system (the thermal bath temperature [Formula: see text], the photons number [Formula: see text], the optomechanical cooperativity [Formula: see text], the squeeze parameter [Formula: see text] and the drive pump power [Formula: see text]). By considering recent experimental parameters, we show that GGD is more robust than entanglement for high thermal bath temperature and low optomechanical cooperativity. We also find that these quantifiers improve with increasing optomechanical cooperativity. The effects of the other parameters are also discussed in detail.

In an optomechanical system consisting of two Fabry–Pérot cavities fed by squeezed light and coupled via Coulomb interaction, we respectively use the logarithmic negativity, Gaussian discord and Gaussian coherence to analyze the behavior of three different indicators of nonclassicality, namely the entanglement, quantum discord and quantum coherence. We perform the rotating wave approximation and work in the resolved sideband regime. In two bi-mode states (optical and mechanical), the coherence is generally found to be greater than entanglement and discord. More interestingly, we show that the Coulomb interaction can be used either to degrade or enhance the nonclassical properties of the optical subsystem. In addition, compared with the discord and coherence, the mechanical entanglement is found strongly sensitive to both thermal and Coulomb effects, and it requires a minimum value of cooperativity to be generated. Remarkably, this minimum increases when increasing the Coulomb coupling strength. Finally, we notice that an optimal transfer of quantum correlations between the optical and mechanical subsystems is achieved in the absence of the Coulomb interaction.

Ultra high quality optical resonators have enabled accumulation of exceptionally high intensities of light from low input powers. This feature opens new horizons in low power observation of physical phenomena such as lasing, sensing and radiation pressure driven oscillations. Radiation pressure instability facilitates transfer of energy from photons to mechanical degree of freedom in optical resonators. In high quality toroidal micro cavities, radiation pressure is demonstrated in the form of dynamic back action and results mechanical oscillations with sub-Hz linewidth. Since the toroidal cavities are symmetrical in nature, the exerted radiation pressure can mainly excite radially symmetric modes such as the first cantilever mode and the radially breathing mode. Study of these modes reveals important information about interaction of light and mechanical mode as well as intrinsic properties of the resonator as a mechanical oscillator. However, there are some unexcited mechanical modes that in some cases have even higher mechanical quality factors compared to the usually excited ones. Most of the properties of these mechanical modes remain unknown because the radially symmetric force does not provide a component to excite them. In this research, we have developed a novel method to fabricate asymmetric toroidal resonators (minor and major diameters), which enables us to regeneratively excite unobserved asymmetric modes. One key feature is that the optical quality factor is relatively high despite the asymmetry. As a result, we are able to excite the asymmetric modes with sub-mW threshold powers. Complementary modeling is also performed, confirming the experimental findings.

Spin qubits in semiconductor quantum dots are an attractive candidate for scalable quantum information processing. Reliable quantum state transfer and entanglement between spatially separated spin qubits is a highly desirable but challenging goal. Here, we propose a fast and high-fidelity quantum state transfer scheme for two spin qubits mediated by virtual microwave photons. Our general strategy involves using a superadiabatic pulse to eliminate non-adiabatic transitions, without the need for increased control complexity. We show that arbitrary quantum state transfer can be achieved with a fidelity of 95.1% within a 60 ns short time under realistic parameter conditions. We also demonstrate the robustness of this scheme to experimental imperfections and environmental noises. Furthermore, this scheme can be directly applied to the generation of a remote Bell entangled state with a fidelity as high as 97.6%. These results pave the way for fault-tolerant quantum computation on spin quantum network architecture platforms.

An impurity-induced gap system as a quantum data bus for quantum state transfer

This study explores the spontaneous emergence of local Fisher information and local quantum uncertainty beyond entanglement in a noisy two-qubit Heisenberg XXX model with Dzyaloshinskii-Moria (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions. Local quantum Fisher information, local quantum uncertainty, and logarithmic negativity are used to examine two-spin non-locality. We find that by employing strong two-spin, Dzyaloshinskii- Moriya, and Kaplan-Shekhtman-Entin-Wohlman-Aharony interactions, we can prevent noise-induced losses in local Fisher information, local quantum uncertainty, and logarithmic negativity. The robustness of the two-spin non-localities is greater for a strong spin’s coupling strength than for the strong DM and KSEA interactions. Local Fisher information and local quantum uncertainty, as well as logarithmic-negativity, display asymmetric behaviors with respect to two-spin coupling and symmetric behaviors with respect to the Dzyaloshinskii-Moriya and Kaplan-Shekhtman-Entin-Wohlman-Aharony interactions. At high bath temperatures, the phenomenon of sudden-death two-spin entanglement emerges. Furthermore, by combining the parameters of the strong two-spin, DM, and KSEA interactions, the robustness of the produced two-spin non-localities can be improved.

Coherent scattering of photons is a novel mechanism of optomechanical coupling for optically levitated nanoparticles promising strong, versatile interactions with light and between nanoparticles. We show that it allows efficient deterministic generation of Gaussian entanglement between two particles in separate tweezers. A combination of red- and blue-detuned tweezers brings a mechanical Bogoliubov mode to its ground state. An additional, dispersively coupled cavity mode can reduce noise in the orthogonal mode, resulting in strong entanglement as quantified by the logarithmic negativity and verifiable with the Duan criterion for realistic experimental parameters. Such an important resource for quantum sensing and quantum simulations is pivotal for current experiments and presents an important step towards optomechanics with multiple particles in the quantum regime.

Quantum control is responsible for many key problems in quantum information processing, such as decoherence suppression, quantum state engineering and quantum gate, etc. In recent years quantum control has become a major topic in the fields of quantum optics and quantum information. Fast control of the state of quantum system is effective for both decoherence suppression caused by the environment and information processing in quantum state transfer and tracking. Comparing the standard Lyapunov control function with bang-bang Lyapunov control function, we design an optimized quantum Lyapunov control function, and analyse the influence of control laws on population transfer probability and control time contrastively. The simulation results indicate that the optimized quantum Lyapunov control strategy effectively shortens the control time and avoids high-frequency oscillation that occurs in bang-bang Lyapunov control, therefore, strengthens the robustness against external interference.

Optical non‐reciprocity that allows unidirectional flow of optical field is pivoted on time reversal symmetry breaking, which originates from radiation pressure because of light–matter interaction in cavity optomechanical systems. Here, the non‐reciprocal transport of optical signals across two ports via three optical modes optomechanically coupled to the mechanical excitations of two nanomechanical resonators (NMRs) is studied under the influence of strong classical drive fields and weak probe fields. It is found that there exists the conversion of reciprocal to non‐reciprocal signal transmission via tuning the drive fields and perfect non‐reciprocal transmission of output fields is realized when the effective cavity detuning parameters are near resonant to the NMRs' frequencies. The unidirectional non‐reciprocal transport is robust to the optomechanical couplings around resonance conditions. Moreover, the loss rates of cavities play an inevitable role in the unidirectional flow of signal across the two ports. Bidirectional transmission can also be controlled by the phase changes associated with the probe and drive fields along with their relative phase. This scheme may provide a foundation for the compact non‐reciprocal communication and quantum information processing, thus enabling novel devices that route photons in unconventional ways such as all‐optical diodes, optical transistors, and optical switches.

Based on a scheme proposed to experience the dynamical Casimir effect in optomechanical systems, we show how to squeeze mechanical motion and entangle the optical field with mechanical motion in an optomechanical system containing a parametric amplification. The scheme is based on optical bistability which emerges in the system for a strong enough driving field. By considering the steady state’s lower branch of the bistability, the system shows weak entanglement and almost no mechanical squeezing. When the steady state is on the upper branch of the bistable shape, both squeezing and entanglement are greatly enhanced. Specifically, the entanglement shows three degrees of magnitude enhancement. However, this giant entanglement is fragile against decoherence and thermal fluctuation. Regarding the mechanical squeezing, it reaches the standard quantum limit (SQL) in the upper branch of the bistability. Our proposal provides a way to improve quantum effects in optomechanical systems by taking advantage of nonlinearities. This scheme can be realized in similar systems such as superconducting microwave, and hybrid optomechanical systems.

Welcome to IPSN 2012, the Eleventh ACM/IEEE Conference on Information Processing in Sensing Networks! This year marks the first time IPSN is held in Asia, recognizing the region's growing interest and activities in the areas of sensor networks, Internet-of-Things (IoT), and Cyber-Physical Systems (CPS). We hope that you will enjoy this diverse conference that is a leading venue for publications and idea exchange on sensor networks. IPSN is unique in its broad coverage of the field, ranging from foundations to system implementation and platforms. It is a meeting point of theory and practice, as embodied in its two tracks: Information Processing (IP) and Sensor Platforms, Tools and Design Methods (SPOTS). In an effort to further unify the conference this year, we formed a joint technical program committee (TPC) and held a single TPC meeting. Authors could select the IP or the SPOTS track for their submissions and TPC members were able to provide their review preferences across all papers submitted to the conference. We believe that in this way, each paper received the most relevant and useful set of reviews. The field of sensor networks has shown a continuing strength over the years as indicated by the number and the quality of submissions this year: 53 in the SPOTS track and 94 in the IP track, for a total of 147 submissions. These submissions underwent a two-stage review process during which each paper received at least three reviews and occasionally up to seven reviews. An online discussion followed the review process during which the set of papers that were discussed in the TPC meeting were selected. The set of accepted papers were decided during a face-to-face TPC meeting. 22 papers were selected for publication out of which 12 were in the IP track and 10 in the SPOTS track. As in the past, the exciting demo and poster session provides an opportunity for attendees to examine and discuss the latest in sensing devices, systems and applications, following a special session with a rapid-fire series of short "pitch" talks from the authors of posters and demos. A new addition to the program this year is the PhD Forum where students working in the field present their dissertation ideas and get critical feedback from a panel of experts. The main conference is complemented by a number of workshops and tutorials in emerging or adjacent areas of sensor networks such as mobile, IoT, and smart objects.

The coupled dynamics of a nanomechanical resonator and superconducting quantum circuits are studied in three experiments, in the context of studying the quantum limit for force detection and quantum physics of macroscopic objects. In the first experiment, the dispersive mechanical resonance shift from the interaction with a Cooper-pair box qubit is studied. The measured coupling strength is large enough to satisfy one of the conditions required to perform many of the proposed quantum nanomechanical measurements. The resonance shift also probes the microwave-driven response of the qubit, showing Rabi oscillation and Landau-Zener tunneling, proving the coherent dynamics of the qubit. Second, the parametric excitation of nanomechanical motion is studied via experiments with a driven qubit. Degenerate parametric amplification and oscillation are demonstrated, with a new observation of nonlinear dissipation. The squeezing of the back-action noise from the detection amplifier is also observed, up to 4dB. It is the first demonstration using a qubit as an auxiliary system to modify the nanomechanical dynamics, showing a possible route for generation of nanomechanical quantum states. Finally, back-action cooling of nanomechanical motion has been investigated, which is implemented by capacitively coupling a high-Q coplanar waveguide microwave resonator to a nanomechanical resonator. The thermal state with 7.5 mechanical quanta on average is reached, a result that is ultimately limited due to increased bath heating with microwave power. The heating is consistent with a model based on two-level systems resonantly coupled to the nanomechanical mode. This additional heating suggests future efforts to improve coupling and for reducing two-level system density in materials employed to reach the motional ground state via back-action cooling.

Harmonic oscillators might be one of the most fundamental entities described by physics. Yet they stay relevant in recent research. The topological properties associated with exceptional points that can occur when two modes interact have generated much interest in recent years. Harmonic oscillators are also at the heart of new quantum technological applications: the long lifetime of high-Q resonators make them advantageous as quantum memories, and they are employed for narrowband processing of quantum signals, as in Josephson parametric amplifiers. The goal of this thesis is to explore different fundamental regimes of two coupled harmonic oscillators using cavity optomechanics as the experimen- tal platform. With consistent progress in attaining ever increasing Q factors, mechanical and electromagnetic resonators realize near-ideal harmonic oscillators. By parametrically modulating the nonlinear optomechanical interaction between them, an effective linear coupling is achieved, which is tunable in strength and in the relative frequencies of the two modes. Thus cavity optomechanics provides a framework with excellent control over system parameters for the study of two coupled harmonic modes. The specific optomechanical implementation employed are superconducting circuits with the vibrating top plate of a capacitor as the mechanical element. Multimode optomechanical circuits are realized, with two microwave modes interacting with one or two mechanical oscillators. The supplementary modes serve either as intermediaries in the relation of the two modes of interest, or as auxiliaries used to control a parameter of the system. Three main experimental results are achieved. First, an auxiliary microwave mode allows the engineering of the effective dissipation rate of a mechanical oscillator. The latter then acts as a reservoir for the main microwave mode with which it interacts. The microwave mode susceptibility can be tuned, resulting in an instability akin to that of a maser and in resonant amplification of incoming microwave signals with an added noise close to the quantum minimum. Second, we study the conditions for a nonreciprocal interaction between two microwave modes, when the information flows in one direction but not in the other. The two modes interact through two mechanical oscillators, leading to frequency conversion between the two cavities. Dissipation in the mechanical modes is essential to the scheme in two ways: it provides a reciprocal phase necessary for the interference and eliminates the unwanted signals. Third, level attraction between a microwave and a mechanical mode is demonstrated, where the eigenfrequencies of the system are drawn closer as the result of interaction, rather distancing themselves as in the more usual case of level repulsion. The phenomenon is theoretically connected to exceptional points, and a general classification of the possible regimes of interaction between two harmonic modes is exposed, including level repulsion and attraction as special cases.

A scheme is proposed to generate long‐distance entanglement and asymmetric steering between mechanical oscillator and magnon mode across the frequency difference of ≈10 GHz in an optomagnonic‐mechanical system composed of a magnon, a mechanical oscillator, and two cavities. The calculated results reveal that the long‐distance magnon–phonon entanglement can be achieved due to the fact that the quantum correlation of the two‐mode squeezed vacuum microwave field is successively transferred to the magnon mode and the phonon mode. Moreover, the entanglement is strong enough such that the quantum steering between magnon mode and phonon mode can be achieved in an asymmetric manner. Furthermore, the direction of quantum steering can be flexibly adjusted via changing the magnon damping rate, coupling strength, squeezing parameter, and bath temperature. The proposed scheme provides the possibility for the generation of macroscopic quantum entanglement and steering and has potential applications in quantum information processing.

Quantum state transfer (QST) is an important task in quantum information processing. In this study, we describe two approaches for the high-fidelity transfer of a quantum state between two opposite quantum dots attached to a multi-channel quantum network. First, we demonstrate that a high-efficiency QST can be achieved with the coherent time evolution of a quantum system without any external control. Second, we present an approach that uses an alternative mechanism for a high-fidelity QST. By adiabatically varying tunnel couplings, it is possible to implement the complete transmission of a quantum state based on this quantum mechanical mechanism.