Controllable Beam Splitter Research Articles

Mechanical resonator cooling to the ground-state by coherent feedback in a double cavity setup including an atomic ensemble

This study concerns the cooling of a mechanical resonator to the ground-state in the unresolved sideband regime theoretically. To this aim, the optical modes of an optomechanical cavity are coupled with an atomic ensemble and an auxiliary cavity. Then, a coherent feedback loop is applied via a controllable beam splitter, which reflects a fraction of the output field to the input mirror of the optomechanical cavity. Considering the proposed feedback scheme, the optical response of the cavity is analyzed for weak optomechanical coupling to obtain the rate equations. Utilizing the electromagnetically-induced-transparency-like shape of the fluctuation spectrum of the optical force, optimal cooling conditions are calculated to place the peaks and dip of the spectrum at the desired frequencies to maximize the difference between cooling and heating rates. It is shown that the coherent feedback loop enhances the cooling effect while the heating rate is not affected. Moreover, by utilizing two coupled auxiliary systems, the effect of heating transitions is better suppressed compared to the case with one auxiliary system. As a result, not only lower limits for cooling but also larger values of net cooling rate are achieved. The results show that the proposed feedback cooling scheme significantly improves the cooling capability of the hybrid system, and the mechanical resonator can be cooled near the quantum limit. Furthermore, it is shown that the proposed method performs well in a wide range of system parameters.

Broadband Chip-Based Source of Quantum Noise with Electrically Controllable Beam Splitter

The theory and practical realization of a broadband quantum-noise generator based on an original integrated optical beam splitter in the form of a Mach-Zehnder interferometer is demonstrated. The beam splitter with a double output, made on a lithium niobate substrate, provides accurate electro-optical balancing of the homodyne quantum-noise detection circuit. The experimentally obtained excess of quantum noise over classical noise is 12 dB in the frequency band over 4 GHz, which is the best parameters of quantum-noise generators known from the literature.

Multifunctional plasmonic metasurface demultiplexer and wavelength-polarization controllable beam splitter

We report the experimental realization of a multifunctional microscale plasmonic metasurface capable of sampling a light beam and performing five functionalities, while allowing high direct transmission and maintenance of the properties of the input light beam. The plasmonic metasurface integrates light-to-surface-plasmon coupling, two-channel wavelength demultiplexing with a channel spacing smaller than 44 nm, wavelength and polarization controllable beam splitting of a monochromatic, single polarization signal, and four-level polarization and wavelength-polarization demultiplexing in an all-in-one structure. Such a device can play a key role for on-chip adaptable integrated circuits for parallel signal processing, communications, and nondestructive sensing.

Light-Alignment Controllable Beam Splitter and Vectorial Displacement Sensor in the Stopped-Light Regime of Plasmonic Metasurfaces

We report the experimental realization of periodically perforated plasmonic metasurfaces capable of integrating several key functionalities, such as light-to-surface plasmon coupling, controllable ...

Controlling spatial mode superposition to channel light flow in a photonic crystal

We present robust control of superposition of spatial modes in a photonic crystal cavity arising from incorporating a weak localized perturbation. As expected, this perturbation breaks the symmetry of the underlying photonic crystal structure, resulting in a frequency shift of the cavity eigen modes. Engineering of the perturbation leads us to discover the comprehensive mathematical structure of the governing superposition of the spatial modes. This superposition is further designed to obtain controllable channeling of light through a cavity–waveguide system, thus demonstrating its applicabitily in realizing narrow (wide) band filters, controllable beam splitters, and wavelength multiplexers.

Establishing Optimal Wave Communication Channels Automatically

We show how multiple optimal orthogonal channels for communicating or interconnecting with waves between two objects can be aligned and optimized automatically using controllable beamsplitters, detectors and simple local feedback loops, without moving parts, without device calibration, without fundamental beam splitting loss, and without calculations. Optical applications include multiple simultaneous orthogonal spatial communication channels in free space or multimode optical fibers, automatically focused power delivery with waves, multiple channel communication through scattering or lossy media, and real-time-optimized focused channels to and from multiple moving objects. The approach physically implements automatic singular value decomposition of the wave coupling between the objects, and is equivalent in its effect to the beam forming in a laser resonator with phase-conjugate mirrors with the additional benefits of allowing multiple orthogonal channels to be formed simultaneously and avoiding the need for any nonlinear optical materials.

Reconfigurable add-drop multiplexer for spatial modes

We show how a spatial mode can be extracted from a light beam, leaving the other orthogonal modes undisturbed, and allowing a new signal to be retransmitted on that mode. The method is self-aligning, avoids fundamental splitting losses, and uses only local feedback loops on controllable beam splitters and phase shifters. It could be implemented with Mach-Zehnder interferometers in planar optics. The method can be extended to multiple simultaneous mode extractions. As a spatial reconfigurable optical add-drop multiplexer, it is hitless, allowing reconfiguration without interrupting the transmission of any channel.

Beam splitter for spin waves in quantum spin network

We theoretically design and analytically study a controllable beam splitter for the spin wave propagating in a star-shaped (e.g., a $Y$-shaped beam) spin network. Such a solid state beam splitter can display quantum interference and quantum entanglement by the well-aimed controls of interaction on nodes. It will enable an elementary interferometric device for scalable quantum information processing based on the solid system.

The dark-state polaritons of a double-Λ atomic ensemble

We study the interaction of two quantized fields with a double-Λ system driven by two classical control fields with variable complex Rabi frequencies. There exists one normal mode of the quantum fields that propagates without absorption. In the two-mode case of dark-state polaritons, we discuss the possibility of storing and retrieving the quantum state in this normal mode. This system can be also used to generate entangled state and, furthermore, it can act as a controllable beam splitter.

A Novel Controllable Beam Splitter for Guided Atoms

We propose a novel atomic beamsplitter for guided atoms composed of aU-shaped current carrying conductor and an additional bias magneticfield, and study the dynamic process of atomic beam splitting in thebeamsplitter by Monte Carlo simulations. Our study shows that thesplitting ratio of the beamsplitter can be continuously adjusted from 0to 1 by changing the additional bias field. In addition, the transversetemperature of guided atoms at the outlets of the beamsplitter are alsoestimated and explained qualitatively.

Coherence of bose condensates

We study the coherence of interacting Bose condensates in recent magnetic trap experiments. The coherent evolution manifests itself in the macroscopic interference of two independent Bose condensates. The theoretical predictions from the time-dependent Gross–Pitaevskii equation are in excellent agreement with the measured interference patterns. A coherent coupling of two condensates represents the atomic analogon of a Josephson junction. The dependence of the magnetic confinement on the nuclear spin orientation allows one to build a controllable beam splitter by magnetic resonance. The application of this beam splitter to realize an atom laser is studied theoretically. The coherence of the output beam is limited only by phase diffusion of the condensate.