arXiv subjects

G. S. Agarwal

Publications and source records attributed to G. S. Agarwal.

At least 91 records · Page 5Linked to original sources

arXiv2013

Nonlocal continuous variable correlations and violation of Bell's inequality for light beams with topological singularities

We consider optical beams with topological singularities which possess Schmidt decomposition and show that such classical beams share many features of two mode entanglement in quantum optics. We demonstrate the coherence properties of such beams through the violations of Bell inequality for continuous variables using the Wigner function. This violation is a consequence of correlations between the $(x, p_x)$ and $(y, p_y)$ spaces which mathematically play the same role as nonlocality in quantum mechanics. The Bell violation for the LG beams is shown to increase with higher orbital angular momenta $l$ of the vortex beam. This increase is reminiscent of enhancement of nonlocality for many particle Greenberger-Horne-Zeilinger states or for higher spins. The states with large $l$ can be easily produced using spatial light modulators.

quant-ph↗

arXiv2013

Robust stationary mechanical squeezing in a kicked quadratic optomechanical system

We propose a scheme for the generation of a robust stationary squeezed state of a mechanical resonator in a quadratically coupled optomechanical system, driven by a pulsed laser. The intracavity photon number presents periodic intense peaks suddenly stiffening the effective harmonic potential felt by the mechanical resonator. These "optical spring kicks" tend to squeeze the resonator position, and due to the interplay with fluctuation-dissipation processes one can generate a stationary state with more than 13 dB of squeezing even starting from moderately "pre-cooled" initial thermal states.

quant-ph↗

arXiv2013

Ramsey spectroscopy with squeezed light

Traditional Ramsey spectroscopy has the frequency resolution $2π/T$, where $T$ is the time separation between two light fields. Using squeezed states and two-atom excitation joint detection, we present a new scheme achieving a higher resolution $π/T$. We use two mode squeezed light which exhibits strong entanglement.

quant-ph↗

arXiv2013

Photon Aided and Inhibited Tunneling of Photons

In the light of the interest in the transport of single photons in arrays of waveguides, fiber couplers, photonic crystals, etc., we consider the quantum mechanical process of the tunneling of photons through evanescently or otherwise coupled structures. We specifically examine the issue of tunneling between two structures when one structure already contains few photons. We demonstrate the possibility of both photon aided and inhibited tunneling of photons. The Bosonic nature of photons enhances the tunneling probability. We also show how the multiphoton tunneling probability can be either enhanced or inhibited due to the presence of photons. We find similar results for the higher order tunneling. Finally, we show that the presence of a squeezed field changes the nature of tunneling considerably.

quant-ph↗

arXiv2013

Multimode Phonon Cooling via Three Wave Parametric Interactions with Optical Fields

We discuss the possible cooling of different phonon modes via three wave mixing interactions of vibrational and optical modes. Since phonon modes exhibit a variety of dispersion relations or frequency spectra with diverse spatial structures, depending on the shape and size of the sample, we formulate our theory in terms of relevant spatial mode functions for the interacting fields in any given geometry. We discuss the possibility of Dicke like collective effects in phonon cooling and present explicit results for simultaneous cooling of two phonon modes via the anti-Stokes up conversions. We show that the bimodal cooling should be observable experimentally.

quant-ph↗

arXiv2013

Fano resonances and their control in optomechanics

The Fano line profiles, originally discovered in the context of photoionization, have been found to occur in a large class of systems like resonators, metamaterials, plasmonics. We demonstrate the existence of such resonances in cavity optomechanics by identifying the interfering contributions to the fields generated at antiStokes and Stokes frequencies. Unlike the atomic systems, the optomechanical systems provide great flexibility as the width of the resonance is controlled by the coupling field. We further show how the double cavities coupled by a single optomechanical mirror can lead to the splitting of the Fano resonance and how the second cavity can be used to tune the Fano resonances. The Fano resonances are quite sensitive to the decay parameters associated with cavities and the mechanical mirror. Such resonances can be studied by both pump probe experiments as well as via the spectrum of the quantum fluctuations in the output fields.

physics.optics↗

arXiv2013

Spontaneous Generation of Photons in Transmission of Quantum Fields in PT Symmetric Optical Systems

We develop a rigorous mathematically consistent description of PT symmetric optical systems by using second quantization. We demonstrate the possibility of significant spontaneous generation of photons in PT symmetric systems. Further we show the emergence of Hanbury-Brown Twiss (HBT) correlations in spontaneous generation. We show that the spontaneous generation determines decisively the nonclassical nature of fields in PT symmetric systems. Our work can be applied to other systems like plasmonic structure where losses are compensated by gain mechanisms.

quant-ph↗

arXiv2013

Phonon mediated electromagnetically induced absorption in hybrid opto-electro mechanical systems

We predict the existence of the electromagnetically induced absorption (EIA) in the double cavity configurations of the hybrid opto-electro mechanical systems (OEMS). We discuss the origin of the EIA in OEMS which exhibit the existence of an absorption peak within the transparency window. We provide analytical results for the width and the height of the EIA peak. The combination of the EIT and EIA is especially useful for photon switching applications. The EIA that we discuss is different from the one originally discovered by Lezama et al in atomic systems and can be understood in terms of the dynamics of three coupled oscillators (rather than two) under different conditions on the relaxation parameters. The EIA we report can also be realized in metamaterials and plasmonic structures.

quant-ph↗

arXiv2013

Non-Gaussian and Gaussian Entanglement in Coupled Leaky Waveguides

We investigate the viability of coupled waveguides as basic units of quantum circuits. In particular, we study the dynamics of entanglement for the single photon state, and single mode squeezed vacuum state. We further consider the case of entangled inputs in terms of the two mode mode squeezed vacuum states and the two photon NOON state. We present explicit analytical results for the measure of entanglement in terms of the logarithmic negativity. We also address the effect of loss on entanglement dynamics of waveguide modes. Our results indicate that the waveguide structures are reasonably robust against the effect of loss and thus quite appropriate for quantum architectures as well as for the study of coherent phenomena like random walks. Our analysis is based on realistic structures used currently.

quant-ph↗

arXiv2013

A quantum dynamical framework for Brownian heat engines

We present a self contained formalism modelled after the Brownian motion of a quantum harmonic oscillator for describing the performance of microscopic Brownian heat engines like Carnot, Stirling and Otto engines. Our theory, besides reproducing the standard thermodynamics results in the steady state enables permits us to study the role dissipation plays in determining the efficiency of Brownian heat engines under actual laboratory conditions. In particular, we analyse in detail the dynamics associated with decoupling a system in equilibrium with one bath and recoupling it to another bath and obtain exact analytical results which are shown to have significant ramifications on the efficiencies of engines involving such a step. We also develop a simple yet powerful technique for computing corrections to the steady state results arising from finite operation time and use it to arrive at the thermodynamic complementarity relations for various operating conditions and also to compute the efficiencies of the three engines cited above at maximum power. Some of the methods and techniques and exactly solvable models presented here are interesting in their own right and, in our opinion, would find useful applications in other contexts as well.

quant-ph↗

arXiv2012

Giant Spin Hall Effect in Single Photon Plasmonics

We show the existence of a very large spin Hall effect of light (SHEL) in single photon plasmonics based on spontaneous emission and the dipole-dipole interaction initiated energy transfer (FRET) on plasmonic platforms. The spin orbit coupling inherent in Maxwell equations is seen in the conversion of sigma + photon to sigma - photon. The FRET is mediated by the resonant surface plasmons and hence we find very large SHEL. We present explicit results for SHEL on both graphene and metal films. We also study how the splitting of the surface plasmon on a metal film affects the SHEL. In contrast to most other works which deal with SHEL as correction to the paraxial results, we consider SHEL in the near field of dipoles which are far from paraxial.

cond-mat.mes-hall↗

arXiv2012

Optical memories and transduction of fields in double cavity optomechanical systems

Using electromagnetically induced transparency we show how the opto-mechanical systems can be used both as memory elements as well as for the transduction of optical fields. We use a double cavity optomechanical system which facilitates such applications. By tuning the frequency of the second cavity one can produce output fields at a variety of frequencies. We present analytical results for the steady state behavior which is controlled by the power and the detuning of the field driving the second cavity.

quant-ph↗

arXiv2012

Observation of electromagnetically induced transparency in evanescent fields

We observe and investigate, both experimentally and theoretically, electromagnetically-induced transparency experienced by evanescent fields arising due to total internal reflection from an interface of glass and hot rubidium vapor. This phenomenon manifests itself as a non-Lorentzian peak in the reflectivity spectrum, which features a sharp cusp with a sub-natural width of about 1 MHz. The width of the peak is independent of the thickness of the interaction region, which indicates that the main source of decoherence is likely due to collisions with the cell walls rather than diffusion of atoms. With the inclusion of a coherence-preserving wall coating, this system could be used as an ultra-compact frequency reference.

physics.atom-ph↗

arXiv2012

Resolution of objects within subwavelength range by using the near field of a dipole

We analyze the far field resolution of apertures which are illuminated by a point dipole located at subwavelength distances. It is well known that radiation emitted by a localized source can be considered a combination of travelling and evanescent waves, when represented by the angular spectrum method. The evanescent wave part of the source can be converted to propagating waves by diffraction at the aperture thereby it contributes to the far field detection. Therefore one can expect an increase in the resolution of objects. We present explicit calculations showing that the resolution at the far zone is improved by decreasing the source-aperture distance. We also utilize the resolution enhancement by the near field of a dipole to resolve two closely located apertures. The results show that without the near field (evanescent field) the apertures are not resolved whereas with the near field of the dipole the far zone intensity distribution shows improved resolution. This method eliminates the requirements of near-field techniques such as controlling and scanning closely located tip detectors.

physics.optics↗

arXiv2012

Sub-binomial light

The click statistics from on-off detector systems is quite different from the counting statistics of the more traditional detectors. This necessitates introduction of new parameters to characterize the nonclassicality of fields from measurements using on-off detectors. To properly replace the Mandel Q_M parameter, we introduce a parameter Q_B. A negative value represents a sub-binomial statistics. This is possible only for quantum fields, even for super-Poisson light. It eliminates the problems encountered in discerning nonclassicality using Mandel's Q_M for on-off data.

quant-ph↗

arXiv2012

True photo-counting statistics of multiple on-off detectors

We derive a closed photo-counting formula, including noise counts and a finite quantum efficiency, for photon number resolving detectors based on on-off detectors. It applies to detection schemes such as array detectors and multiplexing setups. The result renders it possible to compare the corresponding measured counting statistics with the true photon number statistics of arbitrary quantum states. The photo-counting formula is applied to the discrimination of photon numbers of Fock states, squeezed states, and odd coherent states. It is illustrated for coherent states that our formula is indispensable for the correct interpretation of quantum effects observed with such devices.

quant-ph↗

arXiv2012

Optomechanical Systems as Single Photon Routers

We demonstrate theoretically the possibility of using nano mechanical systems as single photon routers. We show how EIT in cavity optomechanical systems can be used to produce a switch for a probe field in a single photon Fock state using very low pumping powers of few microwatt. We present estimates of vacuum and thermal noise and show the optimal performance of the single photon switch is deteriorated by only few percent even at temperatures of the order of 20 mK.

quant-ph↗

arXiv2012

Measurement induced focussing of radiation from independent single photon sources

We present a technique based on multi-photon detection which leads to a strong focussing of photons scattered by independent single photon emitters. For N single photon sources it is shown that if m - 1 photons are detected in a particular direction (with m \leq N) the probability to detect the m-th photon in the same direction can be as high as 100%. This measurement induced focussing effect is already clearly visible for m>2.

quant-ph↗