Gravitational field measurement with an equilibrium ensemble of cold atoms

A new approach to the measurement of gravitational fields with an equilibrium ensemble of ultra-cold alkali atoms confined in a cell of volume $V$ is investigated. The proposed model of the gravitational sensor is based on a variation of the density profile of the ensemble due to changing of the gravitational field. For measurement the atomic density variations of the ensemble the electromagnetically induced transparency method is used.Comment: 4 pages, 1 figure, revte

Quadrature noise in light propagating through a cold 87Rb atomic gas

We report on the study of the noise properties of laser light propagating through a cold 87Rb atomic sample held in a magneto-optical trap. The laser is tuned around the Fg = 2 \rightarrow Fe = 1, 2 D1 transitions of 87Rb. We observe quadrature-dependent noise in the light signal, an indication that it may be possible to produce squeezed states of light. We measure the minimum and maximum phase-dependent noise as a function of detuning and compare these results to theoretical predictions to explore the best conditions for light squeezing using cold atomic Rb

Effective unidirectional pumping for steady-state amplification without inversion

We discuss an opportunity to achieve amplification without inversion in three-level cascade scheme using an effective unidirectional pumping via bidirectional incoherent pump. Analytical solution to the population and the coherence are obtained in the steady-state regime. With a proper choice of the parameters, obtained here, the possibility for amplification without inversion is presented.Comment: 8 Pages, 7 figure

Analytical solution to position dependent mass Schr\"odinger equation

Using a recently developed technique to solve Schr\"odinger equation for constant mass, we studied the regime in which mass varies with position i.e position dependent mass Schr\"odinger equation(PDMSE). We obtained an analytical solution for the PDMSE and applied our approach to study a position dependent mass $m(x)$ particle scattered by a potential $\mathcal{V}(x)$. We also studied the structural analogy between PDMSE and two-level atomic system interacting with a classical field.Comment: 5 pages, 4 figure

Delocalized single-photon Dicke states and the Leggett- Garg inequality in solid state systems

We show how to realize a single-photon Dicke state in a large one-dimensional array of two- level systems, and discuss how to test its quantum properties. Realization of single-photon Dicke states relies on the cooperative nature of the interaction between a field reservoir and an array of two-level-emitters. The resulting dynamics of the delocalized state can display Rabi-like oscillations when the number of two-level emitters exceeds several hundred. In this case the large array of emitters is essentially behaving like a mirror-less cavity. We outline how this might be realized using a multiple-quantum-well structure and discuss how the quantum nature of these oscillations could be tested with the Leggett-Garg inequality and its extensions.Comment: 29 pages, 5 figures, journal pape

Classical Signal Model for Quantum Channels

Recently it was shown that the main distinguishing features of quantum mechanics (QM) can be reproduced by a model based on classical random fields, so called prequantum classical statistical field theory (PCSFT). This model provides a possibility to represent averages of quantum observables, including correlations of observables on subsystems of a composite system (e.g., entangled systems), as averages with respect to fluctuations of classical (Gaussian) random fields. In this note we consider some consequences of PCSFT for quantum information theory. They are based on the observation \cite{W} of two authors of this paper that classical Gaussian channels (important in classical signal theory) can be represented as quantum channels. Now we show that quantum channels can be represented as classical linear transformations of classical Gaussian signa

Slow light in paraffin-coated Rb vapor cells

We present preliminary results from an experimental study of slow light in anti-relaxation-coated Rb vapor cells, and describe the construction and testing of such cells. The slow ground state decoherence rate allowed by coated cell walls leads to a dual-structured electromagnetically induced transparency (EIT) spectrum with a very narrow (<100 Hz) transparency peak on top of a broad pedestal. Such dual-structure EIT permits optical probe pulses to propagate with greatly reduced group velocity on two time scales. We discuss ongoing efforts to optimize the pulse delay in such coated cell systems.Comment: 6 pages, 6 figures, submitted to Journal of Modern Optic

Quantum Communications with Compressed Decoherence Using Bright Squeezed Light

We propose a scheme for long-distance distribution of quantum entanglement in which the entanglement between qubits at intermediate stations of the channel is established by using bright light pulses in squeezed states coupled to the qubits in cavities with a weak dispersive interaction. The fidelity of the entanglement between qubits at the neighbor stations (10 km apart from each other) obtained by postselection through the balanced homodyne detection of 7 dB squeezed pulses can reach F=0.99 without using entanglement purification, at same time, the probability of successful generation of entanglement is 0.34.Comment: 4 pages, 2 figure

Technique of quantum state transfer for a double Lambda atomic beam

The transfer technique of quantum states from light to collective atomic excitations in a double $\Lambda$ type system is extended to matter waves in this paper, as a novel scheme towards making a continuous atom laser. The intensity of the output matter waves is found to be determined by the initial relative phase of the two independent coherent probe lights, which may indicate an interesting method for the measurement of initial relative phase of two independent light sources.Comment: 5 pages, 2 figure

Enhancing the gain by quantum coherence in terahertz quantum cascade lasers

We propose and study GaAs/AlGaAs terahertz frequency quantum cascade lasers in which mid-infrared radiation is used as a coherent drive for enhancing the terahertz gain