Three dimensional winds: A maximum cross-correlation application to elastic lidar data

Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar (light detection and ranging) data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three-dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain-following winds in the Rio Grande valley

Tailoring Single and Multiphoton Probabilities of a Single Photon On-Demand Source

As typically implemented, single photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand.Comment: 4 pages, LaTex, 2 figures, twocolumn and RevTex Style for PR

New, efficient and robust, fiber-based quantum key distribution schemes

We present a new fiber based quantum key distribution (QKD) scheme which can be regarded as a modification of an idea proposed by Inoue, Waks and Yamamoto (IWY) [1]. The scheme described here uses a single phase modulator and two differential delay elements in series at the transmitter that form an interferometer when combined with a third differential delay element at the receiver. The protocol is characterized by a high efficiency, reduced exposure to an attack by an eavesdropper, and higher sensitivity to such an attack when compared to other QKD schemes. For example, the efficiency with which transmitted data contribute to the private key is 3/4 compared with 1/4 for BB84 [2]. Moreover, an eavesdropper can aquire a maximum of 1/3 of the key which leads to an error probability in the private key of 1/3. This can be compared to 1/2 and 1/4 for these same parameters in both BB84 and IWY. The combination of these considerations should lead to increased range and key distribution rate over present fiber-based QKD schemes.Comment: 4 pages, 5 figures, 1 equatio

Quantum key distribution without alternative measurements

Entanglement swapping between Einstein-Podolsky-Rosen (EPR) pairs can be used to generate the same sequence of random bits in two remote places. A quantum key distribution protocol based on this idea is described. The scheme exhibits the following features. (a) It does not require that Alice and Bob choose between alternative measurements, therefore improving the rate of generated bits by transmitted qubit. (b) It allows Alice and Bob to generate a key of arbitrary length using a single quantum system (three EPR pairs), instead of a long sequence of them. (c) Detecting Eve requires the comparison of fewer bits. (d) Entanglement is an essential ingredient. The scheme assumes reliable measurements of the Bell operator.Comment: REVTeX, 5 pages, 2 figures. Published version with some comment

Continuous variable quantum cryptography

We propose a quantum cryptographic scheme in which small phase and amplitude modulations of CW light beams carry the key information. The presence of EPR type correlations provides the quantum protection.Comment: 8 pages, 3 figure

An arbitrated quantum signature scheme

The general principle for a quantum signature scheme is proposed and investigated based on ideas from classical signature schemes and quantum cryptography. The suggested algorithm is implemented by a symmetrical quantum key cryptosystem and Greenberger-Horne-Zeilinger (GHZ) triplet states and relies on the availability of an arbitrator. We can guarantee the unconditional security of the algorithm, mostly due to the correlation of the GHZ triplet states and the use of quantum one-time pads.Comment: 10 pages, no figures. Phys. Rev. A 65, (In press

Proposal of an experimental scheme for realising a translucent eavesdropping on a quantum cryptographic channel

Purpose of this paper is to suggest a scheme, which can be realised with today's technology and could be used for entangling a probe to a photon qubit based on polarisation. Using this probe a translucent or a coherent eavesdropping can be performed.Comment: in pres

Optimization approach to entanglement distillation

We put forward a method for optimized distillation of partly entangled pairs of qubits into a smaller number of more entangled pairs by recurrent local unitary operations and projections. Optimized distillation is achieved by minimization of a cost function with up to 30 real parameters, which is chosen to be sensitive to the fidelity and the projection probability at each step. We show that in many cases this approach can significantly improve the distillation efficiency in comparison to the present methods.Comment: 6 pages, 5 figures, REVTEX. New examples, figures and references, more detailed explanations. To appear in Phys. Rev.

Stokes-operator-squeezed continuous-variable polarization states

We investigate nonclassical Stokes-operator variances in continuous-wave polarization-squeezed laser light generated from one and two optical parametric amplifiers. A general expression of how Stokes-operator variances decompose into two-mode quadrature operator variances is given. Stokes parameter variance spectra for four different polarization-squeezed states have been measured and compared with a coherent state. Our measurement results are visualized by three-dimensional Stokes-operator noise volumes mapped on the quantum Poincare sphere. We quantitatively compare the channel capacity of the different continuous-variable polarization states for communication protocols. It is shown that squeezed polarization states provide 33% higher channel capacities than the optimum coherent beam protocol

Three-dimensional elastic lidar winds

Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three- dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain following winds in the Rio Grande valley