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Direct tunable diode laser absorption spectroscopy at 769.9 and 767.5 nm was used to measure potassium (K) atom concentrations in situ in the high temperature (up to 1650 K) flue gas of two different pulverized coal dust combustion systems (atmospheric or pressurized (12 bar)). Two laser types (Fabry-Pe´rot (FP) and vertical-cavity surface-emitting lasers (VCSEL)) were used for the spectrometer and characterized with respect to the magnitude and linearity of their static and dynamic wavelength tuning properties. The wide continuous current-induced tuning range of the VCSEL of 20 cm−1 (compared to 1 cm−1 for the FP) make this laser ideal for species monitoring in high pressure processes. Two VCSELs were time-multiplexed to realize the simultaneous detection of the potassium D1 and D2 lines. Several oxygen absorption lines in the A-band, which are in close spectral vicinity of the K lines, were detected simultaneously, showing the possibility of multi-species detection with one laser. Using the FP-DL for the atmospheric process and the VCSEL for the high pressure process, the pressure-dependent coefficients for spectral broadening as well as a shift of the K line in the flue gas were determined to be (0.18±0.01) and (−0.060±0.003) cm−1 per atm (at 1540 K and 11.2 bar). The total width and shift of the D1 line (11.2 bar/1540 K) were 60 and −20 GHz, respectively. The K atom concentration was determined continuously for several days in both plants under various operation conditions. Typical concentrations in the atmospheric plant were around 2 μg m−3 with a range of 50 ng m−3–30 μg m−3. Averaging 100 scans for each concentration value, we achieved a time resolution of 1.7 s and a detection limit of 10 ng m−3, which corresponds to a fractional absorption in the 10−3–10−4 range. A strong anti-correlation with the oxygen concentration could be verified. At the 12 bar plant, the concentration was again typically around 2 μg m−3 but K levels up to 60 μg m−3 were observed. Here, a strong dependence of the K-signal on the type of fuel could be verified. [ABSTRACT FROM AUTHOR]

A new harmonic detection scheme for fully digital, fast-scanning wavelength-modulation spectroscopy (DFS-WMS) is presented. DFS-WMS is specially suited for in situ absorption measurements in combustion environments under fast fluctuating transmission conditions and is demonstrated for the first time by open-path monitoring of ambient oxygen using a distributed-feedback diode laser, which is doubly modulated with a fast linear 1 kHz-scan and a sinusoidal 300 kHz-modulation. After an analog high-pass filter, the detector signal is digitized with a 5 megasample/s 12-bit AD-converter card pluged into a PC and subsequently — unlike standard lock-ins — filtered further by co-adding 100 scans, to generate a narrowband comb filter. All further filtering and the demodulation are performed completely digitally on a PC with the help of discrete Fourier transforms (DFT). Both 1 fand 2f-signals, are simultaneously extracted from the detector signal using one ADC input channel. For the 2f-signal, a linearity of 2% and a minimum detectable absorption of 10[sup -4] could be verified experimentally, with the sensitivity to date being limited only by insufficient gain on the 2f-frequency channel. Using the offset in the 1 f signal as a transmission 'probe', we could show that the 2f-signal can be transmissioncorrected by a simple division by the 1 f-background, proving that DFS-WMS provides the possibility of compensating for transmission fluctuations. With the inherent suppression of additive noise, DFS-WMS seems well suited for quantitative in situ absorption spectroscopy in large combustion systems. This assumption is supported by the first measurements of oxygen in a high-pressure combustor at 12 bar. [ABSTRACT FROM AUTHOR]

The T1←S0 absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550–620 nm) and in a seeded cold supersonic jet (580–600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of ∼±5%. In this region 22 harmonic sequences and 18 hot bands were observed. The energetically lowest ground state vibration at 167.5 cm−1 was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm−1. The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S1, 0←S0, 0 absorption was tentatively assigned to a transition at ∼17433 cm−1. [Copyright &y& Elsevier]

Quantum teleportation is a key ingredient in quantum networks and one of the building blocks for quantum computation. Teleportation between distant material objects using light as the quantum-information carrier has been a particularly exciting goal. Here we propose and demonstrate the deterministic continuous-variable teleportation between distant material objects. The objects are macroscopic atomic ensembles at room temperature. Entanglement required for teleportation is distributed by light propagating from one ensemble to the other. We demonstrate that the experimental fidelity of the quantum teleportation is higher than that achievable by any classical process. Furthermore, we demonstrate the benefits of deterministic teleportation by teleporting a sequence of spin states evolving in time from one distant object onto another. The teleportation protocol is applicable to other important systems, such as mechanical oscillators coupled to light or cold spin ensembles coupled to microwaves. [ABSTRACT FROM AUTHOR]

A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are versatility (allowing a wide range of inputs) and preservation of quantum information in a way unattainable with any classical memory device. Here we demonstrate such a quantum memory for continuous-variable entangled states, which play a fundamental role in quantum information processing. We store an extensive alphabet of two-mode 6.0 dB squeezed states obtained by varying the orientation of squeezing and the displacement of the states. The two components of the entangled state are stored in two room-temperature cells separated by 0.5 m, one for each mode, with a memory time of 1 ms. The true quantum character of the memory is rigorously proved by showing that the experimental memory fidelity 0.52±0.02 significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements. [ABSTRACT FROM AUTHOR]

Neutral atoms can be trapped and manipulated with surface mounted microscopic current carrying and charged structures. We present a lithographic fabrication process for such atom chips based on evaporated metal films. The size limit of this process is below 1 μm. At room temperature, thin wires can carry current densities of more than 107 A/cm2 and voltages of more than 500 V. Extensive test measurements for different substrates and metal thicknesses (up to 5 μm) are compared to models for the heating characteristics of the microscopic wires. Among the materials tested, we find that Si is the best suited substrate for atom chips. [ABSTRACT FROM AUTHOR]