A minimum-disturbing quantum state discriminator

We propose two experimental schemes for quantum state discrimination that achieve the optimal tradeoff between the probability of correct identification and the disturbance on the quantum state.Comment: 9 pages, 1 figure, OSID style. Submitted to the special issue of "Open Systems and Information Dynamics", Proceedings of the "38th Symposium on Mathematical Physics", Torun, Poland, June 200

Quantum non-demolition measurement saturates fidelity trade-off

A general quantum measurement on an unknown quantum state enables us to estimate what the state originally was. Simultaneously, the measurement has a destructive effect on a measured quantum state which is reflected by the decrease of the output fidelity. We show for any $d$-level system that quantum non-demolition (QND) measurement controlled by a suitably prepared ancilla is a measurement in which the decrease of the output fidelity is minimal. The ratio between the estimation fidelity and the output fidelity can be continuously controlled by the preparation of the ancilla. Different measurement strategies on the ancilla are also discussed. Finally, we propose a feasible scheme of such a measurement for atomic and optical 2-level systems based on basic controlled-NOT gate.Comment: 5 pages, 2 figure

MESON2000 Conference Summary

This short contribution is a {\it lite} MESON2000 conference summary. As appropriate for the 600th anniversary of the Jagellonian University, it begins with a brief summary of the last 600 years of European history and its place in hadron physics. Next a ``physicist chirality'' order parameter PC is introduced. When applied to MESON2000 plenary speakers this order parameter illustrates the separation of hadron physicists into disjoint communities. The individual plenary talks in MESON2000 are next sorted according to the subconference associated with each of the 36 plenary speakers. Finally, I conclude with a previously unreported Feynman story regarding the use of models in hadron physics.Comment: 11 pages, 3 figures, uses appolb.cps and epsfig. MESON2000 Conference Summary Tal

Frequency Stabilization of 4.7 THz Quantum Cascade Lasers

Heterodyne receivers for astronomy observing at 4.7 THz use Quantum Cascade Lasers (QCLs) as the local oscillator. QCLs are compact, powerful, and easy to use but prone to frequency instability from current noise, temperature fluctuations, and optical feedback, and they also lack absolute frequency reference. This work presents several solutions to this problem. A heterodyne laboratory receiver at 4.7 THz has been developed to host all the experiments. The receiver shows an uncorrected receiver noise temperature of around 5000K at an IF frequency of 5.1 GHz and a total power Allan stability time of around 500 seconds. With this receiver, measuring methanol's emission lines helped to frequency calibrate one of the QCLs. The first experiment uses a methanol absorption line for frequency discrimination and a Hot Electron Bolometer (HEB) as a total power detector. In an active control loop, the experiment locks the laser's frequency to the dip of the absorption line. This method applies a known modulation to the QCL's frequency, dominating the QCL's linewidth with an FWHM of 2.1 MHz. The second and the third experiments down-convert the QCL's frequency with a Superlattice Device (SLD) harmonic generator and mixer. A diode multiplier chain produces a 182.5 GHz signal to pump the SLD. The 26th harmonic is generated and mixed with the 4.7 THz QCL signal. The resulting IF signal at the SLD's output is 10 dB over the noise floor. The second experiment feeds the IF signal into a delay line frequency discriminator to produce the QCL frequency's error information. A power divider divides the amplified and filtered SLD's IF into two. Only one is delayed in 10 meters of coax cable, and homodyne mixing produces a DC voltage as a function of the QCL's frequency. The control electronics turn this into a correction current to the QCL. This method stabilized the QCL with more than 10 MHz of frequency deviations, to an FWHM of 780 kHz, for hours. The experiment even works at very low signal-to-noise conditions, such as 2 dB, and revealed that the optical feedback is the dominant QCL line broadening mechanism caused by the pulse tube refrigerator's forced motions. The third experiment uses a Phase Locked Loop (PLL). A phase detector compares QCL's phase with a reference, producing an error voltage. The loop filter transfers this to a correcting current, compensating the QCL's frequency disturbances. Phase locking is more challenging than frequency locking, and an exact understanding had to be developed on transfer functions and noise modeling. The experiment locked the QCL's phase, reducing the linewidth FWHM from 1.4 MHz to less than 7 kHz, stable for half an hour, and occasionally losing the lock for a few seconds. With the demonstrated works, it is possible to stabilize the frequency of 4.7 THz QCLs

Ten Point Six Micron Optical Heterodyne Communication System. Phase 3 Progress Report, 1 Aug. - 31 Oct. 1967

Improved carbon dioxide lasers and electronic components for 10.6 micron optical heterodyne communication syste

An Efficient, Movable Single-Particle Detector for Use in Cryogenic Ultra-High Vacuum Environments

A compact, highly efficient single-particle counting detector for ions of keV/u kinetic energy, movable by a long-stroke mechanical translation stage, has been developed at the Max-Planck-Institut f\"ur Kernphysik (Max Planck Institute for Nuclear Physics, MPIK). Both, detector and translation mechanics, can operate at ambient temperatures down to $\sim$ 10 K and consist fully of ultra-high vacuum (UHV) compatible, high-temperature bakeable and non-magnetic materials. The set-up is designed to meet the technical demands of MPIK's Cryogenic Storage Ring (CSR). We present a series of functional tests that demonstrate full suitability for this application and characterise the set-up with regard to its particle detection efficiency.Comment: 12 pages, 9 figures, version accepted for publication in Review of Scientific Instrument

Hubble Space Telescope: Fine guidance sensors instrument handbook. Version 2.1

The Fine Guidance Sensors (FGS) are a system of photomultiplier tubes and white light amplitude interferometers (Koester's prism) which are used for the fine guidance of the Hubble Space Telescope (HST). The purpose of the handbook is to provide information to a potential user of the FGS so that he may explore the feasibility of performing various observations. A brief overview is given of how the FGS works, along with an explanation of the instrument in some detail. The procedure for estimating exposure times is explained. The observing modes are described. Some details needed to specify the exposures and observation requirements on the proposal forms are explained. Data reduction procedures are outlined