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| Issue 4, 2024 |
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Extracts from the Internet | ||
Bose Einstein condensate of chromium atoms1 April 2005T Pfau and his colleagues from the University of Stuttgart have for the first time created a Bose-Einstein condensate of chromium atoms. Unlike other Bose-condensed atoms, chromium atoms have a large magnetic moment of 6 Bohr magnetons, making them interact 6 times stronger compared to rare-earth atoms. Using the evaporative cooling techniques, the researchers were able to Bose-condense 50,000 chromium atoms at a temperature of 625 nK. The new condensate can find practical applications in nanolithography and can also be used to study long-range interaction between condensate atoms. In particular, the researchers believe that theoretically predicted phase transitions can be observed using the chromium condensate. Source: cond-mat/0503044 Interfering electrons1 April 2005Researchers from Austria, Germany, and Bosnia and Herzegovina have carried out a new version of the classical electron interference experiment, in which electrons interfere in energy-time rather than in coordinate space. In their experiment a sequence of ultrashort (5 fs, 1.6-cycle) linearly- polarized pulses from a titanium-sapphire laser, all practically identical and having the same phase, were passed through argon gas, and the electrons from the ionized argon atoms were recorded by two detectors lying in the polarization plane. If a laser pulse contained two maxima and one minimum of the electric field, then a interference pattern was seen at one of the detectors (namely, at that toward which the two maxima are directed). Changing the phase of the pulses caused the pattern to be seen at the other detector. The explanation of the interference effect is that any of the two vibrational maxima could produce ionization and that the two ionization path interfere quantum mechanically with each other. The interference pattern observed was one in the electron energy spectrum. Source: http://physicsweb.org/articles/news/9/3/1/1 Quantum correlation of three macroscopic objects1 April 2005Recently, quintuplets of photons have been obtained in the so-called quantum entangled state ( Physics Uspekhi 174 854 (2004)). For macroscopic objects, however, quantum correlations are much harder to obtain. Until recently, only two objects - specifically, two quantum information qubits - have been obtained entangled. Now a University of Maryland team has for the first time observed a quantum-correlated state of three macroscopic objects, an LC oscillatory circuit and a pair of Josephson junctions, each consisting of two superconductors with an insulating layer between. At low temperature, quantized oscillations of electric current were seen to be transferred along the circuit, with all the three devices being in correlated quantum states as determined indirectly from the way they scatter microwave radio pulses. Studies like this are important in creating future quantum computers. Source: Physics News Update, Number 722 Plasma in collapsing bubbles1 April 2005Neither experiment nor theory has yet provided the definitive explanation for sonoluminescence - a phenomenon in which gas bubbles in liquid emit light when subjected to ultrasound. The phenomenon is powered by the spherical shock wave generated by the collapse. While some data suggest that the light is generated by hot plasma in the bubbles ( Physics Uspekhi 171 759 (2001)), the others indicate chemical reactions as the reason ( Physics Uspekhi 172 910 (2002)). Thus far, no evidence has been found to confirm reports of nuclear `bubble fusion' in deuterated acetone ( Physics Uspekhi 172 454 (2000)). Now the first reliable evidence for the presence of plasma in bubbles has come from a new experiment by K Suslick and D Flannigan of the University of Illinois, who studied the way bubbles filled with argon and xenon collapse in sulfuric acid. The analysis of the emission spectrum from single bubbles revealed the presence of plasma with temperatures up to 20,000 K in the bubbles. Because Suslick and Flannigan's experiment differs considerably from previous experiments in the composition of the medium, its results cannot be extended to other cases. Besides, the presence of plasma is a necessary but not a sufficient condition for fusion reaction: much higher temperatures are also required. Source: Nature 434 52 High-power radio bursts1 April 2005Observations with the VLA radio telescope gathered in 2002 revealed a series of five high-power bursts of 0.33 GHz radio emission in the direction of the center of the Galaxy. The bursts were 77 minutes apart and each was 10 minutes in duration, the signal in-between not exceeding the background level. The source of the bursts, which was given the name GCRT J1745-3009, has never been seen neither before nor after the detection of the five bursts. Nor has an associated X-ray or optical radiation been detected from it. The distance of the source is unknown, so its location can be anywhere from close to the Sun to the Galaxy's center (in which latter case it power should be very high. Because similar signals have never been detected from the cosmos, GCRT J1745-3009 may either belong to a new class of radio sources or be yet another form of activity of already known objects. The pulses might have been generated by a brown dwarf - but their characteristics are strongly different from those of the radio emission from brown dwarfs; besides, the periodicity of the pulses is hard to explain in this scenario. Another hypothesis is that the bursts had their origin in a magnetar, a neutron star with a strong magnetic field, and that the 77-min time interval is the orbital period of a binary star system. Source: astro-ph/0503052 |
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources. | |
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