Observation of Microcanonical Atom Number Fluctuations in a Bose-Einstein Condensate.

Quantum systems are typically characterized by the inherent fluctuation of their physical observables. Despite this fundamental importance, the investigation of the fluctuations in interacting quantum systems at finite temperature continues to pose considerable theoretical and experimental challenges. Here we report the characterization of atom number fluctuations in weakly interacting Bose-Einstein condensates. Technical fluctuations are mitigated through a combination of nondestructive detection and active stabilization of the cooling sequence. We observe fluctuations reduced by 27% below the canonical expectation for a noninteracting gas, revealing the microcanonical nature of our system. The peak fluctuations have near linear scaling with atom number ΔN_{0,p}^{2}∝N^{1.134} in an experimentally accessible transition region outside the thermodynamic limit. Our experimental results thus set a benchmark for theoretical calculations under typical experimental conditions.

Observation of Atom Number Fluctuations in a Bose-Einstein Condensate.

Fluctuations are a key property of both classical and quantum systems. While the fluctuations are well understood for many quantum systems at zero temperature, the case of an interacting quantum system at finite temperature still poses numerous challenges. Despite intense theoretical investigations of atom number fluctuations in Bose-Einstein condensates, their amplitude in experimentally relevant interacting systems is still not fully understood. Moreover, technical limitations have prevented their experimental investigation to date. Here we report the observation of these fluctuations. Our experiments are based on a stabilization technique, which allows for the preparation of ultracold thermal clouds at the shot noise level, thereby eliminating numerous technical noise sources. Furthermore, we make use of the correlations established by the evaporative cooling process to precisely determine the fluctuations and the sample temperature. This allows us to observe a telltale signature: the sudden increase in fluctuations of the condensate atom number close to the critical temperature.

A simple laser locking system based on a field-programmable gate array.

Frequency stabilization of laser light is crucial in both scientific and industrial applications. Technological developments now allow analog laser stabilization systems to be replaced with digital electronics such as field-programmable gate arrays, which have recently been utilized to develop such locking systems. We have developed a frequency stabilization system based on a field-programmable gate array, with emphasis on hardware simplicity, which offers a user-friendly alternative to commercial and previous home-built solutions. Frequency modulation, lock-in detection, and a proportional-integral-derivative controller are programmed on the field-programmable gate array and only minimal additional components are required to frequency stabilize a laser. The locking system is administered from a host-computer which provides comprehensive, long-distance control through a versatile interface. Various measurements were performed to characterize the system. The linewidth of the locked laser was measured to be 0.7 ± 0.1 MHz with a settling time of 10 ms. The system can thus fully match laser systems currently in use for atom trapping and cooling applications.

Preparation of Ultracold Atom Clouds at the Shot Noise Level.

We prepare number stabilized ultracold atom clouds through the real-time analysis of nondestructive images and the application of feedback. In our experiments, the atom number N∼10^{6} is determined by high precision Faraday imaging with uncertainty ΔN below the shot noise level, i.e., ΔN

Comparative voice results after laser resection or irradiation of T1 vocal cord carcinoma.

OBJECTIVE: To compare voice results following laser resection or radiation therapy for T1a glottic carcinomas. DESIGN: Objective recordings of acoustical data that were analyzed and calculated by an acoustic analyzer and subjective scores by patients, speech therapists, surgeons, and radiation therapists are compared. SETTING: Academic medical center speech laboratory at an institution where patients had been treated. Archival files were searched and patients were solicited by letter to participate in this analysis. PATIENTS: Men treated at least 6 months previously and who were without active laryngeal disease. Criteria were unilateral vocal cord carcinomatous involvement with no subglottic, anterior commissure, or arytenoid extension and tumor invasion clinically judged to be less than half of the cordal depth. INTERVENTIONS: Thirteen patients had received approximately 63 Gy in 28 fractions, five fractions a week, with laterally opposed fields using a linear accelerator. Eleven patients had had resection of less than half of the cordal depth by using a carbon dioxide laser with a 300-microns spot size working at a 400-mm distance; 13- to 15-W power intensity with a one tenth of a second burn in a noncontinuous mode. RESULTS: No statistically significant differences between the two study groups were found. Patients and physicians subjectively rated (1 indicates normal; 5, aphonic) the quality of voices of patients in the irradiation group (1.5 and 2.0) as slightly better than the quality of voices of patients in the laser group (2.0 and 2.4). Speech pathologists rated the voices of patients in the laser and irradiation group as indistinguishable and mildly abnormal (2.75 and 2.73). CONCLUSION: Voice quality in highly selected patients with vocal cord carcinoma treated by laser resection can be as good as that in patients whose cancer was similarly staged after radiation therapy.

Preparation of retinal vessels for scanning electron microscopic examination using microdissection by ultrasonication.

A method of microdissection by ultrasonication was used to prepare blood vessels of the retina for scanning electron microscopic examination. Eye cups were treated with 2% OsO4 that contained 2% CHAPS or 1% saponin (16 hrs.), dehydrated to 100% acetone, sonicated at 80 kHz (40 min.), and further processed by conventional means. This treatment resulted in the separation of the outer and inner retina at the level of blood vessels in the outer plexiform layer. The overall pattern of the blood vessels was maintained. Venules were distinguished from capillaries. This technique may provide information that is not possible to obtain with corrosion casts or trypsin digests.