224 research outputs found
Bogoliubov theory for atom scattering into separate regions
We review the Bogoliubov theory in the context of recent experiments, where
atoms are scattered from a Bose-Einstein Condensate into two well-separated
regions. We find the full dynamics of the pair-production process, calculate
the first and second order correlation functions and show that the system is
ideally number-squeezed. We calculate the Fisher information to show how the
entanglement between the atoms from the two regions changes in time. We also
provide a simple expression for the lower bound of the useful entanglement in
the system in terms of the average number of scattered atoms and the number of
modes they occupy. We then apply our theory to a recent "twin-beam" experiment
[R. B\"ucker {\it et al.}, Nat. Phys. {\bf 7}, 608 (2011)]. The only numerical
step of our semi-analytical description can be easily solved and does not
require implementation of any stochastic methods.Comment: 11 pages, 6 figure
Π€ΠΈΠ·ΠΈΠΊΠ° ΠΏΡΠΎΠ±ΠΎΡ ΠΆΠΈΠ΄ΠΊΠΈΡ Π΄ΠΈΡΠ»Π΅ΠΊΡΡΠΈΠΊΠΎΠ² (ΠΡΡΠΎΡΠΈΡ ΠΈ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠ΅ ΡΠΎΡΡΠΎΡΠ½ΠΈΠ΅, Π²ΠΊΠ»Π°Π΄ ΡΠΎΠ²Π΅ΡΡΠΊΠΈΡ ΠΈ ΡΠΎΡΡΠΈΠΉΡΠΊΠΈΡ ΡΡΠ΅Π½ΡΡ )
ΠΠ°Π½Π° ΠΊΡΠ°ΡΠΊΠ°Ρ ΠΈΡΡΠΎΡΠΈΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΡΠ΅Π½ΠΈΡ ΠΎΠ± ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΎΠΌ ΠΏΡΠΎΠ±ΠΎΠ΅ Π΄ΠΈΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΆΠΈΠ΄ΠΊΠΎΡΡΠ΅ΠΉ, ΡΠΎΠ²Π΅ΡΡΠ΅Π½ΡΡΠ²ΠΎΠ²Π°Π½ΠΈΡ ΡΠ΅Ρ
Π½ΠΈΠΊΠΈ ΠΈ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΈ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΡΠΎΠ³ΠΎ ΡΠ²Π»Π΅Π½ΠΈΡ. ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ ΠΏΠΎ ΡΠ΅Π»ΠΎΠΌΡ ΡΡΠ΄Ρ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠΉ ΡΠΎΠ²Π΅ΡΡΠΊΠΈΠ΅ (ΡΠΎΡΡΠΈΠΉΡΠΊΠΈΠ΅) ΡΡΠ΅Π½ΡΠ΅ ΠΈ, Π² ΡΠ°ΡΡΠ½ΠΎΡΡΠΈ, ΡΠΎΡΡΡΠ΄Π½ΠΈΠΊΠΈ Π’ΠΎΠΌΡΠΊΠΎΠ³ΠΎ ΠΏΠΎΠ»ΠΈΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠ½ΠΈΠ²Π΅ΡΡΠΈΡΠ΅ΡΠ° ΠΎΠΏΠ΅ΡΠ΅ΠΆΠ°Π»ΠΈ Π·Π°ΡΡΠ±Π΅ΠΆΠ½ΡΡ
ΠΊΠΎΠ»Π»Π΅Π³ ΠΈ Π²Π½Π΅ΡΠ»ΠΈ ΠΎΠΏΡΠ΅Π΄Π΅Π»ΡΡΡΠΈΠΉ Π²ΠΊΠ»Π°Π΄ Π² ΠΏΠΎΠ½ΠΈΠΌΠ°Π½ΠΈΠ΅ ΠΌΠ΅Ρ
Π°Π½ΠΈΠ·ΠΌΠΎΠ² ΠΏΡΠΎΠ±ΠΎΡ ΠΆΠΈΠ΄ΠΊΠΎΡΡΠ΅ΠΉ. ΠΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Ρ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΠ΅ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΌΠΎΠ΄Π΅Π»ΠΈ ΠΈΠ½ΠΈΡΠΈΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΈ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΠ°Π·ΡΡΠ΄Π° ΠΏΡΠΈ ΠΈΠΌΠΏΡΠ»ΡΡΠ½ΠΎΠΌ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΠΈ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ
Two-point density correlations of quasicondensates in free expansion
We measure the two-point density correlation function of freely expanding
quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime.
While initially suppressed in the trap, density fluctuations emerge gradually
during expansion as a result of initial phase fluctuations present in the
trapped quasicondensate. Asymptotically, they are governed by the thermal
coherence length of the system. Our measurements take place in an intermediate
regime where density correlations are related to near-field diffraction effects
and anomalous correlations play an important role. Comparison with a recent
theoretical approach described by Imambekov et al. yields good agreement with
our experimental results and shows that density correlations can be used for
thermometry of quasicondensates.Comment: 4 pages, 4 figures, minor change
Two-point phase correlations of a one-dimensional bosonic Josephson junction
We realize a one-dimensional Josephson junction using quantum degenerate Bose
gases in a tunable double well potential on an atom chip. Matter wave
interferometry gives direct access to the relative phase field, which reflects
the interplay of thermally driven fluctuations and phase locking due to
tunneling. The thermal equilibrium state is characterized by probing the full
statistical distribution function of the two-point phase correlation.
Comparison to a stochastic model allows to measure the coupling strength and
temperature and hence a full characterization of the system
Stochastic optimization of a cold atom experiment using a genetic algorithm
We employ an evolutionary algorithm to automatically optimize different
stages of a cold atom experiment without human intervention. This approach
closes the loop between computer based experimental control systems and
automatic real time analysis and can be applied to a wide range of experimental
situations. The genetic algorithm quickly and reliably converges to the most
performing parameter set independent of the starting population. Especially in
many-dimensional or connected parameter spaces the automatic optimization
outperforms a manual search.Comment: 4 pages, 3 figure
Single-particle-sensitive imaging of freely propagating ultracold atoms
We present a novel imaging system for ultracold quantum gases in expansion.
After release from a confining potential, atoms fall through a sheet of
resonant excitation laser light and the emitted fluorescence photons are imaged
onto an amplified CCD camera using a high numerical aperture optical system.
The imaging system reaches an extraordinary dynamic range, not attainable with
conventional absorption imaging. We demonstrate single-atom detection for
dilute atomic clouds with high efficiency where at the same time dense
Bose-Einstein condensates can be imaged without saturation or distortion. The
spatial resolution can reach the sampling limit as given by the 8 \mu m pixel
size in object space. Pulsed operation of the detector allows for slice images,
a first step toward a 3D tomography of the measured object. The scheme can
easily be implemented for any atomic species and all optical components are
situated outside the vacuum system. As a first application we perform
thermometry on rubidium Bose-Einstein condensates created on an atom chip.Comment: 24 pages, 10 figures. v2: as publishe
Optimal control of a step-by-step transmission of vehicles
Π Π°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°Π΅ΡΡΡ Π°ΠΊΡΡΠ°Π»ΡΠ½Π°Ρ Π·Π°Π΄Π°ΡΠ° ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠ³ΠΎ Π²ΡΠ±ΠΎΡΠ° ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΎΡΠ½ΡΡ
ΡΠΈΡΠ΅Π» ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΈ ΡΡΠ°Π½ΡΠΏΠΎΡΡΠ½ΡΡ
ΡΡΠ΅Π΄ΡΡΠ² (Π’Π‘), ΠΎΡΠ½Π°ΡΠ΅Π½Π½ΡΡ
Π΄Π²ΠΈΠ³Π°ΡΠ΅Π»ΡΠΌΠΈ Π²Π½ΡΡΡΠ΅Π½Π½Π΅Π³ΠΎ ΡΠ³ΠΎΡΠ°Π½ΠΈΡ (ΠΠΠ‘) ΡΠΎ ΡΡΡΠΏΠ΅Π½ΡΠ°ΡΠΎΠΉ ΠΊΠΎΡΠΎΠ±ΠΊΠΎΠΉ ΠΏΠ΅ΡΠ΅Π΄Π°Ρ, ΠΏΠΎ ΠΊΡΠΈΡΠ΅ΡΠΈΡ ΠΌΠΈΠ½ΠΈΠΌΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠ°ΡΡ
ΠΎΠ΄Π° ΡΠΎΠΏΠ»ΠΈΠ²Π°. ΠΠ½Π°Π»ΠΈΠ· Π½Π°ΡΡΠ½ΠΎ-ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΎΠΉ Π»ΠΈΡΠ΅ΡΠ°ΡΡΡΡ ΠΏΠΎΠΊΠ°Π·Π°Π» ΠΎΡΡΡΡΡΡΠ²ΠΈΠ΅ ΠΏΡΠΎΡΡΡΡ
ΠΈ Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²Π°Π½Π½ΡΡ
Π°Π»Π³ΠΎΡΠΈΡΠΌΠΎΠ² ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΡΠ½Π΅ΡΠ³ΠΎΡΡΡΠ°Π½ΠΎΠ²ΠΊΠΎΠΉ Π°Π²ΡΠΎΠΌΠΎΠ±ΠΈΠ»Ρ, ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»ΡΡΡΠ΅ΠΉ ΡΠΎΠ±ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ, ΡΠΎΡΡΠΎΡΡΡΡ ΠΈΠ· ΠΠΠ‘ ΠΈ ΡΠ΅Π³ΡΠ»ΠΈΡΡΠ΅ΠΌΠΎΠΉ ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΈ. Π¦Π΅Π»ΡΡ Π½Π°ΡΡΠΎΡΡΠ΅ΠΉ ΡΠ°Π±ΠΎΡΡ ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΠ΅ΠΎΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΠ΅ Π·Π°ΠΊΠΎΠ½Π° ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΎΡΠ½ΡΡ
ΡΠΈΡΠ΅Π» ΡΡΡΠΏΠ΅Π½ΡΠ°ΡΠΎΠΉ ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΈ, ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡΠ΅Π³ΠΎ ΠΌΠ°ΠΊΡΠΈΠΌΠ°Π»ΡΠ½ΡΡ ΡΠΎΠΏΠ»ΠΈΠ²Π½ΡΡ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ½ΠΎΡΡΡ Π΄Π»Ρ Π»ΡΠ±ΠΎΠ³ΠΎ ΠΌΠΎΡΠ½ΠΎΠ³ΠΎ ΠΈ ΡΠΊΠΎΡΠΎΡΡΠ½ΠΎΠ³ΠΎ ΡΠ΅ΠΆΠΈΠΌΠ° Π’Π‘. Π ΠΎΡΠ½ΠΎΠ²Ρ ΠΏΡΠ΅Π΄Π»Π°Π³Π°Π΅ΠΌΠΎΠ³ΠΎ ΠΌΠ΅ΡΠΎΠ΄Π° ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΎ ΠΎΠ΄Π½ΠΎΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΌΠ½ΠΎΠΆΠ΅ΡΡΠ²ΠΎ Π»ΠΈΠ½Π΅ΠΉΠ½ΡΡ
ΠΏΡΠ΅ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΠΉ, ΡΠ²ΡΠ·ΡΠ²Π°ΡΡΠΈΡ
ΠΌΠΎΠΌΠ΅Π½Ρ Π΄Π²ΠΈΠ³Π°ΡΠ΅Π»Ρ ΠΈ Π΅Π³ΠΎ ΡΠ°ΡΡΠΎΡΡ Π²ΡΠ°ΡΠ΅Π½ΠΈΡ Ρ ΡΡΠ³ΠΎΠ²ΡΠΌ ΡΡΠΈΠ»ΠΈΠ΅ΠΌ ΠΈ ΡΠΊΠΎΡΠΎΡΡΡΡ Π’Π‘. ΠΠ½ΠΎΠΆΠ΅ΡΡΠ²Ρ
ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΎΡΠ½ΡΡ
ΡΠΈΡΠ΅Π» ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΈ ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²ΡΠ΅Ρ ΠΌΠ½ΠΎΠΆΠ΅ΡΡΠ²ΠΎ ΠΎΠ΄Π½ΠΎΡΠΊΡΡΡΠ΅ΠΌΠ°Π»ΡΠ½ΡΡ
ΡΡΠ½ΠΊΡΠΈΠΉ ΡΠ΄Π΅Π»ΡΠ½ΡΡ
ΡΠ°ΡΡ
ΠΎΠ΄ΠΎΠ² ΡΠΎΠΏΠ»ΠΈΠ²Π°. ΠΠ½ΠΎΠΆΠ΅ΡΡΠ²ΠΎ ΡΠΎΡΠ΅ΠΊ Π»ΠΈΠ½ΠΈΠΉ ΡΠ°Π²Π½ΡΡ
ΡΡΠΎΠ²Π½Π΅ΠΉ ΡΠ°ΡΡ
ΠΎΠ΄ΠΎΠ² ΡΠΎΠΏΠ»ΠΈΠ²Π°, ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²ΡΡΡΠΈΡ
Π΄Π²ΡΠΌ ΡΠΎΡΠ΅Π΄Π½ΠΈΠΌ Π·Π½Π°ΡΠ΅Π½ΠΈΡΠΌ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΎΡΠ½ΡΡ
ΡΠΈΡΠ΅Π» ΡΡΠ°Π½ΡΠΌΠΈΡΡΠΈΠΈ, ΠΎΠ±ΡΠ°Π·ΡΠ΅Ρ Π»ΠΈΠ½ΠΈΡ ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΠΏΠ΅ΡΠ΅Π΄Π°Ρ. ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½ ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²ΡΡΡΠΈΠΉ Π°Π»Π³ΠΎΡΠΈΡΠΌ ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΎΡΠ½ΡΡ
ΡΠΈΡΠ΅Π», ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡΠΈΠΉ Π½Π°ΠΈΠ±ΠΎΠ»Π΅Π΅ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ½ΠΎΠ΅
ΡΡΠ½ΠΊΡΠΈΠΎΠ½ΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΡΠ½Π΅ΡΠ³ΠΎΡΡΡΠ°Π½ΠΎΠ²ΠΊΠΈ Π’Π‘ Π² ΡΡΠ»ΠΎΠ²ΠΈΡΡ
ΠΏΠ΅ΡΠ΅ΠΌΠ΅Π½Π½ΡΡ
ΡΠΈΠ»ΠΎΠ²ΡΡ
ΠΈ ΡΠΊΠΎΡΠΎΡΡΠ½ΡΡ
ΡΠ΅ΠΆΠΈΠΌΠΎΠ².The actual problem of optimal selection of means of transport (MT) gear ratios, equipped with internal combustion engines (ICE) with a step-by-step gearbox according to the criterion of minimum fuel consumption is considered in the article. An analysis of the scientific and technical literature has showed the absence of simple and sufficiently justified algorithms for controlling the vehicleβs power plant, which is a system that consists of an ICE and an adjustable transmission. The aim of this work is the theoretical justification of the law of gear ratios shifting of a step-by-step transmission, ensuring maximum fuel efficiency for any power and speed mode of MT. The proposed method is based on set of linear transformations that connect the engine moment and engine speed with a traction force and a speed of MT. The set of gear ratios correspond to the set of one-extremal functions of specific fuel consumptions. The set of points of equal levels lines corresponding to two neighboring values of the gear ratios of the transmission forms a gear shift line. An appropriate algorithm for switching gear ratios is proposed, which ensures the most efficient operation of a power plant of MT in conditions of variable power and speed modes
Matter-wave recombiners fro trapped Bose-Einstein condensates
Interferometry with trapped atomic Bose-Einstein condensates (BECs) requires the development of techniques to recombine the two paths of the interferometer and map the accumulated phase difference to a measurable atom number difference. We have implemented and compared two recombining procedures in a double-well-based BEC interferometer. The first procedure utilizes the bosonic Josephson effect and controlled tunneling of atoms through the potential barrier, similar to laser light in an optical fiber coupler. The second one relies on the interference of the reflected and transmitted parts of the BEC wave function when impinging on the potential barrier, analogous to light impinging on a half-silvered mirror. Both schemes were implemented successfully, yielding an interferometric contrast of similar to 20% and 42% respectively. Building efficient matter-wave recombiners represents an important step towards the coherent manipulation of external quantum superposition states of BECs
Spatial and temporal distribution of sperm whales (Physeter macrocephalus) within the Kaikoura submarine canyon in relation to oceanographic variables
The Kaikoura area is a valuable feeding spot for sperm whales with the presence of a submarine canyon close to shore. Male sperm whales can be found there year around, close to the shore and exhibiting almost constant foraging activities. This thesis investigates the distribution and habitat use, both spatially and temporally, of sperm whales (Physeter macrocephalus) within the Kaikoura submarine canyon, New Zealand. The primary aim was to determine which oceanographic variables and bathymetric features influence the sperm whale distribution patterns off Kaikoura.
A theodolite was used to track surfacing and movement of sperm whales from a shore-based station. The accuracy of positions recorded by the theodolite was investigated by comparing theodolite measurements of an object of known position. A calibration technique was then developed as the vertical angle was not accurately determined by the theodolite.
In addition to investigating the distribution of sperm whales, the daily abundance of sperm whales within the Kaikoura submarine canyon was estimated. Distance sampling and mark-resight models showed an average of 4 (SEM = 0.13) individuals present in the study area at any given time. The mark-resight technique using photo-identification was not possible from a shore-based station so a spatio-temporal model was built in order to track the identity of individuals. The model was tested using photo-identification of sperm whales collected from a boat-based station. Results showed that 88% of the modeled identifications corresponded to the photo-identification database.
Sperm whales off Kaikoura were strongly associated with depth, slope and distance from the nearest coast. They were found in waters between 500 m to 1250 m deep and preferred shallower waters in winter. In spring, sperm whales occurred further from the coast, mainly in the Hikurangi Trough, north-east of the shore-based station. Generalized Additive Models (GAM) were used to identify significant oceanographic variables predicting the presence of sperm whales off Kaikoura. Models indicated that sea surface temperature (SST), chlorophylla (Chla) and distance from sea surface temperature fronts were all important parameters in predicting sperm whales presence. Results showed that sperm whales aggregated in the section of the study area with the lowest SST and near SST fronts. This study provides a detailed insight into the use of the Kaikoura submarine canyon by male sperm whales
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