

The false vacuum decay: towards realization with ultracold atoms
Quantum decay of a relativistic scalar field from a false vacuum is relevant to the inflationary model of the early Universe where the nucleation and the exponential growth of bubbles of the true vacuum gives rise to the creation of matter. We propose a realistic test of this model using the pseudospin 1/2 bosonic gas. The relative phase of two spin components serves as a scalar quantum field and the modulating RF coupling creates the metastable state of the false vacuum. Using the stochastic numerical simulations we clearly demonstrate the seeding and growth of the bubbles in the relative phase domain.
Paper: O. Fialko et al, Europhysics Letters 110, 56001 (2015) arXiv: 1408.1163



Radiofrequency induced association and spectroscopy of cold ^{87}Rb_{2} molecules
We employ powerful RF radiation to couple atomic scattering states 1, 1> and 2,+1> in 87Rb to several weakly bound molecular states. Using the simultaneous imaging of two states we monitor the appearance of molecular resonance by detecting the sudden loss of the atoms in state 2,+1> when RF frequency is tuned into the resonance. We discover five families of molecular states by monitoring their Zeeman dependence. The conversion efficiency can reach 90% for the RF field of 4 G and an interaction time of 420 ms



Precision measurement of swave scattering lengths in a twocomponent BoseEinstein condensate
We use collective oscillations of a twocomponent BoseEinstein condensate of ^{87}Rb atoms prepared in the internal states 1> = 1,1> and 2> = 2, 1> for the precision measurement of the interspecies scattering length a_{12} with a relative uncertainty of 1.6 x 10^{4}. By fitting numerical simulations of the coupled GrossPitaevskii equations to the recorded temporal evolution of the axial width we obtain the values a_{12} = 98.006a_{0} and a_{22} = 95.44a_{0}. We characterize twobody losses for component 2 and obtain the loss coefficients γ_{12} = 1.51 x 10^{14} cm^{3}/s and γ_{22} = 8.1 x 10^{14} cm^{3}/s.
Paper: M. Egorov et al, Phys. Rev. A 87, 053614 (2013)
Paper: M.Egorov et al, Phys. Rev. A 84, 021605(R)
(2011) 


Quantum noise in threedimensional BEC interferometry
We develop a theory of quantum fluctuations and squeezing in a threedimensional BoseEinstein condensate atom interferometer with nonlinear losses. We use stochastic equations in a truncated Wigner representation to treat quantum noise. Our approach includes the multimode spatial evolution of spinor components and describes the manybody dynamics of a mesoscopic quantum system.
Paper: B. Opanchuk et al, Europhysics Letters, 97, 50003 (2012)



Longlived periodic revivals of coherence in an interacting BoseEinstein condensate
We observe the coherence of an interacting twocomponent BoseEinstein condensate (BEC) surviving for seconds in a trapped Ramsey interferometer. Meanfielddriven collective oscillations of two components lead to periodic dephasing and rephasing of condensate wave functions with a slow decay of the interference fringe visibility. We apply spin echo synchronous with the selfrephasing of the condensate to reduce the influence of statedependent atom losses, significantly enhancing the visibility up to 0.75 at the evolution time of 1.5 s. Meanfield theory consistently predicts higher visibility than experimentally observed values. We quantify the effects of classical and quantum noise and infer a coherence time of 2.8 s for a trapped condensate of 55,000 interacting atoms.
Paper: M.Egorov et al Phys. Rev. A 84, 021605(R)
(2011) 



Radiofrequency dressing of multiple Feshbach resonances
We demonstrate and theoretically analyze the dressing of several proximate
Feshbach resonances in ^{87}Rb using radiofrequency (rf) radiation. We present accurate measurements and
characterizations of the resonances, and the dramatic changes in scattering properties that can arise through
the rf dressing. Our scattering theory analysis yields quantitative agreement with the experimental data.
We also present a simple interpretation of our results in terms of rfcoupled bound states interacting with the
collision threshold.
Paper: A. M. Kaufman et al, Phys. Rev. A 80, 050701(R)
(2009) 


Spatially inhomogeneous
phase evolution of a twocomponent BoseEinstein condensate
We investigate the spatial evolution
of the relative phase of an elongated twocomponent BoseEinstein
condensate. The pseudospin 1/2 system is comprised of the
F = 1; m_{F} = 1 and F = 2; m_{F} = 1 hyperfine
ground states of ^{87}Rb , which we magnetically trap
and interrogate with radiofrequency and microwave fields.
By performing Ramsey interferometry with the BEC we probe
the relative phase evolution, and observe temporal decay of
the interferometric contrast which is well described by a
meanfield formalism. We show that this decay is due to inhomogeneous
growth of the collective relative phase, where decoherence
and phase diffusion are not dominant mechanisms in the loss
of interferometric contrast
Paper: R. P. Anderson et al, Phys. Rev. A 80, 023603
(2009) 


Fabricating atom chips with femtosecond laser ablation
We fabricate atom chips using femtosecond laser ablation to sculpt conductive metal films and
permanent magnetic materials. The ablation process is investigated by extracting
the power spectral density of the edge roughness from composite SEM images and by using a MRmicroscope.
A sculptured wire which produces arrays of tunable double wells is fabricated for nearsurface force sensing
with a BEC.
Paper: C. H. Wolff et al, J. Phys. B: At. Mol. Opt. Phys. 42, 085301
(2009), Europhysics News Highlights 40/3 2009: 


Scanning magnetoresistance microscopy of atom chips
Surface based geometries of microfabricated wires or patterned magnetic films can be used to magnetically trap and
manipulate ultracold neutral atoms or BoseEinstein condensates. We have investigated the magnetic properties of such
atom chips using a newly developed scanning magnetoresistive MR microscope with offers high spatial resolution (10μm)
and high field sensitivity (100nT). This provides a convenient and powerful technique for precisely characterizing the
magnetic fields near the surface of atom chips in atmosphere.
Paper: M.
Volk et al, Rev. Sci. Instrum. 79, 023702
(2008) 


Double well sensor of asymmetry in trapping potentials
Adiabatic splitting of a rubidium condensate in an asymmetric doublewell potential leads to an
unequal distribution of atoms in the wells. Precise measurements of the number of atoms in each well provide information about an
asymmetrical component of the trapping potential. This noninterferometric method can be used for the construction of a new sensor
which is sensitive to smallscale variations of a gravitational force.
Paper: B.V. Hall et al, Phys. Rev. Lett. 98, 030402 (2007) 


Disordered potential and multiple BECs
We have found that cold rubidium clouds are fragmented above the magnetic film atom chip. Inhomogeneity in the film
magnetisation generates a corrugation term in the axial trapping potential. Using a combination of RF spectroscopy,
optical imaging and the truncated Boltzmann distribution we qualitatively characterised spatial variations of the
disordered magnetic field. Our model produces analytical expressions consistent with the observations and predicts
a y^{2} decay of the random field amplitude. Ten independent condensates were produced via evaporative
cooling of a highly elongated cloud.
Paper: S. Whitlock et al, Phys. Rev. A 75, 043602 (2007) 


BoseEinstein condensation on a magnetic film atom chip
We have developed a hybrid atom chip comprising a magnetic film TbGdFeCo with perpendicular
magnetisation and currentcarrying silver wires. This design allows us to combine the stability of permanent magnetic
fields with versatility of timevariable magnetic fields. We observe the heating rate of 3 nK/s when the atoms are
confined in the magnetic film trap. We produce a Bose condensate of 200,000 rubidium atoms using either a Zshaped
current or the magnetic film trap.
Papers:
B.V. Hall et al, Journal of Physics B 39, 27 (2006) (Highlights
of J. Physics B for 2006)
B.V. Hall et al, Laser Spectroscopy XVII, 275 (2005)
S. Whitlock et al, Australian Physics 43, No.1, 8 (2006) 


Magnetic films for atom optics
Permanent magnetic materials can produce sophisticated magnetic field configurations and offer an alternative
to currentcarrying wires for the construction of miniature optical elements on atom chips.
Gd_{10}Tb_{6}Fe_{80}Co_{4} magnetooptical films have large perpendicular magnetic anisotropy and
are suitable for the production of periodically grooved, micronscale structures. We studied the deposition process and
properties of GdTbFeCo films that make them suitable for the applications on the atom chips.
Paper: J. Wang et al , Journal of Physics D 38, 4015 (2005) 


Asymmetric potential in doublewell atom interferometry
We examine the effect of asymmetry on a splitting process in a doublewell interferometer.
The interferometer involves a measurement of the first excited state population as a sensitive measure of the asymmetric potential.
The Bloch vector model and multimode numerical simulations account for the effect of asymmetry and the role of adiabaticity throughout
the interferometric process and allow appropriate time scales to be chosenfor the splitting and merging stages.
Paper: A.I. Sidorov et al, Phys. Rev A 74, 023612 (2006) 


Theory of decoherence in BEC interferometry
A theory of BEC interferometry in an unsymmetrical doublewell trap has been developed for small
boson numbers, based on the twomode approximation. The bosons are initially in the lowest mode of a single well trap, which is split
into a double well and then recombined. Possible fragmentations into separate BEC states in each well during the splitting and recombination
processes are allowed for. Selfconsistent sets of equations for the amplitudes of the fragmented states and for the two single boson
mode functions are obtained. The latter are coupled GrossPitaevskii equations. Interferometric effects may be measured via boson
numbers in the first excited mode.
A full treatment of decoherence and dephasing effects in BEC interferometry is being developed, based on using quantum
correlation functions for describing interferometric effects. The BEC is described via a phase space distribution functional of the
Wigner type for the condensate modes and the positive P type for the noncondensate modes. Ito equations for stochastic condensate
and noncondensate field functions replace the functional FokkerPlanck equation for the distribution functional and stochastic
averages of field function products determine the quantum correlation functions.
Papers: B.J. Dalton, J. Mod. Opt. 54, 615 (2007); J. Phys: Conference Series 67 012059 (2007) 