496 research outputs found
Transport, atom blockade and output coupling in a Tonks-Girardeau gas
Recent experiments have demonstrated how quantum-mechanical impurities can be
created within strongly correlated quantum gases and used to probe the
coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M.
K\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a
phenomenological model to simulate such an output coupler for a Tonks-Girardeau
gas that shows qualitative agreement with the experimental results for atom
transport and output coupling. Our model allows us to explore nonequilibrium
transport phenomena in ultracold quantum gases and leads us to predict a regime
of atom blockade, where the impurity component becomes localized in the parent
cloud despite the presence of gravity. We show that this provides a stable
mixed-species quantum gas in the strongly correlated limit
New spin squeezing and other entanglement tests for two mode systems of identical bosons
For any quantum state representing a physical system of identical particles, the density operator must satisfy the symmetrization principle (SP) and conform to super-selection rules (SSR) that prohibit coherences between differing total particle numbers. Here we consider bi-partitite states for massive bosons, where both the system and sub-systems are modes (or sets of modes) and particle numbers for quantum states are determined from the mode occupancies. Defining non-entangled or separable states as those prepared via local operations (on the sub-systems) and classical communication processes, the sub-system density operators are also required to satisfy the SP and conform to the SSR, in contrast to some other approaches. Whilst in the presence of this additional constraint the previously obtained sufficiency criteria for entanglement, such as the sum of the ˆSx and ˆSy variances for the Schwinger spin components being less than half the mean boson number, and the strong correlation test of |haˆm (bˆ†)ni|2 being greater than h(aˆ†)maˆm (bˆ†)nbˆni(m, n = 1, 2, . . .) are still valid, new tests are obtained in our work. We show that the presence of spin squeezing in at least one of the spin components ˆSx , ˆSy and ˆSz is a sufficient criterion for the presence of entanglement and a simple correlation test can be constructed of |haˆm (bˆ†)ni|2 merely being greater than zero.We show that for the case of relative phase eigenstates, the new spin squeezing test for entanglement is satisfied (for the principle spin operators), whilst the test involving the sum of the ˆSx and ˆSy variances is not. However, another spin squeezing entanglement test for Bose–Einstein condensates involving the variance in ˆSz being less than the sum of the squared mean values for ˆSx and ˆSy divided by the boson number was based on a concept of entanglement inconsistent with the SP, and here we present a revised treatment which again leads to spin squeezing as an entanglement test
Quality and safety of genetic testing in Australia and New Zealand: a review of the current regulatory framework
This paper provides an overview of the regulation of quality assurance for genetic testing in Australia and New Zealand and outlines the steps currently being taken to critically appraise and improve the regulatory framework in each country. It aims to contextualize this framework within the broader context of quality and patient safety concerns; and to draw together the concerns and recommendations of the various organizations that have been working to improve quality assurance in this area
Direct detection of bound ammonium ions in the selectivity filter of ion channels by solid-state NMR.
The flow of ions across cell membranes facilitated by ion channels is an important function for all living cells. Despite the huge amount of structural data provided by crystallography, elucidating the exact interactions between the selectivity filter atoms and bound ions is challenging. Here, we detect bound 15 N-labeled ammonium ions as a mimic for potassium ions in ion channels using solid-state NMR under near-native conditions. The non-selective ion channel NaK showed two ammonium peaks corresponding to its two ion binding sites, while its potassium-selective mutant NaK2K that has a signature potassium- selective selectivity filter with four ion binding sites gave rise to four ammonium peaks. Ions bound in specific ion binding sites were identified based on magnetization transfer between the ions and carbon atoms in the selectivity filters. Magnetization transfer between bound ions and water molecules revealed that only one out of four ions in the selectivity filter of NaK2K is in close contact with water, which is in agreement with the direct knock-on ion conduction mechanism where ions are conducted through the channel by means of direct interactions without water molecules in between. Interestingly, the potassium-selective ion channels investigated here (NaK2K and, additionally, KcsA-Kv1.3) showed remarkably different chemical shifts for their bound ions, despite having identical amino acid sequences and crystal structures of their selectivity filters. Molecular dynamics simulations show similar ion binding and conduction behavior between ammonium and potassium ions and identify the origin of the differences between the investigated potassium channel
Rapid cell-surface prion protein conversion revealed using a novel cell system
Prion diseases are fatal neurodegenerative disorders with unique transmissible properties. The infectious and pathological agent is thought to be a misfolded conformer of the prion protein. Little is known about the initial events in prion infection because the infecting prion source has been immunologically indistinguishable from normal cellular prion protein (PrPC). Here we develop a unique cell system in which epitope-tagged PrPC is expressed in a PrP knockdown (KD) neuroblastoma cell line. The tagged PrPC, when expressed in our PrP-KD cells, supports prion replication with the production of bona fide epitope-tagged infectious misfolded PrP (PrPSc). Using this epitope-tagged PrPSc, we study the earliest events in cellular prion infection and PrP misfolding. We show that prion infection of cells is extremely rapid occurring within 1 min of prion exposure, and we demonstrate that the plasma membrane is the primary site of prion conversion
Teleportation of a quantum state of a spatial mode with a single massive particle
Mode entanglement exists naturally between regions of space in ultra-cold
atomic gases. It has, however, been debated whether this type of entanglement
is useful for quantum protocols. This is due to a particle number
superselection rule that restricts the operations that can be performed on the
modes. In this paper, we show how to exploit the mode entanglement of just a
single particle for the teleportation of an unknown quantum state of a spatial
mode. We detail how to overcome the superselection rule to create any initial
quantum state and how to perform Bell state analysis on two of the modes. We
show that two of the four Bell states can always be reliably distinguished,
while the other two have to be grouped together due to an unsatisfied phase
matching condition. The teleportation of an unknown state of a quantum mode
thus only succeeds half of the time.Comment: 12 pages, 1 figure, this paper was presented at TQC 2010 and extends
the work of Phys. Rev. Lett. 103, 200502 (2009
Structure and interactions of ultracold Yb ions and Rb atoms
In order to study ultracold charge-transfer processes in hybrid atom-ion
traps, we have mapped out the potential energy curves and molecular parameters
for several low lying states of the Rb, Yb system. We employ both a
multi-reference configuration interaction (MRCI) and a full configuration
interaction (FCI) approach. Turning points, crossing points, potential minima
and spectroscopic molecular constants are obtained for the lowest five
molecular states. Long-range parameters, including the dispersion coefficients
are estimated from our {\it ab initio} data. The separated-atom ionization
potentials and atomic polarizability of the ytterbium atom (
atomic units) are in good agreement with experiment and previous calculations.
We present some dynamical calculations for (adiabatic) scattering lengths for
the two lowest (Yb,Rb) channels that were carried out in our work. However,
we find that the pseudo potential approximation is rather limited in validity,
and only applies to nK temperatures. The adiabatic scattering lengths for both
the triplet and singlet channels indicate that both are large and negative in
the FCI approximation.Comment: 8 pages, 3 figures, 5 table
Prevalence and determinants of age-related macular degeneration in central Sri Lanka: the Kandy Eye Study
Aims To determine the prevalence, associations and risk factors for age-related macular degeneration (ARMD) in central Sri Lanka. Methods The study was a population-based, cross-sectional survey of residents aged ≥40 years in rural Sri Lanka. ARMD was assessed on dilated fundoscopy using the International Age-Related Maculopathy Epidemiology Study Group classification system. Results Of the 1721 subjects identified, 1375 participated (79.9%). Of the participants, 1013 were aged ≥50 years (73.6%). The prevalence of any ARMD (adjusted for study design) was 4.72 (95% CI 2.22 to 7.20)% with 3.82 (95% CI 1.60 to 6.04)% early ARMD and 1.70 (95% CI 0.14 to 3.27)% late ARMD. Age (p<0.001) and Sinhalese ethnicity (p = 0.016) were significantly associated with ARMD. Men had a tendency toward a higher prevalence of ARMD than women, although this was not statistically significant (p = 0.081). Ocular risk factors such as cortical cataract (p = 0.024) and pseudophakia (p = 0.003) were associated with ARMD on the univariate but not multivariate analyses. Illiteracy and the identification of social supports were significantly associated with ARMD on univariate analyses. However, only social support was statistically significant after multivariate analysis (p = 0.024). Conclusions Although the prevalence of ARMD is slightly lower in Sri Lanka than surrounding regions, it contributes to a higher proportion of visual impairment, including blindness. Risk factors include age and Sinhalese ethnicity.L A Goold, K Edussuriya, S Sennanayake, T Senaratne, D Selva, T R Sullivan, R J Casso
On defining the Hamiltonian beyond quantum theory
Energy is a crucial concept within classical and quantum physics. An
essential tool to quantify energy is the Hamiltonian. Here, we consider how to
define a Hamiltonian in general probabilistic theories, a framework in which
quantum theory is a special case. We list desiderata which the definition
should meet. For 3-dimensional systems, we provide a fully-defined recipe which
satisfies these desiderata. We discuss the higher dimensional case where some
freedom of choice is left remaining. We apply the definition to example toy
theories, and discuss how the quantum notion of time evolution as a phase
between energy eigenstates generalises to other theories.Comment: Authors' accepted manuscript for inclusion in the Foundations of
Physics topical collection on Foundational Aspects of Quantum Informatio
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