80 research outputs found
Orbital physics of polar Fermi molecules
We study a system of polar dipolar fermions in a two-dimensional optical
lattice and show that multi-band Fermi-Hubbard model is necessary to discuss
such system. By taking into account both on-site, and long-range interactions
between different bands, as well as occupation-dependent inter- and intra-band
tunneling, we predict appearance of novel phases in the strongly-interacting
limit
Gravity-induced resonances in a rotating trap
It is shown that in an anisotropic harmonic trap that rotates with the
properly chosen rotation rate, the force of gravity leads to a resonant
behavior. Full analysis of the dynamics in an anisotropic, rotating trap in 3D
is presented and several regions of stability are identified. On resonance, the
oscillation amplitude of a single particle, or of the center of mass of a
many-particle system (for example, BEC), grows linearly with time and all
particles are expelled from the trap. The resonances can only occur when the
rotation axis is tilted away from the vertical position. The positions of the
resonances (there are always two of them) do not depend on the mass but only on
the characteristic frequencies of the trap and on the direction of the angular
velocity of rotation.Comment: 10 pages, 12 figures, to appear in Physical Review
Quantum walk versus classical wave: Distinguishing ground states of quantum magnets by spacetime dynamics
We investigate wave packet spreading after a single spin flip in prototypical two-dimensional ferromagnetic and antiferromagnetic quantum spin systems. We find characteristic spatial magnon density profiles: While the ferromagnet shows a square-shaped pattern reflecting the underlying lattice structure, as exhibited by quantum walkers, the antiferromagnet shows a circular-shaped pattern which hides the lattice structure and instead resembles a classical wave pattern. We trace these fundamentally different behaviors back to the distinctly different magnon energy-momentum dispersion relations and also provide a real-space interpretation. Our findings point to opportunities for real-time, real-space imaging of quantum magnets both in materials science and in quantum simulators
Simulating polaron biophysics with Rydberg atoms
Transport of excitations along proteins can be formulated in a quantum physics context, based on the periodicity and vibrational modes of the structures. Exact solutions are very challenging to obtain on classical computers, however, approximate solutions based on the Davydov ansatz have demonstrated the possibility of stabilized solitonic excitations along the protein. We propose an alternative study based on a chain of ultracold atoms. We investigate the experimental parameters to control such a quantum simulator based on dressed Rydberg atoms. We show that there is a feasible range of parameters where a quantum simulator can directly mimic the Davydov equations and their solutions. Such a quantum simulator opens up new directions for the study of transport phenomena in a biophysical context.Transport of excitations along proteins can be formulated in a quantum physics context, based on the periodicity and vibrational modes of the structures. Exact solutions are very challenging to obtain on classical computers, however, approximate solutions based on the Davydov ansatz have demonstrated the possibility of stabilized solitonic excitations along the protein. We propose an alternative study based on a chain of ultracold atoms. We investigate the experimental parameters to control such a quantum simulator based on dressed Rydberg atoms. We show that there is a feasible range of parameters where a quantum simulator can directly mimic the Davydov equations and their solutions. Such a quantum simulator opens up new directions for the study of transport phenomena in a biophysical context
Melatonin and cortisol profiles in patients with pituitary tumors
The optic tract section at the optic chiasm is expected to disturb the suprachiasmatic nucleus (SCN) rhythm, circadian rhythm and melatonin secretion rhythms in humans, although detailed studies have never been conducted. The aim of this paper was to describe melatonin and cortisol profiles in patients with a pituitary tumor exerting optic chiasm compression. Six patients with pituitary tumors of different size, four of whom had significant optic chiasm compression, were examined. In each brain, MRI, an ophthalmological examination including the vision field and laboratory tests were performed. Melatonin and cortisol concentrations were measured at 22:00h, 02:00h, 06:00h, and 10:00h in patients lying in a dark, isolated room.
One of the four cases with significant optic chiasm compression presented a flattened melatonin rhythm. The melatonin rhythm was also disturbed in one patient without optic chiasm compression. Larger tumors may play a role in the destruction of neurons connecting the retina with the suprachiasmatic nucleus (SCN) and breaking of basic way for inhibiting effect to the SCN from the retina
Quantum Electrodynamics of qubits
Systematic description of a spin one-half system endowed with magnetic moment
or any other two-level system (qubit) interacting with the quantized
electromagnetic field is developed. This description exploits a close analogy
between a two-level system and the Dirac electron that comes to light when the
two-level system is described within the formalism of second quantization in
terms of fermionic creation and annihilation operators. The analogy enables one
to introduce all the powerful tools of relativistic QED (albeit in a greatly
simplified form). The Feynman diagrams and the propagators turn out to be very
useful. In particular, the QED concept of the vacuum polarization finds its
close counterpart in the photon scattering off a two level-system leading via
the linear response theory to the general formulas for the atomic
polarizability and the dynamic single spin susceptibility. To illustrate the
usefulness of these methods, we calculate the polarizability and susceptibility
up to the fourth order of perturbation theory. These {\em ab initio}
calculations resolve some ambiguities concerning the sign prescription and the
optical damping that arise in the phenomenological treatment. We also show that
the methods used to study two-level systems (qubits) can be extended to
many-level systems (qudits). As an example, we describe the interaction with
the quantized electromagnetic field of an atom with four relevant states: one S
state and three degenerate P states.Comment: 23 pages, 6 figure
Ground-state correlation properties of charged bosons trapped in strongly anisotropic harmonic potentials
We study systems of a few charged bosons contained within a strongly
anisotropic harmonic trap. A detailed examination of the ground-state
correlation properties of two-, three-, and four-particle systems is carried
out within the framework of the single-mode approximation of the transverse
components. The linear correlation entropy of the quasi-1D systems is discussed
in dependence on the confinement anisotropy and compared with a strictly 1D
limit. Only at weak interaction the correlation properties depend strongly on
the anisotropy parameter.Comment: 5 pages, 6 figure
DigiCam - Fully Digital Compact Read-out and Trigger Electronics for the SST-1M Telescope proposed for the Cherenkov Telescope Array
The SST-1M is one of three prototype small-sized telescope designs proposed
for the Cherenkov Telescope Array, and is built by a consortium of Polish and
Swiss institutions. The SST-1M will operate with DigiCam - an innovative,
compact camera with fully digital read-out and trigger electronics. A high
level of integration will be achieved by massively deploying state-of-the-art
multi-gigabit transmission channels, beginning from the ADC flash converters,
through the internal data and trigger signals transmission over backplanes and
cables, to the camera's server link. Such an approach makes it possible to
design the camera to fit the size and weight requirements of the SST-1M
exactly, and provide low power consumption, high reliability and long lifetime.
The structure of the digital electronics will be presented, along with main
physical building blocks and the internal architecture of FPGA functional
subsystems.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Software design for the control system for Small-Size Telescopes with single-mirror of the Cherenkov Telescope Array
The Small-Size Telescope with single-mirror (SST-1M) is a 4 m Davies-Cotton
telescope and is among the proposed telescope designs for the Cherenkov
Telescope Array (CTA). It is conceived to provide the high-energy ( few TeV)
coverage. The SST-1M contains proven technology for the telescope structure and
innovative electronics and photosensors for the camera. Its design is meant to
be simple, low-budget and easy-to-build industrially.
Each device subsystem of an SST-1M telescope is made visible to CTA through a
dedicated industrial standard server. The software is being developed in
collaboration with the CTA Medium-Size Telescopes to ensure compatibility and
uniformity of the array control. Early operations of the SST-1M prototype will
be performed with a subset of the CTA central array control system based on the
Alma Common Software (ACS). The triggered event data are time stamped,
formatted and finally transmitted to the CTA data acquisition.
The software system developed to control the devices of an SST-1M telescope
is described, as well as the interface between the telescope abstraction to the
CTA central control and the data acquisition system.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
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