2,852 research outputs found
Soft triaxial roto-vibrational motion in the vicinity of
A solution of the Bohr collective hamiltonian for the soft,
soft triaxial rotor with is presented making use
of a harmonic potential in and Coulomb-like and Kratzer-like
potentials in . It is shown that, while the angular part in the
present case gives rise to a straightforward extension of the rigid triaxial
rotor energy in which an additive harmonic term appears, the inclusion of the
part results instead in a non-trivial expression for the spectrum. The
negative anharmonicities of the energy levels with respect to a simple rigid
model are in qualitative agreement with general trends in the experimental
data.Comment: 4 pages, 2 figures, accepted in Phys.Rev.
Quantum hierarchic models for information processing
Both classical and quantum computations operate with the registers of bits.
At nanometer scale the quantum fluctuations at the position of a given bit,
say, a quantum dot, not only lead to the decoherence of quantum state of this
bit, but also affect the quantum states of the neighboring bits, and therefore
affect the state of the whole register. That is why the requirement of reliable
separate access to each bit poses the limit on miniaturization, i.e, constrains
the memory capacity and the speed of computation. In the present paper we
suggest an algorithmic way to tackle the problem of constructing reliable and
compact registers of quantum bits. We suggest to access the states of quantum
register hierarchically, descending from the state of the whole register to the
states of its parts. Our method is similar to quantum wavelet transform, and
can be applied to information compression, quantum memory, quantum
computations.Comment: 14 pages, LaTeX, 1 eps figur
Rf-induced transport of Cooper pairs in superconducting single electron transistors in a dissipative environment
We investigate low-temperature and low-voltage-bias charge transport in a
superconducting Al single electron transistor in a dissipating environment,
realized as on-chip high-ohmic Cr microstrips. In our samples with relatively
large charging energy values Ec > EJ, where EJ is the energy of the Josephson
coupling, two transport mechanisms were found to be dominating, both based on
discrete tunneling of individual Cooper pairs: Depending on the gate voltage
Vg, either sequential tunneling of pairs via the transistor island (in the open
state of the transistor around the points Qg = CgVg = e mod(2e), where Cg is
the gate capacitance) or their cotunneling through the transistor (for Qg away
of these points) was found to prevail in the net current. As the open states of
our transistors had been found to be unstable with respect to quasiparticle
poisoning, high-frequency gate cycling (at f ~ 1 MHz) was applied to study the
sequential tunneling mechanism. A simple model based on the master equation was
found to be in a good agreement with the experimental data.Comment: 8 pages, 6 figure
Orbital ordering in manganites in the band approach
We consider the orbital ordering in LaMnO3 and similar systems, proceeding
from the band picture. We show that for the realistic magnetic structure of
A-type there exists a complete nesting betweeen two e_g-bands. As a result
there occurs an instability towards an excitonic insulator-like state -- an
electron-hole pairing with the wave vector Q=(\pi,\pi), which opens a gap in
the spectrum and makes the system insulating. In the resulting state there
appeasr an orbital ordering -- orbital density wave (ODW), the type of which
coincides with those existing in LaMnO3.Comment: 4 pages, 2 figure
Mediated tunable coupling of flux qubits
It is sketched how a monostable rf- or dc-SQUID can mediate an inductive
coupling between two adjacent flux qubits. The nontrivial dependence of the
SQUID's susceptibility on external flux makes it possible to continuously tune
the induced coupling from antiferromagnetic (AF) to ferromagnetic (FM). In
particular, for suitable parameters, the induced FM coupling can be
sufficiently large to overcome any possible direct AF inductive coupling
between the qubits.
The main features follow from a classical analysis of the multi-qubit
potential. A fully quantum treatment yields similar results, but with a
modified expression for the SQUID susceptibility.
Since the latter is exact, it can also be used to evaluate the
susceptibility--or, equivalently, energy-level curvature--of an isolated
rf-SQUID for larger shielding and at degenerate flux bias, i.e., a (bistable)
qubit. The result is compared to the standard two-level (pseudospin) treatment
of the anticrossing, and the ensuing conclusions are verified numerically.Comment: REVTeX 4, 16 pp., 4 EPS figures. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: major expansion and rewriting,
new title and co-author; to appear in New Journal of Physics special issue
(R. Fazio, ed.
BRST Algebra Quantum Double and Quantization of the Proper Time Cotangent Bundle
The quantum double for the quantized BRST superalgebra is studied. The
corresponding R-matrix is explicitly constucted. The Hopf algebras of the
double form an analytical variety with coordinates described by the canonical
deformation parameters. This provides the possibility to construct the
nontrivial quantization of the proper time supergroup cotangent bundle. The
group-like classical limit for this quantization corresponds to the generic
super Lie bialgebra of the double.Comment: 11 pages, LaTe
Variation after Particle-Number Projection for the HFB Method with the Skyrme Energy Density Functional
Variation after particle-number restoration is incorporated for the first
time into the Hartree-Fock-Bogoliubov framework employing the Skyrme energy
density functional with zero-range pairing. The resulting projected HFB
equations can be expressed in terms of the local gauge-angle-dependent
densities. Results of projected calculations are compared with those obtained
within the Lipkin-Nogami method in the standard version and with the
Lipkin-Nogami method followed by exact particle-number projection.Comment: 11 pages, 6 figure
Charge Transport Processes in a Superconducting Single-Electron Transistor Coupled to a Microstrip Transmission Line
We have investigated charge transport processes in a superconducting
single-electron transistor (S-SET) fabricated in close proximity to a
two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. The
macroscopic bonding pads of the S-SET along with the 2DEG form a microstrip
transmission line. We observe a variety of current-carrying cycles in the S-SET
which we attribute to simultaneous tunneling of Cooper pairs and emission of
photons into the microstrip. We find good agreement between these experimental
results and simulations including both photon emission and photon-assisted
tunneling due to the electromagnetic environment.Comment: 4 pages, 4 figures, REVTeX
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