579 research outputs found
A Holstein-Primakoff and a Dyson realization for the quantum algebra
The known Holstein-Primakoff and Dyson realizations of the Lie algebra
in terms of Bose operators (Okubo S 1975 J. Math. Phys. 16
528) are generalized to the class of the quantum algebras for
any . It is shown how the elements of can be expressed via
pairs of Bose creation and annihilation operators.Comment: 5 pages, Te
A New Type of distributed Enamel based Clearing Electrode
Clearing electrodes can be used for electron cloud (EC) suppression in high intensity particle accelerators. In this paper the use of low and highly resistive layers on a dielectric substrate are examined. The beam coupling impedance of such a structure is evaluated. Furthermore the clearing efficiency as well as technological issues are discussed
Effect of Randomness on Quantum Data Buses of Heisenberg Spin Chains
A strongly coupled spin chain can mediate long-distance effective couplings
or entanglement between remote qubits, and can be used as a quantum data bus.
We study how the fidelity of a spin-1/2 Heisenberg chain as a spin bus is
affected by static random exchange couplings and magnetic fields. We find that,
while non-uniform exchange couplings preserve the isotropy of the qubit
effective couplings, they cause the energy levels, the eigenstates, and the
magnitude of the couplings to vary locally. On the other hand, random local
magnetic fields lead to an avoided level crossing for the bus ground state
manifold, and cause the effective qubit couplings to be anisotropic.
Interestingly, the total magnetic moment of the ground state of an odd-size bus
may not be parallel to the average magnetic field. Its alignment depends on
both the direction of the average field and the field distribution, in contrast
with the ground state of a single spin which always aligns with the applied
magnetic field to minimize the Zeeman energy. Lastly, we calculate
sensitivities of the spin bus to such local variations, which are potentially
useful for evaluating decoherence when dynamical fluctuations in the exchange
coupling or magnetic field are considered
Design Aspects of the RF Contacts for the LHC Beam Vacuum Interconnects
The LHC requires a very low longitudinal and transverse beam coupling impedance, in particular at low frequencies. This implies an admissible DC contact resistance of less than 0.1 m for the RF contacts inside the vacuum bellows which must carry the image current (up to 50 A peak) of the beam at each vacuum chamber interconnect. Technological aspects, measurement methods and test results are presented for the contacts which will be used in the LHC. The modified mechanical design and the justifications for specific choices will be discusse
Deconfinement Transition and Bound States in Frustrated Heisenberg Chains: Regimes of Forced and Spontaneous Dimerization
We use recently developed strong-coupling expansion methods to study the
two-particle spectra for the frustrated alternating Heisenberg model,
consisting of an alternating nearest neighbor antiferromagnetic exchange and a
uniform second neighbor antiferromagnetic exchange. Starting from the limit of
weakly coupled dimers, we develop high order series expansions for the
effective Hamiltonian in the two-particle subspace. In the limit of a strong
applied dimerization, we calculate accurately various properties of singlet and
triplet bound states and quintet antibound states. We also develop series
expansions for bound state energies in various sectors, which can be
extrapolated using standard methods to cases where the external
bond-alternation goes to zero. We study the properties of singlet and triplet
bound states in the latter limit and suggest a crucial role for the bound
states in the unbinding of triplets and deconfinement of spin-half excitations.Comment: 17 figures, revte
Accurate Results from Perturbation Theory for Strongly Frustrated Heisenberg Spin Clusters
We investigate the use of perturbation theory in finite sized frustrated spin
systems by calculating the effect of quantum fluctuations on coherent states
derived from the classical ground state. We first calculate the ground and
first excited state wavefunctions as a function of applied field for a 12-site
system and compare with the results of exact diagonalization. We then apply the
technique to a 20-site system with the same three fold site coordination as the
12-site system. Frustration results in asymptotically convergent series for
both systems which are summed with Pad\'e approximants.
We find that at zero magnetic field the different connectivity of the two
systems leads to a triplet first excited state in the 12-site system and a
singlet first excited state in the 20-site system, while the ground state is a
singlet for both. We also show how the analytic structure of the Pad\'e
approximants at evolves in the complex plane at
the values of the applied field where the ground state switches between spin
sectors and how this is connected with the non-trivial dependence of the
number on the strength of quantum fluctuations. We discuss the origin
of this difference in the energy spectra and in the analytic structures. We
also characterize the ground and first excited states according to the values
of the various spin correlation functions.Comment: Final version, accepted for publication in Physical review
The 4.8 GHz LHC Schottky Pick-up System
The LHC Schottky observation system is based on traveling wave type high sensitivity pickup structures operating at 4.8 GHz. The choice of the structure and operating frequency is driven by the demanding LHC impedance requirements, where very low impedance is required below 2 GHz, and good sensitivity at the selected band at 4.8 GHz. A sophisticated filtering and triple down-mixing signal processing chain has been designed and implemented in order to achieve the specified 100 dB instantaneous dynamic range without range switching. Detailed design aspects for the complete systems and test results without beam are presented and discussed
Boson representations, non-standard quantum algebras and contractions
A Gelfan'd--Dyson mapping is used to generate a one-boson realization for the
non-standard quantum deformation of which directly provides its
infinite and finite dimensional irreducible representations. Tensor product
decompositions are worked out for some examples. Relations between contraction
methods and boson realizations are also explored in several contexts. So, a
class of two-boson representations for the non-standard deformation of
is introduced and contracted to the non-standard quantum (1+1)
Poincar\'e representations. Likewise, a quantum extended Hopf
algebra is constructed and the Jordanian -oscillator algebra representations
are obtained from it by means of another contraction procedure.Comment: 21 pages, LaTeX; two new references adde
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