840 research outputs found
Circuit QED and engineering charge based superconducting qubits
The last two decades have seen tremendous advances in our ability to generate
and manipulate quantum coherence in mesoscopic superconducting circuits. These
advances have opened up the study of quantum optics of microwave photons in
superconducting circuits as well as providing important hardware for the
manipulation of quantum information. Focusing primarily on charge-based qubits,
we provide a brief overview of these developments and discuss the present state
of the art. We also survey the remarkable progress that has been made in
realizing circuit quantum electrodynamics (QED) in which superconducting
artificial atoms are strongly coupled to individual microwave photons.Comment: Proceedings of Nobel Symposium 141: Qubits for Future Quantum
Informatio
The plasma picture of the fractional quantum Hall effect with internal SU(K) symmetries
We consider trial wavefunctions exhibiting SU(K) symmetry which may be
well-suited to grasp the physics of the fractional quantum Hall effect with
internal degrees of freedom. Systems of relevance may be either
spin-unpolarized states (K=2), semiconductors bilayers (K=2,4) or graphene
(K=4). We find that some introduced states are unstable, undergoing phase
separation or phase transition. This allows us to strongly reduce the set of
candidate wavefunctions eligible for a particular filling factor. The stability
criteria are obtained with the help of Laughlin's plasma analogy, which we
systematically generalize to the multicomponent SU(K) case. The validity of
these criteria are corroborated by exact-diagonalization studies, for SU(2) and
SU(4). Furthermore, we study the pair-correlation functions of the ground state
and elementary charged excitations within the multicomponent plasma picture.Comment: 13 pages, 7 figures; reference added, accepted for publication in PR
Exact Results for 1D Kondo Lattice from Bosonization
We find a solvable limit to the problem of the 1D electron gas interacting
with a lattice of Kondo scattering centers. In this limit, we present exact
results for the problems of incommensurate filling, commensurate filling,
impurity vacancy states, and the commensurate-incommensurate transition.Comment: 4 pages, two columns, Latex fil
Meron excitations in the nu =1 quantum Hall bilayer and the plasma analogy
We study meron quasiparticle excitations in the \nu = 1 quantum Hall bilayer.
Considering the well known single meron state, we introduce its effective form,
valid in the longdistance limit. That enables us to propose two (and more)
meron states in the same limit. Further, establishing a plasma analogy of the
(111) ground state, we find the impurities that play the role of merons and
derive meron charge distributions. Using the introduced meron constructions in
generalized (mixed) ground states and corresponding plasmas for arbitrary
distance between the layers, we calculate the interaction between the
construction implied impurities. We also find a correspondence between the
impurity interactions and meron interactions. This suggests a possible
explanation of the deconfinement of the merons recently observed in the
experiments.Comment: 5 pages, 3 figure
Theory of preparation and relaxation of a p-orbital atomic Mott insulator
We develop a theoretical framework to understand the preparation and
relaxation of a metastable Mott insulator state within the first excited band
of a 1D optical lattice. The state is loaded by "lifting" atoms from the ground
to the first excited band by means of a stimulated Raman transition. We
determine the effect of pulse duration on the accuracy of the state preparation
for the case of a Gaussian pulse shape. Relaxation of the prepared state occurs
in two major stages: double-occupied sites occurring due to quantum
fluctuations initially lead to interband transitions followed by a spreading of
particles in the trap and thermalization. We find the characteristic relaxation
times at the earliest stage and at asymptotically long times approaching
equilibrium. Our theory is applicable to recent experiments performed with 1D
optical lattices [T. M\"uller, S. F\"olling, A. Widera, and I. Bloch, Phys.
Rev. Lett. \textbf{99}, 200405 (2007)].Comment: 27 pages, 23 figures: Edited figures, added reference
Hysteresis in the quantum Hall regimes in electron double quantum well structures
We present in this paper experimental results on the transport hysteresis in
electron double quantum well structures. Exploring the measurement technique of
fixing the magnetic field and sweeping a front gate voltage (Vg), we are able
to study the hysteresis by varying the top layer Landau level fillings while
maintaining a relatively constant filling factor in the bottom layer, allowing
us to tackle the question of the sign of Rxx(up)-Rxx(down), where Rxx(up) is
the magnetoresistance when Vg is swept up and Rxx(down) when Vg swept down.
Furthermore, we observe that hysteresis is generally stronger in the even
integer quantum Hall effect (IQHE) regime than in the odd-IQHE regime. This, we
argue, is due to a larger energy gap for an even-IQHE state, determined by the
Landau level separation, than that for an odd-IQHE state, determined by the
Zeeman splitting
Absence of Domain Wall Roughening in a Transverse Field Ising Model with Long-Range Interactions
We investigate roughening transitions in the context of transverse-field
Ising models. As a modification of the transverse Ising model with short range
interactions, which has been shown to exhibit domain wall roughening, we have
looked into the possibility of a roughening transition for the case of
long-range interactions, since such a system is physically realized in the
insulator LiHoF4. The combination of strong Ising anisotropy and long-range
forces lead naturally to the formation of domain walls but we find that the
long-range forces destroy the roughening transition.Comment: 7 pages, 5 figures, revtex
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