305 research outputs found
Phase diagram of the Bose Kondo-Hubbard model
We study a bosonic version of the Kondo lattice model with an on-site
repulsion in the conduction band, implemented with alkali atoms in two bands of
an optical lattice. Using both weak and strong-coupling perturbation theory, we
find that at unit filling of the conduction bosons the superfluid to Mott
insulator transition should be accompanied by a magnetic transition from a
ferromagnet (in the superfluid) to a paramagnet (in the Mott insulator).
Furthermore, an analytic treatment of Gutzwiller mean-field theory reveals that
quantum spin fluctuations induced by the Kondo exchange cause the otherwise
continuous superfluid to Mott-insulator phase transition to be first order. We
show that lattice separability imposes a serious constraint on proposals to
exploit excited bands for quantum simulations, and discuss a way to overcome
this constraint in the context of our model by using an experimentally realized
non-separable lattice. A method to probe the first-order nature of the
transition based on collapses and revivals of the matter-wave field is also
discussed.Comment: 10 pages, 5 figures, V2: extended discussion of effective
Hamiltonians and mean-field theory, added Fig.
Probing the Kondo Lattice Model with Alkaline Earth Atoms
We study transport properties of alkaline-earth atoms governed by the Kondo
Lattice Hamiltonian plus a harmonic confining potential, and suggest simple
dynamical probes of several different regimes of the phase diagram that can be
implemented with current experimental techniques. In particular, we show how
Kondo physics at strong coupling, low density, and in the heavy fermion phase
is manifest in the dipole oscillations of the conduction band upon displacement
of the trap center.Comment: 5 pages, 4 figure
Persistence of locality in systems with power-law interactions
Motivated by recent experiments with ultra-cold matter, we derive a new bound
on the propagation of information in -dimensional lattice models exhibiting
interactions with . The bound contains two terms: One
accounts for the short-ranged part of the interactions, giving rise to a
bounded velocity and reflecting the persistence of locality out to intermediate
distances, while the other contributes a power-law decay at longer distances.
We demonstrate that these two contributions not only bound but, except at long
times, \emph{qualitatively reproduce} the short- and long-distance dynamical
behavior following a local quench in an chain and a transverse-field Ising
chain. In addition to describing dynamics in numerous intractable long-range
interacting lattice models, our results can be experimentally verified in a
variety of ultracold-atomic and solid-state systems.Comment: 5 pages, 4 figures, version accepted by PR
Laser-free trapped ion entangling gates with AESE: Adiabatic Elimination of Spin-motion Entanglement
We discuss a laser-free, two-qubit geometric phase gate technique for
generating high-fidelity entanglement between two trapped ions. The scheme
works by ramping the spin-dependent force on and off slowly relative to the
gate detunings, which adiabatically eliminates the spin-motion entanglement
(AESE). We show how gates performed with AESE can eliminate spin-motion
entanglement with multiple modes simultaneously, without having to specifically
tune the control field detunings. This is because the spin-motion entanglement
is suppressed by operating the control fields in a certain parametric limit,
rather than by engineering an optimized control sequence. We also discuss
physical implementations that use either electronic or ferromagnetic magnetic
field gradients. In the latter, we show how to ``AESE" the system by smoothly
turning on the \textit{effective} spin-dependent force by shelving from a
magnetic field insensitive state to a magnetic field sensitive state slowly
relative to the gate mode frequencies. We show how to do this with a Rabi or
adiabatic rapid passage transition. Finally, we show how gating with AESE
significantly decreases the gate's sensitivity to common sources of motional
decoherence, making it easier to perform high-fidelity gates at Doppler
temperatures
Non-equilibrium fixed points of coupled Ising models
Driven-dissipative systems are expected to give rise to non-equilibrium
phenomena that are absent in their equilibrium counterparts. However, phase
transitions in these systems generically exhibit an effectively classical
equilibrium behavior in spite of their non-equilibrium origin. In this paper,
we show that multicritical points in such systems lead to a rich and genuinely
non-equilibrium behavior. Specifically, we investigate a driven-dissipative
model of interacting bosons that possesses two distinct phase transitions: one
from a high- to a low-density phase---reminiscent of a liquid-gas
transition---and another to an antiferromagnetic phase. Each phase transition
is described by the Ising universality class characterized by an (emergent or
microscopic) symmetry. They, however, coalesce at a
multicritical point, giving rise to a non-equilibrium model of coupled
Ising-like order parameters described by a
symmetry. Using a dynamical renormalization-group approach, we show that a pair
of non-equilibrium fixed points (NEFPs) emerge that govern the long-distance
critical behavior of the system. We elucidate various exotic features of these
NEFPs. In particular, we show that a generic continuous scale invariance at
criticality is reduced to a discrete scale invariance. This further results in
complex-valued critical exponents and spiraling phase boundaries, and it is
also accompanied by a complex Liouvillian gap even close to the phase
transition. As direct evidence of the non-equilibrium nature of the NEFPs, we
show that the fluctuation-dissipation relation is violated at all scales,
leading to an effective temperature that becomes "hotter" and "hotter" at
longer and longer wavelengths. Finally, we argue that this non-equilibrium
behavior can be observed in cavity arrays with cross-Kerr nonlinearities.Comment: 19+11 pages, 7+9 figure
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