6,183 research outputs found
Quantum computing with alkaline earth atoms
We present a complete scheme for quantum information processing using the
unique features of alkaline earth atoms. We show how two completely independent
lattices can be formed for the S and P states, with one used as
a storage lattice for qubits encoded on the nuclear spin, and the other as a
transport lattice to move qubits and perform gate operations. We discuss how
the P level can be used for addressing of individual qubits, and how
collisional losses from metastable states can be used to perform gates via a
lossy blockade mechanism.Comment: 4 pages, 3 figures, RevTeX
Bound states in weakly deformed waveguides: numerical vs analytical results
We have studied the emergence of bound states in weakly deformed and/or
heterogeneous waveguides, comparing the analytical predictions obtained using a
recently developed perturbative method, with precise numerical results, for
different configurations (a homogeneous asymmetric waveguide, a heterogenous
asymmetric waveguide and a homogeneous broken-strip). In all the examples
considered in this paper we have found excellent agreement between analytical
and numerical results, thus providing a numerical verification of the
analytical approach.Comment: 11 pages, 6 figure
Divergence of an orbital-angular-momentum-carrying beam upon propagation
There is recent interest in the use of light beams carrying orbital angular
momentum (OAM) for creating multiple channels within free-space optical
communication systems. One limiting issue is that, for a given beam size at the
transmitter, the beam divergence angle increases with increasing OAM, thus
requiring a larger aperture at the receiving optical system if the efficiency
of detection is to be maintained. Confusion exists as to whether this
divergence scales linarly with, or with the square root of, the beam's OAM. We
clarify how both these scaling laws are valid, depending upon whether it is the
radius of the Gaussian beam waist or the rms intensity which is kept constant
while varying the OAM.Comment: 4 pages, 2 figure
Lower Bounds for Ground States of Condensed Matter Systems
Standard variational methods tend to obtain upper bounds on the ground state
energy of quantum many-body systems. Here we study a complementary method that
determines lower bounds on the ground state energy in a systematic fashion,
scales polynomially in the system size and gives direct access to correlation
functions. This is achieved by relaxing the positivity constraint on the
density matrix and replacing it by positivity constraints on moment matrices,
thus yielding a semi-definite programme. Further, the number of free parameters
in the optimization problem can be reduced dramatically under the assumption of
translational invariance. A novel numerical approach, principally a combination
of a projected gradient algorithm with Dykstra's algorithm, for solving the
optimization problem in a memory-efficient manner is presented and a proof of
convergence for this iterative method is given. Numerical experiments that
determine lower bounds on the ground state energies for the Ising and
Heisenberg Hamiltonians confirm that the approach can be applied to large
systems, especially under the assumption of translational invariance.Comment: 16 pages, 4 figures, replaced with published versio
Precision spectroscopy and density-dependent frequency shifts in ultracold Sr
By varying the density of an ultracold Sr sample from cm
to cm, we make the first definitive measurement of the
density-related frequency shift and linewidth broadening of the -
optical clock transition in an alkaline earth system. In addition, we
report the most accurate measurement to date of the Sr
optical clock transition frequency. Including a detailed analysis of systematic
errors, the frequency is () Hz.Comment: 4 pages, 4 figures, 1 table. submitte
Suppression of collisional shifts in a strongly interacting lattice clock
Optical lattice clocks have the potential for extremely high frequency
stability owing to the simultaneous interrogation of many atoms, but this
precision may come at the cost of systematic inaccuracy due to atomic
interactions. Density-dependent frequency shifts can occur even in a clock that
uses fermionic atoms if they are subject to inhomogeneous optical excitation
[1, 2]. Here we present a seemingly paradoxical solution to this problem. By
dramatically increasing the strength of atomic interactions, we suppress
collisional shifts in lattice sites containing > 1 atoms; strong
interactions introduce an energy splitting into the system, and evolution into
a many-particle state in which collisions occur is inhibited. We demonstrate
the effectiveness of this approach with the JILA Sr lattice clock by reducing
both the collisional frequency shift and its uncertainty by more than a factor
of ten [3], to the level of . This result eliminates the compromise
between precision and accuracy in a many-particle system, since both will
continue to improve as the particle number increases.Comment: 13 pages, 6 figure
Narrow Line Cooling: Finite Photon Recoil Dynamics
We present an extensive study of the unique thermal and mechanical dynamics
for narrow-line cooling on the 1S0 - 3P1 88Sr transition. For negative
detuning, trap dynamics reveal a transition from the semiclassical regime to
the photon-recoil-dominated quantum regime, yielding an absolute minima in the
equilibrium temperature below the single-photon recoil limit. For positive
detuning, the cloud divides into discrete momentum packets whose alignment
mimics lattice points on a face-centered-cubic crystal. This novel behavior
arises from velocity selection and "positive feedback" acceleration due to a
finite number of photon recoils. Cooling is achieved with blue-detuned light
around a velocity where gravity balances the radiative force.Comment: 4 pages, 3 figures, Phys. Rev. Lett., in pres
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