161 research outputs found
Spin Squeezing in the Ising Model
We analyze the collective spin noise in interacting spin systems. General
expressions are derived for the short time behaviour of spin systems with
general spin-spin interactions, and we suggest optimum experimental conditions
for the detection of spin squeezing. For Ising models with site dependent
nearest neighbour interactions general expressions are presented for the spin
squeezing parameter for all times. The reduction of collective spin noise can
be used to verify the entangling powers of quantum computer architectures based
on interacting spins.Comment: 7 pages, including 3 figure
A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions
We present a solid-state laser system that generates 750 mW of
continuous-wave single-frequency output at 313 nm. Sum-frequency generation
with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This
visible light is then converted to UV by cavity-enhanced second-harmonic
generation. The laser output can be tuned over a 495 GHz range, which includes
the 9Be+ laser cooling and repumping transitions. This is the first report of a
narrow-linewidth laser system with sufficient power to perform fault-tolerant
quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman
transitions.Comment: 9 pages, 4 figure
Sympathetic Cooling of Trapped Cd+ Isotopes
We sympathetically cool a trapped 112Cd+ ion by directly Doppler-cooling a
114Cd+ ion in the same trap. This is the first demonstration of optically
addressing a single trapped ion being sympathetically cooled by a different
species ion. Notably, the experiment uses a single laser source, and does not
require strong focusing. This paves the way toward reducing decoherence in an
ion trap quantum computer based on Cd+ isotopes.Comment: 4 figure
Individual addressing and state readout of trapped ions utilizing rf- micromotion
A new scheme for the individual addressing of ions in a trap is described
that does not rely on light beams tightly focused onto only one ion. The scheme
utilizes ion micromotion that may be induced in a linear trap by dc offset
potentials. Thus coupling an individual ion to the globally applied light
fields corresponds to a mere switching of voltages on a suitable set of
compensation electrodes. The proposed scheme is especially suitable for
miniaturized rf (Paul) traps with typical dimensions of about 20-40 microns.Comment: 3 pages, 5 figure
Optimally squeezed spin states
We consider optimally spin-squeezed states that maximize the sensitivity of
the Ramsey spectroscopy, and for which the signal to noise ratio scales as the
number of particles . Using the variational principle we prove that these
states are eigensolutions of the Hamiltonian
and that, for large , the states become equivalent to the quadrature
squeezed states of the harmonic oscillator. We present numerical results that
illustrate the validity of the equivalence
Entanglement between motional states of a single trapped ion and light
We propose a generation method of Bell-type states involving light and the
vibrational motion of a single trapped ion. The trap itself is supposed to be
placed inside a high- cavity sustaining a single mode, quantized
electromagnetic field. Entangled light-motional states may be readily generated
if a conditional measurement of the ion's internal electronic state is made
after an appropriate interaction time and a suitable preparation of the initial
state. We show that all four Bell states may be generated using different
motional sidebands (either blue or red), as well as adequate ionic relative
phases.Comment: 4 pages, LaTe
Sympathetic cooling of and for quantum logic
We demonstrate the cooling of a two species ion crystal consisting of one
and one ion. Since the respective cooling transitions of
these two species are separated by more than 30 nm, laser manipulation of one
ion has negligible effect on the other even when the ions are not individually
addressed. As such this is a useful system for re-initializing the motional
state in an ion trap quantum computer without affecting the qubit information.
Additionally, we have found that the mass difference between ions enables a
novel method for detecting and subsequently eliminating the effects of radio
frequency (RF) micro-motion.Comment: Submitted to PR
Semiclassical Shor's Algorithm
We propose a semiclassical version of Shor's quantum algorithm to factorize
integer numbers, based on spin-1/2 SU(2) generalized coherent states.
Surprisingly, we find evidences that the algorithm's success probability is not
too severely modified by our semiclassical approximation. This suggests that it
is worth pursuing practical implementations of the algorithm on semiclassical
devices.Comment: 19 pages (RevTex) + 10 Figures (in a separate ps file). Widened
version: analytical discussion of the impact on the period-finding power
added; scaling behaviour of the semiclassical probability addressed; two new
appendices; other minor changes. Accepted for publication in Physical Review
Preparation of spin squeezed atomic states by optical phase shift measurement
In this paper we present a state vector analysis of the generation of atomic
spin squeezing by measurement of an optical phase shift. The frequency
resolution is improved when a spin squeezed sample is used for spectroscopy in
place of an uncorrelated sample. When light is transmitted through an atomic
sample some photons will be scattered out of the incident beam, and this has a
destructive effect on the squeezing. We present quantitative studies for three
limiting cases: the case of a sample of atoms of size smaller than the optical
wavelength, the case of a large dilute sample and the case of a large dense
sample.Comment: 18 page
Stroboscopic Laser Diagnostics for Detection of Ordering in One-Dimensional Ion beam
A novel diagnostic method for detecting ordering in one-dimensional ion beams
is presented. The ions are excited by a pulsed laser at two different positions
along the beam and fluorescence is observed by a group of four
photomultipliers. Correlation in fluorescence signals is firm indication that
the ion beam has an ordered structure.Comment: 7 pages, REVTEX, fig3 uuencoded, figs 1-2 available upon request from
[email protected], to appear in Phys. Rev.
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