15 research outputs found
Implementation of Cavity Squeezing of a Collective Atomic Spin
We squeeze unconditionally the collective spin of a dilute ensemble of
laser-cooled rubidium-87 atoms using their interaction with a driven optical
resonator. The shape and size of the resulting spin uncertainty region are well
described by a simple analytical model [M.H.S., I.D.L., V.V., arXiv:0911.3936]
through two orders of magnitude in the effective interaction strength, without
free parameters. We deterministically generate states with up to 5.6(6) dB of
metrologically relevant spin squeezing on the canonical rubidium-87 hyperfine
clock transition.Comment: 4 pages, 2 figures. To be published in Phys. Rev. Lett. Some
additional details and clarified wording in response to referee comments.
Figures and results unchange
Squeezing the Collective Spin of a Dilute Atomic Ensemble by Cavity Feedback
We propose and analyze a simple method to squeeze dynamically and
unconditionally the collective spin of a dilute atomic ensemble by interaction
with a driven mode of an optical resonator, as recently demonstrated [I. D. L.,
M. H. S., and V. V., Phys. Rev. Lett. 104, 073602 (2010)]. We show that
substantial squeezing can be achieved in the regime of strong collective
ensemble-resonator coupling. The squeezing is ultimately limited either by
photon emission into free space or by the curvature of the Bloch sphere. We
derive both limits and show where each prevails.Comment: 4 pages, 2 figures. Minor revision. To appear in Phys. Rev.
One- and two-axis squeezing of atomic ensembles in optical cavities
The strong light-matter coupling attainable in optical cavities enables the
generation of highly squeezed states of atomic ensembles. It was shown in
[Phys. Rev. A 66, 022314 (2002)] how an effective one-axis twisting Hamiltonian
can be realized in a cavity setup. Here, we extend this work and show how an
effective two-axis twisting Hamiltonian can be realized in a similar cavity
setup. We compare the two schemes in order to characterize their advantages. In
the absence of decoherence, the two-axis Hamiltonian leads to more squeezing
than the one-axis Hamiltonian. If limited by decoherence from spontaneous
emission and cavity decay, we find roughly the same level of squeezing for the
two schemes scaling as (NC)^(1/2) where C is the single atom cooperativity and
N is the total number of atoms. When compared to an ideal squeezing operation,
we find that for specific initial states, a dissipative version of the one-axis
scheme attains higher fidelity than the unitary one-axis scheme or the two-axis
scheme. However, the unitary one-axis and two-axis schemes perform better for
general initial states.Comment: 13 pages, 6 figure
Unitary Cavity Spin Squeezing by Quantum Erasure
Deterministic light-induced spin squeezing in an atomic gas is limited by
photon shot noise or, equivalently, by atomic state information escaping with
the light field mediating the effective atom-atom interaction. We show
theoretically that the performance of cavity spin squeezing [M.H.
Schleier-Smith, I.D. Leroux, and V. Vuleti\'{c}, Phys. Rev. A 81, 021804(R)
(2010)] can be substantially improved by erasing the light-atom entanglement,
and propose several methods for doing so. Accounting for light scattering into
free space, quantum erasure improves the scaling of cavity squeezing from
S^(-1/2) to S^(-2/3), where S is the total atomic spin.Comment: 10 pages, 6 figures; sections reordered and text edited for clarit
States of an Ensemble of Two-Level Atoms with Reduced Quantum Uncertainty
We generate entangled states of an ensemble of 5*10^4 rubidium-87 atoms by
optical quantum nondemolition measurement. The resonator-enhanced measurement
leaves the atomic ensemble, prepared in a superposition of hyperfine clock
levels, in a squeezed spin state. By comparing the resulting reduction of
quantum projection noise (up to 8.8(8) dB) with the concomitant reduction of
coherence, we demonstrate a clock input state with spectroscopic sensitivity
3.0(8) dB beyond the standard quantum limit.Comment: Letter (4 pages, 3 figures) followed by Auxiliary Material (10 pages,
6 figures). Minor changes in presentation and analysis of data. Significant
expansion of Auxiliary Material. Broken images fixe
Optomechanical Cavity Cooling of an Atomic Ensemble
We demonstrate cavity sideband cooling of a single collective motional mode
of an atomic ensemble down to a mean phonon occupation number of
2.0(-0.3/+0.9). Both this minimum occupation number and the observed cooling
rate are in good agreement with an optomechanical model. The cooling rate
constant is proportional to the total photon scattering rate by the ensemble,
demonstrating the cooperative character of the light-emission-induced cooling
process. We deduce fundamental limits to cavity-cooling either the collective
mode or, sympathetically, the single-atom degrees of freedom.Comment: Paper with supplemental material: 4+6 pages, 4 figures. Minor
revisions of text. Supplemental material shortened by removal of
supplementary figur