123 research outputs found
High-precision force sensing using a single trapped ion
We introduce quantum sensing schemes for measuring very weak forces with a
single trapped ion. They use the spin-motional coupling induced by the
laser-ion interaction to transfer the relevant force information to the
spin-degree of freedom. Therefore, the force estimation is carried out simply
by observing the Ramsey-type oscillations of the ion spin states. Three quantum
probes are considered, which are represented by systems obeying the
Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using
dynamical decoupling schemes in the Jaynes-Cummings and Jahn-Teller models, our
force sensing protocols can be made robust to the spin dephasing caused by the
thermal and magnetic field fluctuations. In the quantum-Rabi probe, the
residual spin-phonon coupling vanishes, which makes this sensing protocol
naturally robust to thermally-induced spin dephasing. We show that the proposed
techniques can be used to sense the axial and transverse components of the
force with a sensitivity beyond the yN range, i.e. in the
xN (xennonewton, ). The Jahn-Teller protocol, in
particular, can be used to implement a two-channel vector spectrum analyzer for
measuring ultra-low voltages.Comment: 7 pages, 4 figure
Analytic approximations to the phase diagram of the Jaynes-Cummings-Hubbard model with application to ion chains
We discuss analytic approximations to the ground state phase diagram of the
homogeneous Jaynes-Cummings-Hubbard (JCH) Hamiltonian with general short-range
hopping. The JCH model describes e.g. radial phonon excitations of a linear
chain of ions coupled to an external laser field tuned to the red motional
sideband with Coulomb mediated hopping or an array of high- coupled cavities
containing a two-level atom and photons. Specifically we consider the cases of
a linear array of coupled cavities and a linear ion chain. We derive
approximate analytic expressions for the boundaries between Mott-insulating and
superfluid phases and give explicit expressions for the critical value of the
hopping amplitude within the different approximation schemes. In the case of an
array of cavities, which is represented by the standard JCH model we compare
both approximations to numerical data from density-matrix renormalization group
(DMRG) calculations.Comment: 9 pages, 5 figures, extended and corrected second versio
Suppression of Excitation and Spectral Broadening Induced by Interactions in a Cold Gas of Rydberg Atoms
We report on the observation of ultralong range interactions in a gas of cold
Rubidium Rydberg atoms. The van-der-Waals interaction between a pair of Rydberg
atoms separated as far as 100,000 Bohr radii features two important effects:
Spectral broadening of the resonance lines and suppression of excitation with
increasing density. The density dependence of these effects is investigated in
detail for the S- and P- Rydberg states with main quantum numbers n ~ 60 and n
~ 80 excited by narrow-band continuous-wave laser light. The density-dependent
suppression of excitation can be interpreted as the onset of an
interaction-induced local blockade
Quantum sensors assisted by spontaneous symmetry breaking for detecting very small forces
We propose a quantum-sensing scheme for measuring weak forces based on a symmetry-breaking adiabatic transition in the quantum Rabi model. We show that the system described by the Rabi Hamiltonian can serve as a sensor for extremely weak forces with sensitivity beyond the yoctonewton (yN) per sqrt (Hz) range. We propose an implementation of this sensing protocol using a single trapped ion. A major advantage of our scheme is that the force detection is performed by projective measurement of the population of the spin states at the end of the transition, instead of the far slower phonon number measurement used hitherto
A nano heat engine beyond the Carnot limit
Heat engines extract work by running cyclically between two heat reservoirs.
When the two reservoirs are thermal and at different temperatures, the maximum
efficiency of the engine is given by the Carnot limit. Here we consider a
quantum Otto cycle for a time-dependent harmonic oscillator coupled to an
engineered squeezed thermal reservoir. We show that the efficiency at maximum
power increases with the degree of squeezing, exponentially approaching unity
for large squeezing parameters . Furthermore, we propose an experimental
scheme to implement such a system by using a single trapped ion in a linear
Paul trap with special geometry and coupled to engineered reservoirs. Our
analytical investigations are supported with Monte Carlo simulations that
demonstrate the feasibility of our proposal. For realistic trap parameters, an
increase of up to a factor of four is reached, largely exceeding the classical
limit
Focusing a deterministic single-ion beam
We focus down an ion beam consisting of single 40Ca+ ions to a spot size of a
few mum using an einzel-lens. Starting from a segmented linear Paul trap, we
have implemented a procedure which allows us to deterministically load a
predetermined number of ions by using the potential shaping capabilities of our
segmented ion trap. For single-ion loading, an efficiency of 96.7(7)% has been
achieved. These ions are then deterministically extracted out of the trap and
focused down to a 1sigma-spot radius of (4.6 \pm 1.3)mum at a distance of 257mm
from the trap center. Compared to former measurements without ion optics, the
einzel-lens is focusing down the single-ion beam by a factor of 12. Due to the
small beam divergence and narrow velocity distribution of our ion source,
chromatic and spherical aberration at the einzel-lens is vastly reduced,
presenting a promising starting point for focusing single ions on their way to
a substrate.Comment: 16 pages, 7 figure
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