21 research outputs found
Sensitive Absorption Imaging of Single Atoms in Front of a Mirror
In this paper we show that the sensitivity of absorption imaging of ultracold
atoms can be significantly improved by imaging in a standing-wave
configuration. We present simulations of single-atom absorption imaging both
for a travelling-wave and a standing-wave imaging setup, based on a scattering
approach to calculate the optical density of a single atom. We find that the
optical density of a single atom is determined only by the numerical aperture
of the imaging system. We determine optimum imaging parameters, taking all
relevant sources of noise into account. For reflective imaging we find an
improvement of 1.7 in the maximum signal-to-noise ratio can be achieved. This
is particularly useful for imaging in the vicinity of an atom chip, where a
reflective surface is naturally present
Off-axis dipole forces in optical tweezers by an optical analog of the {Magnus} effect
It is shown that a circular dipole can deflect the focused laser beam that
induces it, and will experience a corresponding transverse force. Quantitative
expressions are derived for Gaussian and angular tophat beams, while the
effects vanish in the plane-wave limit. The phenomena are analogous to the
Magnus effect pushing a spinning ball onto a curved trajectory. The optical
case originates in the coupling of spin and orbital angular momentum of the
dipole and the light. In optical tweezers the force causes off-axis
displacement of the trapping position of an atom by a spin-dependent amount up
to , set by the direction of a magnetic field. This suggests
direct methods to demonstrate and explore these effects, for instance to induce
spin-dependent motion.Comment: 5 pages, 3 figures; plus 3 pages Supplemental Material (accepted
version
Solving correlation clustering with QAOA and a Rydberg qudit system: a full-stack approach
We study the correlation clustering problem using the quantum approximate
optimization algorithm (QAOA) and qudits, which constitute a natural platform
for such non-binary problems. Specifically, we consider a neutral atom quantum
computer and propose a full stack approach for correlation clustering,
including Hamiltonian formulation of the algorithm, analysis of its
performance, identification of a suitable level structure for
and specific gate design. We show the qudit implementation is superior to the
qubit encoding as quantified by the gate count. For single layer QAOA, we also
prove (conjecture) a lower bound of () for the approximation
ratio on 3-regular graphs. Our numerical studies evaluate the algorithm's
performance by considering complete and Erd\H{o}s-R\'enyi graphs of up to 7
vertices and clusters. We find that in all cases the QAOA surpasses the Swamy
bound for the approximation ratio for QAOA depths . Finally,
by analysing the effect of errors when solving complete graphs we find that
their inclusion severely limits the algorithm's performance.Comment: 22 + 11 page
Collective suppression of optical hyperfine pumping in dense clouds of atoms in microtraps
We observe a density-dependent collective suppression of optical pumping between the hyperfine ground states in an array of submicrometer-sized clouds of dense and cold rubidium atoms. The suppressed Raman transition rate can be explained by strong resonant dipole-dipole interactions that are enhanced by increasing atom density, and are already significant at densities of ï°€0.1k3, where k denotes the resonance wave number. The observations are consistent with stochastic electrodynamics simulations that incorporate the effects of population transfer via internal atomic levels embedded in a coupled-dipole model
Classical wave-optics analogy of quantum information processing
An analogous model system for quantum information processing is discussed,
based on classical wave optics. The model system is applied to three examples
that involve three qubits: ({\em i}) three-particle Greenberger-Horne-Zeilinger
entanglement, ({\em ii}) quantum teleportation, and ({\em iii}) a simple
quantum error correction network. It is found that the model system can
successfully simulate most features of entanglement, but fails to simulate
quantum nonlocality. Investigations of how far the classical simulation can be
pushed show that {\em quantum nonlocality} is the essential ingredient of a
quantum computer, even more so than entanglement. The well known problem of
exponential resources required for a classical simulation of a quantum
computer, is also linked to the nonlocal nature of entanglement, rather than to
the nonfactorizability of the state vector.Comment: 9 pages, 6 figure
Solving correlation clustering with QAOA and a Rydberg qudit system: a full-stack approach
We study the correlation clustering problem using the quantum approximate optimization algorithm (QAOA) and qudits, which constitute a natural platform for such non-binary problems. Specifically, we consider a neutral atom quantum computer and propose a full stack approach for correlation clustering, including Hamiltonian formulation of the algorithm, analysis of its performance, identification of a suitable level structure for 87Sr and specific gate design. We show the qudit implementation is superior to the qubit encoding as quantified by the gate count. For single layer QAOA, we also prove (conjecture) a lower bound of 0.6367 (0.6699) for the approximation ratio on 3-regular graphs. Our numerical studies evaluate the algorithm's performance by considering complete and Erdős-Rényi graphs of up to 7 vertices and clusters. We find that in all cases the QAOA surpasses the Swamy bound 0.7666 for the approximation ratio for QAOA depths p≥2. Finally, by analysing the effect of errors when solving complete graphs we find that their inclusion severely limits the algorithm's performance
Solving correlation clustering with QAOA and a Rydberg qudit system: a full-stack approach
We study the correlation clustering problem using the quantum approximate optimization algorithm (QAOA) and qudits, which constitute a natural platform for such non-binary problems. Specifically, we consider a neutral atom quantum computer and propose a full stack approach for correlation clustering, including Hamiltonian formulation of the algorithm, analysis of its performance, identification of a suitable level structure for 87Sr and specific gate design. We show the qudit implementation is superior to the qubit encoding as quantified by the gate count. For single layer QAOA, we also prove (conjecture) a lower bound of 0.6367 (0.6699) for the approximation ratio on 3-regular graphs. Our numerical studies evaluate the algorithm’s performance by considering complete and Erdős-Rényi graphs of up to 7 vertices and clusters. We find that in all cases the QAOA surpasses the Swamy bound 0.7666 for the approximation ratio for QAOA depths p ≥ 2. Finally, by analysing the effect of errors when solving complete graphs we find that their inclusion severely limits the algorithm’s performance
Time and frequency domain solutions in an optical analogue of Grover's search algorithm
We present new results on an optical implementation of Grover’s quantum search algorithm. This extends previous work in which the transverse spatial mode of a light beam oscillates between a broad initial input shape and a highly localized spike, which reveals the position of the tagged item. The spike reaches its maximum intensity after N round trips in a cavity equipped with two phase plates, where N is the ratio of the surface area of the original beam and the area of the phase spot or tagged item. In our redesigned experiment the search space is now two dimensional. In the time domain, we demonstrate for the first time a multiple-item search where the items appear directly as bright spots on the images of a gated camera. In a complementaryexperiment we investigate the searching cavity in the frequency domain. The oscillatory nature of the search algorithm can be seen as a splitting of cavity eigenmodes, each of which concentrates up to 50% of its power in the bright spot corresponding to the solution