193 research outputs found
Entangled collective-spin states of atomic ensembles under non-uniform atom-light interaction
We consider the optical generation and verification of entanglement in atomic
ensembles under non-uniform interaction between the ensemble and an optical
mode. We show that for a wide range of parameters a system of non-uniformly
coupled atomic spins can be described as an ensemble of uniformly coupled spins
with a reduced effective atom-light coupling and a reduced effective atom
number, with a reduction factor of order unity given by the ensemble-mode
geometry. This description is valid even for complex entangled states with
arbitrary phase-space distribution functions as long as the detection does not
resolve single spins. Furthermore, we derive an analytic formula for the
observable entanglement in the case, of relevance in practice, where the
ensemble-mode coupling differs between state generation and measurement.Comment: 5 pages, 3 figure
Topological Waveguide Quantum Sensors
We present an efficient and robust protocol for quantum-enhanced sensing
using a single-spin qubit in the topological waveguide system. Our method
relies on the topological-paired bound states, which are localized near the
spin and can be effectively regarded as a two-level system. Through the lens of
Bayesian inference theory, we show the sensitivity can reach the Heisenberg
limit across a large field range. Inheriting from the topological robustness of
the waveguide, our sensing protocol is robust against local perturbations. The
advantages of our protocol are multifold as it allows for sensing various
parameters and uses a product initial state, which can be easily prepared in
experiments. We expect this approach would pave the way towards robust
topological quantum sensors based on near term quantum platforms such as
topological photonics and Rydberg arrays.Comment: 4.5 + 3 pages, 3 + 3 figure
Numerical Study on the Route of Flame-Induced Thermoacoustic Instability in a Rijke Burner
The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability
Strictly nonclassical behavior of a mesoscopic system
We experimentally demonstrate the strictly nonclassical behavior in a
many-atom system using a recently derived criterion [E. Kot et al., Phys. Rev.
Lett. 108, 233601 (2012)] that explicitly does not make use of quantum
mechanics. We thereby show that the magnetic moment distribution measured by
McConnell et al. [R. McConnell et al., Nature 519, 439 (2015)] in a system with
a total mass of atomic mass units is inconsistent with
classical physics. Notably, the strictly nonclassical behavior affects an area
in phase space times larger than the Planck quantum .Comment: 5 page
Carving Complex Many-Atom Entangled States by Single-Photon Detection
We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity.National Science Foundation (U.S.)United States. Defense Advanced Research Projects Agency. Quantum-Assisted Sensing and Readout (QuASAR) ProgramUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeUnited States. Army Research Office. Multidisciplinary University Research InitiativeNatural Sciences and Engineering Research Council of Canad
Calibrating the absorption imaging of cold atoms under high magnetic fields
We develop a theoretical model for calibrating the absorption imaging of cold
atoms under high magnetic fields. Comparing to zero or low magnetic fields, the
efficiency of the absorption imaging becomes lower while it requires an
additional correction factor to obtain the absolute atom number under the
Beer-Lambert law. Our model is based on the rate equations and can account many
experimental imperfections such as Zeeman level crossing, failures of hyperfine
structures, off-resonant couplings, and low repumping efficiency, etc. Based on
this method, we can precisely calculate the correction factor for atom number
measurement without any empirical or fitting parameters. Meanwhile, we use a
cold-atom apparatus of rubidium-85 to experimentally verify our model. Besides
these, we find our work can also serve as a benchmark to measure the
polarization impurity of a circular-polarized laser beam with high
sensitivities. We believe this work will bring convenience for most of
cold-atom experiments using absorption imaging.Comment: 9 pages, 5 figure
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