News from the Mitchell Group
|Ultracold atoms team creates a magnetic superfluid. When bosonic atoms like rubidium-87 get sufficiently cold, the form a new phase of matter that is both superfluid (no friction at all) and ferromagnetic.|
|Group Leader Morgan Mitchell awarded the Ehrenfest Award for Foundations of Physics. Congratulations, Morgan !|
|Attach:TimingDiagramPlot5.pdf||Cold atoms team publishes article on high-speed, high-sensitivity, real-time detector for Faraday rotation measurement of atoms.|
|Hot atoms team publishes article showing that squeezed light can improve important technique for non-invasive spectroscopy.|
|Three back-to-back articles (250401, 250402, 250403) and cover of special issue on loophole-free Bell tests.|
|Article in Physical Review Letters shows how quantum non-demolition measurements can be used to test Leggett and Garg's ideas of macroscopic realism in macroscopic systems.|
|Loophole-free Bell test contradicts local realism. Article in Nature. Reporting in New York Times, The Economist, The Times of London.|
|Dr. Naeimeh Behbood graduated with the thesis Generation of Macroscopic Spin Singlets in Cold Atomic Ensembles. Congratulations, Naeimeh !|
|Article in PRL shows that suqeezed beams of light consist of entangled photons.|
Article in PRL We observe for the first time the entanglement of microscopic particles (in our case photons) inside of a macroscopic quantum state (in our case squeezed light). Featured in Science News.
|Dr. Yannick Alan de Icaza Astiz graduated with a thesis in Optimal Signal Recovery for Pulsed Balanced Detection. Congratulations, Yannick !|
Article in PRL By applying quantum non-demolition measurements to an unpolarized atomic ensemble, we generate a macroscopic singlet state. At least 500,000 atoms become entangled in the process. Editor's suggestion in PRL Featured in Scientific American.
Ferran Adrià visits the lab, talks about creativity and very cold atoms.
Article in PRX We demonstrate that for some measurements, e.g. measuring atomic spin alignment, a nonlinear measurement beats the best possible "ordinary" measurement. This confirms a proposal by Sergio Boixo and Carlton Caves, and is beyond the standard models of quantum sensitivity limits. Editor's choice in Science.
|Ricardo Jimenez Martinez||Ricardo joins us from NIST Boulder.|
Steven Chu (Nobel 1997) visits the lab, talks about atom interferometry, climate change, and re-creating the culture of Bell Labs.
|Mario Napolitano successfully defended his dissertation Interaction-based nonlinear quantum metrology with a cold atomic ensemble. Congratulations, Mario !|
Jia Kong (visiting PhD student) joins from East China Normal University (Shanghai).
|Article in Optics Express|
We demonstrate 43 gigabits per second randomness generation, using off-the-shelf components. In collaboration with V. Pruneri's group at ICFO. Newspaper report in El Periodico
|Ricardo Jimenez Martinez||Ricardo joins us from NIST Boulder.|
Natalie Martinez (post-doc) joins from Los Alamos National Labs (USA).
|Brice Dubost successfully defended his dissertation Light-Matter Interaction with Atomic Ensembles. Congratulations, Brice !|
|Florian Wolfrgamm successfully defended his dissertation Atomic Quantum Metrology with Narrowband Entangled and Squeezed States of Light. Congratulations, Florian !|
Morgan and Mario honored for work on quantum metrology. Here they are receiving the award "Vanguardia de la Ciencia." Ceremony presided over by Andreu Mas-Colell, conseller de Economia i Coneixement (at right). Article in La Vanguardia (in Spanish)
|Thomas Vanderbruggen?||Joanna Zielinska|
Thomas Vanderbruggen (post-doc) joins from the Institut d'Optique in France, and Joanna Zielinska (PhD), joins from Warsaw, Poland.
|Silvana Palacios||Ferran Martin|
Silvana Palacios (PhD) joins from the Universidad Nacional Autonoma de Mexico, and Ferran Martin (PhD), joins from the Universitat Autonoma de Barcelona.
The project, "Atomic Quantum Metrology," will test revolutionary new proposals in ultra-sensitive measurement using quantum optics.
Morgan has been selected to join the prestigious Catalan research organization ICREA (Institució Catala de Reçerca i Estudis Avancats).
|Silvana Palacios||Silvana, from the UNAM (Mexico), joins the group as a Master student.|
|Pau Gómez Kabelka||Joanna Zielinska|
Pau Gomez Kabelka, from Barcelona and Joanna Zielinska, from Torun, Poland join the group for the summer.
Quantum metrology uses entanglement and other quantum resources to improve precision measurement, resulting in sensitivity limited by the Heisenberg uncertainty principle. But in theory, interactions among particles may allow scaling beyond this limit into 'super-Heisenberg' territory. Napolitano et al. prove experimentally that this can indeed occur in a nonlinear, non-destructive measurement of the magnetization of an atomic ensemble. The work shows that inter-particle interactions could be a useful resource for quantum metrology, although the relative performance of nonlinear versus linear measurements has yet to be explored more generally Nature 471, 486–489 (2011). A collection of press is here.
We present a magnetic field imaging technique based on spatially resolved detection of Larmor precession. An optically trapped, elongated, and cold atomic sample of rubidium serves as magnetic field probe. We detect Larmor precession with a spatial and a temporal resolution of ∼ 50 μm and ∼ 120 μs, respectively. Projection-noise limited absorption imaging, feasible with current technologies, implies a sensitivity of ∼ 10 pT/Hz1/2 at 50 μm resolution; addition of an optical lattice could give ∼ 300 fT/Hz1/2 sensitivity. Appl. Phys. Lett. 98, 074101 (2011)
We demonstrate the generation of rubidium-resonant heralded single photons for quantum memories. Photon pairs are created by cavity-enhanced down-conversion and narrowed in bandwidth to 7 MHz with a novel atom-based filter operating by “interaction-free measurement” principles. At least 94% of the heralded photons are atom-resonant as demonstrated by a direct absorption measurement with rubidium vapor. A heralded autocorrelation measurement shows gc(2)(0)=0.040±0.012, i.e., suppression of multiphoton contributions by a factor of 25 relative to a coherent state. The generated heralded photons can readily be used in quantum memories and quantum networks. PRL, 106, 053602 (2011)
Prof. Nicolas Godbout from Polytechnique Montréal (CA) joins the group for a 3 month visiting period and Giorgio Colangelo, previously at Università di Pisa (IT), starts his PhD in the atom lab.
We organize a workshop on 'Quantum Technology with Atomic Ensembles' inviting the tribunal members of Marco Koschorreck's PhD defense, to present some of their recent researches.
We host the ''International Meeting on Engineering, Manipulation and Characterization of Quantum States of Matter and Light.'' Top researchers from 11 countries participate. quantumoptics.es/EMALI2010
atom–light interfaces and nonlinear quantum metrology in the collective continuous variable formalism. We develop a nonlinear effective Hamiltonian in terms of spin and polarization collective variables and show that model Hamiltonians of interest for nonlinear quantum metrology can be produced in 87Rb ensembles. With these Hamiltonians, metrologically relevant atomic properties, e.g. the collective spin, can be measured better than the 'Heisenberg limit' ?1/N, where N is the number of photons. In contrast to other proposed nonlinear metrology systems, the atom–light interface allows both linear and nonlinear estimation of the same atomic quantities. New J. Phys. 12 093016 (2010)
Something about the QND expt. Phys. Rev. Lett. 105, 093602 (2010)
light-shot-noise-limited magnetometer based on the Faraday effect in a hot unpolarized ensemble of rubidium atoms. By using off-resonant, polarization-squeezed probe light, we improve the sensitivity of the magnetometer by 3.2 dB. The technique could improve the sensitivity of the most advanced magnetometers and quantum nondemolition measurements of atomic spin ensembles. Phys. Rev. Lett. 105, 053601 (2010)
sub-projection-noise sensitivity of a broadband atomic magnetometer using quantum nondemolition spin measurements. A cold, dipole-trapped sample of rubidium atoms provides a long- lived spin system in a nonmagnetic environment, and is probed nondestructively by paramagnetic Faraday rotation. The calibration procedure employs as known reference state, the maximum-entropy or ‘‘thermal’’ spin state, and quantitative imaging-based atom counting to identify electronic, quantum, and technical noise in both the probe and spin system. The measurement achieves a sensitivity 1.6 dB (2.8 dB) better than projection-noise (thermal state quantum noise) and will enable squeezing-enhanced broadband magnetometry. Phys. Rev. Lett. 104, 093602 (2010)